FLIES. 131 



tation or disease. Collie parasites are capable of producing millions of eggs 

 in a year. 



PLACE OF RESIDENCE AND METHOD OF INVASION.— The 



majority of these parasites are fairly constant in the selection of their 

 residence. Those which live in the stomach and intestines, evidently effect 

 their entrance along with the food and drink. The parasites which invade 

 the internal organs or closed cavities like that of the abdomen, or the aqueous 

 humour of the eye, do so by boring their way from the alimentary canal or 

 by their eggs being carried in the blood stream to distant spots, and being 

 deposited there in small blood-vessels, from which they escape on assuming 

 a more developed form, or in which they make their stay. Owing to the acid 

 character of the gastric juice, internal parasites, with the exception of bots, 

 prefer the intestines to the stomach as a place of abode. 



EFFECTS ON THE HEALTH OF THE HORSE.— As parasites feed either 

 on the tissues of the horse or on food which, in then absencCj would be avail- 

 able for the nourishment of the animal, and as their presence in no way con- 

 duces to the well-being of their host ; they must be looked ui)on as undesirable 

 visitors. At the &ame time, they may exist in considerable numbers without 

 doing any apparent harm. On the other hand, they often seriously ali'ect the 

 health of the horse, and not unfrequently cause his death. 



SYMPTOMS AND DIAGNOSIS.— The appearance of these parasites or of 

 their eggs, is often the only sign that the animal is infested. Besides this 

 convincing proof that parasites are either on or in the horse, I do not know 

 any other sign by which we can absolutely say that a horse is suffering from 

 their presence. The only symptoms to be observed are those peculiar to the 

 conditions of ill-health, such as itching, pimples, indigestion, colic and 

 paralysis, induced by them. 



Flies. 



For convenience sake I use the above heading in its i:)Opular, 

 though not scientific acceptation, to denote those two-winged insects 

 that annoy horses whether by ^vounding the skin, or by their pre- 

 sence on it, in which case they cannot of course be correctly termed 

 parasites. Even in temperate climates, on summer evenings, and 

 especially in wooded and marshy ground, gnats, " horse flies," and 

 allied insects are often extremely irritating to horses ; though far 

 less so than in the troi3ics, where, jirobably, the most irritating of 

 all, from their number and 23ersistent attacks, are common house 

 flies or flies nearly akin to them. In the hot weather, and parti- 

 cularly during the rainy season, it is often imi30ssible to utilise 

 with any comfort docked horses on account of these unfortunate 

 animals being unable to defend their hind quarters. 



Time not alone confers comparative racial immunity ; but also 

 more or less individual immunity. Thus we find that horses which 

 have resided for some years in fly-stricken countries like India and 

 South Africa, or are indigenous to such countries, suffer far less 

 from the attacks of flies than recently imported horses. The same 

 law holds good with human beings, as we may see by the extreme 

 sensitiveness of the skin of a recent arrival in the East, to the bites 



9>^ 



