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sugar ingested appears in the urine (alimentary glycosuria).^ This is
apparently due to the fact that the blood vessels of the intestine cannot
carry away all the absorbed sugar with sufficient rapidity to the liver,
and some of it consequently passes to the general circulation by way of
the thoracic duct,"^ and thus to the kidneys, which always immediately
ehminate any excess of sugar in the blood passing through them.
Glycosuria also occurs when sugar solutions are injected into the large
intestine of dogs.^

Cellulose is not readily digested by carnivora nor by man, but in
some forms of food (carrots, cabbage, celery, lettuce) a considerable
proportion of the cellulose present may become dissolved and absorbed ; ^
in herbivora ib undergoes digestion, and is eventually absorbed as
dextrose. Its chief value in the diet of animals seems, however, to
be due to its action in promoting peristalsis of the intestines. Eabbits
die from inflammation of the intestines if devoid of cellulose ; its place can
be supplied in them by horn-shavings, which have the same mechanical
effect. In carnivora and man this is not so important, as the gut is
shorter, but probably the cellulose of mixed fdod tends to prevent
constipation. A purely milk diet is well known to be constipating
(Bunge).

The fate of the carbohydrates after assimilation will be treated of in
a special section on carbohydrate metabohsm.

Fats are taken in largely in the form of animal fat (fats of flesh and
milk), but also largely, especially in some countries, in the form of
vegetable fats, such as olive oil and the fats met with in certain seeds.
In the last-named form they are protected by cellulose, and are far less
easily digested and assimilated. The changes which they undergo in
the processes of digestion and absorption have already been fully con-
sidered (pp. 443-463), also their caloric value, and their importance as
proteid-sparers. Their assimilation to the natural fat of the body, and
their formation within the body, will be treated of subsequently.

Fatty acids and soaps have been shown by I. Munk (in dogs) to
have very nearly the same nutritive value as the fats from which they

1 V. Harley, Arch. f. Physiol., Leipzig, 1893, Suppl., S. 46.

- Hofmeister, Arch. f. exjiar. Path. u. Pharrnakol., Leipzig, 1889, Bd. xxv. S. 240 ; and
1890, Bd. xxvi. S. 355.

2 Worm -Mull er, Arch. f. d. ges. Physiol., Bonn, 1884, Bd. xxxiv. S. 576; Hofmeister,
Arch. f. cxiKr. Path. u. Pharrnakol., Leipzig, 1889, Bd. xxv. S. 240 ; C. Voit, Ztschr.f. Biol.,
Munchen, 1892, Bd. xxviii. S. 265 ; Miura, ibid., 1896, Bd. xxxii. S. 281.

■* Ginsberg, Arch./, d. ges. PMjsiol., Bonn, 1889, Bd. xliv. S. 306.
5 Eichliorst, ibid., 1871, Bd. iv. S. 601.

" Weiske, Ztschr. f. Biol, Miinchen, 1870, Bd. vi. S. 456 ; Knierem, ibid., 1885, Bd,
xxi. S. 67. See also Luntz, Arch. f. d. ges. Physiol., Bonn, 1891, Bd. xlix. S. 477.

VOL. I. — 56



882



METABOLISM.



are formed. This has, however, been abeady discussed (p. 750), and
will be again referred to later on.

Glycerin has been found to act in some measure as a fat and
carbohydrate-sparer, but not as a proteid-sparer.^ Of the total
amount ingested, from 21 to 37 per cent, is secreted in the urine
unaltered, when given in large doses.^ The sparing effect of glycerin
on the conversion of liver glycogen into sugar will be subsequently
referred to.

Alcohol. — The nutritive value of alcohol has been the subject of
considerable discussion, and not a few experiments. Some of these
tend to show that in moderate non-poisonous doses it acts as a non-
proteid food in diminishing the oxidation of proteid, doubtless by
becoming itself oxidised.^ Its action, however, in this respect is
relatively small, and indeed a certain proportion of alcohol ingested
is exhaled with the air of respiration. Moreover, in large doses, it
may act in the contrary manner, increasing the waste of tissue proteid.*
It cannot, in fact, be doubted that any small production of energy
resulting from its oxidation is more than counterbalanced by its
deleterious influences as a drug upon the tissue elements, and especially
upon those of the nervous system.

