With the exception of the fleas and ticks, no insects are so admirably adapted for the conveyance of disease from one animal to another by inoculation; and owing to their enormous numbers, and their capability of flight, their powers of mischief must be far greater than those of either of these other pests. When biting an animal, the mosquito injects into its tissues a fluid specially secreted within its body, which being of an irritating character causes a congestion of blood round the puncture, whereby the insect is secured a full and ample feed of blood. The early life of the mosquito is passed in water, on the surface of which the eggs are laid by the female flying insects. These eggs are of various forms, but are all provided with some arrangement to secure their floating on the surface of the water. In many species they are glued together by their sides so as to form rafts consisting of some hundreds of eggs, while in others, and notably in the special sorts that carry malaria, they are laid separately and float on their sides. In a few rare cases they may be laid on dry surfaces, in situations that will be flooded during the rains. This is notably the case occasionally with the form that carries yellow fever; but for practical purposes it may be considered that the eggs can only be laid on water, and in any case, when the young insects are hatched out, it must needs be into water, as at that stage of their existence they are purely aquatic organisms, and live but a short time if removed from the water. In spite of this they are air-breathers, and in the anatomy of their arrangements for obtaining air, present a curious resemblance to the type of submarine boat that gets its air by means of a small tube reaching just above the surface of the water. The young mosquitoes, or larvæ, are small, wormlike animals, which may often be seen wriggling about vigorously in water, and are especially common, in warm weather, in water standing in small stagnant pools, broken crockery, old tins, and so forth.

When full grown they are about a quarter of an inch in length, and vary in colour from bright green, through brown to black. Two principal forms may easily be distinguished by the difference between the structure of their breathing organs. The first and commonest kind, of which the common English gnat (Culex pipiens, L.) is a good example, has a long breathing tube projecting from the back close to the tail, so that it looks much as if the hinder part of the body were forked.

As will be seen from the above illustration, only the tip of the breathing tube is kept at the surface of the water, while the body and head hang down into it in a slanting position, so that the head is the most deeply immersed portion of the insect. In the other kind there is practically no breathing tube, the air-vessels opening almost flush with the surface, though in the same part of the body; and hence, in order to keep these openings at the surface, the larvæ must needs lie horizontally at the surface, looking much like a small blackened straw, and on closer inspection are seen to have an outline not unlike the ornamental keyhole plates often seen in old-fashioned furniture. They generally lie with their tails supported against some solid object, such as the side of the saucer in which they have been placed for observation.

Owing to their being confused with the line of optical contact of air and water, and the latter being raised by adhesion into curves over their backs, they do not come out as clearly in the photograph as in a drawing, but they are, nevertheless, sufficiently clearly shown for easy recognition, a matter of some importance, as these are the larvæ of the sub-family Anophelinæ, to which belong all the mosquitoes that are concerned in carrying malaria, besides which they are the commonest carriers of blood-worms. The mosquito, however, that conveys yellow fever (Stegomyia) belongs to the Culex sub-family.

For any one possessing a microscope these larvæ form most fascinating examples of “pond-life,” as many species, especially when young, are transparent enough to enable one to follow the entire mechanism of their internal organs; but a great deal of interest can be made out with a simple hand-lens.

On the back of each of the rings of the abdomen, or hindmost division of the body, of the Anopheles larvæ may be made out a pair of structures formed like minute palm leaves, the function of which appears to be that of keeping the little creature flush with the surface of the water.

One of these larvæ, magnified about twenty times, with these structures and certain peculiar hairs on the front of the head, which are of value in distinguishing one species from another, more highly magnified, is figured on the preceding page. By the aid of these illustrations the reader should have no difficulty in recognising these organisms when he meets with them. When disturbed, they dart backwards and seek refuge among the débris at the bottom, but cannot remain there long, and soon resume their resting position on the surface.

The larvæ of many species are said to be carnivorous, and even cannibalistic, though I cannot say I have ever observed this personally, and in any case their main provision is found in the minute vegetable organisms which are abundant in the sites where they are common; the Culicine larvæ confining themselves mainly to those that are found completely immersed, while the young Anopheles browses on those floating on the surface, keeping its head screwed round, a full half-turn, so as to bring the mouth uppermost. The abrupt way in which this action is performed and reversed is extremely quaint, so that, as a writer remarks, one is rather surprised at its not being accompanied by an audible click.

