PHYSIOLOGICAL ABSORPTION. 345 



normal saline caused to pass osmotically from the outer 

 to the inner surface, but that weak alcohol caused an 

 augmentation. 



Some idea of the value of the pressure exerted by 

 the "physiological" action is given by Heidenhain, for if 

 water is absorbed from a sodic chloride solution of higher 

 osmotic pressure than the blood, the pressure against which 

 the absorption occurs can be calculated by the difference 

 between that of the solution and the serum. 



In one case, a 1*46 percent, solution of sodic chloride 

 with A ='9 placed in the gut lost water to the blood with 

 A ='6. The available pressure against the physiological 

 stream which is overcome is represented by A=*3, and 

 this corresponds to a pressure of 2700 mm. of Hg. One 

 can only understand the cells as being capable of withstand- 

 ing such pressures, by thinking of the extremely minute 

 capillary channels through which the fluids must flow. 



The actual rapidity of absorption, though slow, seems 

 to be far quicker in the gut than in an osmometer under 

 somewhat similar conditions. As a maximum, about 7 

 cb. mm. of water is absorbed by 1 sq. cm. of absorbing 

 surface (with allowance for the extension of surface pro- 

 duced by the villi) per minute, so that a depth of 7 p of 

 fluid passes into the cells in a minute. Since a cell is 

 about 35 n in depth, it takes about five minutes to complete 

 the journey from top to base, a result agreeing well with an 

 experiment of Lehmann's, who detected potassic iodide in 

 a mesenteric vein five minutes after placing the solution in 

 the ileum. An osmometer closed with cow's bladder and 

 filled with defibrinated blood, gives a transfer of only 

 •023 cb. mm. per sq. cm. per minute, while even with 

 saturated sodic chloride solution in the osmometer, the 

 rate was but "55 cb. mm. of water per sq. cm. per minute. 

 As is to be expected, if a physiological act of absorption 

 be admitted, differences of absorptive power should exist 

 in different regions of the alimentary canal, though the 

 circumstances for diffusion are much the same. 



Tappeiner showed that in dogs, whilst in the duodenum 

 and jejunum injected taurocholate and glycocholate of soda 



