VARIATIONS IN MILK 227 



food on the composition of the fat has been already 

 noticed, p. 208. Milk fat has a lower heat value than 

 the fats of the animal body; 1 gram of milk fat has 

 a heat value of 9*2 Calories. 



The sugar contained in milk is known by chemists 

 as lactose or lacton. This sugar is not present in the 

 vegetable foods consumed by the cow; these foods, 

 however, contain substances which yield galactose by 

 hydrolysis, and others yielding dextrose by the same 

 process. It is possible that these two sugars together 

 form lactose in the animal, as lactose can be split up 

 into these bodies. 



Besides the three groups of constituents already 

 mentioned, milk contains very small quantities of 

 citrates, and traces of several other organic bodies. 



The constituents of the ash have been already 

 referred to, p. 108. 



Variations in Composition. — The composition of 

 cews' milk is affected by many circumstances ; under 

 extreme conditions it may contain 10 — 17 per cent. 

 of dry matter. The percentage of sugar and ash varies 

 very little, the percentage of albuminoids varies a 

 little more, the fat varies most of all; rich milk may 

 easily contain twice as much fat as poor milk. In the 

 nixed milk of a herd of cows the non-fatty solids very 

 seldom fall below 8*5 per cent., nor the fat below 3*0 

 per cent. : these facts become of great importance 

 A'ben adulteration with water has to be detected. 



A cow in calf is usually in milk for ten months. 



The period of full milk is generally from the second 



to the seventh week; this period is more prolonged 



vben the cow is on grass. As the milk falls off in 



