96 USES OF THE BLOOD. 



blood it may be said that the matter almost resolves itself 

 into an analysis of the different parts of the body, and of 

 the food and drink which are taken for their nutrition, 

 with a subsequent consideration of how far any given con- 

 stituent of the blood may be supposed to be on its way 

 to the living tissues, to be incorporated with and nourish 

 them, or, having fulfilled its purpose, to be on its way in a 

 more or less changed condition to the excretory organs to be 

 cast out. It must be remembered, however, that the blood 

 contains also matters which serve by their combustion 

 to produce heat, and, again, others which possibly sub- 

 serve only a mechanical, although most important, purpose ; 

 as for instance the preservation of the due specific gravity 

 of the blood, or some other quality by which it is enabled 

 to maintain its proper relation to the vessels containing it 

 and to the tissues through which it passes. Lastly, among 

 the constituents of the blood, are the gases, oxygen and 

 carbonic acid, and the substances specially adapted to carry 

 them, which can scarcely be said to take part in the nutri- 

 tion of the body, but are rather the means and evidence of 

 the combustion before referred to, on which, to a great 

 extent, directly or indirectly, all vitality depends. 



Albumen. The albumen, which exists in so large a 

 proportion among the chief constituents of the blood, is 

 without doubt mainly for the nourishment of those tex- 

 tures which contain it or other compounds nearly allied to it. 

 Besides its purpose in nutrition, the albumen of the liquor 

 sanguinis is doubtless of importance also in the maintenance 

 of those essential physical properties of the blood to which 

 reference has been already made. 



Fibrin. It has been mentioned in a previous part of 

 this chapter that the idea of fibrin existing in the blood, 

 as fibrin, is probably founded in error ; and that it is formed 

 in the act of coagulation by the union of two substances, 

 which before existed separately (p. 64). In considering, 

 therefore, the functions of fibrin, we may exclude the notion 



