Animal Parasites and Messmates

There are some animals which are infested at every period of their life, and at every season; others in far greater number only during their youth, and they gather in at the commencement of their life the harvest for the rest of their days. The greater part of parasites, especially of fish, are introduced with the first nourishment. As soon as they issue from the egg, young rays, like young turbots, are already stuffed with worms which afterward obstruct the digestive organs. The stomach of each of these fishes is like a filter which allows every thing which is food to pass, but detains on its passage and without any change all that is living. When we examine the stomach and observe the food in its different degrees of digestion, we see distinctly the worms coming out of their holes, wallowing in that which physiologists call chyle, and choosing afterwards at their convenience the place where they may completely develop themselves. At the end of a few days, the fish may have swallowed an innumerable quantity of small animals, and if each of them introduces some worms, we can easily understand in how short a time the intestine becomes literally filled.

We may even divide parasites into two great categories, according to the organs which they choose: those which inhabit a temporary host, almost always instal themselves in a closed organ—in the muscles, the heart, or the lobes of the brain; those, on the contrary, which have arrived at their destination, and which, unlike the preceding, have a family, occupy the stomach with its dependencies, the digestive passages, the lungs, the nasal fossæ, the kidneys, in a word, all the organs which are in direct communication with the exterior, in order to leave a place of issue for their progeny. The young ones are never enclosed. Even the blood is not free from these animals, but there are few which lodge there, except during the act of migration.

In Egypt, Dr. Bilharz observed a distome in the blood of a man (Distoma hœmatobium); the Strongylus of the horse has been long known, which causes serious injuries in its vessels (Strongylus armatus); as also the strongylus of the dolphin and of the porpoise (Strongylus inflexus), and the filaria of the dog (Filaria papillosa); and some are also found in the blood of many birds, of reptiles, batrachians, and fishes; so that there is no class of vertebrates which escapes.

They do not disfigure themselves, nor put on any special costume, like those which seek a permanent abode. Gluttony is not with them the only moving principle of existence; they do not forget what they owe to the world, and keep up an appearance which allows them at all times to present themselves afresh.

Parasites are scattered over every region of the globe; they choose their place, and observe, like all living creatures, the laws of geographical distribution. All do not inhabit the animal kingdom; some seek for assistance in vegetable life. Many insects lay their eggs in seeds or fruits, and their progeny, as soon as they are hatched, find abundant nourishment in the sap or in the farina stored up for the young plant; others pass into a state of lethargy while the seed is dry, and recover their activity every time that they receive a little humidity.

We have seen that each parasite has its host: we must have a particular name to designate it. But that does not imply that if it find not its dwelling-place it must perish. It may only live some time at the expense of its neighbour, and thus pass for its parasite. Naturalists are occasionally deceived. Thus, they once believed in the passage of the Schistocephalus of the stickleback into the intestines of certain birds which eat them, and in which they are only found accidentally. The Ligulæ of the Cyprinidæ, found in the intestines of the cormorant or the goosander, are not, in our opinion at least, worms peculiar to these birds. They are strangers which must either emigrate again or die. Acari which originally belonged to mammals and birds, have been found living on man, causing prurigo, or even serious maladies, and yet these parasites are not regarded as peculiar to our species. We might cite other examples. Who has not been annoyed by the flea, which abandons for an instant the dog, its natural host?

As we have before said, there are many parasites which require to be studied in order to determine the host peculiar to each of them; although parasites sometimes lose their way, and introduce themselves into the wrong neighbour, yet they can live there but a short time. Instances have been known, in which the larvæ of flies have penetrated into man accidentally by the mouth or the nostrils. Reptiles have been known to live a certain time in the stomach. A German physiologist, Berthold, professor at the University of Göttingen, has given an account of all those which have been found under such circumstances, and the number of them is considerable; he has written a memoir on the abode of living reptiles in man.

The size of parasites is very various: Boerhaave mentions a bothriocephalus three hundred ells in length; at the Academy of Copenhagen, it was reported that a solitary tape-worm (Tænia solium) had been found eight hundred ells long. Female strongyli have been seen from two decimètres to one metre in length; and Gordii of two hundred and seventy millimètres. We have found in a fish a worm which lived rolled up like a ball, and which measured, when unrolled, more than a mètre.

Should an organ infested with worms be considered diseased, simply on account of their presence? We hesitate not to say that, as long as these guests cause no disorders, there is no pathological condition. The child which has Ascarides lumbricoides in its stomach is not necessarily ill. All animals in a wild state always have their parasites; they lose them rapidly when in captivity.

But here, as in all things, excess is hurtful. Certain organisms, developing themselves immoderately, may break the harmony necessary between the parasites and the host which they frequent. It has been found recently that many morbid affections, as the potato and vine diseases, have for their origin only the abnormal development of certain microscopic beings hidden in the organism.

