116 1'IIYSIOLOGY OF THE CIKCULATION. 



when a stream encounters an obstacle in the middle 

 portion of a tube, effusion necessarily occurs through 

 any lateral openings situated behind the impediment, 

 while absorption will, in accordance with the prin- 

 ciple illustrated by one of the experiments to which 

 I have referred, proceed with increased rapidity 

 through the apertures placed on the other side of 

 the obstacle, viz., nearer to the discharging orifice. 



Exp. 3. A leaden pipe, a yard long, and half 

 an inch in diameter the central part of which had 

 previously been much curved was fastened hori- 

 zontally to a reservoir, and two small apertures 

 were made on its upper surface at a short distance 

 from either end of the curved portion of the tube. 

 On passing a stream of water through it, the im- 

 pediments, constituted by the existence of these 

 lateral curves, caused a small jet to escape from the 

 aperture placed behind the latter, while a rapid 

 absorption of air, or of any other stagnant fluid 

 with which it communicated, took place through t he- 

 opening situated nearer to the discharging orifice 

 of the pipe. 



Exp. 4. A piece of the aorta of the horse, 

 eight inches in length, was fastened horizontally to 

 the reservoir, and two bent glass tubes, one arm of 

 which dipped into a coloured liquid, were inserted 

 into two of its lateral branches situated at a distance 

 of four inches from each other, all the other lateral 

 openings being carefully closed. The central portion 

 of the pipe was now grasped at a point equally 

 distant from the insertion of both glass tubes, and 

 its calibre there considerably diminished, so that the 



