USES OF 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 economyThe 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 ; 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 
