1008 EXPERIMENT STATION RECOED. 



"After the milk had stood for 50 hours at constant temperature of 70° F. the average 

 for the total number of bacteria was larger in the milk iron\ the covered pail tlian in 

 that from the open pail; while the average for the acid jiroducing species was larger 

 in the latter than in the former. In the strained milk both the total number and 

 the number of acid bacteria were larger than in the nulk not strained. 



"The milk from the covered pail curdled sooner than that from the open jaail, the 

 average difference being about 7 hours; likewise the strained milk curdled sooner 

 than the milk not strained, the average difference being also about 7 hours. This 

 fact, however, is of but little moment since any of these samples had they been kept 

 at the usual temperatures for handling milk would have remained sweet longer than 

 milk is usually kept. 



"The results of these tests would seem to indicate that the covered pail is more 

 efficient for the production of pure milk than straining milk drawn into an open pail. 

 It is quite evident also that to keeiJ the dirt out of the milk in the first i>lace is much 

 better than straining it out after the milking. A considerable portion of the dirt 

 dissolves quickly in the warm nulk and thus introduces a contamination that can not 

 be strained out." 



The comparative growth of different species of bacteria in normal milk, 

 H. W. Conn and W. I\I. Estex {Cunnertinit A'/orr.s- St((. Rpt. 1901, pp. 13-80) .—The 

 importance of a better knowledge of the development of different species of bacteria 

 in nulk imder normal conditions is briefly discussed, the method of investigation 

 used by the authors is described, and the following 3 series of experiments are reported 

 upon in detail and summarized: (1) The comparative growth of different species of 

 bacteria in milk at 20° C. ; (2) the effect of icing milk upon the development of bac- 

 teria; and (3) the comparative growth of bacteria in milk at temperatures of 20 and 13°. 



The method of study has been noted briefly from another source (E. S. E,., 14, p. 

 907). The culture medium is prepared in practically the same way as ordinary 

 gelatin, with the addition of litmus and milk sugar. The sample of milk to be tested 

 is properly diluted and plate cultures are made. The colonies are counted after 

 several days to determine the total number and the nund^er of different kinds. The 

 necessity of keeping the plates 3 to 5 days or longer is considered the most serious 

 fault of the method, as under certain conditions complete licjuefaction takes place 

 before the colonies can be differentiated. The authors have been able to differen- 

 tiate about 30 species of bacteria by their method. The forms most commonly found 

 in milk a few hours old were Bacillus acidi lactici, B. acidi lactici JI, B. lactis icrogenes 

 ( from which B. coli communis was not differentiated ) , several allied species designated 

 the Streptococcus group, ra])id and slow liijuefying bacteria, and 2 species of Sarcina. 

 While the differentiation is considered only approximate, the authors are convinced 

 that the error is not very great. 



The 3 series of experiments as a whole showed little regularity in the comparative 

 development of the different species of bacteria in milk. The number of bacteria at 

 any stage was found to be more dependent upon temperature than upon the original 

 contamination. As regards the development of the bacteria, 2 periods were recog- 

 nized, the first, in which the number of bacteria was less than 10 million per cubic 

 centimeter, lasting from 24 to 50 hours according as the temperature was 20 or 13°, 

 and the second, in which the lumiber of bacteria was above 10 million, lasting from 

 the end of the first period until the time of curdling. Some of the changes which 

 occurred during the first period may be noted as follows: The number of bacteria in 

 milk was not increased, but was frequently reduced during the first few hours after 

 milking. At 20° most of the species began to increase in absolute numbers after the 

 first 6 hours, B. acidi lactici increased uniformly, the other lactic acid bacteria were 

 irregular in their development, the Streptococcus group always increased, the lique- 

 fying bacteria practically always increased in absolute and sometimes in relative 

 numbers, the species of Sarcina developed but little, and the miscellaneous species 



