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therefore probable that in these animals any extensive bacterial decomposition
of carbohydrates that may occur, like that of proteids, takes place in the
large intestine, and by analogy the same is probably the case in the human
intestine.

Considerable importance has been attached to the normal action of bacteria
in the intestine, and it has even been supposed that the presence of bacteria
is essential to life. Such a view has recently been shown to be erroneous by
an elaborate and painstaking research carried out by Xuttall and Thierfelder,^
who obtained ripe foetal guinea-pigs, by means of a Csesarean section, carried
out under strict antiseptic precautions. They introduced the animals immedi-
ately into an aseptic chamber, through which a current of filtered air was
aspirated, and fed them hourly on sterilised milk day and night for over eight
days.

The animals lived and throve, and increased as much in weight as healthy
normal animals, subjected to a similar diet for the purpose of controlling the
results. Microscopic examination at the end of the experiment showed that
the alimentary canal contained no bacteria of any kind, nor could cultures of
any kind be obtained from it. The same authors, in a subsequent paper,
describe the extension of their research to vegetable food ; this was also digested
in the absence of bacteria. Under such conditions cellulose was not attacked ;
hence they consider that the chief function of this material is to give bulk and
a proper consistency to the food, so as to suit the conditions of herbivorous
digestion.

Action of the intestinal bacteria on proteids.— The changes brought
about in the intestine are very similar and xjrobably identical with those
which occur when proteids undergo putrefaction in the air, with this
important exception, that those putrefactive bacteria which produce the
class of poisonous nitrogenous (alkaloidal) bases known as ptomaines do
not grow under normal conditions in the intestine. This may be due to
the intestinal contents not furnishing a suitable medium for their growth,
or to the time of putrefaction in the intestine not being sufficiently
prolonged. Ptomaines, and especially poisonous ones, are formed only in

^ Journ. Physiol., Camlaridge and London, 1897, vol. xxi. p. 373.

- See " Digestion and Absorption of Fats," p. 454.

^ Zfschr. /. pkysiol. Cliem., Strassbnrg, 1895, Bd. xxi. S. 109; 1896, Bd. xxii. S. 62.

VOL. I. — 30



466 " CHEMISTR Y OF THE DIGESTIVE PROCESSES.

the later stages of putrefaction. It has also been suggested that the
cause may be the absence of oxygen from the intestme, the ptomaine-
formmg bacteria being aerobic. ■ That the bacteria which produce
ptomaines are present in the intestine, is shown by the fact that cultures
producing ptomames may be obtained by sowing from the intestinal
contents into suitable media.^ At any rate, ptomaines even in traces are
not to be found in the intestinal contents ; and it is fairly certain that
they are not produced there, as most of them, absorbed even in minute
doses, are capable of producing profound toxic effects.

The first stages in the action of bacteria on proteids are very similar
to those induced by trypsin ; they can also be brought about by enzymes
extracted from the bacteria,^ but, according to Kiihne,^ are not due to
trypsin, which is never formed in bacterial putrefaction.

The first action is the solution of the proteid, if this is not already
dissolved. Solution takes place much more slowly than in the case of
the digestive enzymes, the complete solution of fresh fibrin thoroughly
infected with intestinal bacteria in faintly alkahne solution being a
X^rocess of some days' duration.^ Albumoses, peptones, and the other
products of tryptic digestion are next formed, but the amount of these
present at any time is never great, since they are gradually broken up
as they are formed into more advanced degradation products. In the
presence of albumoses or peptones, the native proteids are very faintly
attacked by the bacteria, until these have first been disposed of.
Neumeister ^ has shown that, when peptone is added to putrefying blood
or proteid, its quantity is not increased by the continuance of the putre-
factive process, but rather diminished until it finally disappears.

The proteid molecule probably contains a large number of both
fatty and aromatic radicles, but all those belonging to the aromatic
group }deld, under the action of trypsin, only one substance, namely,
tyrosine. The same is true of all artificial modes of decomposition which
do not act too intensely on the primary products of decomposition.^
But with the decomposition produced by bacteria, the case is different,
and several aromatic compounds are formed.

