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p. 194 ; Internat. Monatschr. f. Anat. u. Hisiol., Leipzig, 1885, Bd. ii. S. 6 ; Arch. f. d.
yes. Physiol., Bonn, 1884, Bd. xxxiii. S. 513. Schiifer's observations were chiefly made
upon the frog and rat.

^ JUd., Bd. xxxiii. S. 532.

^ InLernaL. Monatschr. f. Anat. n. Ilistol., Leipzig, 1885, Bd. ii. S. 6.

■1 Archf. d. f/es. Physiol., Bonn, 1888, Bd. xUii. Sup]). Heft, S. 82.

'' It should, however, be pointed out, that after prolonged treatment with osmic acid,
fats tend to become insoluble in these fluids.

'' Arch./, d. rjcs. Physiol., Bonn, 1888, Bd. xliii., Supp. Heft, S. 103, figs. 39 and 40, plate iv.

''Ibid., S. 88.



A B SORPTION OF FA TS. 4 5 9

offers no explanation of tlie mode in whicli tlie fat granules get into
the epithelial cells; he considers that the hile must essentially assist
in the process, partially by aiding the ennilsification of the fats, and
partially by making the surface of the epithelium capable of being
wetted by the fats, which naturally facilitates the absorption. He
is further of opinion that the fat globules are passed on out of
the columnar epithelial cells by means of the contractions of the
cell protoplasm ; and that these on their further path to the lacteal,
apart from the small part eaten up by the leucocytes, pass in a
free condition through the intercellular spaces, and are first broken up
into the very fine granules characteristic of chyle when passing into
the lacteal.

The effects of absence of the pancreatic juice or bile on the
absorption of fats. — The results on record as to the absorption of fat,
when the action of the pancreatic juice is removed by excision of the
pancreas, ligature of the pancreatic ducts, or establishment of a pan-
creatic fistula, vary considerably ; although there is a concurrence of
opinion amongst recent observers ^ that the absorption of fat is
hindered to a greater or lesser extent by the absence of the secretion.
Minkowski ^ and Abelmann ^ found that no fat, except that of milk, was
absorbed after complete removal of the pancreas, and this was only
absorbed to the extent of 28 to 53 per cent. ; the failure of absorption
was not due to absence of fatty acids, for 80 per cent, of the ether
extract of the faeces was found to be free fatty acid.

Minkowski believes that the absorption of the milli fat is due to this emul-
sion being able to withstand an acid reaction, but the absorption of other fats,
when pancreas is given with the fat, points rather to some specitic function
of the pancreatic juice, for this pancreatic tissue could not materiahy aUer the
reaction of the intestine ; besides, fat absorption takes place normahy from
the dog's intestine in presence of an acid reaction. Sandmeyer'^ found in
dogs in which the pancreas had been partiahy extirpated, that the amount of
fat absorption was very variable ; occasionally no fat at all was absorbed,
and at other times, Avith the same animal, 30 and even 78 per cent, of the fat
was absorbed.

Teichmann -^ found by microscopic examination that fat absorption in the
rabbit was not influenced to any marked extent by hgature of the pancreatic
duct. Fr. Midler ^ observed a considerable amount of fat absorption in a patient
with a pancreatic fistula. Yaughan Harley " extirpated the pancreas completely
in dogs, killed the animals a varying number of hours after feeding on milk,

1 On the other hand, Cohu {Bull. Acad, de med., Paris, 1856) found that the absorp-
tion of fat was not affected when the pancreatic juice was allowed to escape from a fistula.
Cash {Arch./. Anat. u. Physiol., Leipzig, 1880, S. 3'23) ligatured both pancreatic ducts in the
dog, and found that fat was still absorbed. Schitf (Jahresb. u. d. Fortschr. d. Thier-
Chem., Wiesbaden, 1872, Bd. ii. S. 222) shut out the pancreatic secretion by injecting
paraffin into the duct, and found that fat to the amount of 120 to 150 grms. per diem was
still absorbed.

