CIRCULATION OF THE BLOOD IN THE VESSELS. 



than the diminution which follows stimulation of the depressor nerves with- 

 without section of the splanchnics. 



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

 rapidity of the arterial circulation has long engaged the attention of physiol- 

 ogists ; but the experiments of Volkmann, with his hsemadrometer, and of 

 Vierordt, with a peculiar instrument which he devised for the purpose, did 

 not lead to results that were entirely reliable. The apparatus devised by 

 Ohauveau, however, is much more satisfactory. This will give, by calcula- 

 tion, the actual rapidity of the circulation, and it also indicates the 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 

 (38*1 mm.) in length and of the di- 

 ameter of the artery (about three- 

 eighths of an inch, or 9-5 mm.), 

 which is provided with an oblong, 

 longitudinal opening, or window, 

 near the middle, about two lines 

 (4'2 mm.) long and one line (2*1 

 mm.) wide. A piece of thin, vul- 

 canized rubber is wound around 

 the tube and firmly tied so as to 

 cover this opening. Through a 

 transverse slit in the rubber, is in- 

 troduced a very light, metallic nee- 

 dle, an inch and a half (38-1 mm.) 

 in length and flattened at its lower 

 part. This is made to project about 



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 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 established, 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 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 withdrawing 

 the instrument, it is applied to a tube of the size of the artery, in which a 

 current ol water is made to pass with a rapidity which will produce the same 



FIG. 30. Chauveau's instrument for measuring the 

 rapidity of the flow of blood in the arteries. 



The instrument viewed in face a, the tube to be fixed half-WaV into the Caliber of 

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

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

 the attachment of a cardiometer, if desired. 



