20 CHEMICAL CONSTITUENTS OF BODY AND FOOD. 



Mohr gives the proportion of the acids in marrow fat as palmitic acid, 22 ; 

 stearic acid, 10; and oleic acid, 63 per cent. 



Among the exceptional forms of fat are the following : 



Spermaceti, obtained from the sperm whale. This fat sets into a solid, 

 white crystalline mass, melting at from 30 to 50 C. Its chief constituent 

 is the palmitate of cetyl alcohol, or ethal (C 1C H 33 OH). This alcohol is the 

 one from which palmitic acid is derived in the same way as acetic acid 

 is derived from ethyl alcohol. Spermaceti contains also small quanti- 

 ties of compounds of lauristic, myristic, and stearic acids, with the 

 radicles of the alcohols lethal (C 12 H 25 OH), methal (C 14 H 29 OH), and 

 stethal (C 18 H 37 OH). 



Beeswax contains three chief constituents : 



(1) Myricin; this is its principal^ constituent ; it is the palmitate of 

 myricyl alcohol (C 30 H C1 OH) ; (2) Cerotic acid (C 27 H 54 2 ) ; and (3) Cerolein, 

 which is probably a mixture of several substances. 



Chinese wax is chiefly the cerotic acid compound of cerotyl alcohol 

 (C 27 H,,OH).i 



Adipocere is the name given to a waxy substance which replaces the 

 muscular tissue in corpses buried in damp soil, or which have been 

 allowed to remain in water some time after death. It consists chiefly 

 of the calcium soaps of palmitic and stearic acids, and in some cases of 

 acid ammonium soaps also. 2 Hoppe-Seyler 3 considered that the change 

 is the result of a ferment action. 



LIPOCHROMES, LECITHIN, CHOLESTERIN. 



Lipochromes. This name is given to the pigments which occur in 

 fat and fatty tissues. They are mostly yellow or yellowish red. They 

 include the pigment of the blood serum (serum lutein) and of the corpus 

 luteum ; the chromophanes or coloured oil globules of the retinal cones ; 

 the yellowish pigment in butter, adipose tissue, and egg-yolk ; tetronery- 

 thrin, a reddish pigment, found in many invertebrates; and several 

 vegetable pigments, such as carrotin, which is found in carrots and 

 tomatoes. The lipochromes have been separated by their various 

 solubilities after saponification ; they give various colour reactions, such 

 as a greenish-blue colour with iodine and sulphuric acid, and a green 

 colour with nitric acid; they show absorption-bands towards the 

 violet end of the spectrum, and especially in the region of the F line. 



Nothing is known about their chemical constitution ; carrotin, which 

 has been examined more fully than the others, has been assigned the 

 formula C 18 H 24 by Husemann, and C 26 H 38 by Arnaud. 4 



1 On these rarer forms of fat and wax, see Liebermann, Ber. d. deutsch. chem. Gesellsch. , 

 Berlin, 1885, Bd. xviii. S. 1975. 



2 Quain, Med.-Chir. Trans., London, 1850, p. 141 ; Virchow, Vcrliandl. d. phys.-med. 

 Gesellsch. in Wurzburg, Bd. iii. ; Wetherill, Journ. f. praH. Chem., Leipzig, Bd. Ixviii. S. 

 26 ; K. B. Lehmann, Centralbl. f. Agric. Chem,., Leipzig, 1889, S. 66. 



3 "Physiol. Chem.," Strassburg, S. 119. According to some authors, its formation is 

 brought about by micro-organisms (Jacobsthal, Arch. f. d. ges. Physiol., Bonn, 1893, Bd. 

 liv. S. 499. 



4 The principal papers on lipochromes are the following : On lutein Thudichum, 

 Centralbl. f. d. med. Wissensch., Berlin, 1869, Bd. vii. S. 1. On colour reactions of 

 luteins Thudichum, loc. cit. ; Piccolo and Lieben. Gior. de sc. nat. ed. ccon., Palermo, 

 vol. ii. p. 258 ; Caprarnica, Arch. /. Physiol., Leipzig, 1877, S. 283.; Schwalbe, 

 "Handb. d. ges. Augenheilkunde," Leipzig/ 187 4, Bd. i. S. 414. On chromophanes 

 Kiihne and Ayres, Journ. Physiol., Cambridge and London, _ 1878, vol. i. 

 p. 109 ; Untersuch. a. d. physiol. Inst. d. Univ. Heidelberg, Bd. i. Heft 4. On 



