The Microbe as a Whole 5 



This concept gave rise to that of "comparative biochem- 

 istry," and so broadened the range of useful potentialities 

 of microbes for biochemical studies that it is not surprising 

 to find, in the course of fifteen years, that biochemists in- 

 terested in fundamental problems became increasingly 

 aware of the advantages offered by Leeuwenhoek's "little 

 animals." Furthermore, the gradual realization that growth 

 factors for yeasts and bacteria bear a close relationship to 

 vitamins required by higher animals soon led to the use 

 of microorganisms for the assay of vitamins and amino acids 

 and for the detection and identification of as yet unknown 

 growth factors. The subsequent proof that several of these 

 substances participate in biochemical processes as co- 

 enzymes or building blocks for coenzyme synthesis, a con- 

 cept first advanced in 1933 by Lwoff in connection with 

 studies on the role of hemoglobin in the nutrition of 

 trypanosomes, increased the usefulness of the microbes still 

 more, especially in view of their high rate of growth and 

 the possibility of controlling the material by the use of 

 pure cultures and chemically defined media. The microbes 

 thus became the material par excellence for studies of 

 special nutritional problems and of enzyme systems. And 

 when at last methods were perfected for the extraction of 

 enzymes from bacteria, yeasts, molds, and other microbes — 

 through preliminary drying, disruption of the cells by 

 grinding, shaking with glass beads, supersonic oscillations, 

 or enzymatic dissolution of the cell walls — our understand- 

 ing of the details of biochemical reaction mechanisms 

 through the use of microorganisms advanced rapidly. 



Unquestionably, biochemistry has profited greatly from 

 these developments. Nevertheless, the microbiologist re- 

 ceiving a request for a pure culture of some bacterium, 

 yeast, or alga, and for directions for growing it, from a bio- 

 chemist who wishes to use it for a specific biochemical 

 investigation cannot always escape the conclusion that the 

 culture in question will be considered as little more than a 



