PHYSIOLOGY 



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 com- 

 pletely 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 modifi- 

 cations of this apparatus have been devised. A simple form 

 of current measurer is shown in Fig. 388. The whole apparatus 

 is constructed of glass. The tube a is connected with the 



FIG. 387. Diagram of central end of a cut artery, and the tube p with the peripheral 

 Ludwig's ' Stromuhr.' end. The blood flows into B and fills it. As soon as it is full 

 and its level rises 



over the level of the bend of the siphon ^ 



tube s, the blood is rapidly siphoned off 



into c whence it flows along p into the 



peripheral part of the artery. The side 



tube B is connected with a mercury or 



membrane manometer. Every time that 



B is emptied into c a depression is pro- 

 duced on the manometer tracing, which 



thus records not only the average pressure 



but also the average velocity of the blood 



in the artery. Each instrument has to 



be calibrated in order to know how much 



blood passes from B to c each time that 



siphonage occurs. 



None of these methods give any infor- 

 mation of 'any rapid changes occurring 



in the velocity of the blood, e.g. during a 



single pulse-wave. For this purpose we 



must have recourse to some instrument 



such as Chauveau's hsemadromograph or 



Cybulski's photohaematachometer. The 



hcemadromograph (Fig. 389) 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 velo- 

 city can be recorded on a blackened 



surface by means of a lever. The photo- FIG. 388. A simple blood-current measurer. 



hcematachometer is based on an interesting (!SHIKAWA and STABLING.) 



application of Pitot's tubes. If a current 



of blood be directed along the tube ab possessing two vertical side tubes c and d 



(Fig. 390), the pressure at c will be greater than that at d, since at c the 



