344 Dr. Poiseuille, on the 



dilated by the tide of blood projected from the heart, the 

 constant jerking, intermittent, and oscillatory circulation, 

 which precede the death of an animal, are easily explained ; 

 the cause of the retrogade circulation presented by the 

 arteries after the death of the animal and that of the heart 

 is similar. 



Having cleared up these points, the author passes on to 

 the examination of the causes of the irregular motions of 

 the globules which he has observed in the capillary vessels. 

 If we study the course of the blood in the arteries and 

 veins of the frog, of very young rats and of young mice, we 

 observe, in proceeding from the axis of the vessel to the 

 coats, that the velocity of the globules is totally different. 

 In the centre, their velocity is at a maximum ; it diminishes 

 gradually as we approach the coats. In the immediate 

 neighbourhood of the coats, a very transparent space can be 

 observed, which is generally occupied by serum ; this space 

 is equal to about the -§■ or ^ of the diameter of the vessel. 

 This transparent part of the vessels observed by Haller and 

 Spallanzani as being occupied by serum, has been again 

 noted by Blainville. 



Since some of the globules, rubbing against each other, 

 are projected into this transparent part of the vessels, the 

 globules placed in the middle possess a very slow motion, 

 and they cease to move when they are almost in contact 

 with the coats of the vessel. The globules which are 

 nearest to this transparent part have a double motion of 

 rotation and translation ; they roll, if the expression may 

 be used, over this part of the serum. 



From these observations, the author concludes that the 

 interior of the vessels is lined with a layer of serum at rest. 

 Since this layer is immoveable in its immediate contact with 

 the coats of the vessels, every time that a globule is placed 

 there it will be at rest, or, rather, its velocity will be more 

 or less diminished, according to the portion of the globule 

 immersed in it. Now, in the capillaries the globules move 

 between two layers of serum. Hence, their motion ought 

 to be less rapid than in the large vessels, since they require 

 to overcome the inertia of this layer. 



If a globule is partly in the layer, this portion of the 

 globule will be at rest, while its remainder, placed in the 



