BACILLUS AEROGENES CAPSULATUS 473 



Pathogenicity. It is extremely interesting that, though a path- 

 ogenic anaerobe, no one has so far been able to show satisfactorily the 

 production of a true exotoxin, though such a claim has been made sev- 

 eral times. Poisonous products that have been obtained from cultures 

 have not conformed with the characteristics of true exotoxins as we 

 recognize them now. Moreover, the reaction of toxin-containing fil- 

 trates, as Simmonds points out, has been almost always acid, and Mc- 

 Campbell and others have suggested that the toxicity of such cultures 

 is due to the presence- of butyric acid. It is interesting in this connec- 

 tion also that Herter, who gave a great deal of attention to the presence 

 of these organisms in the bowel and attributed to them etiological rela- 

 tionship with many intestinal disorders, believed that diarrhea following 

 intestinal putrefaction was due to a very large extent to the irritation 

 produced by ammonium butyrate, the Welch bacilli being responsible 

 for the appearance of the butyric acid. 



The search for endotoxins, too, seems to have been unsuccessful, 

 and hemolysins have been irregularly present in cultures studied by 

 various investigators. 



Great differences in virulence have been observed in the study of 

 various strains. A good many of the strains seem to have great patho- 

 genicity for the ordinary laboratory animals, especially for guinea-pigs 

 and rabbits. Yet certain non-sporulating forms have shown little or 

 no virulence. However, variation in virulence seems to fluctuate con- 

 siderably according to the culture medium and the symbiotic conditions 

 under which the organisms have been cultivated. In man, fortunately, 

 there seems to be a relatively powerful resistance against Welch bacillus 

 infections. In fact, many investigators have believed that the Welch 

 bacillus is primarily a saprophyte and requires the presence of dead 

 tissue or physiological injury before it can penetrate and thrive in 

 the human body. It has been observed in gas cysts of the brain, in 

 "gangrenous" pneumonia, in appendix abscesses, in puerperal sepsis 

 after abortion, in general septicemia, and in many other conditions. 

 However, in many of these cases it may be quite reasonable to question 

 the primary character of the "gas bacillus" infection, and in others 

 again, the Welch bacillus may be regarded as an ante-mortem invasion, 

 a supposition strengthened by the study of terminal infections made by 

 Flexner, in which such a possibility is plainly demonstrated. Thus, 

 while the Welch bacillus may unquestionably invade the human body 

 and do much injury, and even be regarded in many cases as probably 

 the direct cause of death, its invasion in many of these cases must be 



