DR DAVY'S MISCELLANEOUS OBSERVATIONS ON THE BLOOD. 23 



is contained in it in a state, it is presumed, free to act and give rise to putrefac- 

 tive fermentation. 



What is more remarkable is the fact, that blood may be retained in the living 

 body, stagnant, at rest, without undergoing similar changes, at a temperature so 

 favourable to these changes. I may refer to Hewson's collected works, edited 

 by Mr Gulliver, for instances of the kind. In a note, page 17, to mention one, 

 the editor remarks, " occasionally blood is extravasated and stagnant in the 

 living body for an indefinite time, and yet retains fluidity, as Mr Hunter and 

 Mr Caesar Hawkins have noticed." He adds, " I saw a case in a soldier, who 

 had received a bruise in his loins, from his horse bolting with him over a bridge 

 in Hyde Park ; the injured part quickly swelled, evidently from effused fluid, 

 which was let out twenty-eight days afterwards. It measured five ounces, was 

 as liquid as blood just drawn from a vein, and coagulated in a cup in less than 

 three minutes. The corpuscles were observed to be unchanged, and readily col- 

 lected together in the usual way by their broad surfaces. Next day the clot was 

 moderately firm, scarlet at the top, somewhat contracted, and surrounded by a 

 little serum." What a contrast this presents to the blood from which atmospheric 

 air was excluded in the experiments detailed ! Can the difference have been 

 owing to the stagnant blood in the living body having been exposed to the action 

 of the surrounding tissues, by which it is possible that, though a change may 

 have been going on slowly in the blood, the degraded or altered particles may 

 have been carried away as they were produced, leaving the residue in its normal 

 state? I have witnessed something analogous when a mass of fibrin, enclosed in 

 a muslin bag, has been immersed in water under a cock, from which there was a 

 constant small stream keeping the water round the included fibrin in motion. 

 During about a month that the fibrin was thus exposed at a temperature of 

 about 40°, it had undergone little change ; it was firm and only slightly tainted. 

 In instances of aneurism, it is well known that not only the fibrin, but also the 

 crassamentum enclosed in the sac resist for a long time putrid decomposition. 

 May not this resistance be referred to the same cause ? This explanation is sub- 

 mitted conjecturally. The fact that extravasated blood, from contusion and vas- 

 cular rupture, is commonly absorbed with discoloration of the bruised part, may 

 be adduced as somewhat in its favour. The physiologists of the School of Hunter 

 would doubtless refer the liquidity of the blood, in the case in question, to the 

 vitality of the blood ; but that is a doctrine which at present is hardly tenable. 



III. On the Action of the Air-Pump on the Blood. 

 The air-pump I have used in the trials I am about to describe is the same as 

 that with which I made some former experiments on the blood,* and, as then, it 

 was in excellent order. 



* Anatom. and Physiolog. Res. vol. ii. p. 214. 

 VOL. XXIV. PART I. ' G 



