ITS CHEMICAL CONSTITUENTS. 335 



infusorium, which he terms vibrio cyanogeneus ; but Bailleul* 

 ascribes it to a byssus. 



My observations on this subject are limited to the ordinary 

 manner in which the milk acquires this blue colour. When freshly 

 drawn, the fluid is generally perfectly white, assuming this peculiar 

 blue shade of colour on the formation of the cream, which exhibits 

 pale blue specks, extending at first scarcely half a line deep, and 

 appearing in detached groups upon the surface of the otherwise 

 white fluid, These specks become darker, and gradually increase 

 downwards and laterally, until they commingle. The curd which 

 separates from the cream is colourless, and the bluish cream con- 

 tains rod-like, colourless vibriones, similar to those described by 

 Fuchs. I only once observed a distinct formation of byssus. 



We have already become acquainted with the most important 

 chemical constituents of the milk in our considerations of the 

 organic substrata. This is especially the case with casein and 

 milk-sugar, which have already been very fully treated of, not only 

 in reference to their chemical properties, but also to their occur- 

 rence in variable quantities under different physiological and pa- 

 thological conditions (see vol. i., pp. 297 and 383). It still remains, 

 however, for us specially to notice the third organic constituent of 

 the milk, namely, the fat or butter. The fat of women's milk 

 has not yet been subjected to any exact qualitative analysis, 

 but the butter of cows' milk has been carefully analysed by 

 Chevreul,t and more recently by BromeisJ and Lerch. Pure 

 milk-fat is almost colourless, or at most is but faintly yellow ; 

 after being melted it solidifies at + 26'5. It becomes soft and 

 greasy at a temperature exceeding + 18. One part of this fat 

 dissolves in 28'9 parts of boiling alcohol of 0*822 sp. gr. It 

 easily becomes rancid on exposure to the air, and then forms 

 volatile fatty acids ; hence it imparts a somewhat reddish colour to 

 moist litmus paper, even when in a comparatively fresh state. It 

 is perfectly saponifiable, and yields, in addition to glycerine, 

 margaric, oleic, capric, caprylic, caproic, and butyric acids, or in 

 place of the two latter, vaccic acid (see vol. i.,pp. 56-71). Bromeis 

 calculated the composition of butter, from the quantity of the acids 

 which he obtained from it, as equal to 68% of margarin, 30# of 

 olein, and 2-g- of true butter-fat ; but this calculation affords only 



* Compt. rend. T. 17, p. 1138. 

 t Recherches sur les corps gras. Paris, 1822. 

 Ann. d. Ch. u. Pharm. Bd. 42, S. 46 ff. 

 Ibid. Vol. 49, p. 212. 



