SECT. X. PHYSIOLOGY. 91 
more elastic. If the coats of the aorta did not 
possess considerable solidity, they would be in- 
adequate to resist the impetus of the blood, and 
preserve the natural tubular state of this conduit. 
The aorta and its largest branches must therefore 
be almost passive in the motion of the blood, for 
unless their caliber vary by alternate expansion 
and contraction, they would be incapable of com- 
municating any moving power to the fluid which 
they contain. 
_ecrx. If the blood moved solely by the impul- 
sion derived from the left ventricle of the heart, 
it is obvious that the velocity and strength of the 
circulation should be unchangeable, in vessels of 
an equal caliber, and at an equal distance from 
the point of motion; but this uniformity in the 
circulation never exists in diseases of local debility, 
or excitement. 
ccx. In local inflammation, the pulsations of the 
arteries of the part may become preternaturally 
strong and full, without any change in the motion 
of the heart; the whole of this local increased 
action must consequently be owing to the iri- 
tability of the arteries. Sometimes the pulsations 
of the arteries do not even correspond with the 
contractions of the heart: “ Thus, in whitlow of 
the finger,” says Richerand, “ the radial artery 
pulsates a hundred times in the minute, while on 
the sound side its beats are only seventy, and 
