Apeil 23j 1915] 



SCIENCE 



623 



exposed to dextrose and phenol. The former com- 

 pletely inhibited both aeid and gas formation and 

 all the sugars tested in three different strains. In 

 two other strains dextrose varied the fermentation 

 of the sugars as to amount of acid and gas forma- 

 tion, some of which were totally inhibited. Phenol 

 inhibited these fermentations in all of the sugars 

 in only one ease, and in four other strains it at 

 times diminished this reaction to the point of in- 

 hibition. Sodium chloride and sodium sulphate 

 had less eflEect than did phenol, giving usually 

 slight variations in amount of acid or gas pro- 

 duced with an occasional inhibition. 



Inhibition of all the sugar fermentations in any 

 one experiment was almost always accompanied by 

 inhibition in the usual changes in milk, the char- 

 acteristic growth on potato, and the formation of 

 indol. 



Variations in Indol Production. — The produc- 

 tion of indol is regaided by many bacteriologists 

 to be as important a biological characteristic of 

 B. coli as its fermentations of the sugars, and is 

 even thought to be of greater importance in its 

 differentiation. This quality, however, under nor- 

 mal conditions, varies considerably in its quantity 

 and time of appearance with most strains, and at 

 times requires more delicate tests than the usual 

 Salakowsky method for its determination. 



In the experiments here reported it appears that 

 of the variations induced in B. coli that of indol 

 production is the first to take place, often disap- 

 pearing in the third or fourth culture in dextrose 

 broth. This does not hold however when the bac- 

 teria grow in the other media, as evidenced below. 



Each strain of B. coli was grown in plain broth 

 as control, in dextrose, phenol, sodium chloride 

 and sodium sulphate broth and on potato. Thirty- 

 five sub-cultures were made in all. Indol was 

 tested for after the 10th, 15th, 25th and 35th 

 transfers. The tests for indol were made by inoc- 

 ulating one loop of culture from the respective 

 media to which each strain was subjected into 

 standard peptone solutions, grown for seven days 

 at 37° C. and then tested by the Salakowsky 

 method. All the tests were done at the same time, 

 using the same batch of peptone solution through- 

 out the experiment. 



All the controls, grown in plain broth gave good 

 indol tests even after the 35th sub-culture. Those 

 grown in dextrose broth gave none at the 10th sub- 

 culture nor thereafter. In phenol broth the prop- 

 erty of indol production seemed to be somewhat 

 increased, judging from the intensity of the reac- 

 tion. Sodium chloride and sodium sulphate and 

 prolonged cultivation on potato practically ex- 



erted no influence, or if any, showed but a slight 

 inhibitory effect. 



Experiments were then carried out to see how 

 soon the property of indol production is interfered 

 with by growth in three per cent, dextrose broth, 

 and it was found that B. coli lost this property 

 usually on the third and at times on the second 

 transfer over a period of from seven to ten days. 

 In one experiment sub-cultures were made every 

 24 hours, with a total disappearance of the indol 

 tests in 48 or 72 hours in all the strains. 



In order to exclude the possibility of interfer- 

 ence in the indol test by the presence of three per 

 cent, dextrose, several cultures in plain broth, also 

 peptone, were made and grown at 37° for seven 

 days. Dextrose was added to each of the cultures 

 and then tested for indol. Positive tests were ob- 

 tained in all, hence excluding any possibility of 

 such interference by the presence of the carbohy- 

 drate. 



Experiments were then carried out to determine 

 the permanency of this change. The cultures in 

 dextrose broth after the 35th transfer were taken 

 and grown in plain broth, transplanting every 

 day and tested on the seventh day of incubation. 

 Four of the strains of B. coli, Nos. 44, 45, 46 and 

 52, gave slight indol reactions on the third trans- 

 fer. No. 46 gave a good positive on the fifth trans- 

 fer, but the others took five to ten more transfers 

 before they could be called " + " or " + -1- ' ' posi- 

 tive. Nos. 57 and 95 took six transfers before a 

 trace of indol appeared. No. 19, a very feeble 

 indol producer in the control, remained negative 

 up to the fifteenth transfer, at which time the ex- 

 periment was discontinued. 



In summing up then, it can be said that dex- 

 trose and phenol, particularly the former, cause 

 partial inhibition or total disappearance of acid 

 and enzyme formation in some strains of B. coli. 

 These changes, together with the suspension of the 

 production of indol and the characteristic colon 

 growth on potato, make the B. coli approach if 

 not entirely appear like the B. typhosus type or- 

 ganism. These changes have been noted time and 

 again, but in varying degrees, in those strains that 

 are susceptible to variations, but for some unex- 

 plained reason can not be regarded as altogether 

 constant. Indol formation would invariably re- 

 turn when these altered bacteria were transplanted 

 into plain broth at frequent intervals. Lab enzyme 

 would also return in most of the altered strains, 

 but not invariably so. The same can be said of 

 the fermentative properties, but even to a less ex- 

 tent. Very often, however, these characteristics 

 appear to be entirely done away with, the change 



