2$2 BACTERIOLOGY. 



the disease, or bring about the effect. We 

 find only apparent support for this latter view 

 from such facts as that anthrax bacteria always 

 evoke anthrax, and tubercle bacilli tuberculosis 

 in susceptible animals, and that many diseases, 

 such as malaria and pneumonia, have a typical 

 and often cyclical course. If the facts are 

 considered attentively, they reveal a state of 

 affairs really quite different. If we suppose 

 that the pathogenic 'bacteria are " specific en- 

 tities," that they are the true and sufficient 

 cause of disease as Pasteur and Koch have 

 affirmed, then at least four conditions would 

 have to be fulfilled. First, the disease-pro- 

 ducing bacteria should exert no other effect 

 than that of producing disease ; second, their 

 ability to produce disease should remain con- 

 stant ; third, they should affect all animals in 

 the same way without reference to particular 

 species ; and fourth, they should produce only 

 a single, sharply defined, typical and " specific " 

 infectious disease. In such a way as this Koch 

 has really pictured things to himself, this is 

 indeed the leading motive of his school while 

 Pasteur who also originally looked upon the 

 question in the same way, later adopted other 

 opinions. The dogma of the " specificity " of 

 the minute organisms that excite disease, the 

 belief in the existence of pathogenetic or pa- 



