FACTORS OF PATHOGENICITY AND INFECTION 185 



Brieger * 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 pro- 

 teid 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 microorganisms. The poisons, pro- 

 duced 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 vari- 

 ety of other methods. The most important examples of such poisons 

 are those elaborated by Bacillus diphtherise 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 porce- 

 lain 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- 

 ture fluid by filtration, as above, the fluid filtrate will be toxic to only a 

 very slight degree, whereas the residue may prove very poisonous. In 

 these cases, we are dealing, evidently, with poisons not secreted into the 

 medium by the bacteria, but rather attached more or less firmly to the 

 bacterial body. Such poisons, separable from the bacteria only after 

 death by some method of extraction, or by autolysis, were termed by 

 Pfeiffer endotoxins. The greater number of the pathogenic bacteria 

 seem to act chiefly by means of poisons of this class. The first to call 

 attention to the existence of such intracellular poisons was Buchner, 

 who formulated his conclusions from the results of experiments made 



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



