270 OF THE BLOOD: ITS VITAL PROPERTIES, 



large. 1 The effect of certain animal poisons of a still more potent nature, when 

 introduced into the current of the circulation (as by the bite of venomous 

 serpents), appears to be, like that of a high temperature, the entire destruc- 

 tion of the coagulating power of the blood ; possibly, as Dr. Halford 2 has 

 suggested, by the rapid development of corpuscles of germinal matter at 

 the expense of the oxygen contained in it, as well as of the vital endow- 

 ments of the tissues generally. 



211. The proportions of Serum and Clot which present themselves after 

 coagulation, are liable to great variation, independently of the amount of 

 the several ingredients characteristic of each; for the crassamentutn may in- 

 clude, not only the fibrin and red corpuscles, but also a large proportion of 

 the serum, entangled (as it were) in its substance. This is particularly the 

 case when the coagulation is rapid; and the clot then expels little or none of 

 it by subsequent contraction. On the other hand, if the coagulation be slow, 

 the particles of fibrin usually seem to become more completely aggregated ; 

 the coagulum is denser at first, and its density is greatly increased by sub- 

 sequent contraction. When a firm fresh clot is removed from the fluid in 

 which it is immersed, its contraction is found to go on increasing for 24 or 

 even 48 hours, serum being squeezed out in drops upon its surface; and in 

 order, therefore, to form a correct estimate of the relative proportions of 

 Crassamentum and Serum, the former should be cut into slices, and laid 

 upon bibulous paper, that the latter may escape from it as freely and com- 

 pletely as possible. According to the experiments of Mr. Thackrah, 3 coagu- 

 lation takes place sooner in metallic vessels than in those of glass or earthen- 

 ware, and the quantity of serum separated is much less; in one instance, the 

 proportion of serum to clot was as 10 to 24, when the blood coagulated in. 

 a glass vessel ; whilst a portion of the same blood, coagulating in a pewter 

 vessel, gave only 10 of serum to 175 of clot. The specific gravity of Blood 

 is no measure of its coagulating power ; for a high specific gravity may be 

 due to an excess in the amount of corpuscles, which form the heaviest part 

 of the blood ; and may be accompanied by a diminution in the quantity of 

 fibrin, which is the coagulating element. 



212. The surface of the Crassamentum not un frequently exhibits, in cer- 

 tain disordered conditions of the blood, a layer that is nearly free from color ; 

 and this is known as the Buffy Coat. Its presence has been frequently re- 

 garded as a sign of the existence of Inflammation, indicating an undue pre- 

 dominance of fibrin ; but this idea is far from being correct, since, as occurs 

 in chlorosis, it may result from an opposite condition of the blood. Its oc- 

 currence in the human subject, excepting in the female during the latter 

 stages of utero-gestatiou, is certainly pathological; but in some animals, as 

 in the horse, the blood-clot is ordinarily buffy. Conclusive evidence that 

 the formation of the buffy coat is due to the clumping together, and conse- 

 quent more rapid sinking of the red corpuscles, is afforded by the facts that 

 its appearance is hindered by artificially separating the corpuscles, whilst it 

 is hastened or increased as their aggregation increases. Thus, as shown in 

 Gulliver's experiments, dilute solutions of neutral alkaline salts prevent the 

 running together of the corpuscles and retard the formation of the buffy 

 coat. On the contrary, certain viscid matters facilitate the clumping of the 

 corpuscles, and coincidently the quickness of formation and quantity of the 

 buffy coat. But the most curious and decisive proof is the discovery by Gul- 



1 See Mr. H. Leo's excellent Treatise On the Origin of Inflammation of the Veins, 

 and on Purulent Deposits. 



2 On the Condition of the Blood after Death by Snakebite. Melbourne, 1807. 



3 Inquiry into the Nature and Properties of the Blood, 2d edit., p. 66. 