It is found, that in Egypt, a distoma is developed in the blood, and occasions a very severe malady, scarcely known to physicians. In Iceland, a cestode causes the death of a third part of the population. Worms develop themselves in the eye, and may even cause blindness; the Cœnurus of the sheep causes giddiness, and becomes fatal to the animal which harbours it. The chlorosis observed in Egypt and Brazil must, it appears, be attributed to a considerable development of a nematode worm, which lives in the small intestines, and which naturalists know under the name of Dochmius duodenalis; and lately the Trichinæ set all Europe in a state of excitement, and trichinosis was for a time more dreaded than cholera. In spite of all these accidental circumstances we think that the animal which possesses its ordinary parasites, far from being ill, is in a normal physiological condition.

Some years ago they had no idea of the migration of animals from one body to another. As we have said elsewhere, Abildgard, half a century ago, made experiments on the worms of fishes which he caused ducks to swallow, but these experiments had no result, and formed rather an obstacle to ulterior progress, than an approach to truth. The worms of fishes have been known to live in birds; but these worms were only there as adventitious parasites. Liguli live some days in the goosander, but they do not maintain their position.

Our great initiator into the world of parasites, Mons. Siebold, arrived also at a conclusion which could not be maintained. Having observed, with his habitual sagacity, that the cysticercus of the mouse is the same worm which lives in the cat, he published his opinion that the eggs of this tænia had lost their way in the mouse, that the young worms had become sick there, and that in the cat alone, they could be healthily and completely developed. It was like a plant lost on a soil where it could not live, and still less flourish. May I be permitted to state by what means we have arrived at the knowledge of the transmigration of worms?

I had seen the Tetrarhynchus agamus inhabiting a cyst in the peritoneum of the gadidæ, and I had met with the same tetrarhynchus completely developed and sexual in the spiral intestine of the voracious fishes known under the name of squalidæ, or sharks. This caused me to write to the Academy of Brussels, at the meeting on January the 13th, 1849, that the order of vesicular worms, admitted by all helminthologists, ought to be suppressed.

These worms began to be understood when these cysticerci ceased to be regarded as sick creatures. Siebold had mistaken the crèche for the hospital, and instead of seeing in the cysticercus a young animal full of life and of the future, he looked upon it as a gouty individual, ready to breathe its last sigh.

That which adds still more to the difficulty of recognizing them is, that while young they are often enveloped in swaddling clothes which nevertheless permit them to wander freely; then in a simple robe, in keeping with the home which shelters them; and at last in a wedding dress, which hides the eggs and the apparatus which produces them. The nymph in her virgin condition has none of the attributes of future maternity.

It is in this category that we find the Distomes, so common in all the classes of the animal kingdom. This is not all: frequently, among these various forms, these animals when young produce little ones, which in no respects resemble the others, and are not even formed in the same manner. As soon as they quit their swaddling-clothes, they increase by gemmation, and without sexual union, while those which are produced from buds increase sexually. Thus the daughter does not resemble her mother, but her grandmother. This phenomenon has been known by the name of alternate generation; we have called it digenesis.

More unfortunate are those which are kept under the bolts and bars of their host from their early youth to mature age; they have no participation in the great banquet of life, except it be in the pleasures of the table and of love. We also find some parasites which occupy different organs in the same animal, and which have different sexual attributes according to the situation which they inhabit. We know some which are hermaphrodite in the rectum or in damp earth, and whose young ones, having the sexes separate, live as parasites in the lungs.

Parasites are not usually reproductive in the animal which they inhabit. They respect the hearth which shelters them, and their progeny are not developed by their side. The eggs are expelled with the feces, and sown at a distance for other hosts.

Parasites may be divided into several categories. We may bring together in the first of these, a certain number of animals, which, without being true parasites, seek for a place of shelter, and, either on account of their wretchedness or their misery, require this protection in order that they may live.

In the last category we shall arrange true parasites, which take both their lodging and their food. And here, again, we shall meet with three distinct subdivisions.

The first includes those which travel from one hotel to another before they arrive at their destination; to-day they lodge in a prawn, to-morrow in a gudgeon, then in some fish which preys upon others, as the perch or the pike. These are nomadic parasites, which do not stop or think of family life until they have found the hotel for which they are destined.

Sometimes the parasite gets into a wrong train, and not being able to retrace his steps, he remains at a station where no other train will take him up. He is condemned to die in a waiting-room.

In the last subdivision, we have parasites that have arrived at their destination, occupying themselves in future only with the joys of a family.

