122 



THE CIRCULATION OF THE BLOOD AND LYMPH 



on that in b. The amount of this push and pull will vary with the 

 velocity, so that a change in the latter will correspond to an alteration 

 in the difference of level in the two tubes. Instruments on this prin- 

 ciple have been constructed by Marey and Cybulski, the former regis- 

 tering the movements of the two columns of blood by connecting the 

 tubes to tambours provided with writing levers, the latter by photo- 

 graphy (Fig. 50). 



5. The electrical method, described on p. 135, 

 for the measurement of the circulation time, can 

 also be applied to the estimation of the mean 

 velocity of the blood between two cross-sections 

 of the arterial path which are separated by a 

 sufficient distance. For example, salt solution 

 can be injected into the left ventricle or the be- 

 ginning of the aorta, and the interval which it 

 takes to reach a pair of electrodes in contact with, 

 say, the femoral artery determined. Knowing 

 the distance between the point of injection and 

 the electrodes, we can then calculate the mean 

 velocity. 



6. In the calorimetnc method of measuring the 

 quantity of blood which passes through such 

 parts as the hands (or feet) in man, the flow is 

 deduced from the quantity of heat given off by 

 the part in a given time, and the difference be- 

 tween the temperatures of the blood entering and 

 leaving the part. The hands are immersed in a 

 large bath of water (a few degrees below arterial 

 blood temperature) for a sufficient time to permit 

 any change of temperature of the parts due to 

 the difference in temperature between them and 

 the water to be established. The hands are then 

 rapidly transferred to calorimeters previously 

 filled with water at the same temperature as that 

 of the bath. All the heat henceforth given off 

 can be assumed to be due to the cooling of the 

 blood passing through the hands, since the small 

 amount of heat produced in the resting hands is 

 negligible for this purpose. The temperature of 

 the arterial blood at the wrist is taken as 0-5 C. 

 below that of the rectum, this being the relation 

 actually found in a normal man.* The tempera- 

 ture of the venous blood leaving the hand is taken 

 as that of the calorimeter, since it has been found 

 that blood withdrawn from the hand veins by 

 puncture, and collected with suitable precautions 

 to prevent loss of heat as far as possible and to 

 permit the calculation of the unavoidable loss, 

 has a temperature only a negligible fraction 



of a degree above that of the bath in which the hand is im- 

 mersed. The flow in grammes per minute is obtained from the formula 



Q = rr THV ~> where Q is the quantity of blood, H the number 



Wl \\- J. j S 



* The temperature of the arterial blood at the wrist was assumed to be the 

 calorimeter temperature at which the calorimeter neither loses heat to the hand 

 nor g-uns heat from it. If the heat production in the resting hand is negligible, 

 this must correspond to the temperature of the entering blood. 



Fig. 49. Chauveau's 

 Dromograph. A, tube 

 connected with blood- 

 vessel; B, metal cylin- 

 der in communica- 

 tion with A. The upper 

 end of B has a hole in 

 the centre, which is 

 covered by a mem- 

 brane, m, through 

 which a lever, C, 

 passes; C has a small 

 disc, p, at its end, 

 which projects into the 

 lumen of A, and is de- 

 flected in the direction 

 of the blood - stream 

 through A. The de- 

 flection is registered by 

 a recording tambour in 

 communication by the 

 tube E with a tambour 

 D, the flexible mem- 

 brane of which is con- 

 nected with the lever 

 or pendulum C. 



