72 Report of Department of Animal Industry of the 



milking. This is approximately one-fifth of the amount obtained 

 while using the earlier form of teat cup and is an amount closely 

 approximating the natural secretion occurring between the close 

 of the milking and the beginning of the stripping process. 



EFFECT OF CHANGES IN VACUUM. 



With this milking machine the milk is drawn by means of a 

 vacuum, produced by an air pump and intermittently applied to 

 the teat cups. The extent of this vacuum is measured by the 

 inches it would depress a mercurial barometer and is indicated by 

 an instrument similar to a steam gage. This vacuum, alternately 

 formed and destroyed within the teat cup, simulates the sucking 

 action of the calf's mouth. The violence of this sucking action 

 and, within certain limits, the rate of milking depends upon the 

 extent of the vacuum and the duration of the period through 

 which it is applied. As already referred to under the discussion 

 of teat cups, the vacuum, under unfavorable conditions, tends to 

 change the blood flow and produce congestion of the teat. ISTot 

 only does this congestion interfere with the escape of milk but 

 when carried too far it may even result in escape of blood from 

 the interior of the teat. This extreme result occurred with the 

 straight sided teat cups of the Globe machine but has not been 

 observed in connection with the present milking machine. In 

 view of these serious consequences the question of vacuum has 

 received much attention from the machine manufacturers and the 

 influence of this factor has been observed during this study. " It 

 is the conclusion of the manufacturers, after observing the effect 

 of vacuum at several hundred installations during a period of 

 five or six years, that the best results can be obtained by accu- 

 rately maintaining the vacuum at 15 inches."* 



During the spring of 1911 Prof. R S. Breed, of Allegheny 

 College, made an extensive study of the cellular content in the 

 milk from the Station herd and in connection with this study 



1 Letter from Loomis Burrell, dated Nov. 14, 1912. 



