It will naturally be expected that I should give a full account of the parasites of the solipedal, solidungulate, or equine mammals. As regards the horse I regret that I cannot meet this expectation in so complete a manner as the subject deserves; nevertheless, with the aid of an extended bibliography the summary here offered will be found to be tolerably exhaustive. At all events I think I may say that no similar record has hitherto been attempted.
The liver fluke (Fasciola hepatica), though not very frequent in the horse, is not uncommon in the ass. In dissecting-room subjects at the Royal Veterinary College it is often encountered. In France it was originally found in the horse by Daubenton. As I learn from Sonsino, Dr Abbate Bey recently recorded a similar find at Cairo. In solipeds generally the liver fluke appears to be almost harmless, for, notwithstanding the frightful ravages produced by rot amongst a variety of animals besides sheep, we have no evidence of the destruction of horses from this cause. In the German outbreak of 1663–65 multitudes of cattle and deer perished, and in the French outbreak of 1829–30 five thousand horned beasts succumbed in the arrondissement of Montmédy alone. In neither of these epizoötics were the solipeds affected. More importance attaches itself to the study of the amphistomatoid flukes. These parasites, though in a scientific sense only recently discovered in equine bearers, have been long known to the natives of India. They appear to be capable of producing serious intestinal irritation. I have described two forms (Amphistoma Collinsii and A. Coll., var. Stanleyi), which infest the colon. The specimens sent to Prof. Simonds from India by Mr Stanley, V.S., were much larger than those sent to me from Simla by Mr Collins, V.S., some ten years later (1875). As in all other amphistomes obtained from the intestines of elephants and cattle, the worms, when fresh, were of a bright brick-red color. By the natives of India these parasites are called Masuri; but no description of the worms had been published prior to the account which I gave of the contributions forwarded by Major-General Hawkes, Mr Collins, and Mr Stanley.
I shall have occasion to speak of the elephant’s Masuri further on; but in the meantime I must remark that the generally received notion as to the parasitic cause of the earth-eating propensities of various animals seems to have some foundation in fact. Not alone from Major-General Hawkes in Madras, from Mr Folkard in Ceylon, and from various other trustworthy sources, have I been informed of this habit on the part of Indian horses, but Dr Rowe told me that Australian horses, and even sheep, infested with stomach-worms, are in the constant habit of consuming large quantities of sand. From all the facts that have come before me, I am inclined to think that gastric or intestinal irritation, however brought about, may induce the habit in question, parasites being only one of the many sources of irritation giving rise to symptoms of colic in solipeds and pachyderms alike. At all events the African elephants at the London Zoological Society’s Menagerie, as repeatedly witnessed by myself, are in the habit of swallowing large quantities of soft mud during the summer months, but no traces of masuri have as yet been detected in their fæces.
When by letter I informed Major-General Hawkes of an interesting find by Mr Collins of about a thousand Amphistomes in the colon of a horse that had died at Simla, the announcement called forth a reply which is sufficiently instructive to be quoted. Writing from Secunderabad in July, 1875, he says, respecting this “find:”—“Your statement has incidentally thrown light upon a subject which has puzzled many of us in this country. It occasionally happens that a horse, on being opened after death, is found to have accumulated in his intestines large quantities of sand and gravel. In a recent case this accumulation amounted to 141/2 lbs. Until recently it was always held that this gravel or sand could only be introduced with the animal’s food. All grain in this country is trodden out by bullocks on an earthen floor, and the grain undoubtedly contains a proportion of sand and gravel derived from this source. Although this ought to be carefully washed out before it is given to the horse, still, owing to the carelessness of the native horse-keepers, this cleaning is, I expect, often omitted. In the daily ‘feed’ of eight or ten pounds of grain given to each horse the utmost quantity of sand or gravel that could be found admixed therewith would not probably exceed two or three ounces; consequently it would take from 77 to 116 days to accumulate so large a quantity as 141/2 lbs. Now, the advocates of the theory of the gradual accumulation of sand in this way have never been able to explain why the grain, grass, hay, and other ingesta should pass in the ordinary way through the intestines, whilst this sand or gravel remains behind. One can understand the possibility of such substances as wool, hair, or similar matters concreting in the alimentary canal, though I believe they are usually found in the stomach, and not in the intestines; but how a most incohesive substance like sand can possibly accumulate in the gradual way required by their theory I have never heard even plausibly explained. On the other hand, the fact that horses are often excessively addicted to eating earth is well known; and if my memory serves me correctly, it was found necessary, about twenty years ago, to remove the mud-walls of the pickets surrounding some of the horses of a mounted corps in this presidency in consequence of this habit. Now, given the fact that the amphistoma has been found in the horse (as your specimens prove), may we not fairly suppose it possible that the animal resorts to the same mode of ridding himself of this parasite as does the elephant? and also, would it not in a much more natural manner account for the large quantity of gravel or sand found in the intestines than does the theory of gradual accumulation? Reasoning from analogy, as in the case of the elephant, this eating of earth in the horse would be an instinctive effort on the part of the “host” to rid himself of the parasite. This self-taken remedy is doubtless in many cases quite effectual, though unnoticed. The fatal cases are probably those in which the horse has either overdone the remedy or where the system was too debilitated to carry off a quantity of sand or gravel that would otherwise have safely passed through the intestines of a horse in more robust health. The actual fact must, of course, be verified by careful investigation.”
Fig. 62.—Gastrodiscus Sonsinonis. a, Mouth; b, caudal sucker and posterior mesial cleft; c, left lip of the gastric disk; d, anterior mesial cleft; e, e. gastric suckerlets; f, reproductive papilla. Enlarged. Original.
