THE CAUSE OF INFECTIOUS DISEASE. 223 



causes. Physicians, however, were not embar- 

 rassed by such considerations and, under the 

 influence of Koch's ingenious methods, it be- 

 came a pastime to show the causes of disease 

 in pure cultures ; the amusement flourished 

 even in the drawing-room, and the phraseology 

 of the new game became popular everywhere. 

 We shall probably best reach a scientific 

 understanding of the significance of bacteria in 

 the origination of disease if we consider briefly 

 the chief ideas hitherto held concerning disease. 

 The conception, now generally embraced, of a 

 " specific infectious disease " presents itself 

 first in the writings of the great English phy- 

 sician, Sydenham. By this term is understood 

 a sharply defined characteristic malady which, 

 in uncomplicated and " typical " cases, is clear- 

 ly distinguishable in its course and symptoms 

 from other diseases ; measles, smallpox, scarlet 

 fever, malaria, pneumonia, and cholera are such 

 " specific infectious diseases." It was precisely 

 this individuality of the " typical " cases that 

 pointed to an individuality of origin, and in 

 exactly this general sense Sydenham first com- 

 pared " species of disease " with species of plants. 

 In the eyes of this physician, therefore, the 

 " specific " disease itself was an " entity," it was 

 personified. To have done away with this con- 

 ception is one of the great services of Lotze 



