It is more agreeable to me not to dwell further on the comparative failure of science to gain increased influence and support in this country, but to mention some instances on the other side of the account. As long ago as 1842 the British Association took over and developed an observatory in the Deer Park at Kew, which was placed at the disposal of the Association by Her Majesty the Queen. Until 1871 the Association spent annually a large part of its income—as much in later years as 600l. a year—in carrying on the work of the Kew Observatory, consisting of magnetic, meteorological and physical observations. In 1871 the Association handed over the Observatory to the Royal Society, which had received an endowment of 10,000l. from Mr. Gassiot for its maintenance, and had further devoted to that purpose considerable sums from its own Donation Fund and Government Grant. Further aid for it was also received from private sources. From this Observatory at last has sprung, in the beginning of the present century, the National Physical Laboratory in Bushey Park, a fine and efficient scientific institution, built and supported by grants from the State, and managed by a committee of really devoted men of science who are largely representatives of the Royal Society. In addition to the value of the site and buildings occupied by the National Physical Laboratory, the Government has contributed altogether 34,000l. to the capital expenditure on new buildings, fittings, and apparatus, and has further assigned a grant of 6,000l. a year to the working of the laboratory. This institution all men of science are truly glad to have gained from the State, and they will remember with gratitude the statesmen—the late Marquis of Salisbury, the Right Hon. Arthur J. Balfour, Mr. Haldane, and others—as well as their own leaders—Lord Rayleigh, Sir William Huggins, and the active body of physicists in the Royal Society who have carried this enterprise to completion. The British Association has every reason to be proud of its share in early days in nursing the germ at Kew which has at length expanded into this splendid national institution.

I may mention also another institution which, during the past quarter of a century, has come into existence and received, originally through the influence of the late Lord Playfair (one of the few men of science who has ever occupied the position of a Minister of the Crown), and later by the influence of the Right Hon. Joseph Chamberlain, a subsidy of 1,000l. a year from the Government and a contribution of 5,000l. towards its initial expenses. This is the Marine Biological Association,[22] which has a laboratory at Plymouth (see fig. 47), and has lately expended a special annual grant, at the spontaneous invitation of His Majesty’s Treasury, in conducting an investigation of the North Sea in accordance with an international scheme devised by a central committee of scientific experts. This scheme has for its purpose the gaining such knowledge of the North Sea and its inhabitants as shall be useful in dealing practically and by legislation with the great fisheries of that area. The reader will, perhaps, not be surprised to hear that there are persons in high positions who, though admittedly unacquainted with the scientific questions at issue or the proper manner of solving them, are discontented with the action of the Government in entrusting the expenditure of public money to a body of scientific men who give their services, without reward or thanks, to carrying out the purposes of the international inquiry. Strange criticisms are offered by these malcontents in regard to the work done in the international exploration of the North Sea, and a desire is expressed to secure the money for expenditure by a less scientific agency. I do not hesitate to say here that the results obtained by the Marine Biological Association are of great value and interest, and, if properly continued and put to practical application, are likely to benefit very greatly the fishery industry; on the other hand, if the work is cut short or entrusted to incompetent hands it will no doubt be the case that what has already been done will lose its value—that is to say, will have been wasted. There is imminent danger of this perversion of the funds assigned to this scientific investigation taking place. There is no guarantee for the continuance of any funds or offices assigned to science in one generation by the officials of the next. The Mastership of the Mint held by Isaac Newton, and finally by the great chemist Thomas Graham, has been abolished and its salary appropriated by non-scientific officials. Only a few years ago it was with great difficulty that the Government of the day was prevented from assigning the Directorship of Kew Gardens to a young man of influence devoid of all knowledge of botany!

One of the most solid tests of the esteem and value attached to scientific progress by the community is the dedication of large sums of money to scientific purposes by its wealthier members. We know that in the United States such gifts are not infrequent; they are rare in this country. It is, therefore, with especial pleasure that I call attention to a great gift to science in this country made only a few years ago. Lord Iveagh has endowed the Lister Institute, for researches in connection with the prevention of disease, with no less a sum than a quarter of a million pounds sterling. This is the largest gift ever made to science in this country, and will be productive of great benefit to humanity. The Lister Institute took its origin in the surplus of a fund raised (at my suggestion and with my assistance as secretary) by Sir James Whitehead when Lord Mayor, some sixteen years ago, for the purpose of making a gift to the Pasteur Institute in Paris, where many English patients had been treated, without charge, after being bitten by rabid dogs. Three thousand pounds was sent to M. Pasteur, and the surplus of a few hundred pounds was made the starting-point of a fund which grew, by one generous gift and another, until the Lister Institute on the Thames Embankment at Chelsea was set up on a site presented by that good and high-minded man, the late Duke of Westminster.

