MILK. 311 



united with the phosphoric acid as a mixture of di- and tri-calcium 

 phosphate, which is kept dissolved or suspended by the casein. 

 The bases are in excess of the mineral acids in the milk-serum. The 

 excess of the first is combined with organic acids which correspond 

 to 2.5 p. m. citric acid (SOLDNER). 



The gases of the milk consist chiefly of C0 8 , besides a little N 

 and traces of 0. PFLUGER found 10 vols. per cent C0 2 and 0.6 vol. 

 per cent N, calculated at C. and 760 mm. pressure. 



The variation in the composition of cow's milk depends on 

 several circumstances. 



The colostrum, or the milk which is secreted before calving and 

 in the first few days after, is yellowish, sometimes alkaline, but often 

 acid, of high specific gravity, 1.046-1.080, and richer in solids than 

 ordinary milk. The colostrum contains, besides fat-globules, an 

 abundance of colostrum-corpuscles nucleated granular cells 0.005- 

 0.025 mm. in diameter with abundant fat-grains and fat-globules. 

 The fat of colostrum has a somewhat higher-melting point and is 

 poorer in volatile fatty acids than the fat from ordinary milk 

 (NiLSON"). The quantity of cholesterin and lecithin is generally 

 greater. The most apparent difference between it and ordinary 

 milk is that colostrum coagulates on heating to boiling be- 

 cause of the absolute and relatively greater quantities of globulin 

 and albumin it contains. The quantity of the first of these two 

 albuminous bodies may indeed amount to several per cent (SEBE- 

 LIEN). The composition of colostrum is very variable. KONIG 

 gives as average the following figures in 1000 parts : 



Water. Solids. Casein. Albumin and Globulin. Fat. Sugar. Salts. 

 740.5 259.5 46.6 136.2 34.3 26.6 15.8 



The properties of milk are changed during lactation and it 

 becomes richer in casein. A change in the amount of fat is also 

 sometimes observed (EMMERLING). Otherwise we often say that 

 the rnilk becomes poorer in fat during lactation and the fat defi- 

 cient in volatile fatty acids. The evening milk is richer in fat than 

 the morning milk (ALEX. MULLER and ETSENSTUCK ; NILSON). 

 The race of the animal also has a great influence on the milk. 



The influence food exercises upon milk will be discussed in con- 

 nection with the chemistry of the milk secretion. 