The duration of the period of larval existence depends on the temperature of the water and on the abundance or scarcity of food. When first hatched out from the egg, the larvæ are barely visible to the naked eye, whereas when full grown they contain within themselves the entire material of the adult flying insect. Once full-grown, the weather being favourable, they change into “nymphs” or pupæ, not unlike small tadpoles in form, the head and thorax being enclosed in an almost spherical envelope, to which is appended a sort of tail, formed by the abdomen, which is usually kept folded under the body, as shown in the figure below. In this stage the animal breathes through a pair of horns springing from the back of the thorax. The mouth is completely closed, so that the pupa is incapable of feeding, but is in no sense quiescent, as it is capable of lively movements and tries to elude capture almost as briskly as the larva. After a sufficient time has elapsed for the completion of the extraordinary anatomical changes that convert the larva into the adult insect, the pupa-case bursts along the back, and the perfect gnat gradually disentangles itself from its temporary home, and flies away, very shortly to reinitiate the cycle of events by laying a fresh batch of eggs. As has already been remarked, the time required to complete these changes varies greatly in different species and under varying environments, of which climate is the most important factor, but under moderately favourable conditions the time required is a fortnight or three weeks, the greater part of which is passed as a larva. In countries where water freezes during winter for any length of time, all larvæ that have not completed their metamorphosis by the end of autumn, must necessarily perish; and the continuity of the species is maintained entirely by the survival of pregnant females that hide themselves in warm corners and pass the winter in a truly hybernating or dormant condition. Further south, both males and females hybernate, and the dormancy is so much less pronounced that the insects are often tempted to issue from their hiding places on exceptionally warm days. In such climates, which include Italy and most of the sub-tropical zone, the species finds an additional string for its bow in the survival of larvæ, which, though they cannot be said to hybernate in the strict sense of the term, being always lively and alert in their movements, are yet incapable of growing, and appear to remain at whatever size they may have previously attained until the return of warmer weather. Quite recently Dr. Bancroft, of Queensland, has discovered that in some species these wintering larvæ can give birth to small broods of young larvæ, so that in such cases the bow has no less than three strings. Further south again, in truly tropical climates, breeding goes on all the year round.

No adult mosquito can stand the direct rays of the sun, and hence all of them have to seek the shelter of houses, trees, or some such protection, during the heat of the day; moreover, with very few exceptions, they are nocturnal or twilight insects, so that there is comparatively little danger of being bitten during the hours of daylight. For the majority of species too, extreme atmospheric heat has much the same effect as great cold, so that during periods of intensely hot, dry weather the number of species to be met with in a state of activity is very small, and fortunately those that convey malaria are not amongst the number; but on the other hand, the one or two sorts that possess this tolerance are so enormously prolific that their numbers far exceed those of all other species combined.

Another point of importance is that, for practical purposes, mosquitoes cannot fly far, and hence never wander far from the puddle on which they were born. Being tolerably long-lived insects, it is of course possible for them to slowly spread amongst trees or bushes for considerable distances, a few straying further and further away every night from the place of their birth, but the number that can travel in this way for any considerable distance, is so small as to be scarcely worth consideration; and any considerable expanse of bare, open country is practically impassable to them.

Mosquitoes are most active during the periods of twilight, and especially in the evening, at which time they quit the shelter in which they have dozed away the day, and come out into the open to seek their food, remaining outside for the most part throughout the night, though the females of those species that attack man and animals, it is needless to say, will find their way back into houses in search of their favourite food. As soon, however, as the sun has got well above the horizon they may be observed trooping back into the house, and if a window be closed it is very amusing to watch the numbers that will alight on the glass at this time of the day, and their efforts to find a way through the obstruction. The special importance of keeping all means of entry closed at this particular hour can therefore easily be understood, though in ordinary tropical practice, it is the very time at which every door and window is habitually thrown open.

Mosquitoes are found all over the world, it being a great mistake to imagine that they are confined to tropical climates. Some score of species are to be found in England, and though in high latitudes they cease to be dangerous as carriers of disease, there are perhaps no localities where they are so numerous and troublesome as certain parts of the North American Continent, and in Scandinavia, close up to the Frigid Zone.

Almost any collection of water will serve as a nursery for the larvæ, unless indeed, there be a decidedly strong current; but the situations taken by preference during the breeding season are small stagnant pools and domestic collections of water, such as small tanks, broken crockery, empty tins, &c.; while wintering larvæ prefer the larger ponds and marshes which are permanent throughout the cold weather, and especially select those in which there is sufficient vegetation, reaching to the surface of the water, to afford cover and protection from their numerous enemies. Practically speaking, wintering larvæ will never be found in tanks or ponds devoid of fairly robust vegetation, and it may easily be understood from this fact that the clearing away of reeds, grasses, and weeds of all sorts during the cold weather from all such collections of water which may be found near an inhabited site is a most important sanitary measure. Some species prefer the fairly clean water of marshes and ponds, while others luxuriate in the dilute sewage of the domestic waste water, but it would occupy too much space to go into any detail on this subject, and all that the sanitary amateur need remember in this connection, is that any and every collection of water, capable of standing for ten days or a fortnight, should be regarded as dangerous to health in any country where malaria is known to exist.

