1923] 



CAMP — CITRIC ACID AS A SOURCE OF CARBON 



251 



A series of experiments was run to determine the general 

 relation of citric acid to metabolism. The first series was calcu- 

 lated to determine what fungi could profitably use citric acid 

 without any other source of carbohydrate being present. The 

 culture solution previously described was made up, but a mixture 

 of citric acid and potassium citrate was substituted for the dex- 

 trose, 8 gms. of citric acid and 12.35 gms. of potassium citrate 

 (equivalent to 8 gms. of citric acid) per 800 cc. of solution. 

 This solution was used in 100-cc. flasks, and the cultures were in 

 triplicate. The results after 25 days of incubation at 25° C. 

 are given in table vn. The weights of mats as given represent 



averages of 3. 



table vi I 



GROWTH OF FUNGI WITH CITRATE AS SOLE SOURCE OF CARBON 



No 



2 



3 



4 



6 



7 

 11 



Remarks 



Solution light orange-yellow, spores 



plentiful, mat gray. 

 No spores, mycelium white to gray, 



solution yellow. 



Growth with white sediment and clouding. 

 Just beginning growth. 

 Very slight aerial growth. 



A second solution was made up, using the mineral nutrients 

 in 1/5 the usual concentration and with 1 gm. of dextrose per 

 liter. No citric acid was added at the start, but 200 cc. of citric 



acid solution were made up, using 21 gms. of citric acid, and this 



was sterilized in 10-cc. amounts in test-tubes, to be added to the 

 flasks after growth had begun. This amount of citric acid, on 

 being added to the solution in the flasks, gave 35 cc. of 3 per cent 

 citric acid solution. Four 100-cc. flasks were prepared for each 

 of the fungi used. After incubation for 8 days at 25° C. all of 

 the cultures were found to be showing definite growth, and 2 of 

 each 4 flasks inoculated with a fungus were removed to the trans- 

 fer room and a tube of the citric acid solution added to each 

 under sterile conditions. They were then returned to the incu- 

 bator after agitation to mix the citric acid with the rest of the 



