396 INTERNAL PARASITES. 



sponge in the manner just mentioned, care should be taken that 

 there is no chance of the sponge coming off the stem to which it is 

 fixed. An excellent jDlan for the removal of these internal leeches 

 is to keep the horse without water for about twenty-four hours, 

 to water him from a bucket after that period, and to pick off the 

 leeches which come down to drink the water, or to return to the 

 water whence they came. The fact of the horse being deprived of 

 water for a comparatively long time, appears to render his blood 

 somewhat distasteful to the leeches. 



As PREVENTIVE MEANS in leech-infested countries, we may 

 filter the water through cotton cloth, charcoal, or sand. Neumann 

 remarks that eels and other kinds of fish will clear water of leeches 

 by eating them up. The precaution of not allowing horses to drink 

 at water in which leeches are known to reside, is obvious. 



Bots {Gasfrophilcs) 



are the larvae of gadflies, which lay their eggs during the autumn 

 (in England, principally during August) on the skin of horses. 

 These eggs, on becoming hatched (in from 20 to 25 days, according 

 to Joly; and from 4 to 5 days, according to Bracy-iClark), 

 produce small worms, which irritate the skin by their move- 

 ments and thus cause the horse to lick them off and take 

 them into his mouth, with the result that they gain access to 

 various parts of the alimentary canal. The bot having selected 

 its place of residence, attaches itself by hooks to the mucous 

 membrane, and derives its sustenance, during its stay, from the 

 wound made by its hooks. In the summer, the larva, after living 

 inside the horse for about ten months, quits its hold, and is ex- 

 pelled with the dung. Having concealed itself near the surface of 

 the jrround, it becomes chanofed into a chrvsalis, from which the 

 gadfly issues after an inactive existence of from thirty to forty 

 days' duration (Neumann). The female fly becomes impregnated, 

 lays her eggs on those parts of the horse from whidh they can be 

 most easily licked off, and thus completes her cycle of existence. 

 The changes undergone by the gadfly are similar to those of the 

 butterfly, in which we have a^^, caterpillar (or bot), chrysalis, and 

 fly. These flies attack only in the open, and almost exclusively 

 in fields. They are met with in far greater numbers when the 

 season is hot and diy, than when it is cold and damp. 



In New Zealand, bot-flies inflict great distress on horses, and are 

 occasionally the cause of death to them. 



The following are the more frequent kinds of bots : — 



1. The most common form is produced from a gadfly [gastrophilus 



