ITS COAGULATION. 197 



blood also coagulates rapidly in a vacuum, in consequence of. the 

 violent motion induced in the molecules of the blood, by the 

 development of vesicles of gas and aqueous vapour; its coagula- 

 tion is, however, still more rapid in the air, when the latter is 

 strongly agitated, for here the access of the air or oxygen is added 

 to the other accelerating causes. For the same reasons, the 

 rapidity of the coagulation is increased in proportion to the slow- 

 ness with which the blood flows from the vein, the length of 

 the jet, and the width and shallowness of the vessels in which it 

 falls. Since the blood itself contains gases, the different quantity 

 in which they occur, must necessarily influence the period of 

 coagulation ; hence blood which is rich in carbonic acid, coagulates 

 less rapidly than when the contrary is the case ; thus, too, the 

 longer retention of the blood in the veins, after the application of 

 the bandage, appears to be connected with an increase of carbonic 

 acid ; at all events, we find that the blood coagulates far more 

 slowly than usual when the bandage had been applied a long time 

 before venesection. Moreover, when the exchange of gases is not 

 sufficiently carried on in the lungs, the blood must become poorer 

 in oxygen and consequently richer in carbonic acid ; hence the blood 

 coagulates very slowly in cyanosis. A similar reason may also 

 explain, at least in part, the delay frequently noticed in the coagu- 

 lation of inflammatory blood, and the less rapid coagulation of 

 venous than arterial blood. . In prolonged bleeding, the blood that 

 flows last, is found to coagulate much more rapidly than that 

 which escaped first, which is very probably owing to the former 

 containing an increased quantity of oxygen, derived from the deep 

 drawn and jerking inspirations. This mode of explanation is 

 further confirmed by the lighter colour of this blood. The blood 

 taken after death coagulates less rapidly, owing perhaps to its 

 being more abundantly impregnated with carbonic acid. 



Another cause which accelerates the coagulation is the aqueous 

 character of the blood. According to Nasse's experiments, 

 water accelerates the coagulation of the blood when added 

 in small quantities, or at all events, when not exceeding twice the 

 quantity of the blood, whilst larger quantities tend to retard coagu- 

 lation. Hence we find that watery blood, as for instance, that of 

 women or after repeated blood-lettings or other losses of the 

 juices, and anaemic blood, generally coagulate more rapidly than 

 blood in a normal state. 



It has been long known, that certain salts, namely the caustic 

 alkalies and their carbonates, have the property of retarding, or 



