122 MILK 



in the milk from one cow and 0.937 per cent, in that from the other 



cow. 



The variation of the chief constituents of ash, according to 

 Trunz, is, briefly, as follows: 



Potassium is present in smaller quantity in colostrum than 

 in later milk. It reaches a maximum in the second month, then 

 declines slowly at first and rapidly during the last two months. 



Sodium declines shghtly during the first half of the lactation 

 period and rises markedly during the second half. However, it 

 is subject to considerable variation. 



Calcium is higher in colostrum than in normal milk and re- 

 mains about the same after the normal quantity has been reached 

 up to the third month before the close of lactation, when it rises 

 slowly. This rise is probably due to the increased amount of 

 casein present at the end. 



Chlorin is fairly constant throughout the lactation period. 

 The quantity is somewhat smaller in colostrum than in normal 

 milk and rises constantly to the end of lactation. 



Phosphoric acid is higher in colostrum than in normal milk and 

 declines slowly after the colostral period, at first gradually and 

 then more rapidly. In pure ash there is a rise for three weeks and 

 then a slow decline. 



Iron and sulphuric add are present in milk in such small 

 amounts that no change can be observed. 



If a summary is taken of the variations in milk during the 

 lactation period the general aspect is shaped about as follows: 

 During the first three to six weeks of lactation the proteins, fat, 

 and ash decrease; the size of the fat globules declines rapidly; the 

 melting-point of the fat is high and the iodin, Reichert-Meissl, 

 and saponification numbers are variable. After this first period 

 the compensation remains fairly constant for a period up to within 

 about two months of the end of lactation. This period varies 

 according to the whole length of the lactation period. The longer 

 the whole period, the longer will the composition remain practically 

 unchanged. The sugar remains constant; the size of the fat glob- 

 ules declines slowly, as do the Reichert-Meissl and saponification 

 numbers. Within two months 'of the end of the lactation period 

 there are marked changes. Proteins rise markedly, the fat also 

 rises somewhat, the sugar may decline, and the ash rises. The fat 

 globules become very small; the melting-point of the fat rises; the 

 iodin number increases, while the Reichert-Meissl and saponifica- 

 tion numbers decUne. 



Gestation does not influence the composition directly, but may 

 do so indirectly by shortening the period of lactation. A varia- 

 tion of composition accompanying gestation is, therefore, only the 



