GENERAL CHEMISTRY OF MILK 121 



The iodin number was irregular in the beginning, then in- 

 creased gradually to within two or three months of the end of lac- 

 tation, with a rather sharp rise during the last weeks. The co- 

 incident increase of the melting-point is probably due, as Eckles 

 and Shaw suggest, to a decrease in butyrin, which has a melting- 

 point below that of olein. 



The Koettstorfer saponification number declined with fair 

 uniformity throughout the lactation period. 



The chart (Fig. 27) plotted by Eckles and Shaw clearly shows 

 the curves of the size of the fat globules, the Reichert-Meissl, 

 iodin, and saponification numbers, and the melting-point of 

 fat. 



Eckles and Shaw observed an abnormal odor and taste in the 

 milk of some cows near the close of lactation. This peculiarity 

 was not noticeable in the freshly drawn milk, but appeared within 

 twelve hours, even when the milk was kept at 10 C. 



The specific gravity of milk falls for a few weeks after the colos- 

 tral period, and then rises constantly. 



All authorities agree that the ash remains remarkably uniform 

 throughout the lactation period. However, there are slight 

 changes similar to those of the other milk constituents which indi- 

 cate a slight decline during the first three months. This decline is 

 followed by a slight rise for four months and a rather more rapid 

 rise during the last three months. Trunz gives the following 

 figures to illustrate this point: 



THE VARIABILITY OF ASH IN MILK 



Cow 1, Cow 2, 



Period. per cent. per cent. 



Colostrum 0.774 0.758 



First three months 0.659 0.709 



Next four months 0.663 0.764 



Last three months 0.754 0.825 



These figures refer to crude ash. The pure ash gives the fol- 

 lowing results: 



THE VARIABILITY OF PURE ASH IN MILK 



Cow 1, Cow 2, 



Period. per cent. per cent. 



Colostrum 0.705 0.684 



First three months 0.598 0.651 



Next four months 0.599 0.701 



Last three months 0.675 0. 771 



The initial decline of the ash is probably explained by the high 

 ash content of colostrum, which gradually decreases as the lacta- 

 tion period advances. Trunz found 1.052 per cent, of ash in the 

 first milking after the birth of the calf and only 0.687 per cent, on 

 the sixth day. At the end of lactation he found 0.861 per cent, ash 