These are in part produced by further action on tyrosine, formed in
an earlier stage, and in part spring from a specific action of the bacteria
on the proteid, without the intervention of tyrosine. Only some of these
products of bacterial decomposition have been hitherto found in the
intestinal canal ; the others are either, under the different conditions, not
formed there, or are so rapidly absorbed and altered that they cannot
be detected in the intestinal contents.

The chief aromatic compounds derived from the bacterial decomposi-
tion of proteids are : — (a) Tyrosine, and its derivatives, paraoxyphenyl-
propionic acid (hydroparacumaric acid), and paraoxyphenylacetic acid,
as well as phenylpropionic and phenylacetic acids,'' of which the fore-
going are the oxy- or hydroxy-acids, also parakresol and phenol.

^ Brieger, TJeutsche med. Wchnschr., Leipzig, 1887, S. 469; Baumanu u. Udransky,
Ztschr.f. p/'ysiol. C'hem., Strassburg, 1889, Bd. xiii. S. 579.

2 ,See p. 313.

^ Unterstoch. a. d. physioL Inst, zv, Heiddherq, 1S78, Bd. i. S. 291.

^ Bienstock, Ztschr.f. klin. Med., Berlin, 1884, Bd. viii. S. 1.

5 Ztschr.f. Biol, Miinchen, 1890, Bd. xxvii. S. 335; " Lehrbuch, " Tli. 1, S. 207.

^ Ktilme obtained indol by the fusion of proteid with caustic alkali, Ber. d. deutsch.
chcm. GescUsch., Berlin, 1875, Bd. viii. S. 206.

'' See E. Salkowski, Ztschr.f. physM. Chcm., Strassburg, 1885, Bd. ix. S. 491.



ACTION OF INTESTINAL BACTERIA ON PROTEIDS. 467

(6) Substances formed directly and not from tyrosine — indol, skatol, and
skatolcarbonic acid.

Of these substances, Zumft ^ found indol, skatol, phenol, and para-
kresol in the large intestine of man, but skatolcarbonic acid was absent ;
this latter acid has not yet been detected in the intestine. According
to E. Salkowski, it is excreted unchanged in the urine, and he states that
he has detected it in normal urine.^

These several substances may now be considered seriatim.

Derivatives of tyrosine formed in putrefaction.^ — Hydroparacumaric acid,
or paraoxijphenylpropionic acid (HO.CyH^.C^H^.COOH) crystalKses from
water in anhydrous monoclinic crystals, melting at 125°-128'' C, soluble
in water, alcohol, and ether. It gives a transient blue coloration with ferric
chloride, and a red coloration or red preciiDitate when boiled with Millon's
reagent. It is the oxy-acid of phenylpropionic acid, which has also been
found among the putrefaction-products of proteids. Phenylpropionic acid
crystalHses in slender needles, melting at 47°-48° C. (B-Pt, 280° C). As
follows from its constitution, its solutions clo not give Millon's reaction.

Paraoxyphenylacetic acid (H0.C^;II^.CH2.C00II) crystallises from Avater
in prismatic crystals, melting at 148° C., and soluble in water, alcohol, and
ether. With ferric chloride it gives a faint violet coloration, changing to
a dirty grey -green. It also gives Millon's reaction. Phenylacetic acid
crystallises in scales, which melt at 76° "5 C.

Phenol and parah^esol '^ are also formed in the bacterial decomposition of
tyrosine ; they are absorbed from the alimentary canal, and after conversion
into ethereal sulphates are excreted in the urine. The amount of these
ethereal sulphates in the urine gives a measure of the amount of bacterial
decomposition going on in the intestine.^

Tyrosine and its derivatives are very closely related to one another. In
the derivation of these compounds, according to Baumann,'^ tyrosine (paraoxy-
phenyl-a-amidopropionic acid) undergoes reduction, ammonia being split off,
and hydroparacumaric acid (paraoxyphenylpropionic acid) formed. This
compound, by a series of oxidations, accompanied by a splitting off of carbon-
dioxide, yields paraoxyphenylacetic acid and parakresol. Parakresol is said
to similarly yield phenol.