Closely allied to the Masuri is an amphistome which I originally named Gastrodiscus Sonsinoii, but which should be altered as opposite (Fig. 62). It exceeds 1/2″ in length and 1/3″ in breadth (16 mm. long by 10 broad). Its discovery by Dr Sonsino was one of the results of his examination of sixteen carcases of solipeds that died during the Egyptian plague of 1876. Specimens having been forwarded to Panceri, Von Siebold, Leuckart, and myself, most of us at once agreed that the worm was new to science. Pointing to the genera, Notocotylus and Aspidocotylus, I explained its close affinity to the latter more particularly. Whilst Notocotylus has fifty supplementary suckers on its back, Aspidocotylus has nearly two hundred small ventral suckers seated on a convex disk. In Gastrodiscus a still larger number of suckerlets are placed in the deep concavity of a large gastric disk formed by the outstretched and inrolled margins of the body of the parasite. Zoologically speaking, the odd thing about this singular worm lies in the circumstance that its nearest fluke-relation, so to speak (Aspidocotylus mutablis), dwells in a spiny-finned fish (Cataphractus); and this fish itself forms an aberrant genus of the family to which it belongs (Triglidæ). From what has been said it will be seen that our Gastrodiscus must not be confounded with Cotylegaster cochleariform (or with its synonym Aspidogaster cochleariformis), to which parasite Von Siebold was, I believe, induced to refer it. Like most of the true amphistomes, the worm in question infests the intestines. Although discovered by Sonsino at Zagazig in plague-affected corpses, there is no reason to suppose that this helminth was in any way etiologically connected with the Egyptian epizoöty.
The tapeworms of the horse are of great interest practically. Excluding Sander’s Tænia zebræ, which was doubtless T. plicata, at least five species have been described, but they may probably be all reduced to two distinct forms and their varieties. Whilst Tænia plicata acquires a length of three feet, the strobile of T. perfoliata never exceeds five inches. The lobes at the base of the head in the latter are distinctive. The former is usually confined to the small intestine, but the perfoliate worm often occupies the cæcum and colon in great numbers. As regards T. mamillana, I may say that neither Gurlt’s descriptions nor his figures are convincing. The worm is, I believe, identical with T. perfoliata. In like manner, after going into the matter with some care, I am accustomed to speak of Mégnin’s T. inerme as T. perfoliata, var. Mégnini, and of Baillet’s T. innomé as T. perfoliata, var. Bailletii. I have examined great numbers of equine tapeworms, but whether my determinations on this point are correct or not, the case recorded by Mégnin is of remarkable interest. Clinically, indeed, it is not entirely unique, since a somewhat similar case has been recorded by Mr Poulton. In Mégnin’s equine patient the autopsy revealed the presence of 200 bots, 153 lumbricoids, upwards of 400 oxyurides, and several thousand palisade worms, besides numerous tapeworms. In Mr Poulton’s patient large quantities of tapeworms were found in the duodenum (and in large sacs of the walls of other sections of the small intestine), and also myriads of the little four-spined strongyle, in addition to about a score of palisade worms. Both Mégnin’s and Poulton’s patients died suddenly; but the great interest attaching to Mégnin’s case arises from the boldness of manner in which the French savant interprets the phenomena of the intestinal sacculation in relation to the development of the tapeworms. M. Mégnin assumes that the sacs are due to the formation of polycephalous or cœnuroid scolices. Without contradicting Mégnin’s ingenious interpretation of the phenomena in question, I may say that the difficulty I have in accepting his view arises from the circumstance of the rarity of the occurrence of these sacs. In Poulton’s case of Tænia perfoliata, the sacs were present, and they were productive of similar results; but in the scores of other recorded cases of sudden death from the same species of tapeworm (as published by Mr Rees Lloyd, and myself), the presence of such sac-formations is not once mentioned. To be sure, their presence may have been overlooked, but this is scarcely likely, seeing the great care taken by Mr Lloyd in conducting the autopsies. I cannot dwell upon the subject at greater length. The presence of so many sexually-immature strobiles, combined with the existence of the intestinal wall sacs, certainly does seem to point to the existence of cœnuroid bladder-worms, but until the existence of the polycephalous scolex be actually demonstrated one must be cautious in concluding “that the horse nourishes at the same time the strobila and scolex of the unarmed tapeworm.” Practically, we now know for certain that not only are tapeworms capable of producing a fatal issue in isolated cases, such as those recorded by Mégnin and Poulton, but that they may also be productive of disastrous epizoöty, as proved by Mr Lloyd in the case of Welsh mountain ponies.
In this connection I may perhaps be pardoned for saying that this discovery in 1875 was one of the practical results directly issuing from the publication of my ‘Manual’ in 1874. The attention of the veterinary profession having been called to the subject of parasitic epizoöty, Mr Lloyd was the first to make search for helminths amongst some few of the carcases of the hundred and more equine animals that perished in South Wales. Two totally distinct epizoötics prevailed. In the Beacons district tapeworms alone were the cause of death, whilst in the Deangunid district scores of animals perished from strongyles. In another district a hundred animals perished from tapeworms. These parasites I identified as examples of Strongylus tetracanthus and Tænia perfoliata. Taking all the helminthological facts together we have made a great advance both in hippopathology and equine epidemiology; and, as I observed at the time, the scepticism which not unnaturally still exists (in reference to entozoa as a frequent cause of death amongst animals, both wild and domesticated) will sooner or later be dispersed by that wider attention to the subject which our labors have invoked.