MILK FAT. CASEIN. 647 



fat-globules at least cannot contain these two proteins alone. They 

 must contain another protein, and it is still a question whether besides this 

 they also contain casein and lactalbumin. 



The milk-fat which is obtained under the name of butter consists 

 mainly of olein and palmitin. Besides these it contains, as triglycerides, 

 myristic acid, stearic acid, small amounts of lauric acid, arachidic acid, 

 and dioxystearic acid, besides butyric acid and caproic acid, traces of 

 caprylic acid and capric acid. RIEGEL claims that triglycerides of vola- 

 tile fatty acids do not occur, but rather mixed triglycerides of volatile 

 and non-volatile fatty acids. Milk-fat also contains small quantities 

 of phosphatides (lecithin), and cholesterin and a yellow coloring-matter. 

 The quantity of volatile fatty acids in butter is, according to DUCLAUX, 

 on an average about 70 p.m., of which 37-51 p.m. is butyric acid and 

 30-33 p. m. is caproic acid. The non-volatile fat consists of /<$ A olein 

 and the remainder is principally palmitin. The composition of butter 

 is not constant, but varies considerably under different circumstances. 1 

 The question whether the small fat-globules have a different composition 

 from the large ones is still disputed. 



The milk-plasma, or that fluid in which the fat-globules are suspended, 

 contains several different proteins, the statements as to the number and 

 nature of which are somewhat at variance. The three following, casein, 

 lactalbumin, and lactoglobulin, have been most closely studied and are 

 well characterized. The milk-plasma contains at least two carbohy- 

 drates, of which the one, lactose, is of great importance. It also contains 

 extractive bodies, traces of urea, creatine, creatinine, or otic acid, hypoxan- 

 thine (?), cholesterin, citric acid (SOXHLET and HENKEL 2 ), and lastly also 

 mineral bodies and gases. 



Casein. This protein substance, which thus far has been detected 

 positively only in milk, belongs to the nucleoalbumins, and differs from 

 the albuminates chiefly by its content of phosphorus and by its behavior, 

 with the rennet enzyme. Casein from cow's milk has about the follow- 

 ing composition: C 53.0, H 7.0, N 15.7, S 0.8, P 0.85, and O 22.65 per 

 cent. Its specific rotation is, according to HOPPE-SEYLER, rather variable; 

 in neutral solution it is (o:) D = 80; its faintly alkaline solution has a 

 stronger rotation, namely, 97.8 to 111.8, in a solution of N/10-N/5 



1 Riegel, Maly's Jahresber., 34; Duclaux, Compt. Rend., 104. Various statement. 

 as to the composition of milk-fat can be found in Koefoed, Bull. d. 1'Acad. Roys 

 Danoise, 1891, and Wanklyn, Chemical News, 63; Browne, Chem. Centralbl., 1899, 

 2, 883. In regard to the elementary composition of milk-fat see Fleischmann and 

 Warmbold, Zeitschr., f. Biol., 50. 



2 Cited from Soldner, Die Salze der Milch, etc., Landwirthsch. Versuchsstation, 

 35, Separatabzug, 18. 