These changes are illustrated by the following equations : —

OH (p) /OH (p)

C,h/ + H, = C,h/ +NH3

\CH,.CH(NH,).COOH \CH,.CH,.COOH

(paraoxyplienyl-a-amidopropionic (paraoxyphenylpropionic acid

acid or tyrosine) or hydroparacumaric acid)

/OH (p) /OH (p)

2C,h/ -h30, = 2C6H/ -f2COo + 2H,0

\CH,.CH,.COOH ^ \CH,.COOH

(paraoxyphenylpropionic acid) (paraoxyjjhenylacetic acid)

1 Arch. d. sc. biol., St. Petershom-g, 1892, vol. i. p. 497.

'^ Ztschr. f.pliysiol. Chem., Strassbnrg, 1885, Bd. ix. S. 32.

3 SeeBaiimann. Ztschr. f. physiol. Chem., Strassburg, 1877-1880, Bd. i. S. 60 ; iv. S. 301 ;
Ber. d. deutsch. chem. Gesellsch., Berlin, 1879, Bd. xii. S. 1450; ^1880, Bd._ xiii. S. 279;
Baumann and Brieger, Ztsclir. f. physiol. Chem., Strassburg, 1879, Bd. iii. S. 149; E.
and H. Salkowski, Ber. d. deutsch. chem. Gesellsch., Berlin, 1879, Bd. xii. S. 648 ; E.
Salkowski, Ztschr. f. physiol. Chem., Strassburg, 1878-9, Bd. ii. S. 420; Weyl, ibid.,
1877-9, Bd. i. S. 339 ; iii. S. 312.

^ For a description of the physical and chemical properties of these bodies, see
Gamgee, " Physiological Chemistry of the Animal Body," 1893, vol. ii. p. 434.

^ Baumann, Ztschr. f. physiol. Chem., Strassburg, 1886, Bd. x. S. 123.

^ Ber. d. deutsch. chem. Gesellsch., Berlin, 1879, Bd. xii. S. 1450.



468 CHEMISTR Y OF THE DIGESTIVE PROCESSES.

/OH (p) .OH (p)

C,h/ =CeH/ + CO,

^CH2.C00H CHg

(paraoxyphenylacetic (parakresol)

acid)

OH (p) .OH

2C6H/ +30, = 2CeH,( +2CO, + 2H20

\CH, " \H

(parakresol) (phenol)

By a process of reduction, the oxy-acids probably yield the phenylpropionic
and phenylacetic acids which have been found, thus : —

0H(p)
C,H.<; +2H = C^H5.CH2.COOH + H.,0

^^CHg-COOH

(paraoxyphenylacetic (phenylacetic

acid) acid)

Aromatic bodies found in 'putrefaction not formed from tyrosine. — Indol,
skatol, and skatolcarbonic acid are not formed by bacterial action on tyrosine,
and their mode of formation is not very clearly known. According to
Baumann,^ they are not primary products of bacterial action on the proteid
molecule, but are formed in the decomposition of an intermediate body, Avhich
is soluble in a mixture of alcohol and ether. E. and H. Salkowski ^ support
this conclusion. Nothing further is known of this intermediate substance,
except that it is not peptone. Xeumeister ^ considers it possible that these
substances may be synthetically built up by the bacteria from simpler aromatic
compounds. Indol and skatol are formed from this mother substance in
varying proportion, probably due to the action of different bacteria, but these
have never been isolated.

Indol, skatol, and skatolcarbonic acid belong to the indigo group of aromatic
compounds. Indol on oxidation yields indoxyl, and on further oxidation,
this yields indigo blue. By an inverse process of reduction from indigo blue,
indol can be obtained.^ To indol and skatol the fseces owe to a great extent
their peculiar unpleasant odour.

