BIOLOGICAL VARIATIONS OF BACTERIA 



393 



Each strain of B. coli was grown in plain broth as control, 

 and in glucose, 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 inoculating one loop of cul- 

 ture from the respective medium to which each strain was sub- 

 jected into standard peptone solution, growing for seven days 

 at 37°C. and then testing by the Salkowski method. All the 

 tests were done at the same time using the same batch of pep- 

 tone solution throughout the experiment. 



The results were uniform for all strains and may be readily 

 interpreted from the following table: 



TABLE VIII 



NUMBER OP TRANSFER 



Control 



Glucose broth. 

 Phenol broth. . 

 NaCl broth*.. 

 Na2S04 broth* 

 Potato 



+++ 



++++ 



++ 



++ 

 +++ 



* Exposure to these substances gave variable results, at times an increase and 

 at others a decrease in indol production. 



All the controls, grown in plain broth, gave good indol tests 

 even after the 35th sub-culture. Those grown in glucose broth 

 gave none at the 10th sub-cultm-e or thereafter. In phenol 

 broth the property of indol production seemed to be somewhat 

 increased, judging from the intensity of the reaction. Sodium 

 chloride and sodium sulphate, and prolonged cultivation on 

 potato practically exerted no influence, or if any, showed a 

 shght inhibitory effect. 



Experiments were then carried out to see how soon the prop- 

 erty of indol production is interfered with by growth in 3 

 per cent glucose broth, and it was found that B. coli lost this 

 property usually on the thu'd and at times on the second transfer 

 over a period of from seven to ten days. In one experiment 

 sub-cultures were made every twenty-four hours with a total 



