16 PROPERTIES OF 



as it does when suffered to rest and to cool. As the subject 

 seemed to me of importance, I have endeavoured to ascertain 

 the circumstance to which this coagulation is owing by several 

 experiments, in each of which the blood was generally exposed 

 to but one of the suspected causes at a time. Thus, in order 

 to see whether the blood's coagulation out of the body was 

 owing to its being at rest, I made the following experiment : 



EXPERIMENT IV. 



Having laid bare the jugular vein of a living dog, I made a 

 ligature upon it in two places, so that the blood was at rest 

 between the ligatures ; then covering the vein with the skin, 

 to prevent its cooling, I left it in this situation. From several 

 experiments made in this way, I found in general, that after 

 being at rest for ten minutes, the blood continued fluid ; nay, 

 that after being at rest for three hours and a quarter, above 

 two thirds of it were still fluid, though it coagulated after- 

 wards. Now the blood, when taken from a vein of the same 

 animal, was completely jellied in about seven minutes. The 

 coagulation therefore of the blood in the basin, and of that 

 which is merely at rest (x), are so different, that rest alone 



power of the action of the blood-vessels in keeping the blood fluid. 

 Mr. Hewson's conclusion accords with that now proved to be correct. 

 Mr. Hunter d states that coagulation is hastened by shaking the blood in 

 a phial, with or without the exclusion of air. Mr. Thackrah, e Dr. Davy/ 

 Sir Charles Scudamore, g and Mr. Prater, h have proved that even violent 

 shaking of the blood does not prevent coagulation, but merely separates 

 the fibrin into small fragments, which may be collected on a filter ; and 

 that moderate agitation rather hastens coagulation. 



The effect of rest on coagulation is mentioned in Note x, and of 

 heat in Notes in and xvi. 



(x.) The effect of living tissues in retarding coagulation is mentioned 

 in Note xin. Mere rest has no effect whatever on the coagulation of 

 fibrin. In cases of empyema, I have thrice seen the matter, compressing 

 and condensing the lung and depressing the diaphragm, coagulate spon- 

 taneously when set aside in jars, although it was fluid many hours after 

 death, and must have been in a state of comparative repose during 

 life, for the matter completely filled the cavity. Blood sometimes 

 remains fluid and in complete rest for several hours after death, 

 and yet coagulates readily on exposure, as in Mr. Hewson's Exp. xvi. 



d Works, ed. by Palmer, iii, 31. * Essay on the Blood, 8vo, Lond. 1824, 



e On the Blood, p. 68, ed. 1834. p. 40. 



f Researches, ii, 65. h Exp. Inq. in Chem. Phys. Part I, 17. 



