132 



VELOCITY OF THE BLOOD-STREAM. 



( 94), which permits of distension of the lung and retention of the normal circulation in the 

 frog. Cold contracts tin- pulmonary capillaries to one-third of their diameter, and anaesthetics 

 arrest the pulmonary circulation, chloroform being most and ether least active, while ethidene is 

 intermediate in its effect.] 



[Influence of the Nervous System. The pulmonary circulation is much less 

 dependent on the nervous system than the systemic circulation. 

 Very considerable variations of the blood-pressure within the 

 other parts of the body may occur, while the pressure within 

 the right heart and pulmonary artery is but slightly affected 

 thereby. The pressure is increased by electrical stimulation 

 of the medulla oblongata, and it falls when the medulla is 

 destroyed. Section and stimulation of the central or peri- 

 pheral ends of the vagi, stimulation of the splanchnics, and 

 of the central end of the sciatic, have but a minimal influence 

 on the pressure of the pulmonary artery (Aubert).] 



89- VELOCITY OF THE BLOOD-STREAM 



Methods : ( 1 ) A. W. Volkmann's Hseniadromometer 

 (1850). A glass tube of the shape of a hair-pin, 

 60-130 cm. long and 2 or 3 mm. broad, with a scale 

 etched on it, or attached to it, is fixed to a metallic 

 l>asal plate, B, so that each limb passes to a stop- 

 cock with three channels. The basal plate is per- 

 forated along its length, and carries at each end 

 short cannula?, c, c, which are tied into the ends of 

 a divided artery. The whole apparatus is first filled 

 with water, [or, better, with salt solution]. The 

 stop-cocks are moved simultaneously, as they are 

 attached to a toothed wheel, and have at first the 

 position given in fig. Ill, I, so that the blood 

 simply flows through the hole in the basal piece, 

 i.e., directly from one end of the artery to the 

 other. If at a given moment the stop-cock is turned 

 in the direction indicated in fig. Ill, II, the blood 

 has to pass through the glass tube, and the time it 

 takes to make the circuit is noted; and as the length 

 of the tube is known, we can easily calculate the 

 velocity of the blood. The method has very obvious 

 defects arising from the narrowness of the tube ; the 

 introduction of such a tube otters new resistance, 

 while there are no respiratory or pulse-variations 

 observable in the stream in the glass tube. 



mjm 



B L I U 



Fig. 111. 

 Volkmann's hamadromometer (B). I, blood ilows from artery to artery ; 

 II, blood must pass through the glass tube of B ; c, c, cannula for the 

 divided artery. 



Fig. 112. 

 Ludwig and Dogiel's rheo- 

 meter. X, Y, axis of 

 rotation : A, B, glass 

 bulbs ; h, k, cannula? 

 inserted in the divided 

 artery; c, e v rotates 

 on g, f ; c, d, tubes. 



Volkmann found the velocity to be in the carotid (dog) -= 205 to 357 mm.; 

 carotid (horse) = 306 ; maxillary (horse) = 232 ; metatarsal = 56 mm. per second. 



(2) C. Ludwig and Dogiel (1867) devised a "stromuhr" or rheometer for measur- 

 ing the amount of blood which passed through an artery in a given time (fig. 112). 



It consists of two glass bulbs, A and B, of exactly the same capacity. These bulbs com- 

 municate with each other above, their lower ends being fixed by means of the tubes, c and d, 

 to the metal disc, e, c x . Tins disc rotates round the axis, X, Y, so that, after a complete revolu- 

 tion, the tube c communicates with/, and d with </ ; / and g are provided with horizontally placed 