- Von Mering and Minkowski, Arch. f. exper. Path. u. Phannakol., Leipzig, 1890, Bd.
xxvi. S. 371.

3 Inaug. Diss., Dorpat, 1890 ; Minkowski, Berl. Idin. JVchnschr., 1890, S. 333.

* Ztschr.f. Biol., Mlinchen, 1895, Bd. xxxi. S. 12. See also Rosenberg, Arch. f. Anat.
u. Physiol., Leipzig, 1896, Physiol. Abth., S. 535.

s " Mikroskop. Beitr. z. Lehre von der Fettresorption," Diss., Breslau, 1891.

•^ Ztschr. f. Idin. Med., Berlin, 1887, Bd. xii. S. 45. Defective fat absorption, however,
undoubtedly accompanies disease of the pancreas, or occlusion of its duct in most cases ; see
Bright, Med.-Chir. IVaois., London, 1832 ; Ziehl, Deutsche med. JVchnschr., Leipzig, 1883,
S. 538 ; le Nobel, Deutschcs Arch. f. Min. Med., Leipzig, 1888, Bd. xliii. S. 285.

"^ Journ. I-'hysiol., Cambridge and London, 1895, vol. xviii. p. 1.



46o CHEMISTRY OF THE DIGESTIVE PROCESSES.

and estimated the amount of fatty material in the stomach and intestine. The
amount so found was usually slightly in excess of that given in the food, the
surplus being probably due to intestinal secretion or excretion. Lewin,^ as a
result of microscopic examination of sections of the intestine, concludes that fat
absorption does not take place in a normal manner if bile or pancreatic juice, or
both, are kept from entering the intestine. He also found under such circum-
stances that the lacteals did not present the usual milky appearance which
accompanies fat absorption.

The effect of a biliary fistula on fat absorption seems to be identical
with that of a pancreatic fistula ; exactly the same kinds of results have
been recorded in the two cases. All observers are agreed that so much
fat cannot be absorbed in presence of a biliary fistula as when bile has
access to the intestine, but, while some find fat absorption practically
arrested, others have observed that a considerable, nearly normal, amount
of fat can still be disposed of. As in the case of absence of the pan-
creatic secretion, most of the unabsorbed fat is found in the ffeces as
fatty acid.^

Eohmann ^ also found that sodium soaps were not absorbed, but were
converted into free fatty acids, and appeared as such in the faeces. Bidder
and Schmidt ^ state that normal dogs can digest as much as seven times the
quantity of fat which can be disposed of by dogs with listula of the gall bladder,
and that, Avhile during fat absorption in a normal dog the lacteals are filled with
milky chyle, they are, under similar conditions in a dog with a biliary fistula,
filled Avith a yellow or slightly opalescent fluid.

C. Voit^ estimates the average loss of fat at 22*2 to 34-7 per cent.; Munk,^
at 33-1 per cent. ; Eohmann,'^ at 48-5 to 58"4 per cent. ; l^Toel Paton,^ at 34'58
per cent. ; Dastre,^ at 57"65 per cent. Munk^** found that the absorption of fats
of high melting point (mutton) suff'ered more than that of fats of low melting
point (hog's lard) \ of the former but 35*5 per cent, was utilised, of the latter
67 per cent. He also found that the free fatty acids in the absence of bile were
absorbed equally well, in fact slightly better, than the corresponding neutral
fats. Dastre ^^ ligatured the ductus dioledoclius, and made a fistula between
the gall bladder and small intestine much lower down (60-150 cm.) ; he
observed, after a meal of fat, that the lacteals were only injected with milky
chyle below the artificial point of entry of the bile. As Dastre himself
remarks, the result is more elegant than decisive. It is only qualitative in
character, and does not show quantitatively the share taken by pancreatic
juice and bile in fat absorption. Hedon and Yille ^- established first a biliary
fistula, and afterwards removed nearly all the pancreas, leaving just enough of
the tail to preserve the animal alive, and destroying all communication with
the intestine. In this manner both bile and pancreatic juice were kept out of the
intestine, and under such conditions the digestion and absorption of fat was

^ Arch. f. d. ges. Physiol., Bonn, 1896, Bd. Ixiii. S. 171. Lewin removed the influence of
both secretions Ijy making a Thiry-Yella fistula of that part of the duodenum into which
the ducts open.

