164 Report of the Department of Bacteriology of the 



made bearing on this point. These observations are of greater 

 importance because of the fact that all of the machine milkers now 

 being actively pushed on the American market are operated either 

 entirely or partially by means of a vacuum. 



Experiments with the Burrell-Lawrence-Kennedy cow milker 

 have been in progress at the station since 1907 so that the opera- 

 tion of these machines during the time of the experiments here 

 described involved no unaccustomed duties for the employees in 

 the dairy and the animals experimented upon were accustomed to 

 being milked in this manner. The machines milked the cows thor- 

 oughly and no trouble in operating them occurred during the course 

 of the experiments. The makers of this machine recommend that 

 it be operated with a vacuum of approximately one half an atmos- 

 phere (15 inches as indicated by a mercury column). This recom- 

 mendation is based on a large amount of careful observation and 

 experimentation by the makers and users of these machines. 



Three lines of evidence were obtained which had a bearing on 

 the problem whether or not this type of cow milker influences the 

 cellular content of the milk. First, an experiment was carried out 

 during a period of six weeks on three animals, using three other 

 animals as controls, in which the effect of gradually increasing the 

 vacuum from 14.5 inches to 19.5 inches was studied. Second, two 

 cows were milked for five days by hand and then for five days by 

 machine and the milk from each milking was examined to see whether 

 any change in the cellular content of the milk occurred which could 

 be attributed to this change in the method of milking. Third, the 

 cellular content of the milk of all of the machine-milked cows in 

 the herd was compared with the cellular content of the milk of the 

 hand-milked cows. 



A. EXPERIMENTS TO DETERMINE THE INFLUENCE OF INCREASING THE 

 VACUUM ON THE CELL CONTENT OF THE MILK OF MACHINE- 

 MILKED COWS. 



The three cows chosen for the experiment were Gerty F. 2 (No. 

 12), Millie D. (No. 18), and Ruth F. (No. 24), while Gerty F. 1 (No. 

 10), Hammond F. 1 (No. 15), and Mabel S. F. (No. 17) were used 

 as controls. The three experimental animals represented as varied 

 conditions in regard to the cellular content of their milk as could 



