92 ANALYTIC SECT. X. 
perfectly isochronous with the pulsations of the 
heart. 
ccx1, The pulsations of the radial, arteries 
frequently differ in the same individual: in hemi- 
plegia the pulse is always feebler in the paralytic 
arm than in the sound one; at least to this general 
law I have known only one exception, which has 
already been mentioned. (x1.) This. difference in 
the pulsation of the two radial arteries, cannot be 
owing to the heart, which gives the same impul- 
sion to the blood which proceeds to the paralytic 
arm, as to that which goes to the soundone. 
ccxtr. I readily admit, that the heart is the 
primary agent in the circulation of the blood in 
the human species; but in those foetuses which 
are without this organ, the motion of the blood 
must necessarily be caused by the irritability of 
the veins and arteries, for vitality without motion 
is impossible. I do not wish to undervalue the 
action of the heart, I merely contend for the co- 
operating power of the arteries. 
cexu1. Although the aorta, from the pas 
ness of its texture, has little irritability, the 
extreme arteries, and even the considerable trunks, 
possess it in great perfection.. When the blood 
ceases to flow into an artery, it becomes an) im- 
pervious ligament ; which shows that the expansion 
of the arteries is in part. owing to mechanical 
distention; but it is to be recollected, on the 


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