THE FLOW OF BLOOD IN THE ARTERIES 



211 



Thus the velocity is seen to increase considerably after section of the nerves 

 controlling the arteries, and to be considerably greater in the carotid than 

 in the crural. One cannot therefore draw conclusions as to the velocity in one 

 artery from determinations made for another. 



When one carotid is ligated the velocity in the other increases materially, 

 as for example in two dogs of 13.7 kg. mean body weight, on the average 

 from 2.63 c.c. and 266 mm. per second to 3.47 c.c. and 350 mm. per second. 



Likewise the velocity increases considerably after a temporary compression 

 of the artery, as for example in the crural (dog 13.2 kg.) from 0.783 c.c. and 



FIG. 83. Plethysmograph, after Fick. a e, the cylinder; m, rubber cuff by which the cylinder 

 is made to fit air-tight over the arm ; r s, recording monometer. 



149 mm. per second before compression to 1.252 c.c. and 255 mm. after. The 

 pressure in both cases was 89 mm. Hg. 



On account of the dilatation taking place in the arterioles of an organ 

 during its activity, the velocity is increased considerably in the arteries sup- 

 plying it. Thus Chauveau observed that the velocity in the carotid during 

 mastication rose to five or six times its usual height. 



Finally, when the vessels are dilated as a result of section of the spinal 

 cord, the velocity increases during systole, but is extremely small during 

 diastole. 



