520 SELMAN A. WAKSMAN 



treated by the acetone method, and 0.8 gram of the dried myce- 

 Hum was used in each case. The organisms were grown for 3, 

 10, 18, 35 days at 28°C.; the enzyme cultures were in all cases 

 incubated for four days at 37°C. The amino nitrogen produced 

 due to the activities of the enzymes was determined as usual, 

 and results calculated back to 100 cc. of the substrata. 



When we compare the influence of the medium upon the ac- 

 tivities of the enzymes, we see clearly that the presence of pep- 

 tone in the medium greatly increases the activities of the en- 

 zymes, both extra- and intracellular, in their action on peptone 

 and casein, as shown in table 7; this effect is observed with all 

 the periods of incubation studied. It is remarkable that in 

 most cases A. niger produced the strongest enzymes in the first 

 period of incubation, namely in three days, particularly when 

 grown on the peptone free medium. There is a more or less 

 steady decrease in the activities of the enzymes with the increase 

 of the incubation period, and the enzymes obtained from the 

 organism grown on the peptone medium particularly the exo- 

 enzymes, show greater irregularities in this respect. 



In the case of the enzyme obtained from A. ochraceus, we find 

 that the activities of the enzymes increased from the third till the 

 eighteenth day of incubation of the organism, further incuba- 

 tion giving a decrease in the activities of the enzymes. Only 

 in two cases is an increase in the activities of the enzymes found 

 after the growth of the organism was continued for a period 

 greater than eighteen days, namely in the case of the exoenzyme 

 of that organism growing on peptone. The difference in the 

 activities of the two organisms may be explained on the following 

 assumptions: A. niger grows very rapidly and produces a great 

 deal of acid, mostly oxalic and citric, in both media; while 

 A . ochraceus grows comparatively slowly and produces no acid at 

 all or very little. The rapid growth of A . niger will result in an 

 early production of strongly acting enzymes; the acids produced 

 by this organism may act injuriously upon the enzymes and 

 their activity will therefore be strongest in the earliest period of 

 incubation. The slower growth of A. ochraceus will result in a 

 lack of strongly acting enzymes in the early stages of the growth 