It is of interest, in connection with this subject, to point out that
alcohol has been regarded by some physiologists as probably formed
at a stage in the metabolism of carbohydrates prior to their complete
oxidation, traces of alcohol having been obtained from fresh tissues by
distillation with water. ^

Inorganic substances. — ^Mineral salts, especially chloride of sodium
and phosphates of lime and of the alkalies, are essential parts of
any diet. The following table from Bunge gives the proportions





K„0.


Na„0.


CaO.


MgO.


Fe.O-.


P2O5.


CI.


Beef


1-66


0-32


0-029


0-15


0-02


1-83


0-28


Wheat ....


0-62


06


0-065


0-24


0-026


0-94


?


Potato ....


2-28


0-11


0-100


0-19


0-042


0-64


0-13


White of egg


1-44


1-45


0-130


0-13


0-026


0-20


1-32


Peas .....


1-13


0-03


0-137


0-22


0-024


0-99


?


Human milk


0-58


0-17


0-243


0-05


0-003


0-35


0-32


Yolk of egg


0-27


0-17


0-380


0-06


0-040


1-90


0-35


Cow's milk


1-67


1-05


1-51


0-20


0-003


1-86


1-60



1 I. Munk, Virchow's Arcliir, Bd. Ixxvi. S. 119 ; Bd. Ixxx. S. 39.

2 Tschirwinsky, Ztschr. f. Biol., Munchen, 1880, Bd. xv. ; Arnschink, ibid., 1888, Bd.
xxiii. S. 413.

^Strassmann, Arch. f. d. ges. Physiol., Bonn, 1891, Bd. xlix. S. 315. Chittenden
[Journ. Phydol., Cambridge and London, 1892, vol. xii. p. 220), ex2:)erimenting upon
dogs, obtained very little influence on proteid metabolism. For the earlier literature
of this question, of. C. Voit, op. cit., pp. 169 and 415.

■' Miura, Ztschr. f. klin. Med., Berlin, 1892, Bd. xx. S. 137. I. Munk obtained similar
results upon dogs [Verhandl. d. Physiol. Gesellsch., 1878-79, No. 6 in Arch. f. Physiol.).

^ Hoppe-Seyler and Rajewsky, Arch. f. d. ges. Physiol., Bonn, 1875, Bd. xi. S.



INORGANIC SUBSTANCES. 883

per cent, in which the different salts of the ash occur in dried food-
stuffs.^

Animals from whose food the salts have been extracted, some-
times die even more rapidly than animals which have been altogether
deprived of food, with the supervention of various symptoms indicating
a disturbance of the central nervous system and of the digestive system.^
This more rapid end of such animals is due, according to Bunge,^
to chronic acid-poisoning, produced by the oxidation of the sulphur
of the proteids ; such acid being normally neutralised by the basic salts
(phosphates, carbonates, and alkali-albuminates) taken in with the food,
whereas in the absence of these, basic substances are removed from the
tissues to take their place. The experiments of Lunin (in Bunge's
laboratory) upon mice fed respectively upon salt-free food, or upon the
same food to which sufficient sodium carbonate was added to exactly
neutralise the sulphuric acid which would be formed in the oxidation
of the proteid of the food, seem to show that Bunge's conjecture is
correct ; for such animals lived considerably longer than those to which
no soda was given, or than those to which it was given combined with
chlorine.^ This, however, is probably not the whole explanation, for in
both the dog and man the faculty of resisting the effects of acids in the
ingesta depends in part, at least, on their neutralisation by ammonia,
which is derived from metabolised proteid.^

It would appear that some at least of the mineral matters of the
food must be in their natural condition, which is probably that
of combination with the proteid substances. For Lunin found that
although mice will live indefinitely on desiccated milk, yet if they
are given an artificial food consisting of a mixture of salt-freed casein and
lactose, to which have been added the same inorganic salts which are
present in the original milk, the animals will die at about the same period
as if sodium carbonate alone had been added to the casein and sugar.*^

