VELOCITY OF BLOOD AT PAETS OF VASCULAR SYSTEM 933 



inserted into its central end, and b into its peripheral cut end. The tube a is filled with 

 oil and b with salt solution or defibrinated blood. On clamping the artery, blood flows 

 into a and drives the contained oil over into b, the contents of b being meanwhile forced 

 into the peripheral end of the artery. When blood has completely filled the bulb a, the 

 two bulbs are reversed, and the blood now entering the artery displaces the oil in b, 

 and forces the blood which had entered a on into the peripheral end of the artery. 

 Knowing the capacity of the bulbs and the number of times it has been necessary to 

 turn them in the course, say, of one minute, we know also the amount of blood which 

 has passed across the section of the artery under experiment. 



In order to determine from this volume the velocity of the blood across the section, 

 i. e. through the artery, the total volume passing in the minute must be divided by the 

 cross -section. This will give the velocity per minute. Many modifications of this 



m 



FIG. 399. Diagram showing the 

 construction of Chauveau's 

 haemadromograph. 



FIG. 400. Diagram to show principle of 

 construction of Cybulski's photohsemata- 

 chometer. 





apparatus have been devised, but none give any information of the rapid changes 

 occurring in the velocity of the blood during a single pulse wave. For this purpose we 

 must have recourse to some instrument such as Chauveau's ha3madromograph or 

 Cybulski's photohaematachometer. The hcemadromograph (Fig. 399) consists of a 

 pendulum which is hung in a tube, through which the blood is allowed to flow, placed 

 in the course of the artery. The deviation of this pendulum from the vertical will be 

 in proportion to the velocity of the current, and if its upper end be connected, as in the 

 diagram, with a tambour, the variations in velocity can be recorded on a blackened 

 surface by means of a lever. The photohcematachometer is based on an interesting 

 application of Pitot's tubes. If a current of blood be directed along the tube ab pos- 

 sessing two vertical side tubes c and d (Fig. 400), the pressure at c will be greater than 

 that at d, since at c the momentum of the moving mass of blood is added to the 

 lateral pressure of the fluid. A tube of this shape is connected with an artery, such 

 as the carotid, and the tubes h and h' are attached at the points c and d. These two 



