CHAP. I.] PROXIMATE PRINCIPLES. ALBUMEN. 35 



By chemical means we obtain from them a class of substances, 

 called proximate principles, substances but one step removed from 

 the organized tissue, some of which are held in solution in the 

 blood. These, in combination with sulphur, phosphorus, and other 

 simple substances (incidental elements), and salts, form the mate- 

 rial out of which the organized tissues are framed. 



The general chemical constitution of these proximate principles 

 has already been discussed in the Introduction ; and they have 

 been distinguished from another class of organic substances, the 

 secondary organic compounds, among which we must particularise 

 those which are formed by chemical action in the living organism, 

 from materials furnished by it. These are found in various secreted 

 fluids, and are easily obtained from them, either by spontaneous 

 separation, or by simple chemical means ; and they must not be 

 confounded with a vast variety of compounds, which the chemist 

 can create at will, both from them and from the proximate prin- 

 ciples, through the affinities of various chemical substances for 

 them. 



The following table contains a list of substances which, in the 

 present state of our knowledge, may be properly assigned to the 

 two classes of organic compounds, to which allusion has been 

 made : 



PROXIMATE PRINCIPLES. SECONDARY ORGANIC COMPOUNDS. 



Albumen. \ Urea ; ) in the Urine 



Fibrine. > Compounds of Proteine. Uric or Lithic acid ; ) 



Caseine. ) Cholesterine ; in the Bile, 



Gelatine. Biliary matters. 



Chondrine. Pepsine ; in the Gastric juice. 



Elaine. Sugar of milk. 



Stearine. Lactic acid. 



Margarine. 



Hsematosine. 



Globuline. 



Of the Proximate Principles. 1. Albumen. This substance is 

 so called from the white colour it possesses in the solid state. It is 

 very readily obtained from the white of egg, ovalbumen. In the 

 human body it exists in two states : fluid, being dissolved in the serum 

 of the blood, and in some of the secretions; and solid, forming certain 

 of the tissues, which are thence called albuminous tissues. These 

 are, the brain, spinal cord and nerves, and the mucous membranes ; 

 it also enters into the composition of the muscles, and of the aqueous 

 and vitreous humours of the eye. It is also contained in the effusions 

 of serum or pus, which are the products of disease. 



D 2 