As Bunge has pointed out, the addition of chloride of sodium to the
ordinary food appears to be essential to the well-being of all animals
the food of which contains a large proportion of potassium salts, as
occurs in most vegetables. In conformity with this, we find that those
races of mankind which subsist mainly on vegetable food find salt an
absolute necessity of life ; and that the same is the case with herbivorous
animals is shown by the fact that these are often found to travel
hundreds of miles to reach a place where salt is to be found (salt-licks).
Carnivorous animals, on the other hand, and those herbivora which
consume plants and herbage which do not contain a great excess of
potassium salts, show no such inclination to seek salt. The same is true
for those races of mankind who live almost exclusively on fish or flesh,

1 Note especially the small amount of Na20 in wheat and peas ; the large amount of
CaO in milk and egg yolk, and the very small amount of iron in milk. On the other
hand, the ash of the fcctus contains a very large proportionate amount of iron.

^Forster, Ztschr. f. Biol, Mlinchen, 1873, Bd. ix. S. 297.

^ Ztschr.f. ^io/.,' Mlinchen, 1874, Bd. x. S. 130. See also "Lectures," pp. 114-118.

^Ztschr. f. physiol. Ghem., Strassburg, 1881, Bd. v. S. 31. See also Socin, ibid., 1891,
Bd. XV. S. ioO.

^ Schmiedeberg and Walter, Arch. f. exper. Path. u. Pharmakol., Leipzig, Bd. vii.
S. 148 ; Hallervorden and Coranda, ibid., Bd. xii. S. 76.

^ Somewhat similar conclusions were arrived at by Bunge and Socin from experiments
upon another artificial food, which had been first deprived of salts, but to which tliese
were afterwards added. This food, although apparently containing all needful materials
for nutrition, was unable to keep the mice which were fed upon it alive.



884 METABOLISM.

or on such vegetable food, e.g. rice, in which the potassium salts are
only present in small quantity. It is further noteworthy that the
peoples who live on an animal diet, without salt, carefully avoid a loss
of blood when they slaughter the animals, for the blood contains a far
larger amount of sodium in proportion to potassium than any other tissue
or organ. The explanation of these facts is thus offered by Bunge ^ : —

" The amount of salt "vvhich herbivorous animals take in with their food is,
compared with the weight of the body, generally not much less than that
consumed by carnivorous animals. On the other hand, there is a considerable
difference in another constituent of the ash of their food, in the potassium.
Herbivorous animals take at least three or four times as much of salts of
potassium as the carnivora. This fact leads me to imagine that the abundance
of potassium in vegetable food is the cause of the need for salt in the
herbivora. If, for instance, a salt of potassium, such as potassium carbonate,
meets with common salt or chloride of sodium in solution, a partial exchange
takes place — chloride of potassium and carbonate of sodium are formed. Now,
chloride of sodium is well known to be the chief constituent among the
inorganic salts of blood plasma. When, therefore, salts of potassium reach the
blood by the absorption of food, an exchange takes place. Chloride of
potassium and the sodium salt of the acid which was combined with the
potassium, are formed. Instead of the chloride of sodium, therefore, the blood
now contains another sodium salt, which did not form part of the normal
composition of the blood, or at any rate not in so large a proportion. But the
kidneys possess the function of maintaining the same composition of the
blood, and of thus eliminating every abnormal constituent, and any excess of a
normal constituent. The sodium salt formed is therefore ejected by the
kidneys, together with the chloride of potassium, and the blood becomes
poorer in chlorine and sodium. Common salt is therefore withdrawn from the
organism by the ingestion of potassium salts. This loss can only be made up
from Avithout, and this explains the fact that animals which live on a diet
rich in potassiiun have a longing for salt."

