8 PATHOLOGY. 



middle period ; Lut as the predispositions to these affections are 

 supposed to be hereditary, they will receive further consideration. 



The cow is perhaps an exception to that exemption from diseases 

 occurring in middle life, for in this animal we find that when its 

 powers are fully developed, liability to that fatal disease, parturient 

 apoplexy, is much enhanced. 



At the approach of old age, and during its continuance, diseases 

 arising from tumours, degeneration of organs and tissues, manifest 

 themselves ; the heart, liver, &c. undergo fatty metamorphosis ; 

 the circulation becomes feeble ; digestion impaired ; the blood- 

 vessels, particularly those of the brain, undergo a calcareous 

 change; the joints become stiff; the bones brittle, and the cuta- 

 neous surface liable to be infected by various parasites. In the 

 dog, the crystalline lens undergoes a retrograde change, and soft 

 cataracts are commonly seen; whilst deafness and dropsy are 

 not rare amongst dogs of advanced age. 



In the ox tribe, again, we find that age influences the seat of 

 disease : for example, in young animals, charbonous disease mani- 

 fests itself externally, whilst in those of mature age its lesions 

 are generally witnessed in the internal organs. 



Sex. — The difference in the organisation of the male and female. 

 In addition to those variations in diseases necessarily arising 

 from the peculiarities of the generative organs of the two sexes, 

 as affections of the testicles, &c. in the one, and of the ovaries or 

 uterus, as well as hysteria, in the other, we find that sex has to 

 a limited extent an influence at least in one disease, which occurs 

 in both sexes ; thus roaring is much more frequently met with in 

 horses and geldings than in mares. 



Peculiarities of breed and conformation. — In connection with 

 breed and conformation, we often witness predispositions to cer- 

 tain forms of disease ; as, for example, canker and chronic 

 grease, common enough in heavy-legged cart-horses, are but 

 rarely seen in the better bred ones. lioaring is very often asso- 

 ciated with certain conformation of the neck. Large horses with 

 long necks, particularly if fine or small at the throat, are much 

 more predisposed to roaring than those with shorter necks ; 

 smaller horses are more rarely affected, and ponies very seldom 

 indeed become roarers. Eound-chested horses are more liable 

 to become broken-winded. 



There are also certain forms of lameness which conformation 



