THE MILK. 433 



The differences which exist in the composition of full milk, as 

 compared with skimmed milk, cream, buttermilk, and whey, are 

 shown below : 



F (#). k Sk ,8S ed Cream ' Buttermilk. Whey. 



Water 871.7 906.6 655.1 902.7 932.4 



Solids . 128.3 93.4 344.9 97.3 67.6 



Albumins . . 35.5 31.1 35.5 35.5 8.5 



Fats .... 36.9 7.4 267.5 9.3 2.3 



Lactose . . . 48.8 47.5 35.2 37.3 47.0 



Lactic acid . . none none none 3.4 3.3 



Salts 7.4 7.4 6.1 6.7 6.5 



Of gases, milk contains a small amount of oxygen and nitrogen, 

 and from 5.8 to 7.5 per cent, of carbon dioxide, which can be 

 removed with the exhaust pump. 



The Albumins. The albumins which are found in milk are casein- 

 ogen, lactalbumin, and so-called lactoglobulin, which is probably 

 identical with the serum-globulin of the blood-plasma. Of these, 

 caseinogen is the most abundant and the most important. 



CASEINOGEN. Caseinogen is a nucleo-albumin (phosphoglobulin) 

 and probably a hexabasic acid. In the dry state it occurs as a white 

 amorphous powder, which is almost insoluble in water, in dilute acids, 

 and solutions of the neutral salts. In dilute solutions of the alkaline 

 hydrates and in lime-water it dissolves with ease, at the same time form- 

 ing salts. Such solutions are neutral or slightly acid in reaction, accord- 

 ing to the amount of alkali that has been added, which is owing to the 

 formation of neutral or acid salts respectively. When triturated in 

 water with calcium or sodium carbonate, the carbonates are decom- 

 posed with the liberation of carbon dioxide ; the same salts are then 

 formed as in the case of the alkaline hydrates. Sdldner has isolated 

 two calcium salts of caseinogen, containing 1.55 and 2.36 per cent, of 

 calcium oxide ; according to Courant, these are dicalcium and tri- 

 calcium caseinogen respectively. The salts of caseiuogen with the 

 alkalies and alkaline earths are readily soluble in water, even in the 

 absence of neutral salts, and are hence not precipitated on dialysis. 

 On decomposition with dilute acids the free caseinogen is obtained 

 again in insoluble form. Suspended in water, the substance is 

 coagulated on boiling, and can then no longer be dissolved without 

 undergoing denaturization, as on boiling with acids and alkalies. 

 Solutions of the caseinogen salts, on the other hand, do not coagulate 

 on boiling, but form a surface skin, as in the case of milk. The 

 salts can be precipitated from their solutions by salting with sodium 

 chloride or magnesium sulphate to saturation. Metallic salts, such 

 as copper sulphate, also precipitate a neutral solution completely. 



On filtering milk through a Chamberlain filter under pressure 

 caseinogen remains behind, together with the fat and calcium phos- 

 phate, as a jelly-like material. On treating milk with a dilute acid 

 the caseinogen is precipitated, as in the case of the aqueous solution 

 of its salts. To a certain extent this may occur in the stomach, 



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