CHAP. iv.J THE VASCULAR MECHANISM. 125 



instead of two right angles from either of the above positions, G becomes 

 directly continuous with H, both being completely shut off from the 

 bulbs. 



FlG. 20. DIAGRAMMATIC REPRESENTATION OF LUDWIG'S SlEOMTJHR. 



The ends of the tubes H and G are made to fit exactly into two 

 cannulae inserted into the two cut ends of the artery about to be experi- 

 mented upon, and having a bore as nearly equal as possible to that of 

 the artery. 



The method of experimenting is as follows. The disc D, being placed 

 in the intermediate position, so that a and b are both cut off from 

 a and b', the bulb A is filled with pure olive oil up to the mark a?, and 

 the bulb B, the rest of A, and the junction C, with defibrinated blood; 

 and C is then clamped. The tubes H and G are also filled with de- 

 fibrinated blood, and G is inserted into the cannula of the central, H 

 into that of the peripheral, end of the artery. On removing the clamps 

 from the artery the blood flows through G to ff, and so back into the 

 artery. The observation now begins by turning the disc D into the 

 position shewn in the figure ; the blood then flows into A, driving the 

 oil there contained out before it into the bulb B, in the direction of the 

 arrow, the defibrinated blood previously present in B passing by H into 

 the artery, and so into the system. At the moment that the blood is 

 seen to rise to the mark cc, the disc D is with all possible rapidity turned 

 through two right angles; and thus -the bulb B, now largely filled with 

 oil, placed in communication with G. The blood-stream now drives the 

 oil back into A, and the new blood in A through H into the artery. As 

 soon as the oil has wholly returned to its original position, the disc is 

 again turned round, and A once more placed in communication with G, 

 and the oil once more driven from A to B. And this is repeated several 

 times, indeed generally until the clotting of the blood or the admixture 

 of the oil with the blood puts an end to the experiment. Thus the flow 

 of blood is used to fill alternately with blood or oil the space of the bulb A, 

 whose cavity as far as the mark x has been exactly measured; hence if 

 the number of times in any given time the disc D has to be turned round 

 be known, the number of times A has been filled is also known, and 

 thus the quantity of blood which has passed in that time through the 



