INTESTINAL DIGESTION FAECES. 183 



contains taurocholic acid, this acid undergoes changes in passing through 

 the alimentary canal which are identical with those produced by boiling 

 with acids, or with alkalies, or which occur in the act of putrefaction, cho- 

 lalic acid, dyslysiu, and choloidinic acid being produced. On the other 

 hand, in the fk'ces of those animals that, like oxen, secrete bile of which 

 glycocholic acid is the chief constituent, this acid, being comparatively stable 

 and scarcely destroyed even by putrefaction, may be found in considerable 

 quantity. That, the coloring matter of the fteces is in great part derived 

 from the bile, is shown by their paleness when that secretion is not duly 

 poured into the intestinal tube. And it is probable that the peculiar fatty 

 substances usually present, are products of the metamorphosis of its oleagi- 

 nous and resinous matters. The similarity which has been found to exist 

 between the odor of certain components of putrefying bile, and that of fceces, 

 has led Prof. Valentin to suppose that the matter which gives to the latter 

 their characteristic smell, is entirely derived from decomposing bile. We 

 shall presently see, however, that other sources of this matter probably exist 

 ( 131) ; and the recent researches of Bidder and Schmidt upon the amount 

 of sulphur in the fteces, appear to show that not above one-eighth of the 

 solid matter of the bile is normally excreted under this form. The indica- 

 tions of the presence of bile are especially distinct when the fceces have 

 remained for only a short time in the large intestine, and when there has 

 consequently been less time for its reabsorption. 



130. Planer 1 examined the Gases developed in the alimentary canal of 

 Dogs after different kinds of food, and in Man after death. The gas con- 

 tained in the stomach consisted chiefly of air swallowed with the food, and 

 was usually small in quantity. The Oxygen soon disappeared. In the 

 small intestines, Carbonic Acid and Hydrogen are developed in nearly equal 

 proportion, whether the diet be Animal or Vegetable. The experiments of 

 Pasteur 2 afford some explanation of their appearance, at least in Herbivora, 

 by showing that with the development of numerous infusory auimalculse in 

 the intestines, starch and sugar are converted into lactic and butyric acids, 

 and that with the development of the latter there is an evolution of Car- 

 bonic Acid and Hydrogen : thus, one equivalent of Sugar C 12 H ]2 O I2 = (C 8 

 H 7 O 3 ) HO + 4CO, + H 4 . In the large intestine, Carbonic Acid is chiefly 

 present, but is mingled with Sulphuretted Hydrogen (after Animal diet), 

 and if the food have been long retained in the body, with Carburetted 

 Hydrogen (C. 2 H 4 ). It is more than doubtful whether gases can be dis- 

 engaged from the blood, and excreted or secreted into the intestines, as 

 Magendie supposed ; but there seems no reason to doubt that if gas were 

 already developed, exchange, according to the ordinary laws of diffusion, 

 might take place between it and the gases of the blood. In a dog which 

 had been fed for 6 days on pure animal diet, and was killed 5 hours after a 



meal, he found 



C0 2 . 0. N. H. SH. 



In the Stomach, . . . '2520 612 6868 



Small Intestine, . . . 40.1 Traces 45.52 13.86 



Large Intestine, . . 74.19 0.63 23 1.41 0.77 



In another dog fed with bread for 8 days, there was only sufficient gas for 

 analysis in the small intestine ; it consisted of 



C0 2 . O. N. H. 



38.78 Traces 54.2 6.33 



1 Henle and Meissner's Bericht fur I860, p. 274. 



2 Annales de Chumie, 1858, p. 404 et seq. ; Comptes Rendus de 1'Academie des 

 Sciences, 1860. p. 849. See also, for Analysis of the Gases of the Intestines in Dugs 

 and Rabbits, K. B. Hofmann, Wiener Mod. Wochens., 1872, p. 24. 



