THE CAUSE OF INFECTIOUS DISEASE. 253 



thogenic bacteria, meaning thereby belief in 

 unvarying specific character and physiological 

 effect, was especially developed by Henle and 

 later was worked out by Davaine, Pasteur, J. 

 vSchroter, F. Cohn, Klebs, and Koch. Other 

 investigators, among whom I need name only 

 Naegeli and Billroth as the leaders, have main- 

 tained, in opposition to this view, that bacteria 

 are constant neither in kind nor in action. 



Now in the first place, are disease-producing 

 bacteria capable of producing any other effect 

 than that of disease ? By the modern method 

 of pure cultures it has been established beyond 

 all doubt that disease-producing bacteria do 

 indeed display other activities ; the successful 

 culture of pathogenic bacteria is in itself a 

 proof that such bacteria are not restricted to 

 a parasitic existence and to the exciting of 

 disease. Thus for example the bacteria of 

 glanders develop a brown pigment upon 

 potato the cholera bacteria form a yellow 

 or brown pigment upon potato and in 

 sugar solutions cause an acid fermenta- 

 tion ; the so-called golden pus cocci, which 

 are the most common pyogenic bacteria, 

 form in cultures a splendid yellow pigment 

 and in sugar solutions produce acid. Whereas 

 formerly, in accordance with F. Cohn's view, 

 bacteria were distinguished according to their 



