262 president's address — section l. 



There is some difficulty in understanding the natural evolution 

 of this toxin-production in an organism unable to infect animals. 



Tetanus and diphtheria bacilli are more nearly allied to the 

 saprophytes than the parasites; they live in and on dead tissue 

 produced by trauma or intercurrent infections, and do not invade 

 the body. Their virulenoei consists in their ability to secrete exo'- 

 toxins. 



The class of organisms which secretei these exotoxins agreei in one 

 important respect, nam.ely, their toxins are all able to set up the 

 production of antitoxins m animals. Following the discovery by 

 Behring and his collaborators, in 1890^ of this power of toxins to 

 set up antitoxin formation, much investigation was undertaken in 

 the hope that thei method might be of very general application ; 

 but as we now know the exotoixin-secreting organisms are com- 

 paratively fevf, and this method of immunization is proportionately 

 limited. 



An unfruitful search for such a toxin in the case of the choler; 

 vibrio led Pfeiifer to his hypothesis of " endotoxins " as a factoi 

 in the virulence of many bacteria. To quote from one of his own 

 papers : — 



"The essential principle of this theory is that almost ail 

 bacteria, iio matter ivhethcr ■pathogenic or saprophytic, are 

 endowed with poisonous properties contained within, or per- 

 haps identical with their body substances. These endotoxins 

 are not, as a rule, secreted by a vital activity of the bacteria, 

 but their absorption, and the consequent intoxication of the 

 infect«d body, are the result of the destruction and disintegra- 

 tion of the bacteria by the bactericidal inlluences of the 

 body." 



An early experiment of PfeifFer's strongly supports this view. 

 When a culture of cholera vibrios was injected into the peritoneal 

 cavity of a guinea pig, no rise of temperature or other abnormal 

 symptoms occurred for four to five hours, when fever and signs of 

 intoixication began to* manifest themselves. If, however, a short 

 time after the injection of the culture, a dose of anticholera serum 

 were injected into the peritoneum, the symptoms of acute intoxi- 

 cation would at once be shown — rapid fall of temperature and 

 general prostration. This Pfeiffer interpreted as being accounted 

 for by the setting up of rapid bacteriolysis with liberation of th« 

 toxic constituents of the dead bacteria. 



What has toi be noted is that this endotoxic action of different 

 species of bacteria by no means corresponds to their pathogenicity^ 

 e.g., anthrax bacilli cannot be shown to contain any poisonous 

 principles at all, whilst the nGn-pathogenic haciJlns prodigiosus is 

 very toxic. 



