282 BACTERIA AND DISEASE 



(d) The organism must be found and isolated from the circulation 

 or tissues of the inoculated animal. 



It is evident that there are some diseases for example, cholera, 

 leprosy, and typhoid fever which are not communicable to lower 

 animals, and therefore their virus cannot be made to fulfil postulate 

 (c). In such cases there is no choice. They cannot be classified 

 along with tubercle and anthrax. Bacteriologists have little doubt 

 that Hansen's bacillus of leprosy is the cause of that disease, yet 

 it has not fulfilled postulates (b) and (c). Nor has the generally 

 accepted bacillus of typhoid fever fulfilled postulate (c), yet by the 

 majority it is provisionally accepted as the agent in producing the 

 disease. Hence it will be seen that, though there is an academical 

 classification of causal pathogenic bacteria according as they respond 

 to Koch's postulates, yet nevertheless there are a number of patho- 

 genic bacteria which are looked upon as causes of disease provisionally. 

 The bacilli of anthrax and tubercle, with perhaps the organisms of 

 suppuration, tetanus, plague, and actinomycosis, stand in the first 

 order of pathogenic germs. Then comes a group awaiting further 

 confirmation, which includes the organisms related to typhoid fever, 

 cholera, malaria, leprosy, epidemic diarrhoea, and pneumonia. Then 

 comes in a third category, a long list of diseases, such as scarlet 

 fever, small-pox, measles, rabies, and others too numerous to mention, 

 in which the nature of the causal agent is still unknown. Hence it 

 must not be supposed that every disease has its germ, and without 

 a germ there is no disease. Such universal assertions, though not 

 uncommonly heard, are devoid of accuracy. 



In the production of bacterial disease there are two factors. 

 First, there is the body tissue of the individual ; secondly, there is 

 the specific organism. 



Whatever may be said hereinafter with regard to the power of 

 micro-organisms to cause disease, we must understand one cardinal 

 point, namely, that bacteria are never more than causes, for the nature 

 of disease depends upon the behaviour of the organs or tissues with 

 which the bacteria or their products meet (Yirchow). Fortunately for 

 a clear conception of what " organs and tissues " mean, these have 

 been reduced to a common denominator, the cell. Every living 

 organism, of whatever size or kind, and every organ and tissue in 

 that living organism, contains and consists of cells. Further, these 

 cells are composed of organic chemical substances which are not 

 themselves alive, but the mechanical arrangement of which determines 

 the direction and power of their organic activity and of their resist- 

 ance to the specific agents of disease. With these facts clearly 

 before us, we may hope to gain some insight into the reasons for 

 departure from health. 



The normal living tissues have an inimical effect upon bacteria. 



