112 PHYSIOLOGICAL ACTIVITIES 



As previously stated, most of the physiological activities 

 of bacteria are due to the enzymes that they produce. It is 

 evident that for action to occur on substances which do 

 not diffuse into the bacterial cell— starches, cellulose, com- 

 plex proteins, gelatin— the enzymes must 'pass out of the 

 bacterium and consequently may be found in the surround- 

 ing medium. Substances like sugars, peptones, alcohol, 

 which are readily diffusible, may be acted on by enzymes 

 retained within the cell body. In the former case the enzymes 

 are spoken of as extracellular or " exoenzymes,'' and in 

 the latter as intracellular or " endoenzymes." The endo- 

 enzymes and doubtless also the excenzymes may after 

 the death of the cell digest the contents to a greater or less 

 extent and thus furnish substances that are not otherwise 

 obtainable. This process of "self-digestion" is known 

 technically as "autolysis." 



A distinction was formerly made between "organized" 

 and "unorganized ferments." The former term was applied 

 to the minute living organisms, bacteria, yeasts, molds, 

 etc., which bring about characteristic fermentative changes, 

 while the latter term was restricted to enzymes as just 

 described. Since investigation has shown that the changes 

 ascribed to the "organized ferments" are really due to their 

 enzymes, and that enzymes are probably formed by all 

 living cells, the distinction is scarcely necessary at present. 



PRODUCTION OF TOXINS. 



The injurious effects of pathogenic bacteria are due in 

 large part to the action of these substances, which in many 

 respects bear a close relationship to enzymes. The chemical 

 composition is unknown since no toxin has been prepared 

 "pure" as yet. It was formerly thought that they were 

 protein in character, but very pure toxins have been pre- 

 pared which failed to show the characteristic protein reac- 

 tions.^ It is well established that they are complex sub- 



1 Dr. Warden (page 107) claims that the toxin of the diphtheria bacillus 

 at least is a relatively simple fat complex in a colloidal state. He has pre- 

 pared artificial fat complexes which have the same properties. 



