1033] 



CAMP — CITRIC ACID AS A SOURCE OF CARBON 273 



maximum weight occurred very shortly after the dextrose dis- 

 appeared. Following the maximum there was a steady decline 

 in solution 1, but an even more rapid decline in solution 2, which 

 is not so easily explained, especially as the indications are that 

 citric acid was being used fairly rapidly at the same time. In 

 the curves for solution 2 is noted a break at the fifth to seventh 

 day, and at the same time the mats which had become rather 

 gray-green with spores showed signs of renewed growth and the 

 formation of tufts of white mycelium took place. This was noted 

 at other times under similar conditions, but whether it had any 

 significance is doubtful. However, it was peculiar that this should 

 take place at a time when there was also a marked increase in 

 the utilization of citric acid. 



The final disappearance of dextrose from the solution was a 

 little slower in solution 2 than in solution 1, but the mat was 

 heavier in solution 2 at this point than that in solution 1 at the 

 same point in the course of metabolism. This indicated a sparing 

 of dextrose due to the presence of the citric acid, which might 

 have been due to the buffering at a P H somewhat unfavorable 

 to the utilization of dextrose. 



The curves for the trend of P H (fig. 8) showed that in solution 

 1 there was a marked increase in alkalinity as soon as the fungus 

 had begun to grow rapidly. In solution 2, however, as would be 

 expected in such a strongly buffered solution, there was a long- 

 maintained curve at nearly the original acidity, the trend of 

 alkalinity coming very rapidly toward the end of the experiment 

 and coordinate with it a rapid decrease in the weight of the mat. 

 According to data obtained later, if solution 2 had been left longer 

 a P H approaching closely to 9.0 would have been attained. This 

 final falling off should have been coincident with the disappearance 

 of free citric acid and most of the acid salts from the solution. 



The utilization of citric acid here was very complete and com- 

 pared favorably with the utilization by Penicillium sp. (fig. 3). 

 There was considerable loss of acid before the dextrose had dis- 

 appeared from the solution, and although there continued to be 

 a loss of acid after the disappearance of dextrose the mat steadily 

 declined in weight, indicating that citric acid by itself was 

 probably not very efficient as a source of carbon. 