In confirmation of this deduction, Bunge found that the addition of
potassium salts to his diet produced a striking increase in the excretion
of chlorine and sodium. Thus 18 grms. of KgO, taken in the form of
phosphate or citrate, caused the loss of an extra 6 grms. of chloride of
sodium (as well as 2 grms. of sodium in other forms), about one-half of
the common salt which is contained in the 5 litres of a man's blood.
And 18 grms. of potash is an amount much less than may be introduced
with many important articles of vegetable diet, such as potatoes, which
contain 20 to 28 grms. KgO ii^ each 1000 grms. of dehydrated material.
" Having regard to the important part which salt plays in the organism
(as in the formation of the digestive secretion, or in dissolving the
globulins), even a small diminution may be prejudicial to certain func-
tions, and may give rise to the need of recovering the loss." ^

There are two other constituents of the food which need special
consideration, namely, iron and lime.

The amount of iron which is egested is exceedingly small, and it
may be expected therefrom that the amount present in the food
under ordinary circumstances would also be small. Stockman has

1 "Lectures," translated by Wooldridge, p. 119.

-Bunge, 01?. cit., p. 121. The student is referred to Buuge's original publications
("Lectures" and ^tec/w./. Biol., Mtinchen, 1874, Bd. x.) for a full and very interesting
discussion of tliis important subject.



INORGANIC SUBSTANCES.



885



shown that only about 10 mgrms. a day is ingested in an ordinary diet.^
Of this amount, 1 mgrm.is egested by the urine, the remainder by the fseces.
This cannot, however, represent all the iron metabolised, for the iron of
the hffimogiobin of disintegrated blood corpuscles is retained, mainly by
the liver, and is no doulit again built up into blood pigment. The nuclei
of most cells, both animal and vegetable, contain appreciable cpiantities
of iron, and in this form, and in the hemoglobin of meat, it must occur in
most food.^ In both these cases it forms an integral part of the molecule
of the proteid or nucleo-proteid, and under ordinary circumstances there
is no inorganic iron, nor any iron salt of organic acid present in the diet.
Such compounds of iron as are contained in nucleins — such, for instance,
as the nuclein of the yolk of the egg — have been termed by Buuge hcema-
togens. As this nuclein is the only iron-containing constituent of the
yolk, it is clear that the haemoglobin of the developing red corpuscles of
the chick must derive its iron from it. It has further been shown by
Socin, working in Bunge's laboratory,^ that in mammals also hemoglobin
is manufactured when the only iron contained in the food is in the form of
the same yolk-hematogen, and that the urine of animals (dogs) fed freely
with egg yolk shows a marked increase in the amount of iron present.

It is noteworthy, as has been pointed out by Bunge, that the natural
food of the infant, namely, milk, contains mere traces of iron, although
the formation of hemoglobin is actively proceeding. This is accounted
for by the fact that the foetus lays up a store of iron (in its liver and else-
where) before birth, and gradually draws upon such store for the manufac-
ture of hemoglobin. Thus Bunge "^ found 18 '2 mgrms. iron per 100 grms.
body weight in a ne^-born rabbit, as compared with 3'2 mgrms. per 100
grms. in an animal twenty-four days old ; and Zalesky,^ four to nine times as
much iron in the liver of a new-born puppy as in that of a full-grown dog.

In all other respects the composition of the ash of milk nearly
corresponds with the composition of the ash of the sucking animal, as
may be seen in the following table from Bunge, which gives the result
of two experiments : —









Puppy.


Milk oj


Bitch.




A.


B.


A.


B.


K.,0 ....


11-42


8-50


14-98


10-70


Na.,0






10-64


8-20


8-80


6-10


CaO .






29-52


35-8


27-24


34-40


MgO .






1-82


1-60


1-54


1-50


Fe,03






0-72


0-34


0-12


0-14


P,0,. .






39-42


39-80


34-22


37-50


CI .






8-35


7-30


16-90


12-40



^ Brit. Med. Jotorn., London, 1893, vol. i. pp. 881, 942 (contains the literature regard-
ing iron absorption up to that date); Joxirn. Phijsiol., Cambridge and London, 1895, vol.
xviii. p. 485 ; also, with Greig, ihid., 1897, vol. xxi. p. 55.

