90 THE CHEMICAL COMPOSITION OF THE BODY 



line solutions, yet the two atoms of sulfur in cystin are symmetrically com- 

 bined, and the molecule of cystein contains but one sulfur atom. 



"Many proteids, not only the glycoproteids, but also true albumins, as 

 egg albumin, serum albumin, serum globulin, the nucleoproteids, etc., re- 

 act with Molisch's reagent, and, on hydrolysis, split off a carbohydrate 

 group, which is an amido-sugar, usually glucosamin, CHO.CHNH 2 (CHOH) 3 - 

 CH 2 OH, probably existing in the proteid as a polysaccharid complex. Some 

 of the nucleoproteids yield a pentose group, others laevulinic acid. Other 

 proteids, as casein, myosin, and fibrinogen, yield no carbohydrate. 



"The decomposition of proteids by the proteolytic enzymes, pepsin, 

 trypsin, and papain, consists of a series of hydrolyses, and results first in 

 the formation of albumoses and peptones, and later by trypsin, particularly 

 of polypeptids, amido acids, hexon bases, tryptophane, amins, diamins, and 

 ammonia. These changes occur in the processes of digestion." 



The Pigments, etc. A number of pigments make their appear- 

 ance in the body; for example, bilirubin, C 16 H 18 N 2 O 3 , is the common bile 

 pigment. Its crystals are bluish-red in color and are probably derived from 

 hematin of the blood. Biliverdin, C 16 H 18 N 2 O 4 , is an oxidation product 

 of bilirubin. 



Urochrome and Urobilin occur in bile and in urine; the latter is prob- 

 ably identical with stercobilin, which is found in the feces. Uroerythrin is 

 one of the coloring matters of the urine. It is orange red and contains iron. 



Melanin is a dark brown or black pigment which occurs especially in 

 epidermal tissues, where it is associated with keratin. It is found in the 

 lungs, bronchial glands, hair, choroid, skin, etc.; also in the urine and in 

 melanotic diseases, e.g., sarcoma. It is a transformation product of pro- 

 teids, from which it can be derived by boiling proteid with sulphuric acid. 



Lipochromes are pigments, usually yellow or yellowish-red, which are 

 associated with fat, being almost always present in adipose tissue. Little is 

 known about them, but they are thought to consist only of C, H, and O. 



OILS AND FATS. 



The animal oils and fats are for the most part mixtures of tri-palmitin, 

 C 3 H 5 (O.C 16 H 31 0) 3 , tri-stearin, C 3 H 5 (O.C 18 H 35 O) 3 , zndtri-olein, C 3 H 5 (O.C 18 - 

 NsaO);,, in different proportions. They are formed by the union of three 

 molecules of fatty acid with one molecule of the triatomic alcohol, glycerin, 

 C 3 H 5 (OH) 3 , and are ethereal salts or esters of that alcohol. Palmitic acid 

 is C 15 H 31 COOH, stearic acid is C^H^COOR; oleic acid is C l7 H n COOH. 

 Human fat consists of a mixture of tri-palmitin, tri-stearin, and tri-olein, 

 of which the two former contribute three-quarters of the whole. Olein is 

 the only liquid constituent. The fat of milk (and butter) is tributyrin; 

 butyric acid is C 4 H 8 O 2 . 



