246 



ALIPHATIC AND AROMATIC COMPOUNDS 



terest that certain of these amines are significant from the pharmacological stand- 

 point. 



In addition to the amino acids, other compounds may be considered briefly. The 

 purines and their oxidation products, the pyrimidines such as cytosine, uracil, and 

 thymine, the extractive bodies, creatine, creatinine, carnosine, and others present 

 another series of nitrogenous compounds. The utilization of these bodies by various 

 types of micro-organisms has not been studied so extensively as that of the amino 

 acids, and our knowledge concerning them is rather fragmentary. Hypoxanthine, 

 xanthine, and uric acid contain nitrogen only in the purine ring. Evidently nitrogen 

 in such form is of no value to a great many organisms, for many of those which are 

 able to make use of isolated amino acids are unable to develop when the foregoing 

 purines are supplied as the sole source' of nitrogen. On the other hand, allantoin, 

 which is an oxidation product of uric acid and contains a free amino group, frequently 

 yields results quite similar to an amino acid.' In a similar way, it might be expected 

 that the amino purines, adenine and guanine, could be utilized by a number of or- 

 ganisms which are unable to make use of nitrogen in the purine ring. 



NON-NITROGENOUS COMPOUNDS 



Of the non-nitrogenous organic compounds which are used by micro-organisms 

 the best known are the carbohydrates, higher alcohols, and organic acids. Only the 

 last group will be dealt with here since the others are treated elsewhere in this volume'. 

 The structure of some of the commoner organic acids is shown below : Here we have 



Formic H-COOH Malic CHOH-COOH 



Acetic CH,-COOH 

 Propionic CH3-CH.-C00H 



n-Butyric CH3-(CH.).-C00H 



Glycollic CH.OH-COOH 



Lactic CH3 • CHOH • COOH 



Pyruvic CH3-C0-C00H 



Oxalic COOH 



COOH 



/COOH 

 Malonic CH2 



\COOH 



Succinic CH.-COOH 



I 

 CH.-COOH 



Maleic CH-COOH 

 Fumaric || 



CH-COOH 



■ Koser, S. A., and Rettger, L. F. : loc. cit. 



CH.-COOH 



Tartaric CHOH-COOH 



I 

 CHOH-COOH 



Glutaric CH.-COOH 



I 

 CH. 



CH.-COOH 



Adipic CH.-COOH 



(CH.). 



I 

 CH.-COOH 



Citric CH.-COOH 



C(OH) • COOH 



CH.-COOH 



CH-COOH 

 C6H,(0H)-C00H 



Benzoic 

 Salicylic 



- Chapter xvi. 



