1923] 



CAMP — CITRIC ACID AS A SOURCE OF CARBON 



265 



curves compare better with the mat-weight curves, which may be 

 run parallel to them on the same figure, and likewise represent 

 very well the progress of the metabolic activities. On the ordin- 

 ates are plotted weights in tenths of a gram and on the abscissae 

 the time in days, the ordinates in case of the mat-weight curves 

 representing the weight of the mat in grams. The curves repre- 

 sent the actual analytical work, and in order to reduce the amount 

 of detailed material presented the tables from which these curves 

 were plotted are omitted. Dextrose and citric acid are both 

 plotted as carbon, dextrose on the basis of 39.978 per cent carbon, 

 and citric acid as 34.272 per cent, these percentages being cal- 

 culated from the molecular weights of anhydrous dextrose and 

 citric acid with one molecule of water of crystallization. In the 

 following curves besides mat weight will be found: (1) "loss of 

 dextrose" (calculated as carbon) as determined by the Shaffer 

 method; (2) "loss of carbon" calculated from the total carbon 

 determinations; (3) "loss of carbon — loss of dextrose" calculated 



by subtracting the figures for curve (1) from the figures for curve 

 (2) (theoretically if no oxidizable end products were formed from 

 either dextrose or citrate, this curve would represent the loss of 

 citrate — actually it probably roughly approximates it) ; and (4) a 

 curve for loss of acidity calculated from the titrations with NaOH 

 (the results of the titrations in N/10 NaOH were calculated as 

 citric acid and the equivalency of carbon determined from the per- 

 centage of carbon in citric acid) . This latter curve might involve 

 several errors due to such factors as the absorption of titratable 

 phosphates, the production of oxalic acid from the citric acid or 

 the production of acidic substances from the dextrose, nor would 

 it throw any light on such a situation as might be brought about 

 by differential absorption of the anion and cation of the citrate, 

 that is, if the anion were absorbed and the cation remained in 

 the solution to neutralize free citric acid present in the solution 

 the titrations would indicate a utilization of free citric acid rather 

 than combined citrate radical. 



Organism 3 (P enicillium sp.) and organism 9 (Aspergillus sp.) 

 were used in the first series. The solutions were made up to P H 

 2.5. In the curves given for these fungi each figure plotted repre- 

 sents the average of 2 different determinations made on separate 

 flasks of the culture. 



