A STUDY OF DISEASE IN GEXEEAL. 143 



The muscular system is also weak, the sheep being unfitted 

 for laborious exercise, even in its free state, and still more so 

 among the better bred and pampered varieties, where the nature 

 of the food and enforced inactivity tend still further to weaken 

 its energy and vitality. 



In comparison with the weak muscular development we find 

 that the vascular system is also feeble, the amount of blood cir- 

 culating in the system being considerably less in proportion to 

 the body weight than in the horse. 



Exertion requires extra combustion, greater waste of tissues, 

 and a correspondingly greater circulation of blood to supply the 

 tissue and repair its waste. The horse being required to exert 

 muscular force frequently needs a large blood supply, whereas 

 in the sheep these exertions are not necessary, hence the waste 

 of tissue is also less, and a large amount of vascularity is un- 

 needed; and while the sheep consumes a greater amount of food, 

 as compared in size with the horse, we find that it is quickly con- 

 verted into flesh, only a small portion remaining as blood in the 

 system. It will be noticed that the number of specific diseases 

 of sheep as compared to the horse and ox are few, seemingly due 

 to the animal's inherent constitution, which resists certain dis- 

 eases affecting other herbivora, as pleuro-pneumonia contagiosa, 

 glanders, etc., but it is found that the diffusion of races of sheep 

 to other localities has tended to increase the number of con- 

 tagious sheep diseases. Again a large proportion of sheep are 

 sold to be slaughtered before reaching maturity, and the ma- 

 jority before reaching old age, virtually reducing the number 

 of diseases to which they would be liable had they been allowed 

 to reach adult state. For this reason we have few chronic diseases 

 to deal with, such as produce serious changes in the skeletal, cir- 

 culatory, and digestive system — of the horse for an example — 

 resulting from overwork and old age. 



