1923] 



CAMP — CITRIC ACID AS A SOURCE OF CARBON 229 



production of citric acid by Citromyces glaber and other species 

 of this genus. Thorn and Currie ('16) found citric acid to be 

 produced transiently by various species of Aspergillus. Currie 

 ('17), working with cultures of Aspergillus, was able to obtain 

 good yields of citric acid, although Martin had previously dis- 

 carded all such cultures as not producing this acid. The writer 

 obtained citric acid from Aspergillus sp. and a Penicillium sp. 

 on a dextrose medium. 



Citric acid is not limited to the plant kingdom; it was early 

 reported as a constituent of the milk of most mammals and of 

 urine. Recently, quantitative studies have been carried out on 

 the occurrence of citric acid in man. Amberg and McClure 

 ('17) found it consistently present in urine and gave quantitative 

 data for the amount excreted. Leake ('23) studied its occurrence 

 in sweat under various conditions. Salant and Wise ( ? 16) studied 

 the physiological reaction of the animal body to varying doses 

 of sodium citrate. While it is an excretion product in the human 

 metabolism it actually occurs in very small quantities, however. 



THE PHYSIOLOGICAL ROLE OF CITRIC ACID 



As a source of carbon for fungi, citric acid, like most of the 

 other organic acids, has received little attention. Nageli ('80) 

 listed it as second to tartaric acid as a source of carbon for the 

 lower fungi. Waterman ('13) studied the use of citric acid and 

 a number of other acids as compared with sugar, but the work 

 on citric acid was not complete. He showed, however, that for 

 Aspergillus niger this acid is a fair source of carbon. Currie ('17) 

 suggested that citric acid might be one step in the course of the 

 metabolism of sugar by A, niger and that it was used up as meta- 

 bolism progressed, if the conditions were favorable. Butkewitsch 

 ('22), working with Citromyces glaber and some P enicilliurn-like 

 fungi, gave curves for the use of varying amounts of citric acid 

 as well as for its production. 



Numerous writers on pathological subjects have contributed 

 notes on the " tolerance M of the various organic acids by fungi, 

 but the conditions of acidity were usually not controlled and the 

 limiting factors were more likely to be connected with the 

 hydrogen-ion concentration than with the anion of the acid. 



