THE CIRCULATION 



ELASTICITY OF THE ARTERIES. 



It is known that the blood is sent out by the heart in an inter- 

 mittent manner, each contraction of the ventricle pushing a mass, 

 as the stroke of the piston of a force-pump would do. If, however, 

 the movement of the blood in the capillaries is observed with a micro- 

 scope it is ascertained that in the normal state it is perfectly con- 

 tinuous. The movement of blood has been transformed in its course 

 from the heart to the extremities. This transformation of the move- 

 ment is due to the elasticity of the arteries. Hydraulics had ascer- 

 tained this remarkable effect of elasticity in fire engines, for example ; 

 the water from the machine is rendered less jerky by running liquid 

 under a bell filled with air; the elastic force of the gas thus com- 

 pressed transforms the brief and intermittent impulsion of the stroke 

 to a continuous stream. 



Intermittent Afflux Apparatus. Marey has experimentally dem- 

 onstrated that, in the case of intermittent afflux of liquid in a con- 

 duit of a given caliber, the elasticity of that conduit increases the 

 quantity of the liquid that can penetrate there under a given pres- 

 sure. 



Suppose a force-pump, from which runs a tube furnished with a 

 stop-cock ; a tube which bifurcates at a point to be continued by two 

 conduits of the same caliber. One of these is made with elastic walls 

 (C) f the other with rigid walls (B). A valve placed in the elastic 

 tube prevents the liquid from flowing back from the tube, but offers 

 no obstacle to its direct current. Two lips of the same caliber are 

 fitted to the ends of the two tubes. 



When the stop-cock is opened and the outflow is permitted to 

 establish itself in a continuous manner, both the rigid and elastic tubes 

 pour out the same quantity of liquid. If, on the contrary, the stop- 

 cock be opened and shut alternately so as to produce an intermittent 

 access of the liquid, the outflow is greater through the elastic tube 

 than through the rigid tube. 



The blood-circulation being of the intermittent afflux order, the 

 arterial elasticity is favorable to the entrance of the blood thrown off 

 by the heart. 



As the arteries are elastic the volume of blood ejected by the 

 ventricle is accommodated by the temporary enlargement of the 

 larger arteries and is driven forward according to E. H. Weber, by the 

 force stored in their walls, so that only a part of the column must be 

 moved at the systole. The heart is relieved of considerable work by the 



