20 PROPERTIES OF 



and that to this its coagulation when taken from the veins is 

 chiefly owing, and not to cold, nor to rest ? 



But although it appears from these experiments that the 

 coagulation of the blood in the basin is owing to the air alone ; 



Thackrah, c in similar experiments, in which the air was well mixed with 

 the blood, says that it either remained fluid or had its coagulation re- 

 tarded ; but these conclusions require further examination. 



Mr. Hunter's statement/ that blood coagulates more readily in vacuo 

 than in the open air, is negatived by Dr. Davy's experiments, 6 from 

 which it results that the rate of coagulating is much the same under the 

 exhausted receiver as in the atmosphere, certainly not quicker, but 

 rather slower, which he suggests may be owing to the cooling effect of 

 exhaustion. From the experiments of Sir Astley Cooper and Mr. 

 Thackrah/ it appears that blood, when removed from living dogs in 

 such a manner as to cut off all communication with the atmosphere, 

 coagulates in ten or fifteen minutes. In some similar experiments 

 which I made, coagulation was generally, but not invariably, slower 

 than in blood received through the air into a tube. Exclusion of air 

 then from the blood, merely retards coagulation ; and this agrees with 

 the observations of Dr. Babington g and Dr. Davy h on the coagulation 

 of blood covered with oil. 



It results from Sir Humphrey Davy's experiments/ that coagulation 

 is neither materially hastened nor retarded by nitrogen, nitrous gas, 

 common air, oxygen, nitrous oxide, carbonic acid, or hydrocarbon. 

 Dr. Davy's observations^ on the effect of carbonic acid and of oxygen 

 are similar. Neither the cause of the coagulation of the blood, nor of 

 its fluidity in the living animal, is yet known. All that has been clearly 

 determined is, that certain conditions or substances either hasten or 

 retard, suspend or prevent coagulation ; and some of them would appear 

 to have directly opposite effects in different proportions, as noticed in 

 Note vn. 



The causes usually given, on the authority of Mr. Hunter, k as alto- 

 gether destroying the coagulable property of blood and the contractility 

 of muscle, are some of them so doubtful that they all require to be ex- 

 amined anew. Thus, in a man killed by lightning, Dr. Davy 1 observed 

 some soft coagulum in the heart, and that the fingers were rigid, al- 

 though the examination was not made until the body was rather ad- 

 vanced in putrefaction. Sir Charles Scudamore invariably found the 

 blood coagulated as usual in animals killed by electricity. Sir B. Brodie n 



c On the Blood, pp. 76-7, ed. 1834. J Researches, ii, 86. 



d Works, ed. by Palmer, iii, 27. k Works, ed. by Palmer, iii, 34, 1 14. 



e Researches, ii, 89. i Researches, ii, 71. 



f On the Blood, pp. 77, 83, ed. 1834. m Essay on the Blood, p. 126, 8vo, Lond. 

 s Med. Chir. Trans, xvi, 298. 1824. 



h Researches, ii, 90. n Lectures on Pathology and Surgery, 

 * Res. on Nitrous Oxide, 8vo> Lond. 8vo, Lond. 1846, p. 102. 



1800, pp. 380-1. 



