RAPIDITY OF THE AETEKIAL CIRCULATION. 



273 



provided with an rig. 9. 



oblong longitudi- 



o o 



nal opening, or 

 window, near the 

 middle, about two 

 lines long and one 

 line wide. A 

 piece of thin vul- 

 canized rubber is 

 wound around the 

 tube, and firmly 

 tied, so as to cov- 

 er this opening. 

 Through a trans- 

 verse slit in the 

 rubber is intro- 

 duced a very light 



metallic needlCjChauveau's instrument for measuring the rapidity of the flow of 

 "U i i, i blood in the arteries. The instrument viewed in face a, the 

 an incll and a liall tube to be fixed in the vessel; &, the dial which marks the ex- 

 . -I ,1 in- tent of movement of the needle d; e, a lateral tube for the 



111 lengtn, and flat- attachment of a cardiometer, if desired. . 



tened at its lower part. This is made to project about half 

 way into the caliber of the tube. A flat semicircular piece 

 of metal, divided into an arbitrary scale, is attached to the 

 tube, to indicate the deviations of the point of the needle. 



The apparatus is introduced carefully into the carotid of 

 a horse, by making a slit in the vessel, introducing first one 

 end of the tube, directed toward the heart, then allowing a 

 little blood to enter the instrument, so as to expel the air, 

 and, when full, introducing the other end, securing the whole 

 by ligatures above and below. 



When the circulation is arrested, the needle should be 

 vertical, or mark zero on the scale. When the flow is estab- 

 lished, a deviation of the needle occurs, which varies in extent 

 with the rapidity of the current. 



Having removed all pressure from the vessel, so as to al- 

 low the current to resume its normal character, the deviations 

 18 



