ESSAYS ON BACTERIOLOGY. 19 



there still be macli doubt about them, at least raise 

 the question whether some of the supposed infectious 

 diseases may not be due to more than one cause; 

 whether, to put it concretely, an acute, self -limited, 

 croupous in-flammation of the lungs, such as charac- 

 terizes pneumonia, or such lesions as belong to diph- 

 theria, may not be produced by more than one agent. 

 Probably not; yet it must be said that recent bacterio- 

 logical work has opened the question and has left it 

 still open. 



Allied to this is the interesting inquiry whether a 

 pathogenic micro-organism may, in different localities, 

 and under different conditions, produce apparently 

 different diseases. A. connection between erysipelas 

 and ptierperal fever has long been suspected, and re- 

 cent research has strengthened this suspicion. Vari- 

 ous authorities have asserted, on the basis of experi- 

 ment, that the Fehleisen streptococcus of erysipelas 

 would produce puerperal fever, and that the strepto- 

 coccus often found in the latter disease would produce 

 erysipelas. Some believe, partly because of these 

 facts, and partly because of the close resemblance in 

 the organisms, that they are the same. Certain it 

 seems, however, that an organism which would pro- 

 duce erysipelas has a number of times been cultivated 

 from child-bed fever. 



The question of the durability of infectious ma- 

 terial is one which has long interested and often puz- 

 zled the profession. It is not strange that it should 



