GROWTH OF BACTERIA IN NORMAL MILK. 1 3 



THE COMPARATIVE GROWTH OF DIFFERENT 

 SPECIES OF BACTERIA IN NORMAE MIEK. 



BY H. W. CONN AND W. M. ESTEN. 



The Study of the bacteria in milk carried on during the last 

 fifteen years has been confined largely to two lines of inquiry. 

 (i) There has been a large amount of quantitative bacterio- 

 logical study, determining the number of bacteria in mi'lk under 

 different conditions; and (2) there has been a large amount of 

 work done in separating from milk different species of micro- 

 organisms and carefully studying their biological characters. 

 This has continued until there are described in literature more 

 than 200 species of bacteria more or less characteristic of milk 

 or some of its products. Although this work has continued in 

 very large amount for many years, the information which has 

 been obtained in regard to the actual species of bacteria in milk 

 under different conditions, is very slight indeed. Very little 

 attention has been given to the growth of -different species of 

 bacteria under normal conditions. De Freudenreich,* Russell 

 and Winzirl,t and Harrison, | have carried on some such 

 studies in regard to the bacteria present in cheese during the 

 period of ripening, resulting in some considerable change in 

 the belief of scientists as to the real nature of the ripening 

 process in cheese. Practically nothing, however, has hitherto 

 been known of the development of different species of bacteria 

 in normal milk. The increase in numbers has been deter- 

 mined in scores of cases, but no studies have been made upon 

 the question as to whether this increase, occurring as the milk 

 ages, is an increase in all kinds of dairy bacteria, or whether 

 it is only certain species that thus develop at the expense of 

 others. 



*Centbl. f. Bact. It. Par. II., III., 1897. 



+ Wisconsin Exp. Sta. Rept., 1896. 



I Harrison, Trans. Can. Inst., 1901, VII. 