The same host does not always harbour the same worms in the different regions of the globe which it inhabits. This relates both to the parasites of man, and to those of the domestic animals. Thus the large tapeworm of man, which naturalists call Bothriocephalus, is found only in Russia, Poland, and Switzerland. A small tape-worm, Tænia nana, is observed nowhere except in Abyssinia; the Anchylostoma is known at present only in the south of Europe and the north of Africa; the Filaria of Medina, in the west and the east of Africa; the Bilharzia, that terrible worm, has only been found in Egypt.

There are also parasitic insects dreaded by man, as the Chigoe (Pulex penetrans) which, happily, is only known in certain countries. Some, however, have become cosmopolitan, since man has introduced them wherever he has established himself.

We find extinct fossil genera and species in all the classes of the organic world. Is it the same with worms and animals of other classes which are only known in the condition of parasites? Had the Ichthyosauri and the Plesiosauri worms in their spiral cœcum like plagiostomous fishes, which resemble them so much in the digestive tube? We do not doubt this, and we should have been glad to give some demonstration of it. For this purpose, we have made a collection of the coprolites of these animals, but we have not yet succeeded in getting slices thin enough or sufficiently transparent to discover the eggs or the hooks of their cestode worms.

Not long ago, the partisans of spontaneous generation found in the class of worms their principal argument for their old hypothesis, and it was even after the publication of my treatise on intestinal worms that this question, which seemed forgotten, was taken up again by Pouchet. At present, they appear to have given up parasites, which reproduce their kind like other animals, and to have fallen back upon the infusoria, the last intrenchment which remained to the partisans of spontaneous generation, whence Mons. Pasteur has scientifically dislodged them. It is evident to all those who place facts above hypotheses and prejudices, that spontaneous generation, as well as the transformation of species, does not exist, at least, if we only consider the present epoch. We are leaving the domain of science if we take our arms from anterior epochs. We cannot accept anything as a fact, which is not capable of proof.

CHAPTER VI.

PARASITES FREE DURING THEIR WHOLE LIFE.

This first category of parasites includes all those which are not enclosed, and which live at the expense of others, without losing the attributes and advantages of a wandering life; they are as free as the vulture or the falcon which pursues its prey. We shall not, however, include among them the parasitical kite of Daudin, which tears from the hands of the traveller a piece of the flesh which he is preparing in the open air, nor the small Egyptian plover, which keeps the teeth of the crocodile clean. The former is a pirate, a highway robber; the plover, on the contrary, is a kind neighbour, an attendant who performs valuable services.

We are more correct in considering as parasites the Vampires (Phyllostoma), those audacious bats of South America, which settle on the sleeping traveller or his beasts, and suck their blood by means of the sharp papillæ of their tongue. These animals are winged leeches which bleed their victim and pass on. We place among free parasites the greater part of leeches, some insects, and a certain number of arachnida, crustaceans, and infusoria.

Leeches drink the blood of their victim, and when they are gorged to the very lips, they fall off, taking a siesta for weeks or months. Thus enjoying a repast at very long intervals, it is useless for them to continue longer at table; and this is therefore another reason that they should usually preserve their organs of locomotion, that they may use them after their long period of digestion.

The most well-known leeches are those which attack man and the other mammalia, but some are also found on other vertebrate animals, especially on fishes. Their organization is always proportioned to that of the host which they frequent; thus, the simpler their host, the lower is their organization. The mollusc harbours hirudinidæ much lower in the scale than those which are found in fishes, and especially in mammals.

Vampires make use of the papillæ of the tongue, and also of their teeth, which act as so many lancets; leeches apply their toothed lip, saw asunder the epidermis, and with the mouth applied to a network of capillary vessels, suck till they fall off, intoxicated with blood.

We find a great variety in the mode of life of these hirudinidæ; and if we sometimes meet with some which are sober and delicate, the greater part show a voracity of which it is difficult to form any idea. A leech has been met with in Senegal which draws a quantity of blood equal to the weight of its body. There are leeches which devour entire earth-worms. Fortunately the greater species are not the most voracious: we might feel rather uneasy in the midst of leeches similar to that which Blainville has described under the name of Pontobdella lævis, which is not less than a foot and a half in length.

It is generally thought that all leeches are aquatic, but this is a mistake. In the warm regions of the Old and New World, there live in the midst of the brushwood, leeches which attack the traveller as well as his horse, and suck the blood of both without their perceiving it.

Hoffmeister gives the following account with reference to small leeches in the island of Ceylon:—

The aquatic leeches are better known, and with but few exceptions, the accidents produced by them are little to be feared. In Algeria it is not uncommon, as army surgeons tell us, to see soldiers, while drinking spring water, swallow small leeches which may do them injury.