Many other noble gifts to scientific research have been made in this country during the period on which we are looking back. Let us be thankful for them, and admire the wise munificence of the donors. But none the less we must refuse to rely entirely on such liberality for the development of the army of science, which has to do battle for mankind against the obvious disabilities and sufferings which afflict us and can be removed by knowledge. The organisation and finance of this army should be the care of the State.

It is a fact which many who have observed it regret very keenly, that there is to-day a less widespread interest than formerly in natural history and general science, outside the strictly professional arena of the school and university. The field naturalists among the squires and the country parsons seem nowadays not to be so numerous and active in their delightful pursuits as formerly, and the Mechanics’ Institutes and Lecture Societies of the days of Lord Brougham have given place, to a very large extent, to musical performances, bioscopes, and other entertainments, more diverting, but not really more capable of giving pleasure than those in which science was popularised. No doubt the organisation and professional character of scientific work are to a large extent the cause of this falling-off in its attraction for amateurs. But perhaps that decadence is also due in some measure to the increased general demand for a kind of manufactured gaiety, readily sent out in these days of easy transport from the great centres of fashionable amusement to the provinces and rural districts.

Before concluding this retrospect, I would venture to allude to the relations of scientific progress to religion. Putting aside the troubles connected with special creeds and churches and the claims of the clerical profession to certain funds and employments to the exclusion of laymen, it should, I think, be recognized that there is no essential antagonism between the scientific spirit and what is called the religious sentiment. ‘Religion,’ said Bishop Creighton, ‘means the knowledge of our destiny and of the means of fulfilling it.’ We can say no more and no less of Science. Men of Science seek, in all reverence, to discover the Almighty, the Everlasting. They claim sympathy and friendship with those who, like themselves, have turned away from the more material struggles of human life, and have set their hearts and minds on the knowledge of the Eternal.

CHAPTER III.
NATURE’S REVENGES: THE SLEEPING SICKNESS.

Among the strange and mysterious diseases to which mankind is subject in regions less familiar to the civilised world than Western Europe, none is stranger or more appalling in its quiet, inexorable deadliness than the Sleeping Sickness of the West African coast. Apparently it has existed among the natives of that region from time immemorial; but the first printed record we have of it is due to Winterbottom, who, writing in 1803 of Sierra Leone, said, “The Africans are very subject to a species of lethargy which they are much afraid of, as it proves fatal in every instance.” One of the latest notices of the disease, before it became the subject of active investigation within the last five years, is that of Miss Kingsley, who saw a few cases near the Congo estuary, but, though she was impressed by the mysterious fatality of the disease, she did not describe it as very prevalent or as a general source of danger to life. The opening up of the Congo basin and increased familiarity with the inner lands of the West African coast have shown that this disease is widely scattered—though rarely so abundant as to be a serious scourge—through the whole of tropical West Africa. Writers in the early part of the last century described the disease as occurring in the West Indies and in Brazil. Its presence was almost certainly due, in those days of the slave trade, to the importation of negroes already infected with the disease; and a curious theory obtained some favour, according to which the sleeping sickness of the West Indian slaves was a kind of nostalgia, and, in fact, the manifestation of what is sometimes called “a broken heart.”

The signs that a patient has contracted the disease are very obvious. They are recognised by the black people, and the certainly fatal issue accepted with calm acquiescence. The usually intelligent expression of the healthy negro is replaced by a dull apathetic appearance; and there is a varying amount of fever and headache. This may last for some weeks but is followed more or less rapidly by a difficulty in locomotion and speech, a trembling of the tongue and hands. There is increased fever and constant drowsiness, from which the patient is roused only to take food. At last—usually after some three or four months of illness—complete somnolence sets in; no food is taken; the body becomes emaciated and ulcerated; and the victim dies in a state of coma. The course of the disease, from the time when the apathetic stage is first noticed, may last from two to twelve months.

