PHYSIOLOGY OF THE CIRCULATION. 103 



exist in living animals. For in these experiments 

 the force acting on the exterior of the membranous 

 tube never exceeded the weight of a column of water 

 six inches high, while in some cases the height of 

 the external column was only one inch. 



3. In imitation of the rigidity of the terminating 

 portion of the large veins, the upper end of the mem- 

 branous tube was fastened to a short arm of a bent 

 glass tube. But this sudden transition from a flaccid 

 to a perfectly rigid tube occasioned an inconvenience 

 which will, to a certain extent, be avoided in the 

 animal body, in consequence of the change being 

 more gradual. 



4. To compensate for the difficulties which a 

 stream encounters in flowing against gravity, it 

 became necessary to use the slight derivative power 

 of a short syphon, and without this contrivance no 

 absorption could be obtained with an ascending 

 stream. As before mentioned, it has been shown by 

 the experiments of Hales, and more recently by those 

 of Sir D. Barry, that a similar derivative power acts 

 during the expansion of the thorax. This force has 

 been found capable of raising a column of water in a 

 small glass tube to the height of twenty inches. 



It might, from this latter circumstance, be imagined 

 that the use of a more powerful syphon in the appa- 

 ratus would have the effect of increasing the activity 

 of the absorbing process. But I have satisfied my- 

 self, by repeated trials, that any material deviation 

 from the above-stated proportions, whether increasing 

 or diminishing the power of the syphon, rather im- 

 peded than promoted absorption. For when the 



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