For our purposes, it will suffice for the reader to understand the general characteristics of three sorts of mosquitoes. First, there are the common Culex mosquitoes, which are, almost everywhere, far more common than the others. They are usually of a dull grey colour, and with very few exceptions, their wings are quite plain and free from spots. As will be seen from the photographs in the accompanying plate, they sit in rather a humped-up position, and the proboscis is obviously much thinner than the body, its appendages, or palps, being held apart from it. Mosquitoes of this sort cannot convey human malaria, though they are instrumental in conveying a similar disease for certain animals. They are to be found, in greater or less numbers, throughout the year.

The second sort is the Stegomyia, which is the genus concerned in the conveyance of yellow fever. These mosquitoes are seldom to be seen except during the rains, and rest in much the same position as the Culices, which they resemble closely in form. Their wings are never spotted, and almost all are small insects clothed with jetty-black scales, picked out with an ornamentation of dazzling white lines on the body and spots on the abdomen and legs.

The third, or Anopheles, sub-family is that concerned in the transmission of human malaria, and, as may be seen by comparing the two lower photographs of the plate with the upper ones, can easily be recognised by their characteristic form and attitude. In these mosquitoes the feelers are long and thick in both sexes, and as they are held habitually in contact with the proboscis, these together appear to the naked eye as a prolongation of the body as thick, or thicker, than the abdomen. Moreover, except in a few species, their position, when resting, forms a singular contrast to that of the Culices, the whole body and proboscis being held in one straight line, with the abdomen raised from, and the proboscis pointed almost vertically at the surface on which they rest, and almost touching it with its point, as if they were preparing to drive the latter into it; so that, viewed with the naked eye, they look much like minute black thorns, stuck into the surface on which they are sitting. On closer examination, it will be seen that the wings are not plain, but spotted (the number of plain-winged species being unimportant).

The appearance of spotting is usually produced by alternate lengths of the veins of the wings being coloured in finely contrasted dark brown or black, and white or yellow, and varies, of course, in detail in different species, but the above figures of the wings of some of the commoner Indian forms will give an idea of the general effect, as seen under a moderate magnification, for though the spots are quite visible to the naked eye, it requires a fairly powerful hand lens to make out the details properly.

Like the Stegomyiæ, the Anophelinæ are only common during the rains, but stray specimens will be met with for a month or two afterwards; and though they practically disappear during cold weather, a few may be generally met with during the hot dry months of continental hot climates.

From what has been said, it follows that the prevalence of malaria, like that of mosquitoes, must necessarily be seasonal. The survival of the malarial parasite at those times of the year when mosquitoes are scarce or absent, is maintained by the persistence of considerable numbers in a latent condition, in the persons of human beings who have been imperfectly cured of an attack of malaria.

Cases of this sort, which have either been never treated at all, or in which the administration of quinine has been stopped too soon, are extremely common in all malaria-stricken communities, and such persons are always liable to relapses if they are brought below par by any depressing influence, such as chill, too great exposure to the sun, or the incidence of injuries, or of other diseases.

During such periods the latent parasites, which have been perhaps for months lying hidden in the internal organs, will reappear in the blood in large numbers, and there are always a sufficient number of such cases of relapse persisting through the naturally malaria-free season, to suffice to infect the early broods of mosquitoes that come to maturity with the advent of the rains.

This shows that the curing of all cases of malaria is matter by no means confined to the interests of the patient himself, but is of great importance to the entire community of which he is a member; for, despite the fact that the disease is only indirectly transferable through the agency of the mosquito, a case of malaria is as great a danger to his fellow-men as one of any other infectious disease, and should, as far as possible, be dealt with in the same way; only the problem of isolation is in this case easier than usual, as it suffices to prevent mosquitoes getting access to the sick person; and in a properly fitted mosquito-proof house or hospital, malaria cases may quite safely be allowed to mix freely with the healthy, as well as with persons affected with other diseases.

Relapses in persons chronically infected with malaria may occur at any time of the year, but the fresh infections, which always form the bulk of the cases met with, can only happen as the result of a tolerably recent bite by an infected mosquito; and as about a couple of weeks are required for the maturing of the parasite within the insect, and a further period of incubation is necessary within the human subject before the parasites attain sufficient numbers to produce a definite constitutional reaction, fever does not as a rule commence in earnest until some three weeks or a month after the break of the wet season. Once the process is started, infected mosquitoes and malaria-stricken men increase in numbers rapidly, and as numbers of infected mosquitoes survive for a considerable period after the cessation of the breeding season, the prevalence of malaria continues until the advent of cold weather puts a period to the possibility of the survival of the parasite within the insect organism. Hence it is generally quite possible to give a fair idea of the monthly distribution of rainfall in any warm climate from the returns of sickness and mortality, and vice versâ.

