156 ESSAYS ON BACTERIOLOGY. 



main non-suppurative, are very likely to suppurate or 

 show other infection if the simultaneous presence of 

 bacteria be assured. Wandering bacteria are likely 

 to lodge at such a spot, just as vultures are to alight 

 upon carrion. 



Other interesting experiments have been made 

 showing that the introduction of aseptic irritants to- 

 gether with bacteria into the tissties or directly into 

 the circulation is much more likely to be followed by 

 the lodgment and growth of the bacteria than when 

 the latter are introduced alone. And thus in all di- 

 rections the old doctrine of local and general suscep- 

 tibility to infection is confirmed and illuminated, 

 while at the same time the specific causative agency of 

 the bacteria remains unquestioned. 



But not only do agencies affecting the body influ- 

 ence infection. Certain considerations concerning 

 the bacteria themselves are of great importance. 

 Here, too, clinical experience and laboratory experi- 

 ment agree. 



Two children being exposed to apparently the same 

 degree to measles, one takes the disease while the 

 other does not. One child has virulent scarlatina or 

 diphtheria, while others in the same community have 

 but mild attacks. At one time a mild type of scarla- 

 tina prevails, as in this community during recent 

 years; at another we have to confront what a vener- 

 able practitioner among us has described as the dying 

 kind. 