- Rohmann, Arch. f. d. ges. Physiol., Bonn, 1882, Bd. xxix. S. 509 ; I. Munk, Virchoio's
Archiv, 1890, Bd. cxxii. S. 313 ; Hedon and Yille,' Coonpt. rend. Soc.'de bloL, Paris, 1892,
tonie xliv. p. 309. See, however, Dastre, Arch, de phijsiol. norm, ct path., Paris, 1891,
tome xxiii. p. 186.

^ Loc. cit., S. .532. •* '•• Die Verdauungssafte," etc.

5 "Beitr. -/.. Biologic," Juhilaumsschr'ift f. v. Bischoff, Stuttgart, 1882.

" Virchow's Archiv, 1890, Bd. cxxii. S. 302. "^ Loc. cit.

^ Pi,ep. Lab. Roy. Coll. P'hys., Edin., 1891, vol. iii. p. 214. The case was one of a coni-
lilete biliary fistula in a woman.

8 Loc. cit. w Loc. cit., S. 324, 325. ^^ Loc. cit. i- Loc. cit.



A B SORPTION OF FA TS. 46 1

studied. It was found that food passed very rapidly through the alimentary
canal without much modilication, scarcely any fat was absorbed, but it was
nearly all converted into fatty acid.

These varied results may be summed up as showing that both the
pancreatic juice and the bile are powerful aids in the digestion and
absorption of fats, but neither is absolutely indispensable.

The view to be taken of the part played by bile and pancreatic juice
in fat absorption must naturally vary with the view held as to the form
in which fat is absorbed.

1. It may be urged that, in the absence of pancreatic juice, a sufficient
supply of fatty acid is not set free for emulsification of the remainder.
Since bile (or bile salts) very much hastens the fat-splitting action of
pancreatic juice,^ the absence of bile would have a very similar effect to
that of pancreatic juice itself. A serious objection to this explanation
lies in the fact that in defective absorption, due to the absence of either
bile or pancreatic juice, nearly all the unabsorbed fat is found in the
fseces as free fatty acid.

It might be claimed that this fat-splitting, probably by bacterial
action, takes place much lower down in the intestine, at a less favourable
position for absorption, and that a considerable part of the intestine is
traversed before a sufficient amount of fatty acid is formed. But in the
fgeces as much as 80 per cent, of the total fat is as free fatty acid, while
only about 5 per cent, is required for spontaneous emulsion ; besides, the
fat of the food contains nearly sufficient fatty acid to begin with, so that
this contention has little weight.

2. Another view which has been held is, that in the absence of either
bile or pancreatic juice the intestinal reaction is acid, so that no emul-
sion can take place, and hence the fat cannot be absorbed. It is not,
however, claimed that such an acid reaction is due to free hydrochloric
acid, since the remaining alkaline secretions are still more than sufficient
to neutralise this, and active fat absorption has often been observed in
presence of an acid reaction due to organic acids.

3. It has been supposed that the absence of the proteid of the
pancreatic juice has an unfavourable effect on the formation of an
emulsion (Minkowski).

4. A theory advanced by v. Wistinghausen ^ was that the bile aided
fat absorption by mechanically wetting the epithelial cells with a fluid
which rendered the passage of the fat easier. He claimed that oil
stood higher in capillary tubes wetted with bile than in similar tubes
wetted with water, and that oils or melted fats passed more rapidly
through a membrane wetted with bile than through one wetted
with water. These results have not, however, been confirmed by other
observers.^

5. It has also been supposed that the bile directly stimulates
(chemically) the epithelial cells of the intestine to increased fat absorp-
tion, and that in the absence of the bile this stimulus is absent. Under
these conditions the epithelial cells either do not absorb fat as an emul-

^ Racliford, Journ. Physiol., Cambridge and London, 1891, vol. xii. p. 87.

