356 IVAN C. HALL AND LILLIAN J. ELLEFSON 



assumed even in milk passably clean. Ayers (1917) has recently 

 pointed out the significance of large numbers of B. coli in raw 

 milk as indicating temperature conditions suitable for develop- 

 ment rather than heavy initial contamination and his viewpoint 

 is confirmed in its essentials by Harding's condemnation (1917) 

 of the bacterial count as an index of cleanliness. 



In attempting the use of the presumptive test for B. coli as a 

 criterion of unsuccessful pasteurization, Mr. W. H. Stabler, a 

 student in the Department of Veterinary Science, to whom we 

 are indebted for the suggestion, found in a number of cases a 

 situation apparently analogous to that often described in water, 

 namely, gas formation in lactose broth tubes from which no 

 B. coli could be isolated. The result was interpreted as due 

 to sporulating anaerobes resistant to the temperature of 

 pasteurization. 



Accordingly, after testing the use of gentian violet in pre- 

 sumptive tests for B. coli in water (1918), we began testing milk 

 samples under similar conditions, except that 1 cc. of milk 

 was tested in each case, whereas the water tests were made with 

 10 cc. each. The amount of broth in each tube was 20 cc. 



Plates of litmus lactose agar were streaked from tubes show- 

 ing gas for isolation of B. coli. After the first six samples 1 

 part gentian violet in 100,000 was added to the litmus lactose 

 agar to inhibit the growth of Gram positive spores (most of 

 them non lactose fermenters), through whose spreading pro- 

 clivities, combined with rather marked proteolytic activities, 

 the acid produced by B. coli may be masked, as noted in the 

 case of plates from the presumptive tests of water. A further 

 advantage in the case of milk is that lactolytic cocci, which are 

 notably frequent, are also inhibited, thus further favoring the 

 Uklihood of isolated acidifiers proving to be colon bacilli, though 

 there is not much danger of confusing them because of the 

 difference in type of colony. Further details of technic were 

 the same as in the water tests. 



The data obtained are summarized in table 1. 



Thirty-three samples from ten different sources were tested, 

 13 of raw milk from tuberculin tested cows, 14 of pasteurized 



