BIOLOGICAL VARIATIONS OF BACTERIA 409 



This preference for carbohydrate food to the exclusion of 

 proteolysis has also been shown by other investigators to occur 

 both with B. coli and numerous other bacteria, but in the opinion 

 of the writer there is still an open question in regard to the 

 modus operandi, namely, whether it is due to sheer exhaustion, 

 or to a certain yet unexplained carbohydrate effect upon the 

 metaboHc activities of the bacteria. 



Peckham did not return the B. coli into plain peptone to de- 

 termine whether the absence of indol was due to a simple sus- 

 pension or inhibition of proteolytic activities, or whether this 

 inhibition was a pronounced one extending over a period of 

 time. Had she done so, she would probably have found, as 

 did the writer, that this inhibition was a decided one, not readily 

 overcome, that it varied with different strains of B. coli, and 

 also varied with the carbohydrate used. In the Hght of the 

 experiments here reported the writer feels quite convinced that 

 exhaustion, though it may be given a certain amount of credit, 

 cannot explain all of his findmgs. This contention is empha- 

 sized by: (1) The different effects obtamed on different strains of 

 B. coli. (2) Differences in effect by the various sugars, dextrin act- 

 ing much more readily, and permitting an immediate return of 

 indol formation, whereas in the case of glucose, the carbohydrate 

 effect was more gradual and more lasting. (3) The fact that 

 in an occasional experiment, the organism would not revert to 

 its original type, but remam permanently changed in some or 

 even all of its biological characteristics. (4) Differences in 

 the quantity, and time of disappearance or reappearance of 

 the various enzyme activities, with no special sequence of events. 

 (5) Exhaustion, though in spite of the above factors it might 

 still be regarded as being the cause in regard to indol, cannot 

 explain the more gradual loss of lab enzyme, fermentation of 

 carbohydrates with the production of gas, the lack of typical 

 growth on potato and finally loss of acid production. If we 

 were still to insist that it is a matter of exhaustion, we must 

 assume that it was so profound that it could have been handed 

 down from one culture to another over certain periods of time 

 as evidenced in the experiments for reversion. This would 



