XV. MILK AND MILK PRODUCTS 345 



duced in the milk by this treatment. The taste and smell are altered, 

 a portion of the calcium citrate and the albumin are precipitated, and 

 the casein (probably by the precipitation of the calcium compounds) 

 becomes much less coagulable by rennet. Moreover, the milk becomes 

 brown, and the enzyme, originally present in the milk, which has the 

 power of giving a blue colouration with hydrogen peroxide and para- 

 phenylene diamine, C H 4 (NH 2 ) 2 , is destroyed. The fat rises much 

 less readily, and the cream layer, though very thin, is richer in fat 

 than ordinary cream, containing often over 40 per cent instead of 20 

 to 30 per cent as in the case of fresh cream. 



In Pasteurising, a lower temperature about 60 or 80 is em- 

 ployed, and the milk is subjected to this two or three times, with 

 intermediate cooling. The taste and properties of the milk are not so 

 much altered by this treatment, but the albumin is changed, so that 

 practically all of it is precipitated along with the casein on the addition 

 of salts, e.g., magnesium sulphate. The casein, when precipitated from 

 sterilised or Pasteurised milk, is much more finely divided than that 

 from fresh milk. It is therefore probably more easily digested, especi- 

 ally by young children. 



The tendency to rickets in young children which is said to be in- 

 duced by feeding them upon cows' milk cannot be due to deficiency 

 of lime, since cows' milk contains between six and seven times as much 

 of that substance as is present in human milk. The same is true of 

 phosphorus pentoxide. By Pasteurisation or sterilisation, the lime is 

 partially precipitated and the writer found that the ratio of lime to 100 

 parts of P 2 O 5 was 



In fresh milk 

 Pasteurised milk 

 ,, sterilised milk 

 ,, " Ideal " condensed milk 

 Nestle's 



92-5 

 77-2 

 68-5 

 81-0 

 109-0 



and has suggested that it is this ratio that is important as affecting 

 bone formation and nutrition. 1 



The chief difference between human milk and cows' milk is in the 

 character of the curd which is produced by rennet or the gastric juice 

 of young children ; the former yields a finely divided mass, while the 

 latter gives a closely adherent, heavy clot, probably much less easily 

 digested. This difference is ascribed, not to a difference in the casein 

 or even in its amount, but to the different amounts of calcium present. 

 Human milk contains about 0'03 per cent CaO, while in cows' milk 

 there is about 0'16 per cent CaO. It has been shown that the coagu- 

 lation of casein by rennet is dependent upon the presence of calcium 

 compounds and that in their absence no coagulation occurs.' 2 Hence 

 it has been proposed to render cows' milk more like human milk, and 

 therefore more suitable for feeding infants, by the removal of a portion 

 of the lime ("humanised milk"). This, it is said, can be done by 

 adding about 0*5 per cent of sodium citrate. The addition of lime 

 water, it may be noted, though it delays curdling by reason of its 



1 Jour. Roy. Inst. Public Health, 1909. a Arthus and Pages, 1890. 



