RAPIDITY OF THE CURRENT OF BLOOD IN THE ARTERIES 6l 



wrist, the pressure being applied to the brachial artery just above the 

 elbow. 



The following is a summary of the conditions that influence the 

 arterial pressure : 



The pressure is increased by 



1. Increase in the power of the ventricular systole. 



2. Increase in the total quantity of blood. 



3. Increased contraction of the small vessels that supply the capil- 



lary system. 

 The pressure is decreased by 



1. Decrease in the power of the ventricular systole. 



2. Decrease in the total quantity of blood. 



3. Decreased contraction, or relaxation of the small vessels that 



supply the capillary system. 



RAPIDITY OF THE CURRENT OF BLOOD IN THE ARTERIES 



The question of the rapidity of the flow of blood in the arteries has 

 long engaged the attention of physiologists ; but the experiments of 

 Volkmann with the hemodrometer, and of Vierordt with a peculiar in- 

 strument which he devised for the purpose, did not lead to results that 

 were entirely satisfactory. The apparatus devised by Chauveau, how- 

 ever, is more reliable. This will give, by calculation, the actual rapidity 

 of the current, and it also indicates the variations in velocity that occur 

 at different stages 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 (38.1 millimeters) in length 

 and of the diameter of the artery (about three-eighths of an inch, or 

 9.5 millimeters), which is provided with an oblong longitudinal opening, 

 or window, near the middle, about two lines (4.2 millimeters) long and 

 one line (2.1 millimeters) wide. A piece of thin vulcanized rubber is 

 wound around the tube and firmly tied so as to cover this opening. 

 Through a transverse slit in the rubber is introduced a very light metal- 

 lic needle, an inch and a half (38.1 millimeters) in length and flattened 

 at its lower part. This is made to project about halfway into the calibre 

 of the tube. A flat semicircular piece of metal, divided into an arbi- 

 trary scale, is attached to the tube, to indicate the deviations of the point 

 of the needle. 



The apparatus is introduced 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. 