^ Bunge, Ztschr. f. physiol. Cliem., Strassburg, 1885, Bd. ix. S. 49. For the micro-
chemical evidence of the presence of iron in cell-nuclei, see Macallum, Proe. Roy. Soc. London,
1891, vol. 1. p. 277 ; and Quart. Jov,rn. Micr. Sc, London, vol. xxxviii. p. 175. This will
probably account for the fact that the freces, which includes many disintegrated cells of the
alimentary passages, sometimes shows a greater percentage of iron than is present in the
food, although the secretions poured into the intestines only contain iron in minute amounts.

^ Ztschr. f. physiol. Chevi., Strassburg, 1891, Bd. xv. S. 93 and 133.

*IIml., 1892, BcL xvi. S. 177.

5 Ibid., 1886, Bd. x. S. 479 and 495.



886 METABOLISM.

In spite of the fact that it is the general experience of members of the
medical profession, that the administration of iron salts promotes the formation
of haemoglobin in certain forms of anaemia (chlorosis), there is no satisfactory
evidence that the administered iron enters into the formation of the newly-
formed haemoglobin, and it has even been denied that the alimentary canal is
capable of absorbing iron given in snch form. The experiments of Knnkel,!
however, show that if iron salts are administered to animals along with their
food, the blood, liver, spleen, and other organs exhibit an excess of iron over
that of control animals. Hall ^ also obtained distinct evidence of iron
absorption under like circumstances. When iron salts are injected sub-
cutaneously into a vein, most of the iron appears at once in the urine, some
is secreted into the intestine,^ but some is stored in the liver and is only
gradually eliminated. Experiments upon animals, in v/hich the haematogens
of Bunge have been removed from the food and replaced by iron salts, have
been attempted,* but have presented serious diffictilties.^ Marfori,^ however,
working with Schmiedeberg, obtained a large amount of absorption of iron
when given to dogs in artificial combination with albumin. Macallum also
has shown that iron, both in organic and inorganic combination, is absorbed
by the intestinal mucous membrane.'^

Lime is taken in and assimilated by the organism, also in all probability
in the form of organic compounds, probably with proteids.^ It occurs in
large amount in milk, but in most other forms of foodstuffs it is deficient
as compared with other constituents of the ash ; the leguminosse
contain more than most foodstuffs. The only food which has the same
amount as milk is the yolk of egg, which should therefore always
be given to children when milk is either not procurable or cannot be
digested." ^

The withholding of lime from the food of growing animals causes rickets ; ^^^
but rickets may occur in children, in spite of their food containing an adequate
amount of lime.^^ Probably, owing to abnormal conditions of nutrition, the
lime is under these circumstances not assimilated.

In adult animals (pigeons), feeding with foods containing little or no lime
has been found eventually to cause alterations in the bones, which become
unusually brittle and thin (osteoporosis). '^^

^ ArcTi.f. d. ges. PMisioL, Bonn, 1891, Bd. 1. S. 11; 1895, Bd. Ixi. S. 595.

2 Arcli.f. Physiol., Leipzig, 1894, S. 456 ; and 1S96, S. 49.

^ Mayer, Diss., Dorpat, 1850, quoted by Bunge. Quincke {Arcli.f. Anat., Physiol, u.
loissensch. Med., 1868, S. 150) failed to find it in an isolated portion of intestine with a
Thiry fistula, but Macallum {Journ. Physiol., Cambridge a.nd London, 1894, vol. xvi. p.
268) obtained evidence of it in the crypts of Lieberkfilm.

* Socin, Ztsclir. f. physiol. Chem., Strassburg, 1891, Bd. xv. S. 93 ; v. Hosslin, Ztschr.
f. Biol., Miinchen, 1882, Bd. xviii. S. 612 ; Hall, Arch. f. Physiol, Leipzig, 1896, S. 142.

^ Consult upon the subject, Bunge, "Lehrbuch," 1894, 3te Aufgabe, S. 83 ; and Wool-
dridge's translation; also Neumeister, "Lehrbuch," Jena, 1897, 2te Aufl., S. 382-392,
where the subject is very fully treated and many more references to the literature will be
found.

