FACTORS OF PATHOGENICITY AND INFECTION 235 



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

 only a very slight degree, whereas the residue may prove very poison- 

 ous. 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 with a number of microorganisms, notably the 

 Friedlander bacillus and Staphylococcus pyogenes aureus, with dead 

 cultures of which he induced the formation of sterile abscesses in 

 animals and symptoms of toxemia. The conception of "endotoxins," 

 received its clearest and most definite expression in the work of 

 Pfeiffer 2 on cholera poison. 



Some clarity of conception, based on visual perception, may pos- 

 sibly be gained by comparing some of the products of pathogenic 

 bacteria with bacterial pigments and with insoluble interstitial or 

 intercellular substance, which may be seen accompanying bacteria in 

 cover-glass preparations. Soluble toxic secretions are to be compared 

 to such pigments as the pyocyanin of Bacillus pyocyaneus, which 

 is so readily soluble in culture media ; endotoxins proper, to pigments 

 confined to the bacterial cell, or at least, when secreted, being insoluble 

 in culture media, such for instance as the well-known red pigment 

 of Bacillus prodigiosus, which may often be seen free among the 

 bacteria in irregular red granules like carmine powder. That bodies 

 such as this latter might be extruded from pathogenic bacteria and 

 not be soluble in the usual culture fluids, is not improbable, and the 

 fact that more or less insoluble interstitial substances are not infre- 

 quent among bacteria is well known. 



In all bacterial bodies, after removal of toxins and endotoxins, a 

 certain protein residue remains which, if injected into animals, may 

 give rise to localized lesions such as abscesses or merely slight temporary 

 inflammations. The nature of this residue has been carefully studied, 

 especially by Buchner, who has named it bacterial protein and he 

 believes the substance to be approximately the same in all bacteria, 

 without specific toxic action, but with a general ability to exert a 



2 Pfeiffer, Zeit. f. Hyg., xl, 1892. 