.NH
Indol,^ CJl/ /^CH, crystallises from water in small scales (M. P.,

^CH^

52° C, B. P., 245° - 246° C). It is fairly soluble in hot, less so in cold water,
and is easily soluble in alcohol, ether, chloroform, benzol, and petroleum ether.
It distils over with steam ; this property may be used to separate it from
other putrefaction products. "^^ In long-continued putrefaction, indol gradually
disappears ; according to Salkowski, this is due to evaporation.

Indol may be recognised by the following tests : —

1. A wooden match moistened with strong hydrochloric acid and then
dipped into an alcoholic solution of indol turns a cherry-red colour.

' Ber. d. deutscJi. clicm. GescUscli., Berlin, 1880, Bd. xiii. S. 284.

^ Ztschr. f. physiol. CJiem., Strassburg, 1884, Bd. viii. S. 454 ; see also Nencki and Bovet,
Ilonatsh.f. Chcm., Wien, 1889, Bd. x. S. 506.

3 "Lehrbuch. d. physiol. Chem.," Jena, 1893, Th. 1, S. 209.

■* Neucki, Ber. d. deutsch. chem. Gesellsch., Berlin, 1875, Bd. viii. S. 722 ; Baumann,
u. Brieger, Ztschr. f. 2Jh/siol. Chem., Strassburg, 1879, Bd. iii. S. 254.

° Baeyer, Ann. d. Chem., Leipzig, Bdi cxl. S. 295 ; Supp. Bd. vii. S. 56.

•> For method of isolation from these, see Gamgee, "Physiological Chemistry, etc.," vol. ii.
p. 421 ; orE. and H. Salkowski, Ztschr. f. 2^hysiol. Chem., Strassburg, 1884, Bd. viii. S. 417.



A CTION OF INTESTINAL BA CTERIA ON PR O TEWS. 469

2. An aqueous solution of inclol treated with fuming nitric acid turns a
bright red colour, and on standing a red precipitate is formed.

3. When sodium nitroprusside is added to a very dihite sohition of indol,
and afterwards caustic soda, the mixture turns a deep violet-bhie, passing into
a pure bhie on making faintly acid with acetic acid, and disappearing with
excess of acid (Legal's reaction).^

, NH.

Skatol,'^ CpH / / CH, is methyl-indol ; it crystallises in simdar form

to indol (M. P., 95° C, B. P., 265° - 266° C). It also possesses much the
same solubilities as indol, and is volatile with steam. Passed through a red-
hot tube, it decomposes and yields indol.

It is distinguished, in addition to its physical properties, by the following
tests : —

1. Instead of a red precipitate, as in the case of indol, it gives a milky
turbidity when treated with fuming nitric acid.

2. In Legal's test (vide supra) it gives an intense yellow, turning violet
with acid.

3. It dissolves in concentrated hydrochloric acid, giving a highly coloured
solution.

Both indol and skatol, dissolved in benzol in concentrated solution, give,
with a saturated solution of picric acid in benzol, a crop of fine red crystals.
When the compound of indol and picric acid is treated Avith caustic soda, and
distilled, the indol is decomposed ; under similar conditions the skatol picric
acid compound yields skatol which is not decomposed.

/ NH.
Skatol carbonic acid,^ Cgll/ ^C'COOH, crystallises in scales (M. P.,

164° C), sparingly soluble in water, easily soluble in alcohol and ether. Heated
above its melting point, it breaks up into skatol and carbon-dioxide.
It may be identified by the following tests : —

1. Its aqueous solution, treated with pure nitric acid and afterwards with
potassium nitrite solution, turns a cherry -red colour, and deposits a red pre-
cipitate, which is dissolved by acetic ether.

2. Its aqueous solution, treated with an equal volume of hydrochloric acid
(sp. gr. 1 -2), and afterwards with dilute bleaching powder solution, gradually
turns a purple-red colour, and, after long standing, deposits a purple-red
precipitate, easily soluble in alcohol.

3. A very dilute solution (1 in 10,000 of water), treated with a few drops
of hydrochloric acid, then with a fcAV drops of a very dilute solution of ferric
chloride, and heated, gives an intense violet colour. More concentrated solution
gives an intense cherry-red colour.

