1923] 



CAMP — CITRIC ACID AS A SOURCE OF CARBON 



275 



The curve for the "loss of carbon — loss of dextrose" remained 

 very constant around zero until the ninth day when it started 

 to rise very rapidly, indicating that citric acid was being utilized ; 

 as will be seen, this corresponded with the figures for the titration 

 of the free acid. 



Penicillium digitatum. — The curves for the weights of the mats 



10. Owing 



fig. 8, the analytical data in figs. 9 and 



the fact that P 



with 



gen sources, peptone was used instead of KNOi, an 

 amount of the peptone solution formerly made up 

 being used. According to the figures on the carbon deter 



(see p. 



ruinations, peptone gave 



under the conditions of the det 



about 25 per cent oxidizable carbon 



jrmi nations. The amount of 



peptone added was so small, however, as compared to the amount 

 of carbon present that no attempt was made to remove this 

 substance from the solution in making analyses. In the case of 

 sugar determinations it is probable that there are small amounts 

 of copper-reducing substances in peptone but the error is so small, 

 and the removal of peptone before the determinations without 

 taking out some of the sugar is so difficult, that the determinations 

 were run without removing the peptone from the solution. 



In solution 2 separate analyses were made of the citric acid in 

 the following manner: The acid was precipitated by the barium 

 method as previously described and the precipitate dried. The 

 dry precipitate was dissolved in warm concentrated HiPO« and 

 transferred to the reaction flask of the carbon-determination 

 apparatus and the carbon determined in the usual way. As soon 

 as the H2SO4 was added BaS0 4 was thrown down, but this caused 

 no difficulty in carrying out the determinations. The peptone 

 gave a little interference in this procedure but this did not amount 

 to more than 3-6 mgms. of carbon per determination of 75-100 

 mgms. of carbon. This was done because citric acid had been 

 found to disappear in the preliminary cultures and little growth 

 had resulted. 



The growth curves shown in fig. 9 show that as far as the 2 

 solutions were concerned there was little difference in value, if 

 the weight of mat be used as the criterion. Solution 2 produced 

 about the same growth as solution 1, but was a little slower in 