The natural history of the living organisms that are concerned in the propagation of malaria has been described with some detail, as suitable measures for the prevention of the disease must needs be based on a fairly competent knowledge of the subject, and is the more necessary as it is hardly possible to give any “rule of thumb” directions; because the circumstances on which the prevalence of malaria depends vary so greatly in different localities that, to ensure success, our operations must necessarily be modified in each case to meet local conditions.

In the following remarks, however, it is not proposed to deal with the question of prevention on a large and public scale, but only with such as can be adopted as measures of individual and personal hygiene, as the larger question of provincial and municipal anti-malarial sanitation cannot be adequately dealt with in a short treatise like the present.

Keeping always in view the just described data of the life history of the malarial parasite and of its temporary host, the mosquito, it is obvious that our measures of protection must be based on one or more of the following plans of action, any one of which, could it be carried to complete success, would suffice to “stamp out” the disease. These measures are:—

(1) To destroy the mosquitoes.

(2) To prevent mosquitoes biting man.

(3) To prevent mosquitoes from becoming infected, by isolating all cases of malaria in man.

In practice, however, it is extremely rare that anything like complete success can be attained on either of the three above indicated lines of action, especially as concerns the second and third methods, and though here and there localities may be met with in which the breeding places for mosquitoes are so circumscribed and easily dealt with as to render the actual extermination of mosquitoes practicable, in by far the majority of cases we must be content with a partial success all along the line, by adopting such measures as may be locally most practicable, based on any or all three of the above principles of action.

In the case, for example, of habitations placed in the midst of canal irrigation where ample and efficient subsoil drainage is impossible or too expensive, the attempt to destroy mosquitoes can be little better than a waste of time and money; for under such conditions the breeding places are so numerous, and appear so constantly in new and unexpected situations, as to defeat the utmost vigilance; and the thorough protection of all habitations against the invasion of mosquitoes, and the careful treatment of all cases with quinine, is all that can be done. On the other hand, in an exceptional case, such as that of the town of Ismailia in Egypt, where the rainfall is practically nil, and the breeding places all of artificial origin, the practical extermination of mosquitoes may be so easy a matter as to be effected at a small expense in a single year, with the immediate result of reducing the cases of malaria to a tithe of their previous numbers.

Measures of the first class, i.e., the extermination or diminution of the numbers of mosquitoes, can often be undertaken with considerable success by private individuals, the possibilities of success varying, of course, with the extent of the area directly or indirectly under his control.

The resident of a closely inhabited town can, it is needless to say, do no more than contribute his personal mite to the general welfare in this matter, with little chance of reaping much benefit unless his neighbours follow his example; but with the exception of diplomatic officials and merchants residing in places under oriental rule, where the safety of life and property are too badly secured to admit of their living outside town limits, it is rare for any European to be so situated, as in most of our colonies and dependencies the European quarter of the town consists of widely separated villas each surrounded with a garden of some size, with generally a small hamlet of dwellings for native servants and dependents included within its boundaries. In addition to this, there are often open spaces, of considerable extent, between the various “compounds” which, though not directly under one’s control, are so far “no man’s land” that no one will interfere with any one employing on them any of the measures required for anti-malarial sanitation, while the most litigious municipal council is hardly likely to object to the sprinkling of a little paraffin on the roadside puddles. In this way it will generally be possible to effect a good deal within a radius of three or four hundred yards of one’s dwelling, and actual experience has shown me that if all breeding places within such limits can be rendered harmless the number of stragglers that will stray across from places beyond will be too small to be seriously troublesome.

In devising measures for the destruction of mosquitoes it is obvious that while they may be attacked either in the aquatic or aerial stages of their existence, the easily localised larvæ and pupæ will be far more easily dealt with than the elusive flying insect, and it will be therefore best to devote most attention to the destruction of the former.

There are two principal methods of dealing with the insects during their aquatic stage, i.e. (1) by doing away with their breeding places; (2) by poisoning them. Of the two it is clear that the former method is, where practicable, the more valuable, as in nearly all cases its effects are more or less permanent. With either object in view, however, the first step is to seek out the breeding places.

As a preliminary measure, all domestic rubbish capable of holding water, such as disused flower-pots, empty tins, &c., should be carefully sought out and destroyed or disposed of by throwing into some depression of the soil which it is desired to fill in. Next, the entire surface should be carefully inspected after a brisk shower of rain, and all such puddles as are of manageable dimensions carefully filled in and levelled.

The amount of labour that can be profitably afforded in work of this sort will depend a great deal on the probable duration of one’s stay in a place; as temporary residents, such as government officials, will find it much cheaper to employ temporary measures, such as the use of paraffin; while in the case of merchants and other permanent residents, the expenditure of a considerable sum on permanent measures will be more remunerative in the long run. The great difficulty often lies in finding spoil wherewith to fill in the depressions, as unless care be exercised, the only result will be to shift the site of the puddle. Sometimes, however, a bank of earth surrounds the compound by way of a hedge; and as in a level country the existence of such an obstruction to surface drainage is most objectionable such banks should always, if possible, be removed and a hedge of wire or bamboo substituted; when the spoil can be advantageously utilised for filling in hollows. Where no localised elevations are to be found, the material required should be obtained by a general very slight removal of the surface. In other cases it may be possible to drain a depression by cutting a shallow gutter to the nearest surface drain.

