394 INTERNAL PARASITES. 



may expel the parasites by the act of coughing. In the use of a 

 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 plan 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, filter the 

 water through cotton cloth, charcoal, or sand. 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 {Gastrophiles). 



\ 

 These 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 Braoy-Clark), 

 produce small worms, which irritate the skin by their movements 

 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 inembrane, 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 expelled with the dung. Having 

 concealed itself near the surface of the ground, it becomes changed 

 into a chrysalis, from which the gadfly issues after an inactive 

 existence of from thirty to forty days' duration. The female 

 fly becomes impregnated, lays her eggs on those parts of the 

 horse from which 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, consisting of egg, 

 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 dry, 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. 



