DISEASES WHICH ARE INDUCED BY PARTICULAR PARASITES 169 



PARASITES OF THE DIGESTIVE SYSTEM OF THE HORSE 



Numerous organisms derived from the animal and also from the plant 

 world inhabit the digestive system of the horse. The majority of them 

 may be passed over with very slight notice, as it has not yet been proved 

 that they are responsible for any morbid conditions, although it is ex- 

 tremely prol)able that some of them do produce various forms of derange- 

 ment which are referred to other causes. Among the vegetal)le parasites 

 are numerous fungi, such as the common mould, and others \Ahich belong 

 to the same family. These fungi are found in the mouth, and thence quite 

 through the digestive track. 



The parasites which are derived from the animal world are extremely 

 numerous throughout the digestive system. 



Beginning with the lowest forms of life, there are found many of the 

 sporozoa and infusoria, some families of which, the Coccidia, are met with 

 in the liver and the epithelial cells of the mucous membrane. But in the 

 horse it has not yet been demonstrated that any special disease attends 

 their presence. 



Coming to the more important parasites, there are first to be considered 

 the worms which infest the stomach of the horse. 



In this country the minute nematode discovered by Professor J. AVortley 

 Axe in the stomach of the ass, and two varieties described by Professor 

 Peuberthy in the horse, and the larvte of the CEstrus equi, or stomach bot 

 (fig. 273), are the only parasitic worms of the stomach of the equidte; but 

 two varieties of spiroptera, the megastoma and microstoma, are described 

 by Continental helminthologists. The spiroptera, like the Strongylus axei 

 (Cobbold), form small round tumours in the mucous membrane. No 

 special signs of illness appear to attend the presence of these worms in 

 the stomach. With regard to the larvse of the bot-fiy, which are found in 

 clusters attached to the cuticular membrane of the stomach, opinions are 

 very much divided, some authorities contending that they produce irrita- 

 tion in the stomach, and sometimes even bore their way completely through 

 the coats of that organ. The rule, however, is that they simply penetrate 

 the mucous membrane sufficiently to enable them to retain their hold until 

 the time comes for them to quit their temporary habitation and assume the 

 pupa, or chrysalis stage, in which the perfect fly is developed. 



The next illustration was taken from a portion of the stomach, showing 

 the small tumours of the spiroptera and a number of bots attached to the 

 membrane. 



A smaller variety of the bot, of a reddish colour, is sometimes seen 

 clinging to the anus; it is known as the Oestrus hcsnwrrJwidalis. 