Another and very important class of breeding place consists of the comparatively large collections of water formed by the various reservoirs, channels, &c., constructed for obtaining and storing water for various domestic purposes, such as wells, tanks, &c., and especially the appliances for watering gardens. Of these the most harmful of all is canal irrigation, which should undoubtedly be never tolerated near a dwelling by any one valuing his health, malaria or no malaria; for the waterlogging of the soil, that is practically inseparable from the system, is either the exciting or predisposing cause of a variety of diseases, many of which, such as rheumatism, consumption and cancer, are perhaps more seriously dangerous than malaria. Sodden and waterlogged sites are notoriously unhealthy all over the world, and chronic ill-health is a high price to pay for a few flowers and vegetables; so that the settler will be well advised to leave irrigated cultivation to those who are constrained to adopt it for a livelihood, and banish it from his own premises; as much is gained by living on a comparatively dry site of however limited extent.

As a matter of fact, indeed, the possession of a garden of any sort is a more than doubtful benefit in malarious places, for trees and shrubs necessarily form lurking-places for mosquitoes; and even with the greatest care, it is difficult to carry out the necessary watering of the plants without giving rise to puddles; while the various reservoirs, &c., that are almost indispensable, are a constant source of danger unless constantly and minutely supervised.

In India, for example, gardens are commonly watered from wells by means of water lifts of various forms, which are worked either by means of bullocks or by manual labour. In order to facilitate the distribution of the water, masonry channels are usually constructed which carry the water from the well head to all parts of the garden, and as the lift cannot conveniently be worked continuously, a number of small tanks are arranged along the line of channels wherein water is stored, so that it can be dipped out and distributed by means of an ordinary watering can without the gardener ever having to go far to replenish it. Now these small tanks are par excellence the main source of supply of mosquitoes of all species, and therefore of malaria, to the houses to which they are appended. If, therefore, a garden be considered indispensable, all such tanks should be carefully emptied and all deposit cleaned out at least once a week; under which circumstances, though they will probably swarm with larvæ by the end of the time, it is impossible for any of the latter to complete their metamorphoses into adult insects. By far the least objectionable plan of relieving the dust and glare of a bare situation is the cultivation of a well-kept lawn, a few large trees being left and the area of flower beds strictly limited, for as flooding the grass is sure to spoil a lawn, success can only be ensured by careful and moderate waterings at frequent intervals.

Collections of water that are too large to be done away with by filling in or by draining, should be dealt with by oiling the water with paraffin. There are some other agents which may be employed for the purpose, but none of them are so cheap, efficient, and readily obtainable. As an additional advantage, though fatal to all kinds of insects, it is in the quantities employed, not only absolutely harmless to vegetation, but water so treated is actually a most valuable application, owing to its power of destroying other injurious insects. When sprinkled on water paraffin spreads out into an extremely thin film, so that a very small quantity will cover a considerable area. A three-gallon tin, for example, contains enough to cover an area of 100 yards each way, though it may be a day or two before the oil reaches all parts of such a space. It is important to remember that the cheaper and commoner the oil, the better it is for the purpose, and the addition of a little of common bazar ghi, or clarified butter, is said to make the oil spread better and render its action more lasting, though the writer has not personally experimented with the mixture.

In the quantities used there is no possible danger of fire, even though wooden structures, such as the piles of bridges, be immersed in the water, as the film is so thin that it is impossible to ignite it; a matter one would have thought sufficiently obvious, were it not that objections have been gravely raised to the use of paraffin on this score.

The method of application must be varied to suit the size and situation of the piece of water to be dealt with. Small puddles, such as those left in the course of roadside ditches, may most economically be dealt with by, as it were, lightly wiping over the surface with a wisp of rags dipped in the oil; filling in being in such cases out of the question, as to do so would be equivalent to obstructing the drainage; and it is quite impossible to maintain an exact and uniform gradient in an unrevetted channel.

For larger collections of water, by far the best appliance is an ordinary gardener’s watering-pot. The oil should be applied mainly along the windward side of the pool by a coolie, who should, if possible, walk out some distance into the water, and should be trained to sprinkle the oil by rapid single sweeps of the rose of the can, a few steps being taken between each sweep, as there is no need to make the loop-shaped areas of water sprinkled in this way continuous, as the oil will spread laterally and join each of them together even if separated by several yards, and no advantage whatever appears to be gained by applying the oil thickly. In exceptional cases, such as the moats of fortifications, where the water is enclosed within high vertical walls, a garden syringe may be required in place of the watering can.

