I io A MANUAL OF PHYSIOLOGY 



respiratory movements and the pressure caused by muscular 

 contraction in general, which, thanks to the valves, always 

 aids the flow towards the heart. From these two sources 



new energy is supplied, to rein- 

 force the remnant due to the 

 cardiac systole (p. 121). 



Measurement of the Velocity of 

 the Blood. i. Direct Observation. 



(a) This method can be applied to 

 transparent parts by observing the rate 

 of flow of the corpuscles under the 

 microscope. But it is only where the 

 blood moves slowly, as in the capil- 

 laries, that the method is of use. 



(b) Part of the path of the blood 

 through a large vessel may be arti- 

 ficially rendered transparent by the 

 introduction of a glass tube, of ap- 

 proximately the same bore as the vessel 

 (Volkmann). The tube is filled with 

 salt solution, and the blood admitted 

 by means of a stop-cock at the moment 



FIG. 31. STROMUHR OF LUD- of observation. The time which the 



WIG AND DOGIEL. blood takes to pass from one end of 



A, B, glass bulbs ; a, a metal disc, the tube to the other is noted, and the 



SJ^S^Mtfl length divided by the time gives the 



E, F, cannulse attached to b, and velocity of the blood m the tube. If 



connected with the peripheral and t h e calibre of the tube is the same as 



central ends of a divided bloodvessel. , , , arf^nr thi'c io a1cr fV* 



At the beginning of the experiment, that ot the artery, this is also the 



A and the junction between A and B velocity m the vessel ; but if the calibre 



are filled with oil ; B is filled with j s different, a correction would have 



normal saline or dehbnnated blood: ' ,_, , , . 



a being turned into the position to be made. The method is not a 

 shown in the figure, the blood passes good one, for the reason, among others, 

 ^ U r^ F io d a in ^ A si a o n n d as he h= that the long tube introduces an extra 



blood has reached the mark m, the resistance. 



disc a, with the bulbs, is rapidly 2 . Ludwigs Stromuhr. This instru- 



r F 0ta ^eb,oo h d a 'now S pres Xt ent measures the quantity of blood 



and the oil is again driven into A. which passes m a given time through 



When the oil has reached D, reversal tne ves sel at the cross-section where it 



is again made, and so on. . g ingerted Jt CQnsists of ft u^ ha p ed 



tube, with the limbs widened into 



bulbs, but narrow at the free ends, which are connected with a 

 metal disc. By rotating the instrument, these ends can be placed 

 alternately in communication with a cannula in the central, and 

 another in the peripheral portion of a divided artery ; or they can 

 be placed so that none of the blood passes through the bulbs, 

 but all goes by a short-cut. One limb of the instrument is 



