1923] 



CAMP — CITRIC ACID AS A SOURCE OF CARBON 



293 



radical as well as of the dextrose. Moreover, the results might 

 be indirect in that the buffering at an unfavorable P H caused the 

 mat to form in instead of on the solution and that this was the 

 direct cause of the incomplete metabolism. 



Other cultures used failed to produce such evident volatile 

 metabolic products, but both Penicillium stoloniferum and P. sp. 

 produced some odorous compound which was given off when the 

 solution was neutralized. This distilled over readily and formed 



a benzoate by the Baumann and Schotten reaction which had 

 an odor of some rubber compounds. 



These observations are very suggestive 



of a fruitful field for 



investigation in the future. Moreover, they merely add to the 

 data indicating that the metabolism of fungi is far from a simple 

 problem and that the end products may be in many ways inde- 

 pendent of the conditions of the environment. It is quite 

 probable that ethyl and isopropyl alcohols, acetic acid, and 

 possibly acetone may be end products of the metabolism of citric 

 acid by fungi and that they may also be the end products of the 

 metabolism of sugars, providing the correct e i v ironmental 

 conditions are provided. It is likewise probable that these en- 

 vironmental conditions have to do with the ~CO t relations 

 and that any factors affecting this relation ma f have effect upon 

 the ultimate products obtained. 



Summary 



An improved method for the determination of citric acid, 

 especially applicable to culture solutions, has been offered. 



The application of the wet combustion method, for the deter- 

 mination of total carbon, to physiological work has been indicated. 



A number of fungi which attack citrus fruits have been studied 

 with regard to their ability to utilize citric acid as a source of 

 carbon with the following general results: 



(1) None of the fungi tried was found to thrive on citrate as 

 the sole source of carbon. 



(2) Citrate mixtures adjusted to a favorable P H proved to 

 be efficient supplementary carbon sources, when used with small 

 quantities of dextrose, for all the fungi used with the exception 

 of Penicillium digitatum and Phomopsis Citri. 



l 



