MILK-SUPPLY OF LONDON WOEKHOTJSES. 41 



cases are sufficiently well established ; and I consider it to be 

 a well-established fact that the milk of a herd of cows in 

 good condition always contains more than 11.5 per cent, of 

 solids, and that single cows almost invariably (if not always) 

 yield milk containing more than 11.5 per cent, of solids. 



In dealing with milk-supply on the large scale, we are 

 little concerned with the possibility of single animals giving 

 abnormal milk, and need only concern ourselves with milk 

 of normal quality, all departures from the standard being 

 looked upon as sophistications. 



The following, which is the result of several concordant 

 analyses of country-fed milk, may be taken as representing 

 normal milk. In 100 grms. of milk 



Solids (dry at 100 0.) . . 12.5 grms. 

 Water 87.5 &quot; 



100.0 



The 12.5 grms. consist of 9.3 grms. of &quot; solids which are 

 not fat,&quot; and of 3.2 grms. of fat. 



If we consider the changes in composition which the addi 

 tion of water to milk will produce, it will be apparent that it 

 must diminish the proportion of solids in the milk, whilst the 

 effect of skimming is to diminish the proportion of fat, and 

 to leave the proportion of &quot; solids not fat &quot; unaltered (or 

 indeed, strictly speaking, to make a very trifling increase in 

 the proportion of the &quot; solids not fat&quot;). 



Treating the question quite rigidly, which I believe is the 

 proper way of dealing with it, we airive at the following : 



Problem I. Given the percentage of &quot;solids not fat&quot; 

 (= a\ in a specimen of sophisticated milk (i. e., milk either 

 watered or skimmed, or both), required the number of 

 grammes of genuine milk which was employed to form 100 

 grms. of it. 



