148 THE BLOOD. 



from time to time, and observed that they became trans- 

 parent at their upper part, the red particles subsiding. I 

 then made a ligature upon one vein, so as to divide the trans- 

 parent from the red portion of the blood ; and opening the 

 vein, [ let out the transparent portion, which was still fluid, 

 but coagulated soon after. On pressing this coagulum, I 

 found it contained a little serum. The other vein I did not 

 open till after the blood was congealed, and then I found the 

 upper part of the coagulum whitish like the crust in pleuritic 

 blood." ' 



Nothing could more conclusively demonstrate that coag- 

 ulation of the blood depends upon a coagulating principle 

 existing in the liquor sanguinis, than this simple experiment. 

 It also beautifully illustrates the formation of the buffy-coat. 



The facts thus demonstrated by Hewson were confirmed 

 by Miiller in 1832. He succeeded in separating the plasma 

 from the corpuscles in the blood of the frog by simple filtra- 

 tion ; first diluting it with a saccharine solution. The great 

 size of the corpuscles in this animal prevents their passage 

 through a filter, and the clear fluid which is thus separated 

 soon forms a colorless coagulum. 2 



From these observations it is evident that the coagulation 

 of the blood is due to the presence of fibrin in the liquor san- 

 guinis. Coagulation of this principle first causes the whole 

 mass of blood to assume a gelatinous consistence ; and by 

 virtue of its contractile properties it soon expresses the serum, 

 but the red corpuscles are retained. One of the causes which 

 operate to retain the corpuscles in the clot is the adhesive 

 matter which covers their surface after they escape from the 

 vessels, which produces the arrangement in rows like piles 

 of coin, which we have 'already noted under tlie head of 

 microscopic appearances. This undoubtedly prevents those 



1 The Works of William Hewson, F. R. S., Sydenbam edition, p. 32. 

 9 J. MUELLER, Manuel de Physiologic, trad, par Jourdan, Paris, 1851, tome i., 

 p. 96. 