In situations such as the pools in canal beds, ditches, &c., the oiling must obviously be done after each flow of water through the channel; but in most ordinary situations, the effects of a careful oiling may be trusted to last for at least three weeks, as, though larvæ may be beginning to reappear by the end of that period, none of them will have had time to complete their metamorphoses. For the destruction of wintering larvæ, two oilings, one at the commencement, and one towards the end of the cold season, amply suffice; and in Continental hot climates it is needless to repeat the process during the dry hot season, as at that time only artificial breeding places, such as garden tanks, require attention, and these are better dealt with by periodical emptying.

At that season indeed, the undried-up breeding places are so few and far between that people have only themselves to thank if mosquitoes are in evidence at all; and yet in many places there is no season of the year when they are so numerous and tormenting. There are no remaining natural breeding-places, and the pains of a weekly stroll round one’s premises to ensure the emptying and cleaning out of all garden tanks, water-vessels, &c., are all that is required to secure complete immunity at that season of the year, but it is most difficult to induce people to take even this trifling trouble; and the mosquitoes are likely to flourish undisturbed until the existence of breeding places within the premises of any person is treated by the authorities in the same way as other dangerous nuisances; and yet these very people are the loudest in their condemnation of the inertia of the native in sanitary matters, and while they maintain malaria breweries on a scale in which the modest extent of his premises forbids him to compete, inveigh against him for starting a cholera factory on the most modest lines. The native who refuses to avail himself of the protection against plague of a health camp is, they admit, an impracticable fool for his pains; but the sahibs of the civil lines, whose gardens supply a large share of the harmful mosquitoes to the neighbouring city, are merely “common-sense” people who attach no importance to doctor’s fads and “scientific rot” of all sorts. The native, however, has at least usually the excuse that he is unable to read or write; and for the rest, does not pretend to be a very highly civilised person.

Once they have emerged from the pupa case, our means of attacking mosquitoes are comparatively feeble, and for those that habitually pass most of their time in the open air practically nil.

In the case however of domestic species, which habitually shelter in houses, a good deal can be done in this matter; and, just as in the repression of other troublesome insects, such as fleas and bugs, scrupulous tidiness and cleanliness is by far the most important of all agencies. Useless, rarely dusted draperies and curtains, and untidy collections of clothing hung about on nails and pegs, instead of being kept in properly closed wardrobes, are the things that are mainly responsible for attracting and sheltering mosquitoes within houses, for they will not, if they can avoid it, remain in a well-lighted room, with freshly colour-washed bare walls.

In the tropics, the Italian villa with its frescoed walls and minimum of useless furniture, is the ideal that should be aimed at, and not the elaborate lumber warehouse of an English drawing-room; which, though comparatively harmless in our own climate, is about as well adapted for imitation in hot countries as the coat of the Polar bear in the Zoo is suited to our summer.

Perhaps our most effective agency in dealing with adult mosquitoes depends on the intense objection all species of these insects entertain to smoke.

That it is quite possible to effectually protect animals from mosquito bites by the agency of smoke alone, has recently been conclusively shown in the course of Mr. Power’s experiments on the prevention of horse sickness in South Africa; but, though most semi-civilised people seem to live comfortably enough in a smoky atmosphere, Europeans would find such a state of things intolerable; and the plan can only be utilised to drive mosquitoes out of houses, other methods being relied on to prevent their re-entering. Smoke from almost any source will put mosquitoes to flight, and if sufficiently intense will stupefy them; but certain special materials must be burnt if it is desired to kill them outright, and our modus operandi must be varied according to the means at our disposal, for if we can only expect to annoy the insects sufficiently to drive them out of doors, the latter must be left open during the fumigation; whereas, if it is proposed to kill them, all openings must be closed as completely as possible, so that the fumes may reach the insects in as concentrated a form as possible.

For simply driving out mosquitoes, any fuel that produces a dense smoke, such as damp straw, will serve. Maize cobs are excellent for the purpose, but probably the least objectionable is the burning of a little incense (Hindustani, Lobán). To actually kill them, on the other hand, it is necessary to shut up all openings as closely as possible, and to burn certain special substances, such as sulphur, unopened chrysanthemum flowers, the leaves of the neem tree, tobacco, &c., and the degree of success attained will vary a good deal according to the character of the building in which it is attempted; it being obviously extremely difficult to secure an adequate concentration of the fumes in a very pervious structure, like a house with a thatched roof and walls of bamboo matting, such as is often met with in Burmah and the Malay Archipelago. Under such circumstances, the rapid burning of a large amount of the fumigating agent is the only way of meeting the difficulty; and under any conditions, plain sulphur, simply ignited as a powdered mass, or placed on the hot coals of a charcoal brazier, burns so slowly as to be quite useless.

