658 MILK. 



53-72 per cent is not in simple solution. A part of this lime is combined 

 with the casein; the remainder is found united with the phosphoric acid 

 as a mixture of dicalcium and tricalcium phosphates which is kept dis- 

 solved or suspended by the casein. RONA and MICHAELIS 1 found that 

 about 40-50 per cent of the total quantity of lime was diffusable ; accord- 

 ing to them nearly one-half of the calcium is contained in the milk as a 

 non-dissociable casein compound, while the milk only contains the very 

 smallest amounts of suspended calcium phosphate. 



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 mainly of CO2, besides a little N and 

 traces of O. PFLUGER 2 found 10 vols. per cent CO2 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 higher 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 di- 

 ameter with abundant fat-granules and fat-globules. The fat of colos- 

 trum has a somewhat higher melting-point and is poorer in volatile fatty 

 acids than the fat from ordinary milk (NILSON 3 ) . The iodine equivalent 

 of the colostrum-fat is higher than that of milk-fat. The quantity of 

 cholesterin and lecithin is generally greater. The most apparent dif- 

 ference between it and ordinary milk is that colostrum coagulates on heat- 

 ing to boiling because of the absolutely and relatively greater quantities 

 of globulin and albumin that it contains. 4 The composition of colostrum 

 varies considerably. KONIG gives as average the following figures in 

 1000 parts: 



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



746.7 253.3 40.4 136.0 35.9 26.7 15.6 



The influence which food exercises upon the composition of milk will 

 be discussed in connection with the chemistry of the milk secretion. 



1 Bioch. Zeitschr., 21. 



2 Pfluger'sArch., 2. 



See Maly's Jahresber., 21. See also Engel and Bode, Zeitschr. f. physiol. Chem., 

 74. 



4 See Sebelien, Maly's Jahresber., 18, and Tiemann, Zeitschr. f. physiol. Chem., 

 25. See also Simon, ibid., 33; Winterstein and Strickler, ibid., 47. 



