70 FOOD REQUIREMENTS 



Few bacteria are true aerobes or anaerobes, but many gradually 

 blend from one class into another, as some will withstand small 

 quantities of free oxygen but not a full atmospheric pressure of it. 



Vitamines. The extracts of animal organs, as well as those of 

 some plant tissues, are valuable nutrient material for bacteria which 

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

 composition. The composition of these more or less unstable 

 but highly nutritive substances is a matter of purest speculation. 

 For want of a better name they are termed "vitamines" or "acces- 

 sory growth factors." These accessory bodies are moderately 

 heat-stable and are soluble in alcohol and in water. They are 

 rapidly absorbed from solution by filter paper, but not by glass 

 wool. They increase the reaction velocity of the proteolytic metab- 

 olism of the meningococcus and are essential to many other organ- 

 isms. After the first or primary cultivation some organisms become 

 independent of these substances. This phase of bacterial nutri- 

 tion, which is only just beginning to receive attention, is beset by 

 many difficulties. The work being done, however, gives promise 

 of so clearing up the field that much that was impossible of expla- 

 nation in the past will be readily explained. But the present 

 status of the case is well summarized by Rettger when he stated: 

 "We are as yet in the dark regarding the real food requirements 

 of bacteria." 



REFERENCES. 



Marshall: Microbiology. 



Kendall: Bacteriology General, Pathological and Intestinal. 



Kruse: Allgemeine Microbiologie. 



Herman, Nathan, and Rettger, Leo F.: Bacterial Nutrition Further Studies 

 on the Utilization of Protein and Non-protein, Jour. Bacteriol., 1918, iii, 367-388. 



Berman, (Nathan), and Rettger (Leo F.): The Influence of Carbohydrates on 

 the Nitrogen Metabolism of Bacteria, Jour. Bacteriol., 1918, iii, 389-402. 



