431 



glands did not affect the several milk constituents in the same propor- 

 tion, but did affect the milk fat in a relatively greater degree thau the 

 other constituents. 



The author summarizes the results observed with these 10 cows as 

 follows : 



(1) With the advance of the period of lactation, the milk of the individual cows 

 became not only absolutely but also relatively richer in fat; that is not only tlie 

 percentage of fat in the milk, but also the percentage of fat in the solids increased, 



(2) In the majority of cases in which there was a temporary increase in the yield 

 of milk, the milk became relatively richer in fat. 



(3) In general the per cent of solids and soUds-uot-fat in the milk was proportional 

 to the per cent of fiit. 



(4) The milk of those cows which was absolutely richer in fat, was also relatively 

 richer. 



(5) On the average, the cows giving a large quantity of milk also gave milk with 

 a high content of solids. The concentration of the milk of cows giving a large quan- 

 tity was not surpassed by that of cows giving only a small quantity. 



(6) So-called butter cows, the milk of which is relatively rich in fat but poor in 

 solids-not-fat, or so-called cheese cows, the milk of which is relatively poor in fat 

 but rich in solids-not-fat, were not found among the cows on trial. 



(7) In the milk of all the cows the quantity of fat varied more widely than that 

 of any other constituent. 



(8) The specific gravity of the milk of individual cows was found in general to bo 

 directly proportional to the percentage of solids-not-fat. 



(9) The milk relatively richest in fat was yielded by the youngest cow (No. 1),. 

 and that relatively poorest in fat by a cow over 7 years old, which seemed to possess- 

 only inferior ability in the secretion of fat. 



With regard to the manner in which the milk is secreted, the author 

 puts the following questions, which are suggested by the above results: 

 Are we to assume that in the milk glands of the coav as many different 

 and more or less independent forces are at work as there are constitu- 

 ents of the milk, and that each of these forces provides for the formation 

 of a single constituent of the milk? Or shall we think rather of the 

 milk glands as possessed of forces which are first of all directed to the 

 formation of milk fat, and that the other milk constituents occur in a 

 sense as by-products? Or is neither one of the above cases true? The 

 author does not enter into a discussion of these questions. 



It has been shown that the diminution of the activity of the milk 

 glands as the period of lactation advances affects the secretion of fat 

 proportionally less than that of the other milk constituents. It was 

 further observed that fluctuations in the regular flow of the milk during 

 lactation usually affected the secretion of fat. Finally it was observed 

 that not only the degree of concentration of the milk, but to a certain 

 extent the milk yield also seemed to be determined by the relative tend- 

 ency of the milk glands to secrete fat. The paramount importance of 

 the fat secretion is further evidenced by the fluctuations in the per cent 

 of fat, which are greater than those of any other constituent. In fact, 

 the author states that it would almost seem as if the active forces in 

 the milk glands were occupied to a very large extent with the formation 



