Introduction to the Study of Disease 



Byrony, etc., etc. Hence the necessity for the 

 complete exclusion and extermination of such 

 herbage from grazing ground. 



Attention to thorough cleanliness of stables, 

 cow-houses, piggeries, poultry-houses, and kennels, 

 etc., etc., constitute the main principles for the 

 guidance, and regulation, not only of health, but 

 also of disease. 



Heredity 



Under the title of heredity must be included a 

 class of diseases which from time immemorial 

 have been looked upon as capable of being handed 

 from parent to progeny, either directly or in- 

 directly. Some diseases are apparently transmitted 

 either from Sire or Dam to their offspring -, 

 whereas, in other cases, several generations may 

 elapse before the development of the malady. To 

 this the term Atavism is applied, which really 

 means " harking back." It is well known that 

 many of these so-called " hereditary " diseases are 

 not derived from the parent, but are the outcome 

 of causes operating extrinsically, and bear no re- 

 lationship to hereditary predisposition. Peculiarity 

 of conformation does unquestionably play an active 

 part in determining disease, and this constitutes 

 one of the chief factors of hereditary predisposition ; 

 for instance, a horse that has over-bent or sickle- 

 shaped hocks, is more liable " to spring a curb,' 

 than one with good hock conformation ; whilst 



xxix 



