198 OP THE BLOOD. 



with still more potency when the substance injected is rather undergoing degra- 

 dation, than actually dead ; for it then seems to act somewhat after the manner 

 of a ferment, producing a marked diminution in the vitality of the solids and 

 fluids with which it may be brought in contact. Such is pre-eminently the case 

 with pus, as was long since observed by Hunter, and as Mr. H. Lee has lately 

 determined more precisely. It was found by the latter, that healthy blood 

 received into a cup containing some offensive pus, coagulated in two minutes ; 

 whilst another sample of the same blood, received into a clean vessel of similar 

 size and shape, required fifteen minutes for its complete coagulation. When he 

 injected putrid pus into the jugular vein of a living ass, coagulation took place 

 so instantaneously as to produce an immediate obstruction to the current of blood, 

 so that the vessel at once acquired a cord-like character; and in this mode the 

 pus was usually prevented from finding its way into the general current of the 

 circulation. Whilst it thus remains circumscribed by a coagulum of blood, the 

 pus so introduced seems to produce no other constitutional disturbance than is 

 attributable to the local injury ; but if the circumscription should be incomplete, 

 and the pus should be carried into the general circulation, it becomes a source 

 of extensive mischief, determining the formation of abscesses in various parts, and 

 producing a most depressing influence on the system at 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 destruction of the coagulating power 

 of the blood, as well as of the vital endowments of the tissues generally (115). 



188. 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 crassamentum may include, 

 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 subsequent 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 

 proper 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 be pressed from it as completely as possible. According to the experiments 

 of Mr. Thackrah, 2 coagulation takes place sooner in metallic vessels than in 

 those of glass or earthenware, 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. 



189. The surface of the Crassamentum not unfrequently exhibits, in certain 

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

 this is known as the Buffy Coat. The presence of this has been frequently 

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



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

 on Purulent Deposits." 



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



