XIII. 



PATHOGENIC AEROBIC BACILLI NOT DESCRIBED IN 

 PREVIOUS SECTIONS. 



A CONSIDERABLE number of saprophytic bacilli are pathogenic for 

 small animals when injected into the circulation, or subcutaneously, 

 or into a serous cavity in considerable quantity one to five cubic 

 centimetres or more but fail to produce any appreciable effect 

 when introduced into the bodies of these animals in minute doses, 

 and do not multiply in the blood to any considerable extent, al- 

 though in fatal cases they may usually be recovered in cultures from 

 the blood and tissues. These bacilli are pathogenic by reason of the 

 toxic ptomaines produced by them, or because of local inflammatory 

 processes which they induce, or for both of these reasons combined. 

 Some of them may also, under certain circumstances, multiply in 

 the blood and thus give rise to septicaemia as well as to toxaemia ; 

 this is the case, for example, with the " colon bacillus " of Escher- 

 ich. When injected in considerable quantity into the circulation 

 of a guinea-pig it causes the death of the animal within twenty-four 

 hours, and the bacillus is found in the blood in great numbers ; but 

 minute amounts injected into a vein, or larger amounts injected 

 subcutaneousiy, do not usually produce general infection. It is, 

 therefore, not included among the "bacilli which produce septi- 

 caemia in susceptible animals/' There is reason to believe, however, 

 that under certain circumstances this bacillus may have sufficient 

 pathogenic potency to produce a genuine septicaemia in guinea-pigs. 

 Thus the original cultures of Brieger's bacillus, which appears to be 

 a variety or the colon bacillus, are reported to have produced fatal 

 septicaemia in guinea-pigs when injected subcutaneousiy in small 

 amounts. A strict division into pathogenic bacilli which produce 

 general blood infection septicaemia and those which produce a 

 fatal result owing to the production of toxic chemical substances is 

 not possible; for many pathogenic bacteria produce general infection 

 when injected in comparatively large doses, and at the same time 

 give rise to symptoms of toxaemia ; or general infection may occur 

 in animals of one species, and fatal toxaemia without septicaemia in 



