68 FOOD REQUIREMENTS 



dispense with organic nitrogen. These bacteria are able to synthe- 

 size protein substances out of carbohydrates (or organic acids) and 

 ammonia, nitrogen or nitrates. 



"3. Bacteria which, like the higher animals, require both organic 

 carbon and organic nitrogen compounds. These bacteria cannot 

 accomplish either carbohydrate or protein synthesis out of inorganic 

 substances." 



Carbon. The carbon dioxid of the air cannot be utilized by 

 bacteria as a source of energy since it is already fully oxidized. 

 There are, however, some organisms which possess the power of 

 utilizing both carbon monoxid and methane. On the contrary, 

 the carbon of carbohydrates, fats and proteins are readily utilized 

 by bacteria. The hydrocarbo~ns of both the aliphatic and aromatic 

 series are resistant to bacteria, but those compounds which contain 

 oxygen in addition to the carbon and hydrogen are more readily 

 attacked. Many organic acids and oxy-acids are used by some 

 bacteria. Only a few bacteria can use" the simpler alcohols. The 

 more complex alcohols, like glycerin and mannite, are utilized 

 by many. The carbohydrates are especially valuable to most 

 bacteria, those containing six or twelve carbon atoms being the 

 most valuable. 



Nitrogen. The nature of the nitrogen requirements of bacteria 

 are extremely different, depending upon the specific organism. 

 Some organisms, such as the symbiotic nitrogen-fixers and the 

 azofiers, are able to obtain all the nitrogen required from the 

 atmosphere. The nitrosomonas obtains its nitrogen from ammonia, 

 whereas the nitromonas obtain it from nitrites. The majority of 

 bacteria obtain their nitrogen from peptones, proteoses. and even 

 amino-acids. Rettger concludes from oft-repeated experiments on 

 animal and vegetable proteins that bacteria are unable to derive 

 nourishment from native proteins, and that in a medium in which 

 there is no possible source of nitrogen other than the proteins 

 themselves they will thrive no better than in a chemically pure 

 saline solution. When proteolytic enzymes are present the com- 

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

 available for cell nutrition. It would appear that "it is as essen- 

 tial to break down complex nitrogenous food substances into their 

 simple components, before they can be utilized, as it is to reduce the 

 walls of an old church brick by brick before they can be made 

 over into a modern schoolhouse." The more strictly pathogenic 

 organisms, as the gonococcus and the leprosy bacillus, may require 

 nitrogen in the form of highly specific tissue proteins. As a rule, 

 animal proteins are more readily utilized than are plant proteins. 



Hydrogen. Hydrogen is obtained from many organic compounds 

 containing hydrogen and oxygen, such as the carbohydrates, fats 



