PROPERTIES OF THE BLOOD. 443 



gitated in a bottle, its coagulation is delayed, though it will at last take place 

 in shreds or insulated portions ; but that rest is not the cause of its coagula- 

 tion (as some have supposed), is proved by the fact that, if a portion of blood 

 be included between two ligatures in a living vessel, it will remain fluid for a 

 long time. Again, the Coagulation is accelerated by moderate heat, and 

 jetarded by cold ; but it is not prevented by even extreme cold ; for, if blood 

 be frozen immediately that it is drawn, it will coagulate on being thawed. 

 Moreover it is accelerated by exposure to air, but it is not prevented by com- 

 plete exclusion from it, as is proved by its taking place in a vacuum, or in a 

 shut sac within the dead body: complete exclusion from the air, however, 

 retards the change ; as has been shown by causing Blood to flow into a vessel 

 containing oil, which will form an impervious coating on its surface, and will 

 occasion the coagulation to take place so slowly, that the Red particles have 

 time to subside, and the upper stratum of the clot is colourless.* An extrica- 

 tion of Carbonic acid usually takes place to a slight degree during coagula- 

 tion ; but this is not a constant occurrence ; and the process is not prevented, 

 even by agitating Carbonic acid with the Blood. 



585. 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 Coagulum may include not 

 only the Fibrin and Red particles, 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 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 concre- 

 tion is found to continue fqr 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, 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 globules, 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. 



586. The Serum, when completely separated from the Crassamentum, may 

 be said to contain all the Albumen and Saline matter of the Blood ; together 

 with a portion of the Fatty matter (of which some adheres to the Fibrin), and 

 those " ill defined animal principles" which are included under the designa- 



the clot being now taken out of the vessel, it was found that the upper four-fifths of it 

 consisted of buffy coat, and only the lower fifth clot coloured with corpuscles. The serum 

 which continued to be expressed was perfectly transparent, and the blood did not show 

 signs of putrefaction till a month after it had been drawn from the body. A small 

 quantity drawn from another pneumonic patient, and placed under the same circum- 

 stances, was completely coagulated in two hours, and was quite putrid in fifteen days. 

 In fifteen bleedings of the same patient in the following eight days, the blood drawn 

 gradually lost its indisposition to coagulate, the whole process being completed each time 

 in twelve hours or less. The patient recovered. M. C.] 

 * Babington in Medico-Chirurgical Transactions, vol. xvi. 



