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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 x
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 csecum, 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.
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