Jan. 20, 1919 Variations and Mode of Secretion of Milk Solids 



93 



between two days of lactation for morning and for evening milk. The 

 milkings begin in the morning at 4.45 and in the evening at 3.45. The 

 interval therefore is shorter between the morning-to-evening milking. 



Table XII. — Daily variation of the constituents of cow's milk « 



Cow No. 



First half of lactation. 



Morning. 



Fat. 



Average 4. 078 



P.ct 



4 

 4 



Solids- 

 not-fat. 



'.ct. 

 35 

 49 

 48 



55 

 76 



79 

 34 

 05 

 00 



8.646 



Evening. 



Fat. 



' Solids- 

 not-fat. 



P.ct. 



8. 36 

 8.60 

 8.77 

 8.59 

 8.64 

 8.85 

 8.41 

 9.29 



9. 01 



Last half of lactation. 



Morning. 



Fat. 



P. a. 

 4. 20 



4.40 

 4.40 



3. 20 



6.80 

 4.90 



3-50 

 3.60 



4- 50 



4-756 



8.724 



4-389 



Solids- 

 not-fat. 



8.58 



8.777 



Evening. 



Fat. 



P.ct. 

 4.90 

 4.80 

 6. 20 



4. 10 

 8.00 



5. 20 

 3.80 

 4. 20 

 4.90 



5. 122 



Solids- 

 not-fat. 



P.ct. 

 8.76 

 9. 18 

 9-55 

 7-95 

 9.96 

 9. 12 



8.47 



8. II 



9. 00 



8.90 



o The author is indebted to the Chemistry Laboratory of this Station for the careful analysis given in 

 Table XII. 



The average composition of morning milk in the first half of the 

 lactation is seen by Table XII to be 4.078 per cent butter fat and 8.646 

 per cent solids-not-fat. The average composition of evening milk is 

 4.756 per cent fat and 8.724 per cent sohds-not-fat. Thus, the butter- 

 fat constituent increases markedly in the evening milk over that of the 

 morning. The increase of the sohds-not-fat is not as marked, although a 

 slight increase does occur. The significance of this increase is supported 

 further by the same kind of relationship exhibited by the morning and 

 evening milk of the cows in late lactation. The numbers are not large, 

 but the consistency of the increase composition of butter fat of the 

 evening milk over that of the morning leads to the conclusion that this 

 relation is certainly significant. For the increase of solids-not-fat the 

 case is not so clear. It is possible that this increase is slightly significant, 

 but this seems doubtful. In no case is this rise of the solids-not-fat as 

 great as that of the butter fat. This, taken in consideration with the 

 fact that the solids-not-fat are more than twice as great in amount as 

 the butter fat, establishes the conclusion that the butter-fat composition 

 of milk is affected to a much greater extent by these different times of 

 milking than are the other solids. 



This conclusion is further emphasized by the work of Ingle {16) on 

 the same question. In the mixed milk of a herd of 23 animals milk 

 for a period of 18 weeks the average composition of the morning milk 