It is this terrible disease which has lately appeared on the shores of the Victoria Nyanza, in the kingdom of Uganda, administered by the British Government. Until the early part of the year 1901 there was not the slightest suspicion that sleeping sickness occurred in any part of the Uganda Protectorate; nor was it known in East Africa at all, any more than in the north and south of that great continent. It seems gradually to have crept up the newly opened trade-routes of the Congo basin, and thence to have spread into the west of Uganda, the territory known as Busoga. Numbers of Soudanese and Congo men are known to have settled in this region after the death of Emin Pasha. First noticed in 1901, it was estimated in June 1902, by the Commissioner of Uganda, writing officially to the Marquess of Lansdowne, that 20,000 persons had died of this disease in the district of Busoga alone, and several thousands in the more eastern portion of Uganda. At this moment it is probable that the number of deaths in this region due to sleeping sickness since 1901 amounts to more than 200,000; and this though, most fortunately, the disease has not yet spread eastward from Uganda into British East Africa,[23] nor, so far as has been reported, down the Nile. No curative treatment for the disease has yet been discovered; nor is there any authenticated instance of recovery.

The appalling mortality produced by this disease in Central Africa naturally caused the greatest anxiety to his Majesty’s Government, which had but just completed the railway from the East Coast to the shores of lake Victoria Nyanza, and had established a prosperous and happy rule in that densely populated region. The official medical men on the spot, though capable and experienced practitioners, were unable to cope with this new and virulent outbreak. The Foreign Office, having no imperial board of hygiene and medical administration to apply to in this country, sought the assistance of the Royal Society of London.

A committee of that society had already undertaken the study of malaria at the request of the Secretary of State for the Colonies, and had sent out young medical men as a commission to make certain enquiries and experiments on that subject and report to the committee in London. The sleeping sickness enquiry was undertaken by the same committee; but unfortunately very insufficient funds were placed at its disposal. When the South African cattle-owners found their herds threatened six years ago by a new form of mortal disease—‘the East Coast fever’—the South African Government accepted the offer of Dr. Robert Koch, of Berlin, to undertake the investigation of the disease and the discovery, if possible, of a remedy, for the sum of £10,000. No such sum was at the disposal of the committee of the Royal Society. They were obliged to send out young and enterprising medical men, practically without pay or reward, to see what they could do in the way of determining the cause of, and, if possible, the remedy for, the terrible sleeping sickness raging in Uganda and destroying daily hundreds of British subjects. The committee set to work in the summer of 1902, and sent out Drs. Low, Christy, and Castellani to Entebbe, the capital of Uganda.

The guesses as to the cause and nature of sleeping sickness at the time when this commission set forth were very various. Some highly capable medical authorities held that it was due to poisonous food. The root of the manioc, on which the natives feed, was supposed to become infected by some poison-producing ferment. A more generally received opinion was that it was caused by a specific bacterium which invades the tissues of the brain and spinal cord. Several totally different micro-organisms of this sort had been described with equal confidence by French and Portuguese investigators as the cause of the sleeping sickness studied by them in West Africa or on the Congo. Sir Patrick Manson, the head of the British Colonial medical service, an authority of great experience in tropical disease, had put forward the suggestion that the sleeping sickness was due to the infection of the patient by a minute thread worm (allied to the ‘vinegar-eel,’ and one of a great class of parasites) which he had discovered in the blood of negroes and had named Filaria perstans.

The occurrence of minute worms (true worms, neither unicellular plants nor protozoa) in the blood of man was first made known by Dr. Timothy Lewis, who described the Filaria sanguinis hominis, as well as some other most important blood-parasites, some years ago (1878), when officially engaged in an enquiry into the cause of cholera in Calcutta. Subsequently, in China, Manson found that these little blood-worms were sucked up by mosquitoes when gorging themselves on the blood of a patient. It is, indeed, difficult to imagine how they should escape passing into the mosquito with the blood. Manson suggested that the minute worms (known to be the embryos of a worm which, when adult, is about one fifteenth of an inch long) are obliged to pass through a mosquito in order to accomplish their development; but no proof of this suggestion has ever been made. We know by abundant and repeated demonstration and experiment that another blood-parasite—the malaria parasite—must pass through a mosquito, in whose body it develops, and by which it is carried to a new victim of infection. This was suspected long ago by both peasants and doctors, and experimentally proved by Ross; but no such proof has been given of the relation of Lewis’s blood-worm to a mosquito. The so-called Filaria perstans, discovered by Manson in the blood of negroes, appears to be very different from the Filaria sanguinis hominis of Lewis. It is not known how it gets into the blood; and it is very astonishing, and much to be regretted, that none of the medical men who have had it under observation have given a proper anatomical account of it. It appears that this worm is very common in the blood of negroes in tropical Africa; and as it was found in several cases in the blood of individuals attacked by sleeping sickness, Sir Patrick Manson was justified in entertaining the view that this parasite was the cause of the disease.

