Sheehy — Variation in the Quantity and Quality of Cows' Milk. 593 



from the alveolar cells. The longer the interval before milking the greater the 

 store of fat in the cells ; and, therefore, more fat remains in the udder after 

 a milking succeeding a long interval than after a short one. In the ease 

 of the 1915 and 1916 experiments more fat remained in the udder after the 

 morning milking (fifteen hours' interval) than after the evening (nine hours' 

 interval). Assuming, as before, that the gland activity is more or less 

 constant, the total fat produced in the evening is equal to the nine hours' 

 secretion of fat plus the reserve left after the previous morning milking ; 

 and that produced in the morning is equal to the fifteen hours' secretion 

 added to the reserve from the previous evening ; but as the morning reserve 

 is greater than the evening one, the evening total fat is approximately equal 

 to the morning total fat, notwithstanding the shorter interval. The storage 

 of fat in the alveolar cells also explains the increasing richness in fat of the 

 milk during the process of milking. As the already manufactured milk with 

 its low percentage of fat is drawn away, the back pressure on the gland cells 

 is decreased and the fat is liberated rapidly, thereby increasing the percentage 

 of fat in the milk right up to the " stoppings," in which it is greatest. 



Injecting pituitrin into the blood of a milch cow produces a large increase 

 in. the milk, and a proportionately greater increase in the total fat yielded at 

 the next milking. Hammond has shown that by injecting pituitrin into a goat 

 and milking again very shortly after a milking has taken place, it is possible 

 te get away a considerable quantity of the .milk and butter-fat which would 

 come normally at the next milking. When injection and subsequent milking 

 are performed after the afternoon milking, the deficiency at the next milking 

 is less than when the operation is performed in the morning. Furthermore, 

 the milk yielded as a result of injection does not increase in fat percentage 

 from the fore milk to the " strippings." From these facts Hammond con- 

 cluded that milk-precursors are stored in the alveolar cells. It is possible to 

 go further and state that the proportion of fat stored is greater than that of 

 the other constituents of the milk. 



During the process of milking the manipulation of the teats produces a 

 reflex action the result of which is an increased secretion from the gland cells 

 similar to that produced by the action of pituitrin.. The extent of the reflex 

 no doubt depends on the milker, and this agrees with the well-known fact 

 that a quick, thorough milker can obtain more milk from a cow than a slow 

 and careless one. 



[Table. 



SCIENT. PROC. K.D.S., VOL. XV., NO. XLII. 



5A 



