THE BLOOD. 19 



ligatures, and emptied that part of its blood. I next blew 

 warm air into the empty vein, and put another ligature upon 

 it, and letting it rest till I thought the air had acquired the 

 same degree of heat as the blood, I then removed the inter- 

 mediate ligature, and mixed the air with the blood. The air 

 immediately made the blood florid, where it was in contact 

 with it, as could be seen through the coats of the vein. In a 

 quarter of an hour I opened the vein, and found the blood 

 entirely coagulated; and as the blood 'could not in this time 

 have been completely congealed by rest alone, the air was 

 probably the cause of its coagulation. 



From comparing these experiments, may we not venture to 

 conclude, that the air (xn) is a strong coagulant of the blood, 



common medicinal leech may be restored to life after having been com- 

 pletely frozen ; Lister, Bonnet, and others" have observed the same fact 

 in the larvae of insects ; and Hudolphi, in the Filaria capsularia. 



Dr. Davy has proved that the blood of a fowl may be thrice rapidly 

 frozen and thawed, and yet retain its coagulating power. He also froze 

 some human venous blood, which coagulated in about eight minutes 

 after it was gradually and completely thawed ; and on the following 

 day there was a distinct separation of serum from the clot. The results 

 obtained by Mr. Thackrah p to the contrary, are of no weight against 

 the mass of positive testimony above quoted. Mr. Hewson states at 

 pp. 25-26 how he varied his experiments on the freezing of blood. 



The effects of a high temperature in hastening the coagulation of blood 

 and the contractien of muscle are mentioned in Notes in and xvi. 



(xu.) It follows directly from Mr. Hewson's experiments, that 

 though air may promote, it is not the cause of the coagulation of the 

 blood. This lie knew ; for he observed that it coagulates when kept at 

 rest in the veins of living dogs and rabbits, in the sacs of aneurisms, 

 audin the heart and blood-vessels after death; while, in some of his ex- 

 periments, he found that blood when less exposed to the air coagulated 

 sooner than when more exposed, which he ascribed to the retarding in- 

 fluence of cold on coagulation. It has long been known that air may 

 be gradually introduced into the veins of living animals without any ill 

 effect.* Sproegel, b after killing dogs by blowing air into the veins, 

 states that the blood was fluid, even more' so than natural, contrary to 

 the assertion which some persons had made that it is coagulated ; and 



n Carpenter's Gen. and Comp. Pliys. p. searches dePhysiol. 8 vo, Paris, 1811, 



1/5, 8vo, Lond. 1841. p. 34 ; Majendie, Physiol. tr. by Mil- 



Entoz. Hist. Nat. 8vo, Amstel. 1809, ligan, 4th ed. 8vo, Edin. 1831, p. 445. 

 ii, 62. b Exp. circa varia venena in vivis ani- 



p On the Blood, ed. 1834, pp. 37, 67, 68. malibus inst. xliii, Gott. 1753, in 



a Haller, in Boerhaav. Prelect. Acad. 8vo, Haller. Disputat. ad Morb. t. vi, 4to, 



Gott. 1740, ii, 108; Nysten, Re- Lausan. 1758. 