One of the first results obtained by the commission sent by the Royal Society committee to Uganda was the proof—which had, indeed, been already furnished by the resident medical officers of the Uganda Protectorate—that Filaria perstans, though remarkably abundant in the blood of the negroes of Uganda, can have nothing to do with sleeping sickness, since, though it often occurs in persons attacked with that disease, it also exists in districts where sleeping sickness is unknown; and, further, many cases of sleeping sickness have been observed in which no Filaria perstans has been discovered in the blood or other parts of the body.

While Drs. Low and Christy occupied themselves with settling this question as to the connexion of Filaria perstans with the disease and carried out a careful study of its clinical aspects, Dr. Castellani examined the brain and spinal cord of those who died from sleeping sickness, for bacteria. He found again and again an extremely minute globular vegetable parasite—of the kind known as streptococcus—which he concluded to be the cause of the disease, although he had not produced the disease experimentally by inoculating an animal with this microbe.

In the early part of 1903 these were the only results obtained by some six months’ work of the medical men sent out by the Royal Society’s committee; and it was felt that something more must be done. The investigation of a disease hitherto little known and studied is one of the most difficult tasks in the world, requiring the highest scientific qualities. Any serious attempt to deal with the sleeping sickness in Uganda would, it was at length recognised, require the dispatch of a man of proved capacity and experience, provided with full powers and with trained men as his assistants. No such men are provided by the public service of the British Empire. To detach a medical man of recognised insight and experimental skill from his practice—even were it possible to find one specially qualified for the present enquiry—would involve the payment of a large fee, which neither the Royal Society nor the Foreign Office could command.

What, then, was to be done? Fortunately there was one man in the public service, recently appointed to be one of the chiefs of the educational arrangements of the Army Medical Department, who had shown himself to be especially gifted in the investigation of obscure diseases. This was Colonel David Bruce, F.R.S., who, some fifteen years ago, established the existence of Malta fever, as an independent disease, by his clinical observations and by the isolation and cultivation of the parasitic bacterium causing it; and who, further, when employed by the governor of Zululand a few years later (1895) to investigate the celebrated tsetze-fly disease of South Africa, had discovered, contrary to the assertions and prejudices of a large number of African sportsmen and explorers, that the horse and cattle disease known as nagana or tsetze-fly disease was due to the presence in the blood of the affected animals of a peculiar cork-screw-like animal parasite, the Trypanosoma Brucei. This is carried by the bite of the tsetze-fly from the blood of wild game, such as buffalo and antelope, where it does no harm, to the blood of domesticated animals, in which it multiplies and proves to be the source of a deadly poison causing death in a few weeks. The experiments by which Colonel Bruce demonstrated this relationship of tsetze-fly, trypanosome parasite, wild big game, and domesticated animals, were universally regarded as masterly both in conception and execution, and absolutely conclusive.

The committee of the Royal Society came to the conclusion that the thing to be done was to get Colonel Bruce to consent to proceed to Uganda, and to recommend the Foreign Office to obtain from the War Office the temporary detachment of Colonel Bruce for this service. Accordingly Colonel Bruce arrived in Uganda in the middle of March, 1903. Dr. Low and Dr. Christy had already departed, but Dr. Castellani was still at Entebbe engaged in the study of his streptococcus. He mentioned to Colonel Bruce on his arrival that he had on more than one occasion seen a trypanosome in the cerebro-spinal fluid of negroes suffering from sleeping sickness; but, inasmuch as Dutton on the West Coast and Hodges in Uganda had described a trypanosome as an occasional parasite in human blood, he had not considered its occurrence in sleeping-sickness patients as of any more significance than is the occurrence of Filaria perstans. Castellani regarded the trypanosome, like the filaria, as a mere accidental concomitant of sleeping sickness, the cause of which he considered to be the bacterial streptococcus which he had so frequently found to be present.

