CHEMICAL COMPOSITION OF THE HUMAN BODY 27 



The most reliable statements on this subject are concerning 

 the crystallized serum albumin of the horse, which is supposed to 

 have a molecular weight of 17,070 and the empirical formula 

 C H .N,^S 1A O., Q .. This number is calculated from the amount 



joo 1215 15 1U **> 



of sulphur. The sulphur of most proteids exists in two forms: 



1 . Easily split off by hot alkali ; with lead acetate it forms lead sul- ' 

 phide : reduced sulphur. 



2. Firmly bound to the proteid molecule, only demonstrable as sul- 

 phuric acid after the decomposition of the proteid: oxidized sulphur. 



Such proteids must contain at least two atoms of sulphur. 



In serum albumin the proportion between the firmly and the 

 loosely combined sulphur is as 2 : 3 ; the molecule, therefore, 

 contains at least five atoms of sulphur. This number must be 

 doubled as the serum albumin splits up into at least seven diges- 

 tion-products which contain sulphur; of these, three contain 

 sulphur in both forms. With ten atoms of sulphur in the mole- 

 cule the calculations from the elementary composition [C = 

 53.08$; H = 7-12$; N = 15.93$; S = 1.875$; O = 21.995$] 

 furnish us with the above formula. According to the method of 

 determining the freezing-point, the molecular weight of 15,000 

 has been assigned to egg albumin. 



($) The Decomposition Products of Proteids. 



By boiling with alkalies or acids and by putrefaction, proteids 

 are decomposed. The decomposition products are : 



1. If the decomposition is long continued: ammonia, carbon 

 dioxide, acetic acid, oxalic acid, phenol, indol, skatol. 



2. If the decomposition is not continued for a long time : amido 

 acids and hexon-bases. 



The following are the most important amido acids : 



Glycocoll, amidoacetic acid, NH 2 .CH 2 .COOH, is found chiefly 

 among the decomposition products of gelatin. 



Leucin, amidocaproic acid, C 4 H 9 .CH(NH 2 ).COOH, crystallizes 

 in radially striated spheres. 



Tyrosin, oxyphenol-amidopropionic acid, 



OH. C 6 H 4 . CH r CH (NH 2 ). COOH, 



crystallizes in rosette-like clusters and is colored red by Millon's 

 fluid. 



Aspartic acid, amidosuccinic acid, 



COOH. CH 2 .CH(NH 2 ). COOH, 



is extensively found as the amid (asparagin), in plants. 



The Hexon-bases, lysine, arginine, and histidine, are nitrogen- 

 ous substances having strong basic properties, and containing six 



