108 LEO F. RETTGER 



We have been led through oft-repeated experiments on animal 

 and vegetable proteins to conclude that all bacteria are unable 

 to derive nourishment from native proteins, and that in a 

 medium in which there is no other possible source of nitrogen 

 than the proteins themselves they will thrive no better than in 

 a chemically pure saline solution. When cleavage-producing 

 agents, like a proteolytic enzyme, are present, the complex 

 protein molecules are broken up and, at least in part, made 

 available for cell nutrition. 



We have been able to show also that albumoses and the more 

 complex peptone fractions of Witte's and other commercial 

 peptones are like stone to the bacterial cell. Not only are 

 bacteria unable to utilize these substances without preliminary 

 cleavage or separation into their constituent parts, but many 

 organisms are without the ability to produce the enzymes neces- 

 sary to prepare these complex organic substances for cell nutri- 

 tion. The Coli-typhi-dysenteriae group furnishes notable 

 examples of such organisms. With but few exceptions there 

 appears to be a correlation between this property and that of 

 gelatin liquefaction. 



The question may well be asked, "Is not bacterial action 

 essentially synthetic?" The limited knowledge at our command 

 would, I believe, dictate the answer "Yes." If this question 

 can be answered in the affirmative, our present system of media- 

 making and culture study will need thorough revision ; but before 

 there can be much intelligent revision, further and more far- 

 reaching investigations into the real requirements of a bacterial 

 culture medium are indeed necessary. 



We are told again and again that the so-called "parasitic" or 

 "pathogenic" bacteria require a medium which simulates that 

 of the natural animal host of these organisms. As a consequence 

 of this prevailing idea fresh blood, blood agar, blood serum and 

 ascitic fluid bouillon and agar, are regarded as indispensable in 

 the isolation and cultivation of certain of the pathogens. In 

 many instances sterilization by heat is avoided, in order that 

 the natural nutrient properties may be preserved. 



