FACTS AND PROBLEMS OF IMMUNITY 309 



severely and detrimentally infecting the animal body. In view of this 

 unquestioned fact, the teaching which considers all poisonings as due 

 either to true soluble secreted poisons, or to true endotoxins liberated 

 only on disintegration of the bacterial cell, is probably too narrow. 



The work of recent years has even cast some doubt upon the 

 existence of preformed endotoxins in the bacterial cell and has indi- 

 cated that the bacterial protein as such may be regarded merely as a 

 foreign protein which would do no special harm unless it reacted 

 with substances in the animal body which brought about its disinte- 

 gration. In such a case the toxic substances formed would not rep- 

 resent preformed poisons, integral parts of the bacterial body, but 

 rather protein split products derived from the bacteria by proteo- 

 lytic action on the part of the plasma constituents. 



Some clarity of conception may, as we have suggested, be gained 

 by comparing some of the products of pathogenic bacteria with bacterial 

 pigments and with insoluble interstitial or intercellular substance, 

 w,hich may be seen accompanying bacteria in cover-glass preparations. 

 Soluble toxic secretions are to be compared to such pigments as the 

 pyocyanin of Bacillus pyocaneus, 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 ex- 

 truded from pathogenic bacteria, and not be soluble in the usual culture 

 fluids, is not improbable, and the fact that more or less insoluble inter- 

 stitial substances are not infrequent among bacteria is well known. 

 Among pathogenic germs these characters are often more marked in 

 freshly isolated cultures. The sticky, almost slimy character of cul- 

 tures of meningococcus may be recalled, a character which tends to 

 disappear after a few generations of artificial cultivation, and the highly 

 mucinous capsule of the Streptococcus mucosus which tends to decrease 

 under artificial cultivation, as do also the capsules of pneumococci and 

 streptococci. 



Now, it seems and this view has been supported by Walker, 

 Deutsch, Welch, and Eisenberg, and is, in fact, but an axiom which 

 would be recognized immediately by any trained biologist that all 

 microorganisms will adapt themselves so far as is permitted by their 

 physiologic peculiarities to the stress of the environment, the exact 

 direction which this adaptation will take being determined by the char- 



