234 INFECTION AND IMMUNITY 



ing from the absorption or diffusion of the poisons produced by the 

 bacteria themselves. 



Bacterial Poisons. It was plain, even to the earliest students 

 of this subject, that mere mechanical capillary obstruction or the 

 absorption of the products of a local inflammation were insufficient 

 to explain the profound systemic disturbances which accompany 

 many bacterial infections. The very nature . of bacterial disease, 

 therefore, suggested the presence of poisons. 



It was in his investigations into the nature of these poisons that 

 Brieger 1 was led to the discovery of the ptomains. These bodies, first 

 isolated by him from decomposing beef, fish, and human cadavers, 

 have found more extended discussion in another section. Accurately 

 classified, they are not true bacterial poisons in the sense in which 

 the term is now employed. Although it is true that they are produced 

 from protein material by bacterial action, they are cleavage products 

 derived from the culture medium upon the composition of which 

 their nature intimately depends. The bacterial poisons proper, on 

 the other hand, are specific products of the bacteria themselves, 

 dependent upon the nature of the medium only as it favors or retards 

 the full development of the physiological functions of the micro- 

 organisms. The poisons, produced to a greater or lesser extent by all 

 pathogenic microorganisms, may be of several kinds. The true toxins, 

 in the specialized meaning which the term has acquired, are soluble, 

 truly secretory products of the bacterial cells, passing from them 

 into the culture medium during their life. They may be obtained 

 free from the bacteria by filtration and in a purer state from the 

 filtrates by chemical precipitation and a variety of other methods. 

 The most important examples of such poisons are those elaborated 

 by Bacillus diphtherias and Bacillus tetani. If cultures of these 

 bacteria or of others of this class are grown in fluid media for several 

 days and the medium is then filtered through porcelain candles, the 

 filtrate will be found toxic often to a high degree, while the residue 

 will be either inactive or comparatively weak. Moreover, if the residue 

 possesses any toxicity at all, the symptoms evidencing this will be 

 different from those produced by the filtrate. 



There are other microorganisms, however, notably the cholera 

 spirillum and the typhoid bacillus, in which no such exotoxins are 

 formed. If these bacteria are cultivated and separated from the cul- 



1 Brieger, "Die Ptomaine," Berlin, 1885 and 1886. 



