196 OF THE BLOOD. 



such time as their solutions retain a certain strength ; for if they be diluted, 

 coagulation will then take place, although in most cases less perfectly than it 

 would have done at first. There appears to be no limit to the time during 

 which the coagulation may be thus postponed ; thus Mr. Gulliver 1 mentions 

 that he has kept horse's blood fluid with nitre for fifty-seven weeks, and that it 

 still readily coagulated when diluted with water (op. cit., p. 12). It is not so 

 difficult, therefore, as it might otherwise seem, to give credit to the statement 

 of Dr. Polli, that, in a case witnessed by himself, complete coagulation of the 

 blood did not take place until fifteen days after it had been withdrawn from the 

 body; and that fifteen days more elapsed before putrefaction commenced in it. 

 The upper four-fifths of the clot were colorless, the red corpuscles occupying 

 only the lowest fifth. It is additionally remarkable, that the patient (who was 

 suffering under acute pneumonia) being bled very frequently during the suc- 

 ceeding week, the blood gradually lost its indisposition to coagulate. 3 



185. It has been maintained by some observers, that a certain amount of 

 heat is liberated during coagulation ; but this idea would seem to have been 

 founded on a fancied analogy between coagulation and freezing; and it is nega- 

 tived by the careful observations of Hunter, Schroeder Van der Kolk, J. Davy, 

 and Denis. Again, it has been asserted that the act of coagulation is attended 

 by the extrication of a small quantity of carbonic acid; but there is no suffi- 

 cient proof that blood in coagulating gives out more carbonic acid than it 

 ordinarily does by exposure to the air ( 163). Moreover, it has been shown 

 by the experiments of Sir H. Davy 3 and Dr. J. Davy, 4 that no effect is produced, 

 either in accelerating or retarding coagulation, by placing blood in an atmosphere 

 of nitrogen, nitrous gas, nitrous oxide, or carbonic acid ; and it has been found 

 that coagulation still takes place, even if the blood be agitated with carbonic 

 acid. 



186. The vital condition of the walls of the bloodvessels appears to have an 

 important influence upon the fluidity of the blood. Thus it has been found by 

 Sir A. Cooper and Mr. Thackrah, that whilst blood inclosed in a living vein re- 

 tained its fluidity for some time, blood similarly inclosed in a dead vein, the 

 atmosphere being completely excluded, coagulated in a quarter of an hour. 

 Moreover, inflammation of the walls of the bloodvessels (which is a condition 

 of depressed vitality, CHAP. xi. SECT. 3) promotes the coagulation of the blood 

 which they contain ; and thus it is that the trunks both of arteries and veins 

 frequently become choked up by coagula. 5 Moreover, although there can be no 



1 Mr. Gulliver considers this fact, together with the occurrence of coagulation on the 

 thawing of blood which has been frozen whilst yet fluid, as conclusive against the vital 

 character of the act ; remarking that if we believe the coagulation to be an eifect of life, 

 we must admit that we can freeze and pickle the life (op. cit., p. 21). No such admission, 

 however, is necessary. We do not freeze and pickle the life ; but we simply preserve the 

 vital properties of the substance by preventing it from undergoing spontaneous change ; 

 thus doing the same for the blood as may be done for seeds, eggs, and even highly organ- 

 ized bodies, which may be kept in a state of "dormant vitality" for unlimited periods, by 

 cooling or drying them, or by secluding them from the atmosphere. See "Princ. of Phys., 

 Gen. and Comp.," CHAP. in. Sect. 4, Am. Ed. 



2 "Gazetta Medica di Milano," Genn 20, 1844; cited in Mr. Paget's "Report" in "Brit, 

 and For. Med. Rev." vol. xix. p. 252. 



a "Researches on Nitrous Oxide," pp. 380-1. 



4 "Anatomical and Physiological Researches," vol. ii. p. 71. 



* It was observed by Hunter, and has been frequently noticed since, that when amputa- 

 tion is performed on account of spontaneous gangrene of the lower extremities, there is 

 no jet of blood from the divided arterial trunk, which is obstructed by coagulum far above 

 the line to which the gangrene has extended ; and there is good reason to regard the gan- 

 grene as, in these cases, the result of a previous arteritis, which has thus put a stop to the 

 circulation through the limb. (For evidence in support of this doctrine, see the "Essai 

 sur les Gangrenes spontanees" of M. Fra^ois, Paris, 1832.) The author, whilst a pupil 



