158 BLOOD. 



in far less number than the coloured corpuscles : they are more 

 globular, although not perfectly spherical, and their diameter 

 averages ^i/' (which = 0-005'" or 0'01128 mm ); they have a 

 granular capsule, and either a single round, or occasionally an 

 oval or reniform nucleus, or several small nuclei heaped on one 

 another ; in consequence of their containing a larger quantity of 

 fat, and of their being deficient in the ferruginous hsematin, they 

 are specifically lighter than the red corpuscles : these cells were 

 formerly regarded by some writers as products of coagulation, 

 but independently of their appearance under the microscope, which 

 shows that they unquestionably are cells, we may also readily con- 

 vince ourselves that they are contained pre-formed in the living 

 blood by a microscopical examination of the circulation in the 

 capillaries of the frog (in the web-membrane, the mesentery, or the 

 tongue). 



It is seldom, except in whipped blood, that other formal 

 elements, namely fat-globules and the so-called fibrinous flakes 

 (Faserstoffschollen), are detected by the microscope. 



The fluid in which the blood-corpuscles are suspended, has 

 received the names of Liquor sanguinis, Plasma, and Intercellular 

 fluid ; in the circulating blood it contains in solution, together with 

 other matters, the substance on which the coagulation of the blood 

 depends. 



The Clot consists of the coagulable matter of the blood 

 together with the blood-corpuscles, which it encloses in the 

 process of separation ; it is moistened by a varying amount of 

 serum. 



The specific gravity of the serum is less variable than that of 

 the blood itself; it averages 1'028. 



The blood, consequently, is divisible mechanically into three 

 parts : the coagulating substance, the serum, and the blood- 

 corpuscles. Hence, nature appears to aid the efforts of the chemist, 

 who, next to a perfect chemical separation, always desires also to 

 accomplish a mechanical separation of the constituents of the 

 object which he is engaged in examining ; but unfortunately this 

 very circumstance constitutes one of the principal grounds which 

 have hitherto stood in the way of a scientifically accurate analysis 

 of the blood. The impracticability of a perfect separation of the 

 blood-corpuscles, which are moist cells filled with water and 

 soluble substances, from the surrounding intercellular juice, (which 

 we shall presently examine,) always prevents the possibility of 

 our obtaining any certain approach to the knowledge of the 

 processes which are at work in the blood, and which principally 