A few instants’ exposure to an atmosphere containing a fairly high percentage of sulphurous acid will kill any insect, whereas they will be merely stupefied or unaffected by prolonged exposure to a weaker mixture of the poison. I am quite aware that sulphur has been decried as almost useless by several observers, but this is simply because they have not used it properly; for to secure success, something must be added to the sulphur which will make it burn quickly, and what is wanted is, in fact, a weak firework. In well-constructed buildings the sulphur pastiles prescribed in the second edition of my work on the “Gnats or Mosquitoes” answer sufficiently well, but subsequent experience has shown that the proportion of nitre is not enough to secure a sufficiently rapid combustion to instantly flood the air with sulphurous acid, and that nothing short of a slow burning firework, such as a Roman candle or Bengal light, will do this in a building roofed with tiles or thatch. Possibly it might be advantageous to raise the proportion of sulphur; and it is undoubtedly better to pack the material as a powder in paper cases, than to mould it into pastiles. Proper precautions against fire must of course be taken, but in fireworks of this sort the sparks do not fly far, and it is quite safe to use them in any ordinary room if the precaution be taken of placing the cases under a low shield, formed of a sheet of corrugated iron supported on four piles of bricks.

The occasional fumigation of a dwelling in this way is a useful adjunct to the destruction of the larvæ; and where combined with proper wire-gauze protection, after the plan described below, may be relied upon to secure immunity from the attacks of insects, even where measures for the destruction of larvæ are impracticable. It has the further advantage that it is fatal not only to mosquitoes, but also to insect pests of all sorts, such as flies, hornets, bugs, or fleas, and even to such more awesome foes as scorpions and centipedes, all of which delight to share the home of the dweller in tropical climes.

Mosquitoes are always greatly attracted by draperies, especially those of dark colour, and the fact may be utilised to trap them by means of deep bags of black gauze (chiffon), the mouths of which are held open by an oval loop of cane, or some such material. Such bags, if hung up mouth down-wards in tempting dark corners, will usually be found swarming with mosquitoes each morning, and the insects can easily be killed by crumpling the bag in the hands and then shaking out the dead insects.

By working on the above lines, especially where one has the co-operation of neighbours, it is in all cases quite possible to materially diminish the nuisance of mosquitoes, and under favourable circumstances to practically extirpate them; though, in a usual way, complete success must not be expected. In the exceptional cases where this is possible, there is, of course, no need for the adoption of any other sort of measures; but, in the majority of cases, an amelioration only in the numbers of insects is all that can be attained; and it is necessary to guard against the risk of some of the survivors becoming infected, by the adoption of measures of the second and third classes. Of these the second, i.e., the protection of man from mosquito bites, is in most cases the most easily practicable.

A variety of ointments and applications of various sorts have been from time to time vaunted as protectives, and the presence of certain plants, such as the eucalyptus and the castor-oil shrub, have also been stated to be so obnoxious to mosquitoes of all sorts that they might be trusted to make themselves scarce wherever these plants might be found. For these ideas there is doubtless this much foundation in fact, that most strongly smelling bodies really are obnoxious to mosquitoes; but unfortunately, whatever objection they may have to strong scent is not very deeply rooted, and in default of more congenial shelter they will settle upon either eucalyptus or castor-oil plants, and will brave even the hated smell of paraffin to secure a good feed on the blood of a human or animal subject. All these special applications to the skin, too, have the further disadvantage that, though some of them are fairly effectual for a few minutes after they have been just applied, and so enable the user to get sleep, they leave those who are deluded into depending upon them to fall unresisting victims, as soon as the thick of the scent has evaporated. So that, though valuable for securing rest, they are worse than useless from the point of view of the prevention of malaria. With these untrustworthy exceptions, all available measures are of a mechanical character, and consist in modifications of our housing and clothing.

It must be remembered that during the working hours of the day there is little chance of being attacked, at any rate in the open air, and the same is the case in well-lighted rooms. Thus men whose work takes them into the open air for some considerable portion of the day, or are occupied in well-lighted offices, run much less risk than ladies, who, when they attempt to face the hot weather at all, are too fond of shutting themselves up in a darkened room, devoid of light or fresh air, and filled up with hangings and other superfluities, so as to form a perfect mosquito paradise in which the insects can fly about and bite during the day as comfortably as during the night. With such exceptions, there is therefore no need to modify costume to diminish the chance of mosquito bites as long as the sun is up, or even during the twilight, as long as one is in motion. It is when people are resting after the evening game of golf, racquets, or tennis, that they are most commonly attacked while awake; but the time of greatest danger is the period passed in sleep. During the waking hours it is uncommon for a mosquito to get the chance of an undisturbed meal by attacking the face and hands, but she often does so by attacking the ankles, and even thick stockings are no adequate protection. Trousers are therefore more suitable than knickerbockers for evening wear, and should be made extra long; so that when turned down after taking one’s evening exercise, they thoroughly protect this very vulnerable portion of the person. A lady can generally arrange her dress so as to protect herself, but the ordinary costume of children is extremely dangerous, and certainly should be modified to meet this danger during the hours when mosquitoes are active. In the case of little boys a “sailor suit” with long voluminous trousers meets the difficulty; and—fashion or no fashion—it is a clear duty on the part of mothers to devise some cool but adequate protection for the little girls. The alternative lies between doing so and wilfully offering them as sacrifices to the god of dress by needlessly exposing them to the danger of infection.

