118 



MILK 



These figures show that the relation of casein to albumin re- 

 mains constant up to the ninth month, after which the albumin 

 increases more rapidly than the casein. 



Fat. The fat declines for about three months, to remain con- 

 stant for the following four to five months, and finally to increase 

 rapidly at the end of lactation. There is a parallelism between the 

 increase or decrease of protein and fat, although the protein in- 

 crease is somewhat greater than the fat increase. Therefore the 

 protein is influenced in larger measure by the period of lactation 

 than the fat. It should be remembered that other causes for 

 variation in fat may be in operation at the same tune that the 

 change caused by progress of lactation is taking place. Among 

 these causes are the differences in fat content between winter and 

 summer milk; further, differences between changeable conditions 

 of the animal, such as accumulation of body fat during pregnancy 

 and other abnormal conditions. Any sudden decline in milk pro- 

 duction is usually accompanied by a marked increase in solids, 

 especially in fat. 



The relation of fat to total protein, casein, and milk-sugar is 

 demonstrated in the following table, compiled from the work of 

 Eckles and Shaw. The fat is uniformly placed at 1. 



RELATION OF FAT TO TOTAL PROTEIN, CASEIN, AND MILK-SUGAR 



Period. 



1 



2 



3 



4 



5 



6 



7 



8 



9 

 10 

 11 

 12 

 13 

 14 



Fat : total protein. 

 1 :0.81 

 1:0.79 

 1 :0.81 

 1 :0.83 



0.85 



0.86 



0.87 



1 :0.86 



1 :0 90 



1 :0.93 



1:0.92 



1 : 0.90 



1:0.93 



1 :0.80 



Fat : casein. 

 :0.67 

 :0.61 

 :0.66 

 :0.66 

 :0.69 

 :0.71 

 : 70 

 :0.71 

 :0.72 

 :0.74 

 :0.76 

 :0.74 

 :0.78 



1:0.73 



Fat : milk-sugar. 

 .22 

 .30 

 .36 . 

 .31 

 .29 

 .30 

 .32 

 .28 

 .20 

 1.13 

 1.16 

 1.12 

 1.05 



1.06 



In total protein and casein the figures approach each other, 

 which shows that, as the lactation period advances, protein and 

 casein increase at a more rapid pace than does the fat. The figures 

 giving the relation of milk-sugar and fat also approach each other, 

 but this shows that the fat increases while the milk-sugar remains 

 practically unaltered. 



The ratio between fat and total protein is reduced constantly 

 as shown in the above table. This is due, of course, to a greater 

 increase of fat than of protein. The relation of fat to casein is 

 shown in the following table of Van Slyke and Publow: 



