The Rot in Sheep. 



57 



Although distomata are so widely diffused, it is an established 

 fact that ruminating animals are more frequently affected with 

 them than others, and sheep most of all. We have directed 

 attention to this circumstance in treating of the causes of rot, 

 and have there said that the probable explanation of it is that 

 the natural habits of the sheep lead to its cropping the short 

 grasses and feeding near to the moist ground, where the penulti- 

 mate forms of distomata mostly abound. The greater susceptibility, 

 however, of ruminating animals would also seem to be partly 

 accounted for by reference to the special functions of their 

 digestive organs. Encysted ccrcarice received with the food of 

 ruminants are not at once exposed to the solvent action of the 

 gastric juice, but are detained for an indefinite length of time 

 within the rumen reticulum and omasum (first, second, and third 

 stomachs), whose secretion is non-digestive. Within these organs, 

 therefore, no special cause of destruction to the vitality of the 

 entozoa exists, and hence a greater number of flukes are pro- 

 bably perfected, which in due course find their way into the 

 bile-ducts by passing firstly into abomasum, the true digestive 



Fig. 13. 



Encysted Cercaria ephemera. After Huxley. 



stomach, and then onwards into the duodenum. The converse 

 is the case with regard to the simple-stomached herbivora and 

 other mammals, viz. that the encysted cercaria', on entering the 

 digestive system, are immediately exposed to the action of the 

 gastric juice, by which many of them are doubtless destroyed, 

 and consequently do not reach their proper habitat — the liver. 



This circumstance may account in part lor the well-known 

 fact that horses graze almost with impunity on pastures where 

 both oxen and sheep become affected with flukes. Other causes, 

 without doubt, influence this immunity ; among which must be 

 placed the general plan adopted in rearing horses, which, toge- 

 ther with much of their food, even when they arc \ oung, contrasts 

 greatly with the food as well as system adopted in the bringing-up 

 ot cattle or sheep. Later on in life the uses to which horses arc 

 put likewise prevent to a great extent their liability to receive 

 the penultimate forms <>l the fluke. Nevertheless, distomata 



