BACTERIOLOGY AND ITS RELATION TO OTHER SCIENCES 109 



That these animal fluid media are valuable, and, in some 

 instances, to all appearances necessary, cannot be denied. The 

 common notion, however, that the peculiar nutrient properties 

 are inseparably linked with the proteins as such, and that the 

 value of the media depends upon these proteins, has little to 

 support it. It is far more probable that the food-giving sub- 

 stances in the body fluids or tissues are nitrogenous substances 

 of very simple constitution, perhaps of the nature of amines and 

 amino acids. It must be assumed that in the profound chemical 

 changes which take place in these fluids in the animal body, 

 and in the process of autolysis after death or after their removal 

 from the body, many and varied nitrogenous substances are 

 formed which possess different degrees of stability. Some of 

 the products are without doubt easily transformed into more 

 stable substances, but, because of the extraordinary ease with 

 which they are transformed, serve as excellent grist for bacteria, 

 very much in the same way that a high grade of gasolene ex- 

 plodes more readily in the gasolene motor than one of much 

 lower boiling point. Others, while less readily appropriated by 

 the bacterial cell, are sufficiently unstable to be seized and 

 utilized. The latter may in a large measure resist short periods 

 of heat sterilization, while the more unstable intermediate 

 products are destroyed in the process. 



The extracts of animal organs, as well as those of some plant 

 tissues, contain valuable nutrient material for bacteria which it 

 is as yet impossible to supply in any medium of known chemical 

 composition. Even commercial peptone possesses much value 

 as an early stimulator of growth. Ihis may be demonstrated 

 readily on the diphtheria bacillus. The bacillus of Loeffler does 

 not adapt itself to synthetic media. If but a very small amount 

 of commercial peptone be added to the ordinary Uschinsky 

 medium, however, growth soon takes place. Peptone is in- 

 deed a highly complex food, but it owes its value primarily 

 to the substances of simple constitution which it contains. A 

 peptone prepared without the application of heat in any stage 

 of its preparation, if this were possible, would without doubt 

 possess still greater value as a food for bacteria. 



