44 BACTERIOLOGY 



exercised by living tissues in repelling the invasion of 

 parasites. 



In the foregoing brief sketch of the manifold transfor- 

 mation resulting from bacterial activity there is no dis- 

 cussion of the mechanism through which such changes are 

 wrought. In the case of the saprophytes the various analyses 

 and syntheses that accompany their growth are in general 

 believed to be manifestations of fermentations; while the 

 activities of the parasites in producing disease are referred 

 to poisons elaborated by these that have a destructive action 

 upon the tissues in which the parasites are operating. In 

 the following paragraphs an effort will be made to elucidate 

 this phase of the subject. 



FERMENTS, ENZYMES, TOXINS, BACTERIAL PROTEINS, 

 AND PTOMAINS. 



There is perhaps no department of either biology or physics 

 that relates to more important phenomena, more widespread 

 phenomena or more inexplicable phenomena than that 

 having to do with fermentation and the agencies that cause 

 it. 



The phenomenon has attracted the attention of the ablest 

 investigators for years and we are scarcely nearer to an 

 understanding of its intimate nature today than we were 

 at the beginning. 



In its older sense, the word fermentation related to all 

 reactions that are accompanied by the evolution of gas and, 

 indeed, it is probable that the word originated with the word 

 fervere, meaning to seethe, to boil, to bubble. In its modern 

 usage, however, the word comprehends many reactions, 

 believed to be caused by ferments, but during which no 



