DIGESTION OF PROTEIDS. 399 



supposition is negatived by the rapidity of the action, and its progress 

 in presence of antiseptics ; and both by the recent observations of 

 Miura, 1 which show that the mucous membrane of the intestine of 

 newly-born animals, under antiseptic conditions, causes inversion. No 

 inversion was obtained with the mucous membrane of the stomach or 

 large intestine. 



Brown and Heron 2 have shown that the dried mucous membrane 

 of the small intestine is much more powerful, both in its diastatic action 

 on starch and in its inverting action on cane-sugar and maltose, than 

 are infusions of the same material. Starch also disappears from an 

 intestinal fistula (Thiry) much more rapidly than it is possible for the 

 succus entericus, 3 judging from other experiments, to convert it into 

 sugar. These facts point to a possibility that the epithelial cells of 

 the intestinal mucous membrane may possess the power of absorbing 

 starches and saccharoses, and submitting them to diastatic and inverting 

 processes, in passing them on to the lymph spaces of the villi ; that, in 

 fact, cellular digestion of absorbed carbohydrates may take place in the 

 epithelial cells after absorption. 



The secretion of the small intestine is generally stated to be 

 inactive towards lactose, so that the inversion of this sugar probably 

 occurs after its absorption by the columnar cells. 4 



Human succus entericus has been investigated by Ewald, 5 by Demant, 6 

 and by Tubby and Manning ; 7 they all agree as to its diastatic action on starch 

 and inverting action on cane-sugar. Tubby and Manning also tested its action 

 on maltose, and found that this was converted into dextrose. The ferment or 

 inverting material adhered to mucus whenever a precipitation of this took 

 place in the fluid, so that the mucus was more effective than the clear 

 fluid. 8 



DIGESTION OF PROTEIDS. 



The digestion of proteids is a much more complex process than that of 

 either the fats or carbohydrates, and one of which our knowledge is still 

 less exact. In the digestion of carbohydrates we are absolutely certain 

 that we have to do with a hydrolytic process, and that from a body 

 of absolutely fixed percentage composition, though often of unknown 

 molecular weight, there is produced in digestion a substance of known 

 formula, and to a certain extent of known structure. In proteid digestion, 

 while it is probable that a very similar action is taking place, we have 

 no such certainty. The digestive process begins with material, the 

 different proteids, which varies considerably in percentage composition. 



1 Ztschr.f. Biol., Miinchen, 1895, Bd. xxxii: S. 266. 



2 Proc. Roy. Soc. London, 1880, vol. xxx. p. 399. See also Shore and Tebb, Journ. 

 Physiol., Cambridge and London, 1892, vol. xiii. (Proc. Physiol. Soc.), and M. C. Tebb, ibid. 

 vol. xv. p. 421. 



3 Rohmanii, Arch. f. d. ges. Physiol., Bonn, 1887. Bd. xli. S. 424. 



4 Meyer, "Die Lehre von den chemischen Fermenten," 1882 ; Dastre, Arch, de physiol. 

 norm, etpath., Paris, 1890, tome xxii. p. 103 ; C. Voit and Lusk, Ztschr.f. JBioL, Miinchen, 

 1891, Bd. xxviii. S. 275 ; Mendel, Arch. /. d. ges. Physiol., Bonn, 1896, Bd. Ixiii. S. 425. 

 See, however, Pautz and Vogel, Ztschr.f. Biol., Miinchen, 1895, Bd. xxxii. S. 304 ; Rohmann 

 u. Lappe, Ber. d. deutsch. chem. Gesellsch., Berlin, 1895, Bd. xxviii. S. 2506. 



5 Virchow's Archiv, 1879, Bd. Ixxv. S. 409. 6 Ibid., S. 490. 



7 Guy's Hosp. Rep., London, 1891, vol. xlviii. p. 271 ; Centralbl. f. d. mcd. Wissensch., 

 Berlin, 1892, S. 945. 



8 Paschutin (loc. cit.) found that the inverting enzyme was mechanically precipitated 

 along with collodion. 



