xliv THE BLOOD. 



fibrin (or spontaneously coagulating matter), and docs not form a true clot. The 

 serum contains less albumen and fat, and much less saline, but more extractive 

 matter. The hepatic venous blood, moreover, yields sugar, derived from glycogen 

 formed in the liver. 



The blood of the renal veins is said by Bernard and Brown-Sequard not to coagu- 

 late in the normal state of the kidney and its function, from which they infer that it 

 contains little or no fibrin ; but it may be that there is something present which 

 prevents the two constituents of the fibrin from reacting on each other. 



COAGULATION OP THE BLOOD. 



In explaining the constitution of the plasma, we have been obliged so far 

 to anticipate the account of the coagulation of the blood. The following are 

 the phenomena which usher in and which accompany this remarkable change. 

 Immediately after it is drawn, the blood emits a sort of exhalation, the 

 " halitus " having a faint smell ; in about three or four minutes a film 

 appears on the surface, quickly spreading from the circumference to the 

 middle ; a minute or two later the part of the blood in contact with the 

 inside of the vessel becomes solid, then speedily the whole mass ; so that, 

 in about eight or nine minutes after being drawn, the blood is completely 

 gelatinised. At about fifteen or twenty minutes, or it may be much later, 

 the jelly-like mass begins to shrink away from the sides of the vessel, and 

 the serum to exude from it. The clot continues to contract, and the serum 

 to escape for several hours, the rapidity and degree of the contraction 

 varying exceedingly in different cases ; and, if the serum be poured off, 

 more will usually continue to drain slowly from the clot for two or three 

 days. 



The nature of the change which takes place in the coagulation of the 

 blood has been already spoken of ; it is essentially owing to the coagulation 

 of the liquor sanguinis, the fibrin being generated in that liquid by the con- 

 currence of its two constituents in the way already explained, and separating 

 in form of a solid mass, which involves the corpuscles but allows the serum 

 to escape from it in greater or less quantity. But although the solidification 

 of the fibrin and formation of a red clot would undoubtedly take place inde- 

 pendently of any mechanical co-operation on the part of the corpuscles, still 

 it must not be forgotten that the red disks are not altogether indifferent 

 while coagulation goes on ; for they run together into rolls, as already 

 described, and the circumstance of their doing so with greater or with less 

 promptitude materially affects the result of the coagulating process. Thus 

 there seems good reason to believe that, as H. Nasse has pointed out, one 

 of the causes and in inflammatory blood probably the chief cause of the 

 production of the buffy coat, is an exaltation of the natural tendency of the 

 red disks to run together, whereby being more promptly and more closely 

 aggregated into compact masses, they more speedily subside through the 

 liquid plasma, leaving the upper part of it colourless by the time coagulation 

 sets in ; and Mr. Jones has drawn attention to another influential circum- 

 stance depending likewise on the corpuscles, in inflammatory blood, namely, 

 the more rapid and close contraction of the network, or sponge work as he 

 terms it, into which the little rolls of corpuscles unite, and the consequent 

 expulsion of the great part of the liquor sanguinis from its meshes before the 

 fibrin solidifies, in which case the mass of aggregated corpuscles naturally 

 tends to the lower part of the vessel, whilst the expressed plasma, being 

 lighter, accumulates at the top. Of course it is not meant to deny that 

 more tardy coagulation of the plasma would produce the same result as more 



