542 DIGESTION. 



up; after resection of the jejunum the large intestine seems to have a 

 compensating action. 



After the exclusion of the colon in rabbits, BERGMANN and HULT- 

 GREN 1 could find no definite action upon the availability of the cellu- 

 lose nor could any diminution in the utility of the other constituents 

 of the food be observed. ZUNTZ and USTJANZEW 2 .also found that the 

 removal of the caecum had no influence on the utilization of nitrogen; 

 but in respect of other factors they arrive at different results. They 

 found, namely, that the caecum of the rodent is of great importance for 

 the digestion of crude fiber and the pentosans. On feeding hay and 

 wheat to rabbits after the removal of the caecum, the digestion coefficient 

 for crude fiber fell from 42.8 to 23.4-18.7 per cent, and for pentosans 

 from 50 to 40-28.7 per cent. 



The question as to the forces which are active in the intestine during 

 absorption has not been satisfactorily answered. Attempts have been 

 made to explain absorption as a filtration, due to a certain difference 

 in the hydrostatic pressure between the intestinal contents and the 

 blood. A sufficiently great difference in pressure does not seem to 

 exist and besides this the absorbed solution on account of its composi- 

 tion cannot be considered as a filtrate from the intestinal contents. 

 Diffusion processes without doubt play a much more important role. 

 These attempt to keep the same concentration of all dissolved sub- 

 stances on both sides of the intestinal epithelium (in intestinal contents 

 and in the blood). Such processes must be influenced, as mentioned 

 in Chapter I on the osmotic pressure, to a high degree upon the perme- 

 ability of the intestinal membrane for dissolved solids and for water. 

 Nevertheless the diffusion stream does not give sufficient explanation 

 for the absorption, as, according to COHNHEIM, 3 the result is different 

 according to whether the intestine is alive or is dead and in general a 

 streaming from the lumen of the intestine into the outside fluid is 

 noticeable in the living intestine quite independent of the differences 

 in concentration. How this streaming is brought about has not been 

 explained. 



Other investigators have suggested the question whether surface- 

 tension forces (adsorption phenomenon) are active in absorption. 4 

 Still it has not been possible to bring the absorbability of a substance 

 in simple relation to its influence on the surface-tension of the water. 



1 Skand. Arch. f. Physiol., 14. 



2 Verhandl. d. physiol. Gesellsch. zu Berlin, 1904-1905. 



3 Zeitschr. f. physiol. Chem. 36-39. 



4 J. Traube, Bioch. Zeitschr. 24, 324 (1910) which also contains literature. 



