194 OF THE BLOOD. 



shown, however, that the difference of specific gravity is by no means the only 

 cause of the separation of the Corpuscles from the Liquor Sanguinis ( 189). 



182. That the Coagulation of the Blood is not, as some have supposed, a proof 

 of its death, but is rather an act of vitality, appears evident from what has been 

 already stated ( 27) of the incipient organization which may be detected even 

 in an ordinary clot ; and still more from the fact that, if the effusion of Fibrin 

 take place upon a living surface, its coagulation is the first act of its conversion 

 into solid tissues which become constituents of the living fabric. It is absurd 

 to suppose that the Blood dies, in order to assume a higher form. A complete 

 demonstration of the truth of the Hunterian doctrine, that the Blood might 

 become organized, like plastic exudations of " coagulable lymph," has been 

 afforded by the researches of Dr. Zwicky/ on the changes occurring in the 

 clots of blood which form in bloodvessels, above the points where they have 

 been tied. He has traced the successive stages of the metamorphosis of 

 the coagulum into fibro-cellular tissue, and the formation of vessels in its sub- 

 stance ; the whole process taking place exactly as in an inflammatory exudation, 

 and the blood-corpuscles exerting no other influence upon it than that of slightly 

 retarding it. Similar observations have been made by Mr. Paget. 3 



183. Instances occasionally present themselves in which the Blood does not 

 coagulate after death, or coagulates very imperfectly. It was affirmed by Hun- 

 ter 3 that no coagulation occurs in the blood of animals hunted to death, or of 

 those killed by lightning, by electric shocks, or by blows upon the epigastrium ; 

 and this statement has been generally received upon his authority. It is far, 

 however, from being constantly true ; for Mr. Gulliver has collected numerous 

 cases in which coagulation was found to have taken place in the blood of ani- 

 mals killed in each of these modes ; in some of them, however, the coagulation 

 was very imperfect. 4 It is not improbable that some of the instances of appa- 

 rent absence of coagulation were really cases of retarded coagulation ( 184) ; and 

 Dr. Polli goes so far as to maintain that the complete absence of coagulating 

 power is a phenomenon which has no real existence. He states that he has 

 never met with an instance in which the blood, when left to itself, and duly 

 protected from external destructive influences, did not coagulate before becom- 

 ing putrid ; and that he has more than once found blood to coagulate, which 

 had been taken in a fluid state from the vessels thirty-six or forty-eight hours 

 after death. 5 Still there seems no reasonable doubt that non-coagulation may 

 occur, when the blood has been previously subjected to conditions which affect 

 the vitality of its fibrin. Such is often the case, for example, when death occurs 

 from Asphyxia, as by hanging, drowning, or breathing of irrespirable gases, 6 

 and the same has been observed in cases of poisoning by hydrocyanic acid, in 

 which asphyxia seemed to have been the immediate cause of death. In certain 

 diseased states, again, we have seen that the coagulating power seems to be 

 completely deficient ( 173). 



184. The length of time which elapses before Coagulation, and the degree 

 in which the clot solidifies, vary considerably ; in general, they are in the in- 

 verse proportion to each other. Thus, if a large quantity of blood be with- 

 drawn from the vessels of an animal at the same time, or within short intervals, 

 the portions that last flow coagulate much more rapidly, but much less firmly, 



1 "Ueber die Thrombus ;" Zurich, 1846. 



2 See his "Lectures on the Processes of Repair and Reproduction," in the "Medical 

 Gazette" for 1849, vol. xliii. p. 1066. 



> "The Works of John Hunter," edited by James F. Palmer, vol. iii. pp. 34, 114. 

 4 See "Edinb. Med. and Surg. Journ." Oct. 1848, pp. 367, 418; and his edition of 

 " Hewson's Works," pp. 20, 21. 



6 "Annali Universal!," 1845; and "Ranking's Abstract," vol. ii. p. 337. 



6 See Dr. J. Davy's "Physiological and Anatomical Researches," vol. ii. p. 192. 



