PllOTEIiN. 5 



II. ORGANIC CONSTITUENTS. 



The Organic Constituents may be arranged in two principal 

 groups, tlie former embracing the nitrogenous, the latter the 

 non-nitrogenous matters. In the nitrogenous group we have 

 protein, and its various modifications — gelatin, bilin, and the pro- 

 ducts of its metamorphosis — haematin, urea, uric acid, &c. : in 

 the non-nitrogenous we place the animal sugars, fats, lactic and 

 acetic acids, &c. &c. 



CLASS I. NITROGENOUS CONSTITUENTS. 



1. Protein. 



Under this head we shall consider three very important com- 

 pounds which are formed in the vegetable kingdom, and wdiich 

 are also found to constitute the greater part of the animal body. 

 These are Albumen, Fibrin, and Casein. Two most important 

 discoveries have recently been made regarding these substances. 

 The first is the discovery made by Mulder that albumen, fibrin, 

 and casein are nothing more than modifications of one com- 

 pound to which he has given the name of Protein, (from 

 TrfwTEuw, I am first,) which may be regarded as the commence- 

 ment and starting-point of aU the tissues : the second is, that 

 protein, in every respect identical Avith that which forms the 

 basis of the three aforesaid animal principles, may be obtained 

 from similar elements in the vegetable kingdom. When the 

 newly-expressed juices of vegetables are allowed to stand, a 

 separation takes place in a few minutes. A gelatinous preci- 

 pitate commonly of a green tinge is deposited, and this, Avhen 

 acted on by liquids which remove the colouring matter, leaves 

 a grayish white substance, which has been named vegetable fibrin. 

 It separates from the vegetable juice in which it was originally 

 dissolved exactly as fibrin does from blood. 



When the clarified juice of nutritious vegetables, such as 

 cauliflower, asparagus, mangel-^iirzel, or turnips, is made to boil, 

 a coagulum is formed which it is absolutely impossible to dis- 

 tinguish from the substance which separates as a coagulum, 

 when the serum of blood, or the white of an egg, diluted with 

 water, is heated to the boiling point. This is vegetable albumen. 