Naturally enough, Bruce was impressed by the fact that trypanosomes, of the deadly nature of which he had had ample experience, had been found, even once, in the cerebro-spinal fluid of sleeping-sickness patients; and he immediately set to work to make a thorough search for this parasite in all the cases of sleeping sickness; then under observation at Entebbe. He generously allowed Castellani to take part in the investigation, which resulted in the immediate discovery of the trypanosome in the cerebro-spinal fluid of twenty cases, out of thirty-four examined, of negroes afflicted with the disease; whilst in twelve negroes free from sleeping sickness the trypanosome could not be found in the cerebro-spinal fluid. Castellani returned to Europe three weeks after Bruce’s experiments were commenced, and announced the discovery, which has been, in consequence, erroneously attributed to him, although mainly due to Bruce.

Bruce continued his work in Uganda until the end of August, 1903, having been joined there by Colonel Greig of the Indian Army, who has continued the work of the Royal Society’s commission since Bruce left. Other valuable observations have been carried out by various medical men officially connected with the Uganda Protectorate. Bruce soon showed that in every case of sleeping sickness, when examined with sufficient care, the trypanosome parasite is found to be present in the cerebro-spinal fluid. He also showed that it is absent from that fluid in all negroes examined who were not afflicted with the disease, but made the very important discovery that the trypanosome is present in the blood (not the cerebro-spinal fluid) of twenty-eight per cent. of the population in those areas where sleeping sickness occurs, the persons thus affected having none of the symptoms of sleeping sickness, but being either perfectly healthy or merely troubled with a little occasional fever. The subsequent history of all the cases thus observed has not as yet been recorded. But in many such, even in some Europeans, the earlier presence of the trypanosome in the blood has been followed by its entry into the cerebro-spinal lymphatics, and by the fatal development of sleeping sickness.

As already indicated, it was found by Bruce, on recording the cases of sleeping sickness brought into or reported in Entebbe, that there were certain “sleeping-sickness areas” and other areas free from sleeping sickness. The theory now took shape in Bruce’s mind that the trypanosome first gets into the blood, and then after a time, makes its way into the cerebro-spinal system, only then producing its deadly symptoms. Very generally, when once in the blood, the trypanosome multiplies itself, and sooner or later—apparently, in some cases, even after two or three years—gets into the cerebro-spinal fluid. It is probable that it may be destroyed by natural processes in the human body before this final stage is reached; and thus the infected person may recover and escape the deadly phase of the disease. But nothing certain is known, as yet, on this head. Later observations show that the trypanosome is found alive and in large quantity in the lymphatic glands, especially those in the region of the neck in infected persons. These glands were known to be enlarged in persons suffering from the disease.

Colonel Bruce’s next step was to ascertain the mode in which the trypanosome is introduced into the blood. Naturally he looked for a kind of tsetze fly, such as carries the trypanosome in the nagana disease of horses and cattle already studied by him in Zululand. It is a fact that the Glossina morsitans and Glossina pallidipes, which are the tsetze flies of the “fly-districts” where nagana disease is rife, are unknown in Central or Western Africa; and also it is a fact that no tsetze fly had been observed in the neighbourhood of the Victoria Nyanza when Colonel Bruce began his enquiries. He employed, through the good-will of the native chiefs and rulers, a large number of natives to collect flies throughout the country forming a belt of twenty or thirty miles around the north of the lake. Many thousands of flies were thus brought in, and the localities from which they came carefully noted. Among these flies Colonel Bruce recognised a tsetze fly; and when these collections were received at the Natural History Museum in London, it was at once determined by Mr. Austen, the assistant in charge of our collections of Diptera (or two-winged flies), that the Uganda tsetze fly was not the same species as that of Zululand and the fly country, but a distinct species previously known only on the West Coast and the Congo basin, and described by the name Glossina palpalis. The story thus developed itself: the trypanosome of sleeping sickness is probably carried by this West Coast tsetze fly just as the trypanosome of nagana is carried in the south-east of Africa by the Glossina morsitans and pallidipes, the regular and original “tsetze” flies.

Sleeping sickness thus presented itself as a special kind of human tsetze-fly disease. To test this hypothesis, Colonel Bruce pursued two very important and distinct lines of enquiry. In the first place he found that those places on his map which were marked as “sleeping-sickness areas” were precisely those places from which the collected flies included specimens of tsetze fly, whilst he found that there were no tsetze flies in the collections of flies brought in by the natives from the regions where there was no sleeping sickness.

