NOTES AND MEMORANDA. 407 



coagulate, that which remained in the heart to continue 

 liquid for a considerable time. But no such contrast Avas 

 observable, both portions of blood remained perfectly fluid 

 for an indefinite time. I say apparently, for, in fact, on 

 subsequently turning out the blood, a slight film of coagu- 

 lated fibrin was observable attached to the walls of the tube. 

 Of course the corpuscles being the heavier gravitate to the 

 bottom, and the blood thus becomes divided into two por- 

 tions, a clear fluid above and a mass of red corpuscles below, 

 with a thin filmy stratum of white again on the surface of 

 the latter. 



To show that the clear fluid is plasma and not merely 

 serum, that is to say, that it fully retains its coagulability, 

 it is sufiicient to take a little up into a very fine, almost capil- 

 lary, glass tube. The extent of surface to which it is thus 

 exposed very quickly determines its coagulation. 



Following up the subject still further, I found the same 

 thing to happen Avhen the blood is allowed to drop into a 

 glass vessel : the whole remaining fluid, except that portion 

 in immediate contact with the sides, the corpuscles subsiding 

 as before, the supernatant liquid being readily coagulable in 

 a capillary tube. 



But frog's blood does not always behave in this manner. 

 It is not unfrequently the case, especially at this season of 

 the year, to find that the blood of these animals behaves to 

 all appearance precisely as we are in the habit of expecting 

 that blood should beliave, that is to say, the commencing 

 subsidence of the corpuscles is arrested, the fluid solidifies, 

 seemingly throughout. And, indeed, in rare instances, the 

 coagulation is complete to the centre, and the mass soon 

 separates into clot and serum, which latter, in these cases, 

 never yields a coagulum in a capillary tube. More fre- 

 quently, however, on breaking the surface with a knife, the 

 interior of the coagulated mass is seen to be occupied by 

 still fluid blood. 



In either case, the coagulated fibrin soon begins to con- 

 tract; and this contraction proceeds to such an extent that 

 not only is the serum of the blood expressed from it, but it 

 comes to pass that there is no longer room in its meshes for 

 the involved corpuscles, which consequently begin to be 

 squeezed out and to fall to the bottom of the glass. This 

 diniinu.tion in volume of the clot may proceed so far that in the 

 course of a few hours the blood may present an ajDpearance 

 precisely as if it had not undergone coagulation at all, there 

 being a mass of corpuscles at the bottom of the vessel, and 

 a clear supernatant fluid. The contracted remains of the 