The low-necked, sleeveless dresses worn by ladies in the evening must, we can well understand, be very temptingly cool wear in the climates with which we are dealing, but are obviously extremely dangerous, as they leave a large surface of the person exposed at the very time when mosquitoes are most active. A dress covering these parts should be therefore substituted, which, however, may safely be made of the lightest materials, provided that it be so puffed or otherwise “confectioned” as to make it difficult for a mosquito to get within reach of the skin. Mosquitoes are always fond of collecting under tables, as they are there sheltered from the glare of the lamps, and on this account it is advisable for men to wear straps to their trousers when dressing for dinner; and though the plan is a very old-fashioned one, I have some hope that the suggestion may meet the approval of our better halves, as, whatever its real object, the adoption of the plan certainly gives the wearer the air of having sacrificed comfort to appearances.

There would, however, be no need of modifying costume for indoor wear in any way were houses properly protected against the entrance of mosquitoes by means of suitably planned wire-gauze protection to all openings.

The plan in question was devised by Professor A. Celli, the Principal of the Institute of Hygiene in the University of Rome, and in Italy at least has long passed its experimental stage; though, owing probably to the small number of Englishmen who are familiar with the Italian language, it appears to be practically ignored even by our specialists on the subject.

Within a few miles of the great city of Rome there are large areas where malaria, far more virulent than the type of disease we usually meet with in India, is so rife that, during the malarious months, the country is practically deserted by all but a few necessary railway officials and caretakers. Amongst the former the mortality and invaliding used to be so heavy that the working of the lines was a matter of the greatest difficulty.

The majority of the peasantry, being only temporary inhabitants, live in grass huts not a whit in advance of those of the savages of Central Africa, and from the migratory nature of their employment, are among the most ignorant and backward of the Italian populace, and so about the last people likely to lend themselves to the adoption of any “new-fangled” custom. As a matter of fact, however, the object lesson of the advantages of the system have been so obvious that, after the first year, there has been no difficulty in securing the eager co-operation of the simple railway men and scarce civilised farm hands. As the system is necessarily being very gradually introduced, there are plenty of unprotected houses for comparison, and after personally conversing with the inhabitants, the writer found that all who had enjoyed the benefits of the plan were convinced of its efficacy.

It must be remembered, however, that it has been long a matter of popular belief in the Campagna that malaria was, in some way, caused by mosquitoes; and it is the difficulty of convincing those in high authority of this fundamental fact that is at the root of the indifference and inertia which oppose all attempts at amelioration in India and in many of our colonies.

During the first two years’ experiments on the Campagna, out of 25 protected cottages, with a population of 173 persons, only 8 persons contracted malarial fever; while in 30 unprotected cottages, having a population of 220, only 17 escaped the disease; although the protected and unprotected cottages were, as far as possible, paired as regards the site, and were otherwise of a uniform plan of construction, and all inhabited by the same class of railway subordinates.

The system is the one above all others most suited for adoption by private persons, because it secures an almost complete immunity in spite of the most unfavourable surroundings, and renders the user quite independent of the sanitary lapses of his neighbours; but in spite of this, the plan is almost ignored in our English colonies and dependencies, though the writer has recently received an interesting communication from a medical man practising in China who has adopted it with signal success.

Professor Celli’s plan consists in rendering habitations impervious to the entry of insects by closing all openings with wire gauze (mesh of about 12 strands to the inch). All windows, as well as such doors as only serve as such, and are not absolutely required for ingress and exit, are permanently closed by frames covered with the gauze, and all indispensable exterior doors are fitted with double spring doors of the same material, sufficiently separated from each other to secure the closure of the first door before the second can be opened.

In most Tropical residences, the number of doors is far in excess of actual needs, it being nothing uncommon to find rooms with four or five doors, all opening in the exterior. Though desirable and even necessary for free ventilation, no room can possibly require more than a single door opening on the outside, and in a well-planned house with suitable corridors, there is no real necessity for more than one or two exterior doors to the whole house. All outside doors, then, not absolutely necessary as such, should be treated as windows and permanently closed with single frames of wire gauze, so that the number of the more expensive double spring doors may be reduced to a minimum. In Tropical climates it is, however, essential that a considerable area of verandah should be included within the protected area, as a good deal of time is necessarily most pleasantly spent in the verandah, not only in the evening, but during the rains throughout the whole day. On this account a northern verandah should be the one selected for protection in this way.