432 CHEMISTR Y OF THE DIGESTIVE PROCESSES. 



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 0'5 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, 1888, Supp. Heft, Bd. xliii. S. 70. 



2 See Busch, Firchow's Archiv, 1858, Bd. xiv. S. 171 ; Tappeiner, Ztschr. f. JBioL, 

 Miinchen, 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, Ferhandl. d. Cong. f. 

 innere M< ed. , Wiesbaden, 1893; CcntralU. f. PhysioL, Leipzig u. Wien, 1893, Bd. viii. 

 S. 533. 



3 Edkins, Journ. PhysioL, Cambridge and London, 1892, vol. xiii. p. 445 ; v. Mering, 

 loc. cit.; Gley and Rondeau, Compt. rend. Soc. de. biol., Paris, 1893, p. 516. 



4 Brandl, Ztschr. f. Biol., Miinchen, 1892, Bd. xxix. S. 277. 



5 See F. Hofmeister, Ztschr. f. physiol. Chem., Strassburg, 1882, Bd. vi. S. 69. 



6 See " Digestion and Absorption of Fats," p. 457. 