We find from official reports that the French soldiers often suffered, during the campaigns in Egypt and Algeria, from an aquatic leech (Hœmopis vorax), which attacked the mouth and the nostrils, and did not respect man any more than horses, camels, and oxen. The leech discovered by Dr. Guyon under the eyelids and in the nasal fossæ of the crab-eating heron of Martinique, is probably a monostomum, and not one of the hirudinidæ. Leeches have also been found on turtles under the name of Eubranchella Branchiata. Say saw one on a chelonian, and others on tritons and frogs.

It is especially upon fish that these worms are found, and we cannot hesitate to consider the greater part of them as true parasites. We have described a whole series of them which live upon marine fishes, especially on the barbel, the bass or sea-wolf, the halibut, the dab, and different species of gadidæ. A. E. Verril published last year the description of several kinds of American leeches, among which we see two which infest a fish (Fundulus pisculentus) of West River, near Newhaven. A large and beautiful species, which is known by the name of Pontobdella, is also found upon the Rays.

Many naturalists have considered these curious worms worthy of attention, and have made many interesting observations upon them. One of the finest memoirs on this subject is that of Mons. A. de Quatrefages. We may here mention, in connection with their mode of life, that neither Leydig nor Quatrefages found globules of blood in their digestive cavity. The branchellions live on the mucous products of the secretions of the skin, and instead of being parasites, we may consider them as worms paying liberally for the room which they occupy in their host, by maintaining his skin in good condition. They ought rather to be classed among animals which render service to others; that is, among mutualists.

There are different leeches which inhabit invertebrate animals. Rang mentions a little creature of this kind in Senegal, living as a parasite upon the respiratory apparatus of an anodont. Gay discovered in Chili one of the Hirudinidæ in the pulmonary sac of an Auricula, and another on the branchiæ of a crab (Branchiobdella Chilensis). Mons. Blanchard has noticed a malacobdella in the branchiæ of the Venus exoleta; and it was known in the last century that the Mya truncata of our coast also lodges a malacobdella which lies always under the foot of the animal. This is the hirudinean of which we have spoken above, which is allied transitionally to the trematoda.

Together with the Hirudinidæ, we find very small worms, transparent, bristling with daggers and spikes of every form, which are found everywhere in fresh water. They are known by the name of Naïs. They are so completely transparent that we can see the action of all their organs through the substance of the skin. They have been the subject of several remarkable works.

They live freely among the leaves of Lemna and other aquatic plants; but there is one species much more restricted in their habitat than the others; these seek assistance from the Lemneæ, and live at their expense. It is because of this kind, of which the genus Chœtogaster has been formed, that we mention them here. Their long bristles are veritable halberds, which they employ with astonishing skill, both in attack and defence.

Of this kind are gnats, fleas, lice, bugs, and a great many others, among which we ought not to forget the acaridæ, nor those singular parasites of bats, which bear no slight resemblance to spiders swimming in the midst of the fur. Volumes might be written concerning the organization and the habits of these parasites. These small creatures inspire the naturalist with no more disgust than the earth-worm of our flower-beds, or the salamanders of marshy places. Each one plays its part according to its conformation, and the most abject in appearance is not always the least useful.

We will select among these parasites some two-winged insects, among which there are many which suck blood. Those which are generally called flies are divided into two groups, under the name of Nemocera and Brachycera; many of these live only on blood, and are more terrible than the lion and the tiger; in many countries man can defend himself against those fierce carnivora, but he is there completely powerless and without defence against these insects.

In Davis’s Straits, in lat. 72° N., Dr. Bessels, on board the Polaris, was obliged to interrupt his observations on account of these insects. A great number of them have been seen up to the 81st degree of latitude. Besides gnats, there were also found Chironomi, Corethræ, and Trichoceræ. As Dr. Bessels was able to save from the Polaris some small collections of insects, we shall soon know the names of the species which live in these high latitudes. It is said that the Esquimaux and the Lapps cover their skin with a coating of grease, not only to lessen the effect of the cold, but to defend themselves from the stings of gnats.

De Saussure has alluded to curious relations which exist in Mexico between a bird, a beast, and an insect. “Bulls bury themselves in the mud,” says this learned traveller, “in order to avoid the attacks of gnats, leaving in the air only the tip of their nostrils, on which a beautiful bird, the Commander, posts himself, in this position the Commander watches for the Maringouin which is bold enough to enter the nostrils of the animal.”

Gnats are parasites in the same manner as leeches, since, like them, they suck the blood, and live at the expense of others. There is, however, this difference, that the females only are greedy of blood; if this fail them, they live, like the males, on the juices of flowers. Another difference is that they are completely harmless till they have wings, and though they live long under their first form, in damp earth or in water, the duration of their life as perfect insects is of short duration.