-Translation in Arch. f. Anat. to. Physiol., Leipzig, 1873, S. 137, by J. Steiner. See
also Schiff, Untersuch. z. Naturl. d. Mensch. u. d. Thiere, 1857, Bd. ii. S. 345 ; Heiden-
hain, Arch. f. d. ges. Physiol., Bonn, 1888, Bd. xliii. Supp. Heft, S. 91.

^ Groper, Arch. f. Anat. u. Physiol., Leipzig, 1889, S. 505.



462 CHE MIS TR Y OF THE DIGESTIVE FRO CESSES.

sion at all, or only absorb it at a greatly diminished rate."^ There is no
experimental evidence in support of this theory, and a great objection to
it is that bile is constantly present in the intestine, and is not poured
out in association with the presence of fat ; such are not the proper
conditions for a stimulus, which ought, if it is to be effective, to be inter-
mittent, and only be called into action when required.

6. All the previous views rest on the assumption that the fats are
absorbed in the form of an emulsion. If, on the other hand, the fats are
absorbed in soluble forms as fatty acids or soaps and glycerin, the most
obvious explanation of the action of bile and pancreatic juice in assisting
absorption is, that these secretions increase the solubility of the fatty
acids or soaps.

In the absence of bile or pancreatic juice, the fatty acids are not so
soluble in the intestinal fluid, and so the absorption is defective, and the
insoluble fatty acids appear in the fteces. In support of this the fact
may be recalled that the bile salts possess the power of dissolving the
insoluble soaps of the alkaline earths.^

Channels of absorption of the fats. — There is no doubt that the
lacteals are the main channel by which the fats are carried away from
the intestine, but it is by no means so clear that all the fat goes by this
route. The amount of fat absorbed from the intestine after a fatty meal
can easily be determined by weighing the amount of fat ingested, and that
remaining in the alimentary canal when digestion is nearly complete, and
taking the difference, which must be the amount absorbed. The amount
of fat poured into the blood by the thoracic duct during the same period
can also be determined, by inserting a cannula into the duct and collecting
the chyle, from which the fat is afterwards extracted and then weighed.
The amount thus carried by the thoracic duct during the period of active
absorption is always much less than the total quantity absorbed ; it has
never been found to amount to more than 60 per cent., and is usually
much less than this.^ The fate of the balance of the fat is unknown ; the
first suggestion occurring to the mind, that it travels by the alternate
path of the portal circulation, has not been found to fit the experimental
facts. The portal vein during fat digestion does indeed contain an
abnormal amount of finely emulsified fat, but so does all the blood of the
body, and the presence of the fat is due to the admixture with the blood
of the chyle carried by the thoracic duct. On diverting from the blood
this supply of fat, by means of a cannula inserted into the thoracic duct,
Zawilski found scarcely any fat in the blood during fat absorption.
Neither is there any difference during fat absorption in the percentages
of fat present in portal and carotid blood.* It would seem from this
that almost all the fat is carried by the lacteals, but that part is
removed somewhere in the lymphatic system between the lacteals and
the opening of the thoracic duct ; it may be in the lymphatic glands,^
but the subject requires further investigation.

1 Rolimann, Arch. f. d. ges. Physiol. , Bonn, Bd. xxix. S. 509 ; Minkowski, Berl. med.
Wchnschr., 1890, No.'l.5, S. 333; Lewiu, Arch. f. d. ges. Physiol., Bonn, 1896, Bd. Ixiii.
S. 186.

2 See p. 392.

^ Zawilski, Arh. a. d. physiol. Anst. zu Leipzig, 1867, Bd. xi. S. 147 ; "Walther, Arch,
f. Anat. u. Physiol., Leipzig, 1890, S. 329; Frank, ibid., 1892, S. 497 ; Munk u. Rosen-
stein, Virchoiv's Archiv, Bd. cxxiii. S. 484.

■' Heidenhain, Arch. f. d. ges. Physiol., Bonn, 1888, Bd. xliii., Supp. Heft, S. 95.