The aromatic compounds resulting from bacterial decomposition in the
intestine are to a considerable extent absorbed. Tyrosine absorbed as such
disappears ; it is decomposed and completely oxidised in the tissues without
the formation of urea. The non-nitrogenous substances resulting from its de-
composition by bacteria (as well as indol and skatol) are not completely
oxidised, but are excreted in modified form in the urine, combined chiefly
with sulphuric acid, as ethereal sulphates, but also in part with glycocoll and
glycuronic acid. In this way the poisonous properties of the phenols and
similar compounds are removed, for the ethereal sulphates formed are very

1 Breslau. arztl. Ztschr., 1893.

" Bvieger, Ber. d. deutsch. chem. Gesellsch., Berlin, 1877, Bd. x. S. 1028.

^ E. and H. Salkowski, Ztschr. f. physiol. Chem., Strassburg, 1885, Bd. ix. S. 8.



470 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

acid respectively, S0o\ . SOo\ .

Indol and skatol are to a considerable extent excreted with the faeces.
The portion Avhich is absorbed is first oxidised, yielding indoxyl and skatoxyl,
and these are then united to form sulphates with potassium-hydrogen sulphate,
thus : —

/CR\ /C-OH.\ ..C-(OSOo.Kk

C,h/ >CH C,h/ >CH CeH / ^CH

(indol) (indoxyl) (potassium indoxylsulphuric 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, CQH5.COISrH.CHo.COOH).
The phenylacetic acid unites directly with glycocoll to form phenaceturic
acid (CeH^.CHg.CO— NH.CH2.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 (CH3.SH).

Action of the intestinal bacteria on carbohydrates. — The carbo-
hydrates suffer 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,^ 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^ isolated seven different intestinal
bacilli, of which five acted only on carbohydrates (dextrose), and the
other two mainly on proteids.

Cellulose is altogether unattacked 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,^ and even shavings and paper mixed with hay
and given to sheep only partially reappear in the fteces. Experiments
on man show that, according to the condition and form of the cellulose,
amounts varying from 4 to 60 per cent, are digested.^

Of the manner in which this cellulose is broken up or dissolved we
know nothing with certainty. Bunge ^ supposes that the epithelial cells

^ Wortman, Ztsclir. f. 2}hysiol. Chem., Strassburg, 1882, Bd. vi. S. 293 ; Lander Brunton
and Macfadyen, Froc. Roy. Hoc. London, 1889, vol. xlvi. p. 542.

- Arch. f. exjycr. Path. u. Pharmakol., Leipzig, 1891, Bd. xxviii. S. 311. Reprinted in
Jonrn. Ancct. and Physiol., London, 1891, vol. xxv. p. 390.

^ Haubner, Ztschr. f. Landwirthschaft, 1885, S. 177.

■" Weiske, Ztschr. f. Biol., Mlinchen, 1870, Bd. vi. S. 456 ; v. Kiiioriem, ihid., 1885,
Bd. xxi. S. 67.

" " Lehrbuch del' i)liysiol. u. path. Oheni.," 1894, S. 174.



A CriON OF INTESTINAL BA CTERIA ON FA TS. 4 7 1

of the intestine possess the function, by means of a ferment, of dissolving
the cellulose ; this may be so, but no such ferment has ever been shown
to exist. Bunge supports his suggestion by analogy with the action
of some unicellular organisms on cellulose.^

Exposed to the action of certain organisms, cellulose undergoes
fermentation with the setting free of marsh gas (CH4), and the forma-
tion of acetic and butyric acids ; how much of the altered cellulose goes
in this way in the digestive process is unknown. Tappeiner^ tested
the action of the intestinal bacilli on cotton-wool, by soaking this in a
1 per cent, solution of bouillon and inoculating with the bacilli. Fer-
mentation with development of gas commenced, and there were formed
in the solution free fatty acids (up to and including valerianic acid),
while the cotton-wool nearly all dissolved. The gases set free were
marsh gas and carbon-dioxide. The nature of the products varies with
the organism acting on the cellulose ; thus Hoppe-Seyler ^ obtained the
same gases accompanied by a dextrin-like substance, by the action of
pond bacteria on cellulose in the form of filter paper, but did not observe
the formation of any fatty acids.

