112 BOVINE PATHOLOGY. 



defined, but rather while strictly applicable to the central 

 figure of the group allows us to arbitrarily decide its out- 

 lying limits. Thus, some authors include rheumatism 

 and tetanus among specific disorders, while others refuse 

 tubercle, cancer, and influenza a place in the list. We 

 have included under this heading diseases which seem to 

 be due to minute living organisms, the nature of which 

 varies in different cases. On the one hand, we have 

 cancer consisting of body cells which have a high degree of 

 vital energy, as manifested by their reproductive power. 

 They resemble certain natural components of the tissues, 

 but are remarkable for retaining their vitality when 

 grafted on to a fresh organism, after removal from that in 

 which they originated. Tubercle is closely allied to 

 cancer in its general nature. On the other hand, we 

 have anthracoid affections which are undoubtedly due to 

 the presence of minute, independent, and entirely foreign 

 organisms in the system. Of the diseases lying between 

 these extremes some have been traced to certain relations 

 with foreign minute organisms, while the cause of others 

 remains a mystery. In no branch of medical inquiry is 

 more progress being made than in the study of specific 

 disorders. This is a direct result of the fact that they, 

 more than any other disorders of domesticated animals, 

 make themselves felt by the community, for they spread 

 rapidly among herds, are generally very fatal in their 

 effects, and not unusually can originate disease of like 

 kind in man. Though it has not been proved in every 

 case that these diseases are due to special organisms, we 

 shall find it advantageous to adopt the ^' germ theory '' as 

 a hypothesis for working purposes. "We may safely do 

 so, for it has already explained many previously obscure 

 facts, and no positive evidence has been brought to bear 

 against it. Given this supposition we must then conclude 

 that the organised generators of disease have certain 

 special characters of form, composition, and life conditions. 

 Among the latter we must consider their origination, 

 metamorphoses, habitat, products, &c. On some of these 

 points we are profoundly ignorant, there are many of the 



