

GENERAL USES OF THE CIRCULATION. 181 



fibrine is extracted from the blood; but the movement of the 

 circulation brings the different parts of the mass of blood 

 into continual contact with the inner coat, the endothelium 

 of the vessels. Among the more or less well-defined causes 

 already mentioned (page 125), influencing the coagulation 

 of the blood, the least disputed, though most difficult to ex- 

 plain, is the still puzzling influence of the inner coat of the 

 living vessel?. This influence was pointed out by Briicke : 

 contact with the living coat is a powerful obstacle to coagula- 

 tion; the fibrine cannot become solid, while the blood is cir- 

 culating, and while each of its particles comes constantly in 

 contact with the living coat. 



As soon as the circulation ceases, the central layers of the 

 blood current have a tendency to coagulate : examination of 

 the manner in which this coagulation is produced, constitutes 

 the study of clots formed after death, and is no less important 

 to the physiologist than to the pathologist, whom it teaches 

 how to distinguish recent from ancient clots. The blood in a 

 corpse does not directly coagulate when the action of the heart 

 ceases ; the mechanism by means of which the dying arteries 

 drive their contents into the veins (see natural form of the 

 arteries, page 153), forms still a kind of circulation, prevent- 

 ing this coagulation : in a corpse, therefore, clots are gener- 

 ally found only in the veins. 



When the veins of a corpse are gorged with blood, which 

 has poured in from the arterial system, coagulation begins to 

 take place in the central layers, because the most distant from 

 the coat ; here the fibrine coagulates rapidly, entangling the 

 red globules in this part of the blood, which explains the fact 

 that the centre of the venous clots is always red or black, 

 in short, appears cruoric. 



From 20 to 24 hours, at the least, elapse before the most 

 peripheral parts of the contents of the veins are completely 

 coagulated ; here the influence of contact with the living 

 coat is still felt. It rarely happens that the death of all the 

 anatomical elements coincides with the general death, the 

 last breath and the last pulsation of the heart ; we have seen 

 that the muscles and the nerves continue excitable long after 

 this, and that the epithelium of the bladder still resists the 

 phenomenon of absorption for several hours ; we shall find 

 that the vibratory epitheliums continue their movements 

 during from 8 to 10 hours ; the case is the same with the 

 endothelium of the blood-vessels, and it is only at its com- 

 plete death, at the end of 20 .or 24 hours, that coagulation of 



