1923] 



CAMP — CITRIC ACID AS A SOURCE OF CARBON 



285 



seems reasonable 



that the smaller the amount of 



carbohydrate in the solution, in proportion to the absorbing 

 surface, the more difficult it becomes for the fungus to absorb 

 it in sufficient quantities to show a continued increase in growth. 

 Where growth is very rapid, as in some species of Penitillium, 

 this effect would be masked by the rapid and complete disappear- 

 ance of the sugar from the solution, but in the case of A. Citri 

 this difficulty would manifest itself to a greater degree. 



The curves representing the daily change in P H of the two 

 solutions of organism 14 (figs. 16, 17) are very interesting and prob- 



Da^ 8 



Fig. 17. Alternaria sp. in solution 2. 



ably represent the typical results for this type of fungus. The 

 curve for solution 1 rises very slightly and then falls off rapidly 

 to a comparatively high alkalinity and remains there for the 

 remainder of the duration of the experiment. In solution 2 

 the P H remained constant for a considerable time and then 

 showed a very slow falling off toward alkalinity. This maintaining 

 of the P H in the early stages of metabolism is an expression of 

 the buffer activity of the citrate mixture ; the rapidity with which 

 the subsequent falling off occurs depends entirely upon the rapid- 

 ity with which the citric acid is used. If in this case the buffer 

 was not consumed at all by the fungus the stability would be 

 even greater and an organism would be required to produce a 

 considerable amount of either alkaline or acid substances to move 



