USES OP SEPARATE CONSTITUENTS OF BLOOD. 213 



240. The following appear to be the chief uses of the 

 principal constituents of the Blood, considered separately, in 

 the general economy : The fibrin is the material which is 

 most assimilated to the condition of the solid tissues, having 

 the power of passing from the liquid state into a low and 

 simple form of organization. It was formerly supposed to be 

 the nutritive material at the expense of which the solid 

 tissues generally are immediately produced; the muscular 

 substance, in particular, being regarded as chemically identical 

 with it. But there is now good reason to think that the 

 greater part of the tissues form themselves at the expense of 

 the albumen of the serum and perhaps of the globulin of the 

 red corpuscles j and that the purpose of the fibrin is chiefly 

 to give origin to those simple forms of fibrous or connective 

 substance, the production of which is the first step in the 

 reparation of injuries. Were it not for its power of coagula- 

 tion, the slightest cut or scratch might become fatal, from the 

 gradual draining-away of the blood ; and such, in fact, has 

 actually happened, in cases of disease in which the fibrin is 

 deficient. The presence of fibrin also gives a degree of vis- 

 cidity to the blood, which, as experiment proves, favours 

 (instead of resisting, as might have been expected) its passage 

 through capillary tubes ; and thus, when there is a deficiency 

 in this ingredient, local stagnations and obstructions in the 

 circulation of the blood are very liable to occur. The albumen 

 of the blood may be considered, like that of the egg, as the 

 raw material, at the expense of which (in combination with 

 fat) every other organic compound in the body is generated. 

 It is, as we have seen, the substance to which all the tissue- 

 forming elements of the food are reduced in the process of 

 digestion ; and in this condition it seems to be continually 

 appropriated by the acts of self-formation that are taking 

 place, with varying rapidity, throughout the body, just as the 

 albumen of the egg is appropriated by the self-formative 

 operations of the embryo. There is strong reason to believe that 

 a large proportion of the solid tissues regenerate themselves 

 by the direct appropriation of this material ; and if (as has 

 been already stated to be probable) the simple fibrous tissues 

 find their material in the fibrin, and the muscular substance 

 in the globulin of the red corpuscles, it is from the albumen 

 that these substances are themselves elaborated, both of them 



