22 CHEMICAL COMPOSITION OF HUMAN BODY. 



the forms in which it naturally occurs, it is combined with 

 about six per cent, of fatty matter, phosphate of lime, 

 chloride of sodium, and other saline substances. Its most 

 characteristic property is, that both in solution and in the 

 half-solid state in which it exists in white-of-egg, it is coa- 

 gulated by heat, and in thus becoming solid, becomes 

 insoluble in water. The temperature required for the 

 coagulation of albumen is the higher the less the propor- 

 tion of albumen in the solution submitted to heat. Serum 

 and such strong solutions will begin to coagulate at from 

 150 to 170, and these, when the heat is maintained, be- 

 come almost solid and opaque. But weak solutions require 

 a much higher temperature, even that of boiling, for their 

 coagulation, and either only become milky or opaline, or 

 produce flocculi which are precipitated. 



Albumen, in the state in which it naturally occurs, ap- 

 pears to be but little soluble in pure water, but is soluble 

 in water containing a small proportion of alkali. In such 

 solutions it is probably combined chemically with the 

 alkali ; it is precipitated from them by alcohol, nitric, and 

 other mineral acids, by ferrocyanide of potassium (if before 

 or after adding it the alkali combined with the albumen be 

 neutralised), by bichloride of mercury, acetate of lead, and 

 most metallic salts. 



Coagulated albumen, i.e., albumen made solid with heat, 

 is soluble in solutions of caustic alkali, and in acetic acid if 

 it be long digested or boiled with it. With the aid of 

 heat, also, strong hydrochloric acid dissolves albumen pre- 

 viously coagulated, and the solution has a beautiful purple 

 or blue colour. 



Fibrin is found most abundantly in the blood and the 

 more perfect portions of the lymph and chyle. It is very 

 doubtful, however, whether fibrin, as such, exist in these 

 fluids, whether, that is to say, it is not itself formed at 

 the moment of coagulation. (See Chapter on the Blood.) 



If a common clot of blood be pressed in fine linen. 



