620 THE POPULAR SCIENCE MONTHLY. 



tococcus pyogenes, which, is probably identical with Streptococcus 

 erysipelatos of Fehleisen, although some bacteriologists still in- 

 sist that slight differences exist in the mode of growth in certain 

 culture media which justify the view that they are well-defined 

 varieties if not distinct species. I am of the opinion that the strep- 

 tococcus obtained from erysipelatous inflammations is identical 

 with the streptococcus of pus ; and we have ample evidence that 

 the pathogenic power of this micro-organism differs as a result 

 of conditions relating to its environment. In artificial culture 

 media it becomes more or less attenuated, but when obtained from 

 the tissues invaded in erysipelas, or in puerperal septicaemia, it 

 has an increased virulence. Like the micrococcus of pneumonia, 

 this is a widely distributed micro-organism ; it has frequently 

 been obtained in cultures from the surface of the body or from 

 exposed mucous membranes of healthy persons. This is also true 

 of the other pus cocci concerned in traumatic infections. And, in 

 the light of our present knowledge, it appears that erysipelas, 

 wound infection, abscess formation, etc., do not depend alone 

 upon the presence of the specific etiological agents which induce 

 such localized infectious processes, but also upon predisposing 

 and secondary causes relating to the infected individual, as well 

 as upon the origin and virulence of the pathogenic micro-organ- 

 ism. Thus the Streptococcus pyogenes from a case of erysipelas 

 or of puerperal septicaemia introduced into a recent wound upon 

 a healthy person would be likely to cause a severe and possibly 

 fatal infection, while an attenuated culture of the same would 

 perhaps give rise to no symptoms, or at most to slight local 

 inflammation. On the other hand, if the vital resisting power 

 of the individual is reduced by previous ill-health, by insufficient 

 food, by sewer-gas poisoning, crowd-poisoning, etc., an attenuated 

 variety of Streptococcus pyogenes may perhaps give rise to an 

 erysipelatous inflammation, or to an acute abscess, if introduced 

 by accident into an open wound. Again, in contused and lacerated 

 wounds the vital resisting power of the tissues is diminished ; and 

 wound infection is likely to occur from the accidental introduc- 

 tion of the pus cocci, which lead a saprophytic existence upon the 

 surface of the body and exposed mucous membranes, where under 

 ordinary circumstances they are quite harmless. Secondary in- 

 fections clue to these now well-known pyogenic micrococci are 

 not infrequent as sequelae to the specific infectious diseases, such 

 as scarlet fever, yellow fever, etc. 



In 1882 Koch published his famous discovery of the tubercle 

 bacillus. This will always rank as one of the most important 

 events in the history of medicine, and as a notable triumph of 

 well-directed scientific research. The proof that the bacillus re- 

 ferred to is the specific cause of tuberculous processes and that 



