GROWTH OF BACTERIA IN NORMAL MILK. 25 



this particular organism is very readil}' differentiated and the 

 chance of error is thus greatlj' reduced. It is only in the 

 older samples of milk that this method has been adopted, and 

 was not used in any of the tables given below except Tables i 

 and 2, since the milk was fresh and the differentiation of each 

 type of colony could be made directly. 



The topics which have been studied at the Station b}- the 

 method here outlined during the last year have divided them- 

 selves into several distinct problems. Some of them have been 

 worked out in the laboratory at Wesleyan University, and others 

 in the newly equipped bacteriological laboratory' at Storrs. 



I. THE COMPARATIVE GROWTH OF DIFFERENT SPECIES OF 



BACTERIA IN MILK KEPT AT A TEMPERATURE 



OF 20 DEGREES CENTIGRADE. 



The first series of experiments to be described were carried 

 on with milk preserved at ordinary room temperatures. In 

 order to determine the effect of different conditions upon the 

 growth of bacteria in milk, it is necessary to have a knowledge 

 of their normal growth under ordinary conditions. For this 

 purpose it was thought best to study with considerable detail a 

 number of samples of milk preserved at an ordinar}- room tem- 

 perature, and this series of e\;periments will be described first, 

 although not actually the first to be carried out. 



It will be seen by the tables that follow that the study of 

 this milk did not extend beyond the first twentj'-four hours. 

 The reason for this is as follows: So far as concerns the bac- 

 teriological study of normal market milk the first twenty-four 

 hours are of special significance. It is true that sometimes milk 

 of our cities is considerably older than this by the time it is dis- 

 tributed to the customers, but when that is the case the milk 

 has been kept at a low temperature, which as will be seen later 

 modifies the problem. The milk which is furnished the cus- 

 tomers of our cities is never supposed to be sour, or even upon 

 the verge of souring; but our own experience has shown that 

 after twent^^-four hours at a temperature of 20° C, the milk 

 begins to become strongly acid and before many hours is likel}' 

 to curdle. It has appeared to us therefore, that the study of 

 the growth of bacteria during the first twenty-four hours, 