Experiments on the artificial digestion of cellulose in the form of
new hay were made by Hofmeister,* who showed that the intestinal
juices of the horse were capable of dissolving nearly 80 per cent, of this
material. No formation of sugar but some fermentation and develop-
ment of gas were observed.

The most important uses of cellulose lie, however, not in its value
as a nutrient foodstuff, but in giving bulk and looseness to the food and
in mechanically inducing peristalsis by irritation of the intestine.^ For
this reason cellulose becomes an absolute necessity for animals with a
long intestine, such as the herbivora. Eabbits fed on food free from
cellulose rapidly die from intestinal inflammation ; but if the same food
be mixed with such an inert substance as horn shavings, nutrition goes
on quite normally, and the animals continue in perfect health, although
the horn shavings remain entirely unaltered.^ The carnivora with their
short intestine require no such aid to peristalsis ; but in animals in an
intermediate position, such as man, bulky or cellulose-containing food,
while not indispensable, is from a dietetic point of view exceedingly
desirable.

Action of the intestinal bacteria on fats.— Under a normal con-
dition of the intestine, it is probable that very little decomposition of
the fats by bacteria takes place, but under abnormal conditions, such
as the absence of the bile or pancreatic juice, they are almost completely
decomposed into fatty acids, which pass out unabsorbed along with the
faeces. The first action of bacteria on fats consists in setting free the
corresponding fatty acids ; these are afterwards partially broken down
into mixtures of fatty acids lower in the series.'^

Lecithins undergo a similar decomposition by bacteria under anix'-
robic conditions ; they at first are split up into glycerophosphoric acid,
fatty acids, and choline. Afterwards, the choline is decomposed with

^ E.g., Vampyrella ; Cienkowski, Arch. f. mikr. Anat., Bonn, 1865, Bd. i. S. 203.

2 Ztschr.f. Biol., Mttnchen, 1884, Bd. xx. S. 52 ; ibid., 1888, Bd. xxiv. S. 105.

^ Ztschr. f. physiol. Chcm., Strassburg, 1886, Bd. x. S. 401.

■* Arch.f. wiBsensch. u. prakt. Thierh., Berlin, 1885, Bd. xi. S. 46.

^ Bunge, "Physiological and Pathological Cliomistry," 1894, p. 75.

''v. Knieriem, Ztschr.f. Biol., MUnchen, 1885, Bd. xxi. S. 67.

^ Groger, Ztschr.f. ang. Chem., Berlin, 1889, S. 62.



4 7 2 CHEMISTR Y OF THE DIGESTIVE PR O CESSES.

formation of carbon-dioxide, methane, and ammonia ; but if air is present,
neurin and mnscarin are also formed in the process.^



COMPOSITION^ OF F^CES.

Amount and consistency. — The consistency of the contents of the
small intestine in the upper two-thirds to three-fourths of its length
is fairly uniform, the amount of water absorbed in this part being
approximately balanced by that added in the digestive fluids. But
in the lower part of the small intestine the amount of water absorbed
begms to exceed that secreted ; the intestinal contents become
thicker, and the thin fluid, with lumps of solid, undigested, or
partially digested food of various kinds floating in it, which is usually
found in the higher part of the intestine, is replaced by a pasty
or senu-soHd mass. As this mass passes along the large intestine the
process of absorption continues with increased intensity, and a large
amount of water, together with anything it holds in solution of service
to the economy, is removed. The residue, a complex mixture of various
useless or unused material, usually acquires the consistency of a soft
sohd before the completion of the process, and is finally ejected from the
rectum. The consistency of the faeces, as well as the amount excreted



Online LibraryE. A. (Edward Albert) Sharpey-SchäferText-book of physiology; (Volume v.1) → online text (page 67 of 147)