m] THE CONSTITUENTS OF MILK 33 



soluble in water or alcohol, and hence possesses only 

 a slightly sweet taste. The brown coloration which 

 milk is seen to assume, when heated to a compara- 

 tively high temperature, is due to the decomposition 

 of this body. When heated between 100 and 131 

 C. (212 Fahr. and 268 Fahr.) it shows signs of 

 decomposition and becomes brown. * At 131 C. (268 

 Fahr.) it loses its water of crystallisation and under- 

 goes further decomposition, which gives rise to the 

 formation of galactine and perhaps also grape-sugar. 

 With an increase of temperature the brown coloration 

 deepens, and at 175 C. (347 Fahr.) the formation of 

 a dark brown substance called lactocaramel takes 

 place. In a watery solution of sugar, such as in 

 milk, this decomposition takes place when the 

 temperature rises above 70 C. (158 Fahr.). 



The percentage of milk-sugar in milk may be said 

 to vary between 3 and 6 per cent, amounting, on an 

 average, to 4'68 per cent. Another carbohydrate is 

 supposed also to be present in milk, but regarding it 

 we know very little. 



Ratio of the different Constituents of the Milk. 

 With regard to the variation in the different con- 

 stituents, it may be added that the relation of the 

 casein to the albumin is more or less variable ; the 

 fat is rarely less than the casein and albumin. The 

 average proportion is T2 Ib. of fat to 1 Ib. of casein 

 and albumin, or 1-5 Ib. of fat to 1 Ib. of casein. A 



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