220 



The Secretion of Milk. 



[JULY, 



are contributed by the early breaking down of the cell. It may 

 also be concluded that colostrum is due to an intensification of 

 the first phase at the beginning of the milking period. 



It is a well-known fact that in the cow and other animals 

 the last-drawn milk, the " strippings," is richer in fat than that 

 first removed. It has been usual to explain this as being due 

 to a process of creaming in the udder. It has also been 

 suggested that the more fluid portions would descend more 

 readily than the fat. Such explanations, however, are not 

 convincing, but with these morphological considerations before 

 us it is possible to re-state the problem, and to indicate its. 

 solution. 



An average cow yields, say, ij gallons at each milking, or 

 say, 1,400 c.c. from each quarter. It has, however, been com- 

 puted that the total capacity of the udder is only 3,000 c.c, or 

 750 c.c. per quarter. This would mean that during the process 

 of one milking as much again is added to the milk contained in 

 the quarter at the commencement of milking. The process of 

 milking one quarter, however, does not take longer than two 

 and a-half to three minutes. It may, therefore, be concluded 

 that the calculation of the distended capacity of the udder is 

 erroneous. If it be the fact that milk secretion begins at this 

 astounding rate so soon after milking has commenced, then it 

 would be impossible to strip the udder of its contents, and 

 milking might be presumed to go on continuously. It is, how- 

 ever, well known that the milk can be practically completely 

 removed, and that no further milk can be withdrawn until some 

 time has elapsed. Furthermore, it is manifestly impossible for 

 the secretory cells to regain in the short time of milking a 

 condition of activity which would account for an appreciable 

 portion of the supply which is yielded. The capacity of the 

 udder may therefore be said to be measured by the quantity of 

 milk which may be removed at a single milking. 



If this be the case, then, that the act of milking removes, 

 simply the milk which has accumulated since the previous 

 milking, it is at once plain that the richness of the strippings. 

 is due to a re-absorption by the lymphatics of the liquid or 

 watery constituents in the acini when the latter are in a. 

 state of distension. 



