BIOLOGICAL VARIATIONS OF BACTERIA 403 



subjected to saccharose for over forty days, suggested the pos- 

 sibihty that they had acquired the function of fermenting sac- 

 charose, and that the resultant glucose, in its turn, had its effect 

 upon the indol production as evidenced in the other experiments. 

 Planting these organisms after the seventh subculture into 

 saccharose agar proved this to be the case, as each of the strains, 

 3, 5 and 6, now fermented saccharose with the production of 

 gas to a moderate degree. 



The writer desires to emphasize at this juncture what appears 

 to him a certainty, namely, that it is the carbohydrate per se 

 that causes the fluctuating biological modification noted in 

 those experiments, though a definite modus operandi is not 

 known. This is well seen in the action of saccharose which 

 had but slight effect upon three of seven strains of B. coli until 

 the organisms were capable of splitting it into glucose, which, 

 in its turn, effected the amount of indol produced. The fact 

 that the inhibition was not complete, does not contradict this 

 supposition, for it can be accounted for either by the presence 

 of individual bacteria that remained unaltered by virtue of 

 their greater resistance, or by the fact that the attack on sac- 

 charose was sufficiently slow to permit a small amount of pro- 

 teolytic cleavage. Further proof of such effects of carbohydrates 

 will be offered below. 



The cholera spirillum, though it produced a large amount of 

 indol in the control, readily succumbed to the action of the 

 various carbohydrates, and, in several instances, even sooner 

 than the B. coli. The fact that this strain of cholera spirillum 

 produced but very little acid would indicate that the inhibitory 

 action was not due to acid accumulation. The possible effect 

 of excess acid is likewise shown to be negligible by the results 

 obtamed in the carbohydrate media, wherein, as may be seen 

 by consulting the tables, the differences were so slight that they 

 cannot be regarded as having any bearing. 



It is of interest to note the differences in the action of the 

 various carbohydrates. Saccharose has already been commented 

 upon. Galactose, it appears, had the most pronounced effect 

 upon all of the organisms, permitting but a single trace of indol 