His second test inquiry consisted in ascertaining whether the tsetze flies of Uganda are actually found, experimentally, to be capable of carrying the trypanosome from one infected person to another. For this purpose it was necessary to make use of monkeys, certain species of which were ascertained to be liable to the infection of the sleeping sickness trypanosome when this was introduced by means of injection through a syringe. Such monkeys were found to develop the chief symptoms of sleeping sickness, and ultimately died of the disease, their cerebro-spinal fluid being invaded by the parasites. Accordingly it was possible to use monkeys as test animals. It was found by Colonel Bruce that tsetze flies (Glossina palpalis) which had been made to bite infected negroes could carry the infection to the monkeys; and it was also found that even when a number of tsetze flies, not specially prepared, were allowed to bite a monkey, the latter eventually developed the trypanosome in its blood and cerebro-spinal fluid, thus showing that the tsetze flies, as naturally occurring in the country around Entebbe, contain many of them, the trypanosome ready to pass from the fly to a human or simian victim, when casually bitten by the fly.

Experiments such as these of infection by the fly, and the use of monkeys in the research, require very great care; and it is quite reasonable to ask that they shall be repeated and most carefully checked before they are considered as demonstrative and absolutely certain. It may, however, be considered as practically certain that the sleeping sickness is due to the presence in the cerebro-spinal fluid of quantities of a minute parasite, the Trypanosoma Gambiense, which is carried from man to man by the palpalis tsetze fly, which sucks it up from the blood of an infected individual and conveys it to previously uninfected individuals. The natives in Uganda lie about and sleep under the shade of trees where the tsetze flies are especially abundant; and they are quite indifferent to the bites of flies of one kind and another.

It is the dislike to the mere touch of a fly, still more to its bite, which has protected Europeans almost entirely from the sleeping sickness. Unfortunately there is no immunity for Europeans in the matter; and the existence of half a dozen or more cases of white people infected with the trypanosome, who have ultimately died in England or elsewhere in Europe from sleeping-sickness contracted through the bite of a fly in Africa, is abundant proof that there is not, as has been supposed, any special freedom from the disease for white people.[24]

The foregoing description of the nature and mode of the infection of sleeping sickness will not cause any astonishment to the layman of the present day who knows anything of recent medical science. We are all familiar with the danger of fly-bites, even in this country, where deadly bacteria are occasionally carried by biting flies, such as the horse-flies, into the human subject; and nowadays every one is more or less familiar with the discovery of the minute blood-parasite which causes malaria or ague and is carried by a particular kind of gnat in the interior of which it multiplies by a process of sexual conjugation. At the same time the reader who is interested in sleeping sickness will probably desire to know more about the nature of the tsetze flies and some further details as to the parasite spoken of as trypanosome.

The tsetze flies form a genus called by Wiedemann (in 1830) “Glossina.” They are only found in Africa; and some seven species in all are known. They are little bigger than a common house-fly, and much like it in colour (fig. 48). They differ in appearance from the house-fly in the fact that the wings, when the insect is at rest, are parallel to one another, and slightly over-lap in the middle line, instead being to a small extent divergent at their free extremities. The bite, like that of all flies, is rather a stab than a bite, and is effected by a beak-like process of the head, the blood of the animal pricked in this way being drawn into the fly’s mouth by a sucking action of the gullet. The tsetze flies appear to be especially greedy and are said to gorge themselves to such an extent that the blood taken in from one animal overflows the gullet, and so contaminates the wound inflicted by the fly on the next animal it visits. It is at the present moment assumed very generally that this is the way in which infection is produced. But it is not at all improbable that the trypanosome undergoes some kind of multiplication and change of form when sucked into the tsetze fly as happens in the case of the malaria parasite when swallowed by the Anopheles gnat. No such change has yet been discovered in regard to the trypanosome of sleeping sickness: but it cannot be said that the matter has been exhaustively studied, or that a negative conclusion is justified.[25]

As to the parasite itself—the trypanosome—a long and very interesting story has now to be told. The first blood-parasite ever made known to naturalists and medical men was that to which Gruby, in 1843, gave the name Trypanosoma sanguinis. He found it in the blood of the common frog. We have here reproduced a figure of this original trypanosome (fig. 49). Similar parasites had been seen, but not named, in the blood of fishes. These trypanosomes are all very minute and of a somewhat elongated form, a fair average length being one thousandth of an inch. They are simple protoplasmic animals, consisting of one single nucleated corpuscle. The protoplasm is drawn out at one end of the creature into a motile undulating thread, and from the point where this joins the body a membranous undulating crest extends along the greater part of the animal’s length. There is no mouth, nutrition being effected by the imbibition of soluble nutrient matter.

