THE FA TS OF MILK 133 



with acid. Landwehr 1 identified it as animal gum, Be"champ 2 as dextrin. 

 J. Herz 3 found granules in milk, which behave towards iodine like starch ; 

 he called them "animal amyloid." 



The fats of milk. Milk fat has a specific gravity of from 949 

 to 996. 4 It consists of palmitin, stearin, and olein, with small quantities 

 of triglycerides of butyric, caproic, caprylic, capric, myristic, and arachic 

 acids in addition. 5 It also contains small quantities of lecithin, choles- 

 terin, and a yellow lipochrome. 



The amount of fat in cream varies from 14 to 44 per cent. In butter, 

 besides fat, there are small quantities of caseinogen and lactose. The 

 fats of cows' butter consist of 68 per cent, of palmitin and stearin, 30 

 per cent, of olein, and 2 per cent, of the specific butter fats. 6 Their 

 melting point is 31 to 34 C. The volatile fatty acids in cows' milk, accord- 

 ing, to Duclaux, 7 amount to 7 per cent., of which 3 '7 to 51 is butyric, and 

 2'0 to 3'3 is caproic acid. Some analysts give still higher percentages. 



By exposure to the air butter becomes rancid ; this is partly due to 

 the production of lower fatty acids from the higher fats (see p. 19), 

 partly to the formation of acrolein from glycerine, and partly, and 

 according to Hagemann chiefly, to the formation of lactic acid from the 

 entangled lactose. 



The composition of butter is very variable. Thus, in Finland butter, 

 Koefoed 8 found two fatty acids of the acrylic series in addition to oleic 

 acid; 100 parts of the fatty acid contained 66 of these acids, 28 of 

 palmitic, 22 of myristic, 8 of lauric, 1-5 of butyric, 2 of caproic, 2 of capric, 

 and 0*5 of caprylic acid. According to Wanklyn, 9 there is no true palmitic 

 acid in butter ; the acid is aldepalmitic acid (C 16 H 30 2 ). 



The fats of human milk are somewhat different from those of cows' 

 milk. They have been the subject of two recent researches one by 

 Kuppel, 10 the other by Laves. 11 



Their melting point is 34 C., and solidifying point 20'2 C. Their 

 specific gravity at 15 C. is 966. The fatty acids found are butyric, 

 caproic, capric, myristic, palmitic, stearic, and oleic acids, all combined 

 with glycerine. The presence of formic acid 12 is also inferred from its 

 reducing action, but not by any further tests. Human milk is poor in 

 volatile acids (Kuppel). 



Laves confirms this work, and gives some quantitative results. The 

 fat contains 14 per cent, of volatile acids, 1-9 of acids soluble in water, 

 and 49 -4 (a very high percentage) of unsaturated acids. The volatile 



1 Arch.f. d. ges. Physiol., Bonn, Bde. xxxix. and xl. 



2 Bull. Soc. cMm., Paris, Ser. 3, tome vi. 



3 Chem. Zig., Cothen, Bd. xvi. S. 1594. 



4 Bohr, Jahresb. it. d. Fortschr. d. Thier-Chem., Wiesbaden, Bd. x. S. 182. 



5 Grunzweig, Ann. d. Chem., Leipzig, Bd. clxii. S. 215; E. Wein, Diss., Erlangen, 

 1876; Chevreul, " Recherches sur le corps gras," Paris, 1823; Lerch, Ann. d. Chem., 

 Leipzig, Bd. xjix. S. 212 ; Heintz, ibid., Bd. Ixxxviii. S. 300. 



6 Bromeis, ibid., 1842, Bd. xlii. S. 46. 



7 Compt. rend. Acad. d. sc., Paris, tome civ. 



8 Overs, o. d. k. Danske Vidensk. Selsk. Fork., Kjobenhavn, 1891. 



9 Chem. Neivs, London, vol. Ixiil. 



10 Ztschr.f. JBiol., Munchen, Bd. xxxi. S. 1. 



11 Ztschr.f. physiol. Chem., Strassburg, Bd. xix. S. 369. 



12 Duclaux (loc. cit.) found formic acid in cows' butter which had been exposed to 

 sunlight. 