^ See M. Foster, "Text-book of Physiology," pt. ii. j). 513.



BACTERIAL DIGESTION. 463

After a full meal of fat, absorption, in the case of the dog, goes on
for about thirty hours. At the height of absorption, the chyle in the
thoracic duct may contain as much as 15 per cent, of fat. Twenty-one
hours after a meal of 150 grms. of fat, Zawilski ^ still found in the stomach
9-74 gmis., in the intestine 6 '24 grms. ; in thirty hours all but traces
have disappeared from both stomach and intestine. Throughout this
period of digestion, according to the same observer, the amount of fat in
the intestine at any time remains practically constant (6"24 to 9'9 grms.),
from which it would seem that the rate at which the fat is allowed to
pass the pylorus is regulated by the amount of fat already present in the
intestine.

None of the soap which may be formed during fat digestion and
absorption probably ever enters the general circulation as such, but is
reconverted into neutral fat beforehand; as Munk^ has shown, soaps
of the alkalies intravenously injected produce poisonous effects, closely
resembling those obtained on injection of albumoses.

As might be expected from their similar chemical constitution, the
lecithins are decomposed in the same manner as the fats by the steapsin
of the pancreatic juice, the products of the reaction being glycero-
phosphoric acid, neurin, and fatty acids. These products are probably
absorbed, as is shown by their absence in the faeces after the administra-
tion of lecithin by the mouth ; as well as by the increase of phosphates
in the urine after feeding on foods, such as yolk of egg, rich in lecithin.^



BACTERIAL DIGESTION.

The food in the alimentary canal is acted upon, not only by the
digestive secretions and their enzymes, but to a greater or less extent by
certain bacteria which are never entirely absent, although the amount of
their action varies greatly, under healthy conditions, with the nature of the
food and the class of animal. Under abnormal conditions the growth of
these organisms may be greatly increased, and nutrition be seriously
impaired, by their turning to their own uses the products of normal
digestion, and leaving only for the service of the animal, degradation-
products, inadequate or wholly unsuited for the purposes of its meta-
bohsm. Along with this increased growth of the bacteria normally
present in the stomach, conditions may become so changed as to favour
the growth of other bacteria, often pathogenic in character, which find
under normal conditions no favourable soil for their growth in the
intestinal contents, and thus various forms of disease may be introduced.
We have here, however, only to deal with the changes induced by
bacteria under a normal condition of the alimentary canal.

In dealing with the function of the free hydrochloric acid of the
gastric juice, it has already been stated that this completely stops all
bacterial action,* so that it is only in the first stage of gastric secretion,
before the acidity has become marked, that any bacterial changes can occur.

Proteids are not attacked during this first short stage (twenty to
forty minutes) of gastric digestion, but carbohydrates undergo to a

1 hoc. cit. " Arch. f. Anat. u. Physiol., Leipzig, 1890, Snpp. Bd., S. 116.

"A. Bokay, Ztschr. f. physiol. Ohem., Strassbnrg, 1877, Bd. i. S. 157; see also Hase-
broek, ibid., 1888, Bd. xii. S. 148.
" See p. 364.



464 CHEMISTR Y OF THE DIGESTIVE PROCESSES.

slight extent lactic fermentation.^ A certain amount of decomposition
of neutral fats also occurs during gastric digestion, yielding fatty acids,
but it is not certainly known whether this is due to bacterial action or
not.^

Intestinal bacterial digestion — Reaction of the intestine. — There
is considerable difference of opinion l:)oth as to the amount of decom-
position of foodstuffs due to bacterial action which goes on in the
intestine, and as to the importance of such a decomposition as a normal
factor in digestion.

The extent of bacterial action can evidently be more accurately
gauged by the amount of bacterial decomposition products formed than
by the presence in the intestine of bacteria, which may not there be in
a very active condition.