After a long interval Gruby’s trypanosome was re-discovered in 1871; and then several kinds were described in the blood of tortoises, fishes and birds. In 1878, Dr. Timothy Lewis found a parasite in the blood of rats, at first in India, and subsequently in the common rats of London sewers. This parasite resembles a trypanosome in many respects (fig. 46A), but was very properly given a distinct name by Savile Kent, who called it “Herpetomonas.” This name has, however, been dropped; and the rat’s-blood parasite is spoken of as a trypanosome. It is the Trypanosoma Lewisii, and was the first of these trypanosomes to be found in the blood of a mammalian animal. The Trypanosoma Lewisii of the rat’s blood seems to do no harm to the rat, in which it swarms, multiplying itself by longitudinal fission; nor is it at present known to produce any trouble in other animals when transferred to their blood. Similarly, the frog’s trypanosome seems to exist innocently in the frog’s blood.

The next trypanosome discovered (1880) was, however found in the blood of camels, horses, and cattle suffering from a deadly disease known in India by the name “surra.” It is called Trypanosoma Evansii, after the observer who detected it. Trypanosomes now began to get a bad name, for the next was discovered in animals afflicted by a North African disease known to French veterinaries as “dourine.” This trypanosome was called T. equiperdum.

A little later, namely, in the year 1895, came Bruce’s discovery of a trypanosome associated with a tsetze fly in the production of the terrible nagana disease of the “fly-belts” of South Africa, which renders whole territories impassable for horses or cattle (fig. 46B). The remarkable and important observation was made by Bruce that this trypanosome (known as T. Brucei) inhabits the blood of big game without injuring them, just as the rat’s trypanosome inhabits the rat’s blood without producing disease; and that it is only when the trypanosome is carried from these natural wild “hosts” to domesticated animals introduced by man, such as horses asses, cattle, and dogs, that disease results. The wild animals are “immune” to Bruce’s trypanosome; the introduced animals are poisoned by the products of its growth and fissile multiplication in their blood.

Since Bruce’s researches on nagana, a trypanosome, T. equinum (fig. 46D), has been discovered in the horse-ranches of South America, where it causes deadly disease, the mal de caderas, among the collected horses; and a curiously large-sized trypanosome has been found by Theiler in the blood of cattle in the Transvaal. Down to a recent date no trypanosome had been found in the blood of man; and indeed it is almost certain that none of the kinds hitherto mentioned can survive in his blood. But in 1902 Dutton discovered a trypanosome in the blood of a West African patient; and a few other cases were noted. This trypanosome of human blood was called by Dutton T. Gambiense. It was not found to be connected with any serious symptoms, a little fever being the only disturbance noted. It now, however, appears that this trypanosome in the blood is the preliminary stage of the infection which ends in sleeping sickness; and, as we have seen, in a population seriously attacked by sleeping sickness, as is that of Uganda, as many as 28 per cent. of the people have trypanosomes in their blood.

There is no ground at present known for distinguishing Dutton’s T. Gambiense of human blood from that which Bruce has found to be so terribly abundant in Uganda, and to be the cause of sleeping sickness. Indeed all the trypanosomes of the blood of the larger mammalia are singularly alike in appearance; and the figure which is here given (fig. 50) of the trypanosome of sleeping sickness (T. Gambiense) might quite well serve to represent the T. Evansii of surra disease, the T. Brucei of nagana disease, or the T. equinum of the South American mal de caderas.

A most characteristic feature, which has been made out by the careful study of these trypanosomes by means of colouring reagents and very high powers of the microscope, is that, whilst there is a large granular nucleus there is also a small body at the anterior end of the animalcule which readily stains and is placed at the end of the root (so to speak) of the vibratile flagellum or free thread. This smaller nucleus has been variously called the “micronucleus,” the “centrosome,” and the “blepharoplast.” It is identical with a structure similarly placed in non-parasitic microscopic animals to which trypanosoma is undoubtedly related. We find it in the phosphorescent noctiluca of our seas, and in various animalcules called “Flagellata.”