CHAP. iv. 



THE VASCULAR MECHANISM. 



221 



sake of simplicity, by which when the disc D is turned through one 

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

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

 bulbs. 



FIG. 32. LUDWIG'S STBOMDHR AND A DIAGKAMMATIC REPRESENTATION OF THE SAME. 



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

 cannulse 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 Z>, 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 x, and 

 the bulb B, the rest of A, and the junction (7, 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 H, 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 , in the direction of the 

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

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

 seen to rise to the mark x, 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, 



