GENERAL CHEMISTRY OF MILK 117 



126, 136, and 138. The casein apparently declines for three pe- 

 riods, the next two periods are about equal to the original 

 amount, and after these there is at first a slow, and later a rapid 

 increase. 



Albumin also varies according to the same rule as casein and 

 total protein up to the last month or two and during the final 

 stage of lactation there is a rapid increase. Again, taking the 

 amount of casein in the milk during the first period as 100, the rela- 

 tion, as lactation progresses, is expressed in the following figures: 

 100 (first period), 95, 85, 85, 87, 89, 91, 89, 93, 102, 111, 119, 97, 96. 

 The last two figures are from three cows whose lactation period 

 exceeded that of the others, and, therefore, are likely to have no 

 significance. 



The relation of casein, albumin, and residual protein to total 

 protein is expressed in the following table of Eckles and Shaw: 



RELATION OF CASEIN, ALBUMIN, AND RESIDUAL NITROGEN TO TOTAL NITROGEN BY 



FOUR- WEEK PERIODS 



Casein N., Albumin N., Residual N., 



Period. Total N. per cent. per cent. per cent. 



100 82 9 9 



100 78 9 13 



100 80 8 12 



4 100 80 8 12 



5 100 81 8 11 



6 100 81 8 11 



7 100 81 8 11 



8 100 82 8 10 



9 100 82 8 10 



10 100 81 8 11 



11 '.100 83 9 8 



12 100 83 9 8 



13 100 84 7 9 



14 100 82 6 12 



Average 100 81.4 8.1 11 



The relative quantities of casein, albumin, and total protein 

 are consistent throughout the lactation period. 



Van Slyke and Publow give a table on the relation casein and 

 albumin bear to total protein, which shows also that the amount 

 of these substances rises in nearly the same ratio during the lac- 

 tation period. The figures of these authors follow: 



INFLUENCE OF LACTATION UPON THE RELATION OF CASEIN TO ALBUMIN 



Per cent. 



Relation of casein in 



Per cent. Per cent. Per cent. albumin to total Per cent. 



Month. protein. casein. albumin. casein. protein. fat. 



1 3.16 2.54 0.62 1 :4.1 80.4 



2 2.99 2.42 0.57 1 : 4.2 80.9 



3 3.04 2.46 0.58 1 :4.2 80.9 



4 3.13 2.52 0.61 1:4.1 805 



5 3.25 2.61 0.64 1 :4.1 80.3 



3.33 2.68 0.65 1:4.1 805 4.53 



3.40 2.74 0.66 1:4.2 80.6 4.57 



3.47 2.80 0.67 1:4.2 80.7 4.59 



3.57 2.90 0.67 1:4.3 81.2 4.67 



10 3.79 3.01 0.78 1:3.9 79.4 4.90 



11 4.04 3.13 0.91 1:3.4 77.5 5.07 



