Causes of the Motion of the Blood. 343 



or by a cutting instrument — motions which even yet are 

 designated by the title of circulation. 



In fact, an attentive examination of this pretended circu- 

 lation shews us, that the part being in a horizontal plane, 

 the motion of the globules in the capillaries is totally at an 

 end ; that all the vessels, arteries and veins, carry the 

 blood from the extremities to the amputated surface ; that 

 this motion, becoming more and more slow, ceases after the 

 expiration of some time, and at the same time the organ 

 presents a much smaller quantity of blood. These motions 

 result, then, simply from the approximation of the coats of 

 the vessels towards their axis ; they necessarily, therefore, 

 drive the blood towards their open extremities. The tail of 

 the frog, the foot of the same animal, the mysentery of 

 very young rats, of young mice, separated from the trunk 

 by a cutting instrument, have presented constantly the same 

 phenomena. This pressure which he has established with 

 regard to the blood of animals, exists also in the liquids of 

 vegetables ; he also believes that this kind of circulation, 

 which may be observed in the stipula of the Ficus elastica, 

 detached from the trunk, is due to the same cause. 



The action of gravity, as well as that of heat, are also 

 causes, but confined within more narrow limits of the 

 motion of the globules in parts separated from the trunk, 

 especially when the blood has not yet coagulated in the 

 vessels. 



Numerous experiments made, 1st, upon the heads of the 

 salamander and frog, animals in which the circulation is, 

 as it were, suspended at pleasure, shew that it is established 

 gradually from the centre to the circumference ; 2nd, upon 

 the foot of the frog, dividing the crural vessels ; 3rd, upon 

 the mesentery of the frog and salamander, by cutting the 

 heart; 4th, upon the mesentery of young rats and mice. 

 All these experiments, of which several are confirmed by 

 those of the two celebrated physiologists, Haller and Spal- 

 lanzani, have convinced Dr. Poiseuille that the heart and 

 elasticity of the arterial coats are the sole agents in the 

 capillary circulation in question. 



In resting upon the preceding facts, that is to say, the 

 action of the heart and arteries, and tbe tendency which 

 the latter have to collapse when they are not sufficiently 



