43 2 CHEMISTR Y OF THE DIGESTIVE PR O CESSES. 
for, on the basis of physical diffusion from the intestinal contents to the 
lymph. 1 
4. If the dissolved products of digestion are carried through by 
diffusion, it must be passively in a diffusion stream due to salt diffusion, 
their own diffusive powers being too feeble to suppose they are carried 
by these. Now, not only would such a stream be too slow, but, in such 
a case, the amount of fluid which must be absorbed by the epithelial 
cells would be enormous. There is at the height of proteid digestion, 
even in an animal with such digestive powers as the pig, rarely more 
than 2 per cent, of albumoses and peptones together in solution in the 
intestine, and usually much less. If it be supposed that this is passively 
and not selectively absorbed, then to carry 100 grms. of digested proteid 
out of the intestine, 5 litres of water at least, and probably a great 
deal more, would be required. During the digestion of starch, only 
traces of sugar are found at any given time in the intestine, and 
generally it may be stated that absorption takes place from very dilute 
solution. There is no reason to believe that such enormous quantities 
of fluid are thrown into the intestine during digestion, to be afterwards 
absorbed from it, and hence it must be concluded that dissolved 
substances are not passively absorbed by their solutions passing 
unchanged into the epithelial cell. 
Seat of absorption.— Absorption of some substances begins in the 
stomach, 2 but the main part takes place in the intestine. Water is 
practically not absorbed at all in the stomach, 3 while alcohol is readily 
taken up. The absorption of chloral hydrate and of sugar by the 
stomach is increased by the presence of alcohol. 
Gastric absorption is said to be increased by greater concentration of 
the substance to be absorbed, while the reverse holds for intestinal 
absorption. A solution of grape-sugar is most rapidly absorbed from 
the intestine when its concentration lies at - 5 per cent. ; as the 
concentration increases from this the rate of absorption diminishes ; 
while the rate of absorption in the stomach increases up to a concen- 
tration of 20 per cent. 4 According to v. Mering, all forms of sugar are 
absorbed in the stomach to a greater or less extent. The products of pro- 
teid digestion are also probably absorbed to a slight extent in the stomach. 5 
Channels of absorption.— The new materials formed by the action 
of the intestinal epithelial cells on the absorbed products of digestion, 
pass out of these cells into the lymphoid tissue of the villus underlying 
them. The modified carbohydrates and proteids pass in solution into 
the lymph which bathes the tissue, and in soluble form are absorbed 
from this lymph by the capillary vessels of the villus, thus passing 
directly into the portal circulation, while the fats leave the epithelial 
cells as fat globules, and are carried as such past the capillary network 
of the villus, to enter the lacteal situated in the axis of the villus. 6 
1 Heidenhain, Arch. f. d. ges. Physiol., Bonn, 188S, Supp. Heft, Bd. xliii. S. 70. 
2 See Busch, Virchow's Archiv, 1858, Bd. xiv. S. 171 ; Tappeiner, Ztschr. f. Biol., 
Miincheu, 1880, Bd. xvi. S. 497 ; v. Anrep, Arch. f. Anat. u. Physiol., Leipzig, 1881, 
S. 504; Meade-Smith, ibid., Leipzig, 1884, S. 481 '; v. Mering, Verhandl. d. Cong. f. 
innere Med. , Wiesbaden, 1893; Centralbl. f. Physiol., Leipzig u. Wien, 1S93, Bd. viii. 
S. 533. 
3 Edkins, Joum. Physiol., Cambridge and London, 1892, vol. xiii. p. 445 ; v. Mering, 
loc. cit.; Gley and Rondeau, Compt. rend. Soc. de. biol., Paris, 1893, p. 51C. 
4 Brandl, Ztschr. f. Biol., Miinchen, 1892, Bd. xxix. S. 277. 
5 See F. Hofmeister, Ztschr. f. physiol. Chem., Strassbnrg, 18S2, Bd. vi. S. 69. 
G See " Digestion and Absorption of Fats," p. 457. 
