47o CHEMISTR Y OF THE DIGESTIVE PROCESSES. 
stable compounds, which are excreted unchanged ; thus phenol and kresol are 
eliminated as potassium salts of phenylsulphuric acid and kresolsulphuric 
7 oc 6 h 5 /Ocya^-CH, 
acid respectively, S0 O \ « SO.,\ • 
x OK " x OK 
Indol and skatol are to a considerable extent excreted with the fa?ces. 
The portion which is absorbed is first oxidised, yielding indoxyl and skatoxyl, 
and these are then united to form sulphates with potassium-hydrogen sulphate, 
thus :— 
c 6 h/ >ch c h 4 / x ch c h/ X CH 
\M/ N N H / ^\ NH^ 
(indol) (indoxyl) (potassium indoxylsulplmric acid) 
The aromatic oxy-acids in part are found in the urine as simple salts, 
and in part combined with sulphuric acid. The simple aromatic acids (phenyl- 
acetic and phenylpropionic acids) are chiefly found united with glycocoll. 
The phenylpropionic acid is first changed into benzoic acid, and then unites with 
glycocoll to form hippuric acid (benzoylglycocoll, C H 5 .CONH.CH 2 .COOH). 
The phenylacetic acid unites directly with glycocoll to form phenaceturic 
acid (C 6 H 3 .CH 2 .CO— NH.CHo.COOH). 
Besides these substances belonging to the aromatic series, there are formed, 
during the putrefactive decomposition of proteids, a number of substances 
belonging to the fatty series. The chief of these are leucine, the ammonium 
salts of a number of volatile fatty acids (caproic, valerianic, and butyric), 
methane, hydrogen, sulphuretted hydrogen, and methylmercaptan (CH...SH). 
Action of the intestinal bacteria on carbohydrates. — The carbo- 
hydrates suller much more bacterial decomposition in the intestine 
than do the proteids. Not only are the sugars formed in digestion 
attacked, but starch is directly attacked by some bacteria, 1 and 
cellulose, so far as it is decomposed, owes its changes to bacterial action. 
The products formed in such bacterial actions on the carbohydrates 
are simpler in their composition than those produced during putrefaction ; 
they consist chiefly of ethyl alcohol, lactic (active and inactive), butyric, 
and succinic acids, accompanied by carbon-dioxide and hydrogen. 
Nencki, Macfadyen, and Sieber 2 isolated seven different intestinal 
bacilli, of which five acted only on carbohydrates (dextrose), and the 
other two mainly on proteids. 
Cellulose is altogether unattached by any of the digestive juices in 
vitro; nevertheless it disappears to a very considerable extent in natural 
digestion. Experiments on herbivora show that 60 to 70 per cent, of 
the cellulose disappears, 3 and even shavings and paper mixed with hay 
and given to sheep only partially reappear in the faeces. Experiments 
on man show that, according to the condition and form of the cellulose, 
amounts varying from 4 to 60 per cent, are digested. 4 
Of the manner in which this cellulose is broken up or dissolved we 
know nothing with certainty. Bunge 5 supposes that the epithelial cells 
1 "Wortman, Ztschr. f. physiol. Chem., Strassburg, 1882, Bd. vi. S. 293 ; Lauder Brunton 
and Macfadyen, Proc. Boy. Soc. London, 1889, vol. xlvi. p. 542. 
2 Arch. f. exper. Path. it. Pharmakol., Leipzig, 1891, Bd. xxviii. S. 811. Reprinted in 
Journ. Aaat. and Physiol., London, 1S91, vol. xxv. p. 390. 
3 Haubner, Ztschr. f. Lwndwirthschaft, 1885, S. 177. 
4 Weiske, Ztschr. f. Biol., Miinchen, 1870, Bd. vi. S. 456: v. Knieriem, ibid., 1885, 
Bd. xxi. S. 67. 
5 " Lehrbuch der physiol. u. path. Chem.," 1894, S. 174. 
