58 BOVINE PATHOLOGY. 



utilising his locomotory system^ and not indulging in 

 either excess of alimentary or reproductive pleasures. He 

 is hardy, but gives us examples of diseases of the locomotor 

 system as also of the cloven hoof. 



Such marked subjection to the uses of man has led to 

 two results ; increase in varieties of the ox and increased 

 liability to disease. As varieties differ from the original stock 

 so in direct proportion do they become liable to disease, and 

 when by culture we generate remarkable activity of an organ 

 we render it correspondingly predisposed to disorder. 



In the production of a breed with special qualities there 

 is a transmission of hereditary tendency to special pecu- 

 liarities of structure and to activity of function, conditions 

 predisposing to disease, and these predispositions are very 

 marked as a result of " breeding in and in,^^ which pre- 

 vents the counteraction of family tendency to some special 

 degeneration by the introduction of new blood. Excessive 

 development of one part of the body tends to cause a want 

 of reciprocity of different parts of the body, to the preju- 

 dice of the whole ; only by very gradual development can 

 modifications of species occur; nature shows us this, for 

 variation under domestication tends to disease. The mere 

 fact of breeding from near relatives is not prejudicial, if 

 both be in a state of thorough health. 



Gregariousness is not favorable to individual peculiari- 

 ties, nevertheless, when epizootic disorders occur certain 

 individuals will exhibit immunity under extreme conditions 

 of exposure ; this seriously complicates experiments on 

 the transmission of these disorders. A similar immunity 

 from the effects of altered conditions may be noted after 

 the ingestion of medicinal or toxic agents ; some 

 individuals require immense doses, while others become 

 seriously influenced by small quantities. The latter con- 

 dition is termed intolerance ; the former, tolerance^ may 

 be due to frequent administration of the same agent when 

 it is of a non-cumulative character. Immunity in certain 

 blood diseases is secured often by an attack either of the 

 same or of a closely allied disorder. 



Diet acts as a predisposing cause of disease either by 



