162 PHYSIOLOGY. 



power, whereby they may, in their contraction, communicate to 

 the moving blood more than was lost of the force of the heart 

 in dilating them. That they are indued with a muscular con- 

 tractility (LXXXII.) is probable, from the appearance of the 

 muscular fibres in their structure ; from their irritability ap- 

 pearing in the experiments of Verschuir ; from their becoming 

 flaccid on tying the nerves belonging to them ; from the motion 

 of the blood being supported, when the force of the heart is con- 

 siderably weakened; from the motion of the blood becoming lan- 

 guid, when the action of the arteriesis destroyed; from the velocity 

 of the blood in the extreme arteries being greater than was to be 

 expected from the velocity of the blood issuing out of the heart, 

 exposed to so many causes of retardation as constantly occur ; 

 and, lastly, from the velocity and impetus of the blood in 

 different parts of the body, and at different times, being un- 

 equal, while the action of the heart continues the same. 



It is probable, that the muscular fibres of the arteries become 

 more irritable as the arteries are more distant from the heart. 



CLX. The tone and action of the arteries, as a muscular 

 part, may be increased by stimuli immediately applied to them, 

 or by the increased force of the nervous and animal powers with 

 regard to them ; and they may be diminished by sedative powers 

 applied, or by weakening the nervous and animal powers. 



CLXI. There does not appear to be any oscillatory motion 

 in the extreme arteries independent of the action of the heart. 



CLXII. There does not appear to be any operation of ca- 

 pillary attraction in the extreme arteries ; nor does there seem 

 to be any occasion for such a power in any part of the arte- 

 rial system. 



CLXIII. The power of derivation (Vis Derivationis III. 

 Halleri, 174.) in the sanguiferous system, seems to be no other 

 than that which arises from the fulness of contractile vessels. 



CLXIV. The motion of the blood in the arteries of any 

 particular part, is promoted by the action of adjoining muscles. 



CLXV. The blood in the vena cava and its branches, is 

 moved by the action of the heart and of the arteries. These 

 powers are assisted by the action of muscles, which, in their 

 contraction, press the veins lying between their several fibres, 

 and also, by the swelling of their whole mass, press the adjoin- 



