Chap. XXI.] 



Lunwids STROMUHR. 



231 



U-tube ; in the second case, the fluid would require to 

 pass the long route through the bent tube. In 

 Fig. 108, A illustrates the complete instrument; B 

 shows how, by turning the cocks, the fluid would pass 

 straight through, and c shows how it would be diverted 



O O ' 



into the bent tube. The bent tube is filled with 

 water, or, better, serum, and the cocks turned so as 

 to shut it ofi from the through passage. The cut ends 

 of a severed artery are then ligatured to the two 

 canules. In this position the blood passes straight 

 through the basement piece, just as if it were part of 

 the length of the artery. At a given moment the 

 cocks are turned, the blood passes up one limb of the 

 bent tube and down the other, driving the serum 

 before it. The time it takes to travel the whole 

 length of the tube can be counted, and the length is 

 known, so that the rapidity is easily estimated. An 

 objection to this instrument is that the time occupied 

 by the blood in traversing the tube is very short, 

 and no account can be taken of vari- 

 ations produced by respiration and 

 the shock of the heart. 



The stromuhr of Ludwig (Fig. 

 109) permits of a much longer obser- 

 vation, while constructed on a similar 

 principle. It consists of two glass 

 flasks, 1 and 2, of equal capacity, com- 

 municating with one another above by 

 an arch, surmounted by a metal cap AB. 



The flasks are supported on 

 a metal disc 5 5', which is capable 

 of revolving on the metal support 

 6 6', below. Through 5 5' and 

 66' is a tube on each side, continuous with 1 and 

 2, and terminating in the canules 8 and 9. In 

 the position shown in the figure, 1 communicates 

 with 8, and 2 with 9, but, by a half turn of the flasks, 



Fig. 109. Ludwig's 



Stromuhr. 



Tlie left-band side is 



shown in section. 



