336 IVAN C. HALL AND LILLIAN J. ELLEFSON 



None of the cultures grew in glucose agar containing 1-1,000 

 gentian violet and only 14 out of 33 showed growth in a con- 

 centration of 1-10,000. Of these latter 6 grew within one day, 

 2 within two days, 1 in three days and 5 only within five days. 

 In all of these there was marked evidence of restriction by the 

 dye. In a concentration of 1-100,000 all the cultures but 2 

 grew — mostly quite vigorously, with gas formation and marked 

 decolorization of the dye. All the controls grew vigorously 

 except 3 cultures of B. putrificus which, not fermenting glucose, 

 are characterized by somewhat more sluggish development. 

 The tests were repeated with most of the cultures three times 

 with essentially similar results. 



In spite of the fact that according to the above tests more 

 than 1 part gentian violet in 10,000 of agar is required to com- 

 pletely inhibit the growth of these organisms, we conceived 

 that a smaller amount might suffice to inhibit spurious presump- 

 tive tests in lactose broth due to organisms of this group. There 

 are two reasons supporting such a supposition, first, the condi- 

 tions of anaerobiosis in the Durham fermentation tube are not 

 so favorable, second, it is believed that the colloidal nature of 

 the agar reduces the efficiency of the dye, thereby making a 

 higher concentration necessar}^ to accomplish a given result. 



A test of these organisms was therefore made in Durham 

 fermentation tubes with 1-100,000 gentian violet in 1 per cent 

 lactose broth. The test was controlled by means of a series of 

 tests without the dye, all of which developed growth excepting 

 cultures 115 and 192; their failure is attributed to the fact that 

 in these tests no special precautions were taken to eliminate 

 oxygen. All but six of the control tests produced gas in addi- 

 tion to turbidity. Of the dye tests however only one produced 

 either gas or turbidity and this was shown to be aerobically 

 contaminated. It may be mentioned that the somewhat inferior 

 anaerobiosis of the Durham tube for pure culture of anaerobes 

 is compensated in routine presumptive tests for B. coli in water 

 by the practically constant presence of aerophilic organisms 

 which reduce the oxygen tension sufficiently to provide suitable 

 conditions of anaerobiosis. We may admit also that the writer's 