Judged by this standard, the amount of proteid decomposition due
to bacteria which takes place in the small intestine is excessively small,
while a considerable amount takes place in the csecum and large intes-
tine generally. When carbohydrates and proteids are present in the
same solution along with various bacteria capable of attacking them,
the carbohydrates are first attacked, the action being accompanied by
the formation of certain organic acids ; at a later stage the proteids are
attacked and decomposed. This has been shown by Maly,^ who took
mucous membrane of the stomach, placed it in a solution of cane-sugar,
and kept the mixture at body temperature for several days. The lactic
acid formed by the decomposition of the sugar was neutralised from
time to time, and it was found that the process continued without a
trace of putrefaction appearing, until all the sugar had been converted
into lactate ; then first appeared, often somewhat suddenly, an intense
putrefactive odour, and the proteids began to be decomposed.

It is probable from this that, in the body, bacterial action on carbo-
hydrates precedes that on proteids ; and it has been supposed by some
that such an action commences with considerable intensity in the
duodenum, and persists throughout the entire length of the small
intestine, so involving bacterial decomposition of a large share of the
carbohydrate food.

This opinion rests chiefly on the observation that the acid reaction
of the chyme in the stomach, due to hydrochloric acid, becomes replaced
by an acid reaction, due to organic acids, in the small intestine. These
organic acids are supposed to be set free by the action of certain bacteria,
found in the small intestine, upon the carbohydrate food.

Sucli a result has been obtained by Macfadyen, Kencki, and Sieber,* from
observations made on a case of anus prceternaturalis in man, in which the
fistula occurred quite at the lower end of the ileum. The intestinal contents
arising from a mixed diet, consisting principally of animal food, had as they
flowed from the fistula an acid reaction, equivalent to that of a solution of
1 per mille of acetic acid ; this reaction was principally due to acetic acid,

^ In this process hydrogen gas is set free along with lactic and traces of other acids ;
under abnormal conditions the amount of gas may be greatly increased. See E. Wissel,
Ztschr. f.jjhysiol. Chem., Strassburg, 1895, Bd. xxi. S. 234, where the literature of this
subject up to that date is given.

- Marcet, Proc. Eoy. Soc. London, 1858, vol. ix. p. 306 ; Cash, Arch. f. Anat. u.
Physiol., Leipzig, 1880, S. 323.

3 Hermann's "Handbuch," Bd. v. (2), S. 239.

^ Arch./, exper. Path. u. Pharmahol., Leipzig, 1891, Bd. xxviii. S. 311, reprinted in Jouroi.
Anat. and Physiol., London, 1891, vol. xxv. p. 390. See also C. A. Ewald, FirchoivsArchiv,
1879, Bd. Ixxv. S. 409 ; and Jakowski, Arch. d. sc. MoL, St. Pc^tersbourg, 1892, tome i. p. 539.



A CTION OF INTESTINA L BA CTERIA ON PR O TEWS. 465

accompanied by traces of fermentation and paralactic acid, volatile fatty acids,
succinic acid, and bile acids. Hydrochloric acid was not present. The
mixture had very little odour ; occasionally the slight odour it had was faintly
putrefactive, resembling indol, but usually it was more like that of volatile
fatty acids. These authors state that it is the organic acids present in the
small intestine which limit the bacterial decomposition of carbohydrates, and
prevent the jDutrefaction of proteids.

On the other hand, Moore and Rockwood ^ state that the reaction of the
intestine in various classes of animals (dog, cat, white rat, guinea-pig, and
rabbit) is not normally acid throughout its entire length, and that the
alkalinity increases in passing down the intestine.

The presence of fat in the food causes in carnivora an acid reaction, which
persists until the lower third of the intestine is reached. This acid reaction is
due to very weak organic acid, most probably to the acids of the fats dissolved
by the agency of the bile.^ The alkalinity is much greater in herbivora than
in carnivora, although herbivora consume much more carbohydrate food than
carnivora. Also, in carnivora, the alkalinity is markedly increased by carbo-
hydrate food ; this would not be the case if any considerable bacterial
decomposition of carbohydrates took place in the small intestine, but the
alkalinity would diminish from increased formation of organic acids. It is



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