GENERAL CHEMISTRY OF MILK 73 



often more than 16 per cent. Perhaps the colostrum corpuscles 

 are responsible in part for the large amount of albumin. The 

 percentage of fat, casein, and milk-sugar are lower in colostrum, 

 while that of ash is higher than in normal milk; the ash may be 

 twice as high. The quantity of fat in colostrum is small, the 

 normal emulsion is not properly developed, and the globules are 

 large and irregular. The total solids of colostrum may be as high 

 as 28 per cent. Colostrum has a strong odor, a bitter taste, and 

 is more decidedly yellow than normal milk. It has an acid reac- 

 tion and thickens when boiled because the albumin coagulates. 

 The gradual transition of colostrum to normal milk is well illus- 

 trated in a table given by Leach : 



THE COMPOSITION OF COLOSTRUM AND TRANSITION TO NORMAL MILK 



rr- r* . ■ Specific Total 



lime after calvmg. gravity. Fat. Casern. Albumin. Lactose. Ash. solids. 



Immediately 1.068 3.64 2.65 16.56 3.00 1.18 26 93 



After 10 hours 1.046 4.66 4.28 9.32 1.42 155 2123 



After24hours 1.04.'i 4.75 4.50 6.25 2.85 1.02 1937 



After 48 hours 1.042 4 21 3.25 2.31 3.46 0.96 14 19 



After 72 hours 1.035 4 08 3.33 1.03 4.10 0.82 13.56 



Removal of cream disturbs the normal relation of milk con- 

 stituents to a considerable degree. The total solids in cream are 

 much greater; in skimmed milk smaller than in whole milk, owing 

 to the increased fat content in cream and the diminished fat 

 content in skimmed milk. The water is naturally present in 

 greater percentage in skimmed milk than in whole milk, and 

 greater in whole milk than in cream. The relation of the soluble 

 substances is not greatly changed by skimming. 



The composition of two samples of cream, one with a mod- 

 erate amount of fat, the other rich in fat, is given by Richmond as 

 follows : 



COMPOSITION OF CREAM 



Thick cream. Thin cream. 



Water 39 . 37 per cent. 63 . 94 per cent. 



Fat 66.09 " 29.29 " 



Sugar 2.29 " 3.47 



Protein 1.67 " 2.76 



Ash 0.38 " 0.54 " 



Contrary to earlier beliefs are the results of the analyses made 

 by Richmond, who has shown that the relation of plasma solids 

 to water in cream is the same as in milk. Errors in analysis are 

 liable to occur if the cream has lost water by evaporation. This 

 occurs when gravity cream is exposed to the air for some time. 

 The percentage of plasma solids to the volume of cream de- 

 creases in proportion to the increase in the percentage of fat. This 

 is illustrated in the following table, given by Richmond: 