^ Arch. f. cxper. Path. u. Pharmakol., Leipzig, 1892, Bd. xxix. S. 212.

■^ Op. ciL, 1894.

8 Fokker, Arch. f. d. ges. Physiol., Bonn, 1873, Bd. vii. S. 274.

^ Bunge, " Lectures," Wooldridge's translation, p. 111.

1" J. Forster, Zfschr. f. Biol., Miinchen, 1873, Bd. ix. S. 369 ; and 1876, Bd. xii. S. 464 ;
E. Voit, ihid., 1880, Bd. xvi. S. 55 ; Baginsky, Arch. f. Physiol., Leipzig, 1881, S. 357 ;
and Virchow's Archiv, 1882, Bd. Ixxxvii. S. 301 ; Seemann, Ztschr. f. klin. Med., Berlin,
1882, Bd. V. S. 1 and 152.

" Riidel, Arch. f. exper. Path. u. Pharmakol., Leipzig, 1893, Bd. xxxiii. S. 90 ; 0.
Vierordt, Verhandl. d. xii. Cong. f. inn.ere Med., Wiesbaden, 1893, S. 230.

^^ Chossat, Compt. rend,. Acad. d. sc, Paris, 1842, tome xiv. p. 451 ; C. Voit, Ber. d. Vers,
d. Naturf. z. Miinchen, 1877, S. 243; Art. " Erniihrung" in Hermann's "Handbuch,"
Bd. vi. S. 379 ; the earlier literature of the subject will be found in this article.



ME TAB OLISM D URING INANITION. 887

Metabolism duking Inanition.

The problems of metabolism naturally subdivide themselves into
those which concern the fate of the foodstuffs after they are absorbed
and before they reach the tissues, and those which concern the fate
of the stuffs which form the tissues, or which undergo changes within
and by the agency of the tissues. The simplest condition of meta-
bolism is therefore obtained when food is altogether withheld, as under
these circumstances we have only to determine the changes which
occur in the bodystuffs. On this account a very large amount of
attention has been paid, both recently and previously, to the changes
which occur in the tissues, as evidenced by the excreta during inanition
in animals and man.

There is one main fact which comes out in all experiments on
inanition, namely, that in spite of the withholding of food, all the
excretions continue, not certainly to their normal amount, but at least
to a considerable extent. This is even the case with the fasces
which, in the absence of food, might be expected not to be formed.
But, as a matter of fact, it is found that, during starvation, animals
pass, if not every day, at least every two or three days, a fairly regular
amount. This is composed of mucus and of inspissated digestive juices,
a good deal altered in their composition, together with epithelial cells
and other debris. Urine is also regularly passed during a period of
inanition. The secretion of the skin is given off; carbon dioxide and
water continue to be exhaled from the lungs ; and in consequence of all
these losses from the body the animal gradually loses in weight.
The greatest proportionate amount lost is always during the first day
of a fasting period. This is owing to the fact that the products of
metabolism of the proteid food previously absorbed and that still within
the alimentary canal are then got rid of. But after the first day or two
it is found that the loss in weight is pretty definite, and nearly regular
from day to day, and that fairly regular, or at least only gradually
decreasing, amounts of the various excreta are lost daily.^ Thus Voit,^
experimenting upon a cat, found that about 4 to 5 grms. of urea were
passed each day, representing a loss of tissue of from 25 to 30 grms.,
and this with great regularity until the twelfth day, when there was a
marked rise in the amount of urea eliminated. And similar results
have been obtained both with other animals and men in a condition
of inanition.

The time at which this regular daily loss of nitrogen begins, depends
upon the previous condition of nourishment. Thus, in a dog experi-
mented upon by Voit, three series of experiments were made, each
extending over eight days of total deprivation of food. The animal had
received before the first series, 2500 grms. of flesh daily ; before the
second, 1500 grms. ; and before the third, a mixed diet with relatively
little proteid. The results obtained are shown in the table on ^ p.
888. It will be seen that the regular loss begins at once in the third



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