THE VITAL PRINCIPLE — THE BLOOD. 15 



salts in a state of solution, such as hydro- 

 chloride of soda and potass, subcarbonate and 

 phosphate of soda, sulphate of potass, phos- 

 phate of lime, magnesia, and iron, with sub- 

 carbonate of lime and magnesia. It also yields 

 an oily and a crystallizable fatty matter. The 

 crassamentum, on its separation from the 

 serum, assumes the form of two layers, not, 

 however, rigidly distinct from each other, but 

 rather blending together. The upper layer 

 appears in the form of a yellowish white glaze, 

 or tenacious skin, and on minute examination 

 will be found to be moderately firm, tough, and 

 elastic, and to consist of a vast number of 

 minute threads or fibres, disposed in various 

 directions, crossing and recrossing each other. 

 From this circumstance it has received (he 

 expressive term of fibrin. Under microscopic 

 analysis these fibres are precisely similar to 

 those of a muscle when deprived of its envelop- 

 ing membrane and its colouring matter. The 

 fact is that the two are identical, for the basis 

 of all muscles, and of the solid parts of the body 

 generally, the bones excepted, consists of fibrin. 

 It is the most important constituent of the 

 blood ; whatever other may be absent, this 

 is invariably present in the blood of all ani- 

 mals which possess blood,. whether coloured or 

 colourless. Below the glaze of fibrin, which 

 varies in thickness under influencing circum- 

 stances, we find a deep red mass, consisting of 

 the colouring particles of the blood, which 

 being of a greater specific gravity than fibrin, 



