S. A. KOSER " 249 



origin — aerogenes and others — are able to break down the citrate and to appropriate 

 it for their own needs. The salts of organic acids have also been suggested for sepa- 

 rating different types within the paratyphoid group. By the use of citrate, d-, 1-, and 

 m-tartrate, fumarate and mucate, certain distinctions are brought out.' These may 

 be especially useful in this or other groups of organisms where sugar fermentations 

 at times fail to differentiate certain serologically well-defined types. 



A consideration of the salient points in the utilization of aliphatic and aromatic 

 compounds brings out in a striking manner the ability of many bacteria to satisfy 

 their food and energy recjuirements from the simpler chemical compounds. Many bac- 

 teria, like plants, are able to build up their own protoplasmic structure from a variety 

 of non-nitrogenous organic substances and ammonia. One is impressed by the wide 

 range of chemical groupings which may be broken down and appropriated by the 

 micro-organisms for their own needs. Nitrogen may be utilized in various forms: as 

 an inorganic ammonium compound and in the amino, amide, or imino groups. Partic- 

 ularly striking is the ability of some organisms to tear apart complex ring structures 

 such as the imidazole or purine rings. Others apparently are not so well equipped with 

 the necessary tools for making use of such structures and are compelled to satisfy 

 their needs by the utihzation of a side chain while the ring structure is left intact. 

 Whatever the form of nitrogenous organic grouping attacked, ammonia is usually 

 liberated. After separation of the nitrogen in this form the carbonaceous residue, an 

 organic acid or perhaps an alcohol, may be further used by the organism. It may be 

 oxidized to supply energy, or perhaps rearranged and combined with ammonia for 

 synthesis of the organism's own particular protoplasm, or if a more readily available 

 source of carbon is present to satisfy these purposes, it may remain as an end-product 

 of metabolism. 



' Brown, H. C, Duncan, J. T., and Henry, T. A.: loc. cit. 



