SECT. XT. PHYSIOLOGY. 97 
: SECTION XI. 
Venal Irritability. 
cexxiv. According to the laws of hydraulics, 
the motion of the blood should become slower 
in passing from the capillaries into the veins, in 
consequence of the larger caliber of the latter 
vessels ; but here the laws of irritability counteract 
the laws of hydraulics. 
ccxxv. The extreme arteries are more expansible 
than their trunks, the capillaries than the extreme 
arteries, and the veins than the capillaries. On 
the back of the hand, the veins are at one time 
scarcely visible through the skin; at another, they 
are gross as goose-quills. Immersion of the hand 
alternately into hot and cold water, shows the 
expansibility and contractibility of the veins in 
great perfection. What, then, is the effect of 
this superior irritability of the veins on the cir- 
culation? 
ccxxvi. It is quite plain, that if one end of a tube, 
whose caliber is incessantly changing, be in con- 
tact with a liquid, expansion of the tube, as well 
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