FLIES, 131 



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, of 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 the^r absence, would 

 be available for the nourishment of the animal, and as their presence in no 

 way conduces to the well-being of their host, they must be looked upon as 

 undesirable visitors. At the same time, they may exist in considerable 

 numbers without doing any apparent harm. On the other hand, they often 

 seriously affect the health of the horse, and not infrequently 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 there is no 

 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 the above heading' is used in its popular, 

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

 annoy horses whether by wounding the skin, or by their presence 

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

 parasites. Even in temperate climates, on summer evenings, 

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

 and allied insects are often extremely irritating to horses ; though 

 far'less so than in the tropics, where, probably, the most irritating 

 of. all, from their number and persistent attacks, are common 

 house flies or flies nearly akin to them. In the hot weather, par- 

 ticularly during the rainy season, it is often impossible to utilise 

 docked horses with any comfort 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 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 fropi the 

 attacks of flies than recently imported horses. The same law 

 holds good with human beings, as may be seen by the extreme 

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

 bites of. mosquitoes, and the indifference displayed by Egyptian 



9* 



