22 Dr. Young’s Lecture on the Functions 
the artery itself, when at rest, somewhat harder or softer ; 
and, if the longitudinal fibres give way to the tending force, it 
may become also tortuous : possibly too a very delicate touch 
may in some cases perceive a difference in the degree of dila- 
tation, although it is seldom practicable to distinguish the 
artery, in its quiescent state, from the surrounding parts. 
But the sensation, which is perceived when the artery is com- 
pressed, as usual, by the finger, is by no means to be con- 
founded with the dilatation of the artery ; for in this case an 
obstacle is opposed to the motion of the blood, against which 
it strikes, with the momentum of a considerable column, al- 
most in the same manner as a stream of water strikes on the 
valve of the hydraulic ram ; and in this manner, neglecting 
the difference of force arising from the different magnitudes 
of the sections, the pressure felt by the finger becomes 
nearly equal and similar to that which is originally exerted 
by the heart: each pulsation passing under the finger, in the 
same time, as is required for the contraction of the heart, 
although a very little later; and more or less so, in pro- 
portion as the artery is more or less distant ; the artery re- 
maining then at rest for a time equal to that in which the 
heart is at rest. When therefore an artery appears to throb, 
or to beat more strongly than usual, the circumstance is only 
to be explained from its greater dilatation, which allows it to 
receive a greater portion of the action of the heart, in the 
same manner as an aneurysm exhibits a very strong pulsa- 
tion, without any increase of energy, either in itself, or in the 
neighbouring vessels ; and on the other hand, when the pul- 
sations of the artery of a paralytic arm become feeble, we 
cannot hesitate to attribute the change to its permanent con- 
