FROM THE SMALL INTESTINE 635 



to be that, when the pressure was zero or negative, the mucous 

 membrane would be pressed against the cage and absorption 

 stopped by interference with the circulation, and that when the 

 mucous membrane was lifted off the cage by the slightest positive 

 pressure, absorption began again. The intestines during life 

 undoubtedly contain a positive pressure, but for nitration to be 

 possible, the intra-intestinal pressure would have to be greater 

 than that in the venous end of a capillary. It is, therefore, 

 necessary to inquire how great these two pressures are. Ham- 

 burger considered that intra-intestinal pressure was due to three 

 causes respiratory movements, peristalsis, and gravity. During 

 inspiration the diaphragm is thrust down into the abdomen and 

 will exert pressure upon the abdominal viscera. He measured 

 the respiratory rise in intra-intestinal pressure, and the highest 

 value obtained was about 8 mm. Hg. During the peristalsis of 

 one coil pressure will be exerted upon neighbouring coils, and 

 gravity could affect intra-intestinal pressure by the weight of coils 

 pressing on each other and by acting also upon the contents of 

 the individual coils. In order to eliminate these three forces, 

 Hamburger introduced an aluminium cage into one coil, and 

 found that the absorption from it was still considerable, although 

 less than from a neighbouring coil. This experiment would 

 appear to show that intra-intestinal pressure is not really of 

 great importance to absorption, and the result obtained is in 

 marked contrast to those of Hamburger's previous experiments, 

 in which the importance of filtration was insisted on. Hamburger 

 never measured simultaneously the fluid pressure in the gut and 

 the blood pressure in the mesenteric vein, and has consequently 

 brought forward no real evidence that filtration could ever take 

 place. Reid, however, has determined these pressures simultane- 

 ously, and found that during absorption the pressure in the 

 mesenteric vein may be four times greater than the fluid pressure 

 in the gut. We may therefore conclude that absorption may 

 take place when filtration is impossible, and that no one has yet 

 brought forward evidence to show that the intra-intestinal pres- 

 sure is ever sufficiently great to make filtration possible. But we 

 cannot conclude that the intra-intestinalpressure has no influence on 

 the rate of absorption. Both Leubuscher and Edkins have found, 

 like Hamburger, that a pressure of about 8 mm. Hg is the 

 optimum ; above that, absorption falls off and the outflow from 



