RAPIDITY OF THE CURRENT OF BLOOD IN THE ARTERIES. 79 



pressure, while no such result follows stimulation of the peripheral extremity ; and the 

 effect is manifested when the pneumogastrics have been divided and no direct nervous 

 influence is exerted over the heart. It is thought that the reduction in the arterial press- 

 ure following galvanization of the so-called depressor nerves is mainly due to the action 

 of the splanchnic nerves, by which the abdominal vessels become largely dilated. If the 

 abdomen be opened and one or more of the splanchnic nerves be divided, the arterial 

 pressure is immediately diminished, and the pressure is restored if the divided ends of 

 the nerves be galvanized. If, after division of the splanchnic nerves and the conse- 

 quent diminution of the arterial pressure, the depressor nerves be galvanized, the press- 

 ure still undergoes some additional diminution, but this is much less than the diminution 

 which follows galvanization of the depressor nerves without section of the splanchnic. 

 The action of these nerves will be more fully considered in connection witli the physiology 

 of the nervous system. 



Rapidity of the Current of Blood in the Arteries. The question of the rapidity of 

 the arterial circulation has long engaged the attention of physiologists; but the experi- 

 ments of Volkrnann, with his hasmadrometer, and of Yierordt, with a peculiar instru- 

 ment which he devised for the purpose, did not lead to results that were entirely 

 satisfactory. 



The best instrument for measuring the rapidity of the circulation in the arteries was 

 devised by Chauveau, of the Veterinary School at Lyons. This will give, by calculation, 

 the actual rapidity of the circulation ; and, what is more interesting, it marks accurately 

 the rapid variations in velocity which occur at different periods of the heart's action. 



The instrument to be applied to the carotid of the horse consists of a thin brass tube, 

 about an inch and a half in length and of the diameter of the artery (about three-eighths 

 of an inch), which is provided with an 

 oblong, longitudinal opening, or window, 

 near the middle, about two lines long and 

 one line wide. A piece of thin vulcan- 

 ized rubber is wound around the tube 

 and firmly tied so as to cover this open- 

 ing. Through a transverse slit in the 

 rubber, is introduced a very light metallic 

 needle, an inch and a half in length and 

 flattened 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 



FIG. 26. Chauveau" s instrument for measuring the ra- 

 pidity of thefloiv of blood in the artertes. 

 The instrument viewed in face a, the tube to be fixed 

 in the vessel; 6, the dial which marks the extent ol 

 movement of the needle d ; e, a lateral tube for the at- 

 tachment of a cardiometer, if desired. 



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 established, a deviation of the needle occurs, which varies in 

 extent with the rapidity of the current. Having removed all pressure from the vessel f 

 as to allow the current to resume its normal character, the deviations of the needle are 

 carefully noted, as they occur with the systole of the heart, with the diastole, etc. After 



