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PERIPHEIUC ORGANS OF THE CIRCULATION. 155 



uantity of blood must produce great dilatation of the aorta, 

 the coats of which, reacting in their turn on the blood, 

 drive it into the arterial cone, where, by a series of dilatations 

 and successive windings, becoming less and less sensible, the 

 flow of the blood which, in the summit of the cone, was 

 jerky, becomes nearly regular in the region of the capillaries 

 (base of the cone). 



There is, thus, at the summit of the arterial cone, at each 

 systole of the ventricle, a very sensible wave, which is still 

 felt in the lesser arteries, and disappears in the capillaries. 

 This phenomenon constitutes the pulse. The pulsative wave 

 is very sensible to the touch in the radial artery : the pulse 

 is thus the impression made upon the finger (sense of touch) 

 by the approach of a wave. 1 A physician often produces, in 

 fluids, phenomena exactly similar to that of the pulse, such 

 as the fluctuation observed as the result from a sudden blow 

 upon a pouch or bag filled with liquid ; the heart produces a 

 real percussion on the mass of the blood, by the shock of its 

 systolic expulsion ; the pulse, therefore, coincides with the 

 beating of the heart, but follows it at a short interval ; which 

 is, for the radial pulse, one-seventh of a second, the time nec- 

 essary for the wave to flow from the heart to the radial artery 

 at the level of the wrist. 



Under certain circumstances the pulsative wave is trans- 

 mitted more or less strongly and rapidly, according as the 

 arterial coats are more or less stretched out. If the coat be 

 soft, the pulsation is transmitted slowly ; and rapidly, if the 

 coat, on the contrary, be hard ,and resisting. Thus a stone 

 falling into the water produces waves more slowly in propor- 

 tion to the depth of the water ; if the water be covered with 

 a layer of ice, the propagation of the waves will be more 

 rapid. As the phenomena of fluctuation,, observed in sur- 

 gery, are more or less distinct, according as the coats of the 

 pouch containing the liquid are more or less stretched (in a 

 bladder which is too much distended, the flow of the blood 

 can hardly be detected), so the state of the physiological 

 coat (of the arteries), and especially the state of the arterial 

 muscle, influences the form of the pulse. We know that, 

 owing to the elasticity of this element, the arteries are not 

 rigid, and this circumstance, while allowing the presence of 

 the wave to be felt, finally exhausts it. (See above, that 



1 Undo, non est materia progrediens, sed forma materice pro- 

 grediens. 



