GENERAL STRUCTURE AND COMPOSITION. (9 



or derived from the Body may be classified as organic and in- 

 organic, and the former be subdivided into those which con- 

 tain nitrogen and those which do not. 



Nitrogenous or Azotized Organic Compounds. These 

 fall into several main groups: proteids, peptones, albuminoids, 

 enzymes, crystalline substances, and coloring matters. 



Proteids are by far the most characteristic substances 

 obtained from the Body, since they are only known as exist- 

 ing in or derived from living things, either animals or plants. 

 The type of this class of bodies may be found in the white of 

 an egg, where it is stored up as food for the developing chick-; 

 from this typical form, which is called egg-albumin, the pro- 

 teids in general are often called albuminous- bodies. Each 

 of them contains carbon, hydrogen, oxygen, sulphur and 

 nitrogen united to form a very complex molecule, and although 

 different members of the family differ from one another in 

 minor points they all agree in their broad features and have 

 a similar percentage composition. The latter in different 

 examples varies within the following limits: 



Carbon 50 to 55 per cent. 



Hydrogen 6.8 to 7.3 



Oxygen 22.8 to 24.1 " 



Nitrogen.. 15.4 to 18.2 " 



Sulphur ." 0.4 to 5.0 " 



In addition a small quantity of ash is usually left when a 

 proteid is burnt. 



Proteids are recognized by the following characters: 



1. Boiled, either in the solid state or in solution, with strong 

 nitric acid they give a yellow liquid which becomes orange on 

 neutralization with ammonia. This is the xantho-proteic test. 



2. Boiled with a solution containing subnitrate and per- 

 nitrate of mercury they give a pink precipitate, or, if in very 

 small quantity, a pink-colored solution. This is known as 

 Millon's testf 



3. If a solution containing a proteid be strongly acidulated 

 with acetic acid and be boiled after the addition of an equal 

 bulk of a saturated watery solution of sodium sulphate, the 

 proteid will be precipitated. 



Among the more important pfoteids obtained from the 

 Human Body are the following: 



Serum-albumin. This exists in solution in the blood and 



