EXPERIMENTS ON DIGESTION. 
589 
2. The intestinal mucus, which has the property of dissolving 
water and other fluids, serves, by this means, as a kind of inter- 
mediate agent between the dissolved aliment, the pancreatic juice, 
and the bile. It is on this account that it is more fluid, and more 
prominent during digestion, and when the animal is fasting, at 
which time it has a much greater consistence. 
3. As this mucus covers the intestinal villosities, it is probably 
also the medium through which absorption takes place in the small 
intestine. 
4. The liquid portion of the intestinal fluid appears to exercise 
a solvent action on the portions of aliment which have passed into 
the small intestine with the chyle, and which the stomach has not 
completely dissolved. It should be borne in mind, in reference to 
this, that these residual portions become gradually smaller as they 
pass along the canal, and that, at length, they altogether disappear. 
5. Finally, the aqueous portions of the intestinal fluid, and, 
principally, the animal matters which they contain, are absorbed 
with the dissolved portions of the food, by the mucous membrane 
of the small intestines, and by the lymphatic vessels : thence it re- 
sults that the mucus acquires greater consistence in proportion as 
it advances towards the caecum. The combination of the intestinal 
fluid Avith the dissolved aliment determines the assimilation of the 
latter. It might also be alleged in confirmation of the assimilative 
action of this fluid, that the length of the intestinal canal, and the 
number of glands that are scattered over its parietes, have a per- 
fect and beautiful relation in the different families of the mam- 
malia to the nature of the aliments on which they live. The small 
intestine is very short in the carnivora ; it is longer in those who 
live upon fruits, and sweet and farinaceous roots, oleaginous grains, 
and tender herbs; and it is longest of all in those whose food con- 
sists of the harder grasses and leaves. 
The mixture of the chyme, the intestinal aqueous fluid, the in- 
testinal mucus, the bile, and the pancreatic juice, acquire more 
and more consistence as it advances through the intestine, by 
means of the contractions of the muscular coat. The fluid portions, 
and those expressed from the general mixture, are attracted by the 
mucous membrane, which imbibes them almost like a sponge, and 
the numerous lymphatic vessels of which effect their absorption. 
The intestinal mucus becomes more consistent, and mingled with 
the remnants of the undissolved aliment, particularly with those 
that are not soluble in the digestive fluids, as un bruised oats, the 
hard fibres of plants and of wood, hair and feathers, much of the 
fatty matter : the resin, the colouring principle, and the mucus of the 
bile, constitute the commencement and the foundation of the ex- 
crementitious bouillie , and this does not begin to assume a decided 
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