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after some diseases occur exceedingly rapidly, there is a further production of
heat due to putrefaction. In some cases the temperature of a corpse does not
fall to that of the atmosphere even in four or five days.^''

1 "Researches," London, 1839, vol. i. p. 228.

'Ann. d. Ghar.-Krankenli. . . . zio Berlin, 1865, Bd. xiii. Heft 2, S. 1.

3 Penn. Hosp. Rep., Philadelphia, 1868, vol. i. p. 369.

^ Arch. d. Heilk., Leipzig, 1861, Bd. ii. S. 547.

'" London Hosp. Rep., vol. iii. p. 454.

^ CentralM.f. d. med. Wissensch., Berlin, 1866, No. 5.

'' Brit. Med. Journ., London, 9th July 1870.

^ Quoted from Valentin, Deutsdics Arch. f. Min. Med., Leipzig, 1869, S. 201.

^ Schmidt's Jahrb., Leipzig, 1868, Bd. cxxxix. S. 241.

10 Deutsches Arch./. Min. Med., Leipzig, 1879, Bd. xxiv. S. 284.

11 Churchill, quoted from Hutchinson, Lancet, London, 1875, vol. i. p. 713.

12 Besides those above enumerated, the following may be mentioned :— Seume, Thesis,
Leipzig, 1856 ; Erb, Deutsches Arch. f. Min. Med., Leipzig, 1865 ; Thomas, Arch. d. Heillc,
Leipzig, 1868, Bd. ix. S. 17, 31 ; Goodhart, Brit. Med. Journ., London, 1874, vol. i.
p. 303 ; Huppert, Arch. d. Heilk., Leipzig, 1867, Bd. viii. S. 321 ; Pick and Dybkowsky
Vrtljschr. d. naturf. GescUsch. in Zurich, 1867 ; Schiffer, CentralU. f. d. med. Wissensch.
Berlin, 1867, S. 849 ; Arch./. Anat., Physiol, u. wissensch. Med., 1868, S. 442.

I'* The author is indebted to Drs. Haldane, Hale, White, and Waller for valuable
suggestions on various points, dealt with both in this and in the preceding article.



METABOLISM.

By E. A. SCHAFEE.

Contents : — Introductory, p. 868 — Balance of Nutrition, p. 871 — Composition of
Foodstuffs, p. 872 — Heat Value of Foodstuffs, p. 874 — Necessarj"- Amount of
Proteid, p. 875 — Special Constituents of Diet, and their Effect on Metabolism,
p. 878 — Gelatin, p. 878 — Carboliydrates, p. 880 — Fats, j). 881 — Inorganic Sub-
stances, 23. 882 — Sletabolism in Inanition, p. 887 — With, purely Proteid Diet,
p. 891 — Relative Metabolic Activity of Tissues, p. 895 — Nitrogenous Meta-
bolism, p. 896 — Influence of the Liver on Proteid Metabolism, p. 900 — Influence
of Muscular Activity on Proteid Metabolism, p. 911 — Metabolism of Carbo-
hydrates, p. 916 — Glycogen formation, j). 919 — Phloridzin Diabetes, p. 920 —
Glycogenesis, p. 922 — Puncture Dialoetes, p. 926 — Action of Pancreas on
Carbohydrate Metabolism, p. 927 — Metabolism of Fat, p. 930 — Source and
Formation of Fat, p. 931 — Action of Liver on Metabolism of Fat, p. 935.

Introductory. — The word " metabolism " has come into use in this
country as the equivalent of the German word Stoffwechsel, which
strictly means " exchange of material." The subject which it denotes
embraces all that is known or conjectured regarding the changes which
occur within the body in the materials of the food, or foodstuffs, and
in the materials which compose the tissues and organs of the body
itself, or bodystuffs. Generally, however, the digestive changes in the
food are excluded from the scope of the expression. There is no special
reason, other than that of convenience of description, why this should be
the case, for the digestive changes in the food must, like all other
chemical changes occurring within the body, influence the general con-
ditions of the economy. The usual course will, however, be followed
in this article, and I shall confine what I have to say to the changes that
occur after the food is absorbed, in so far as they have not been already
treated of in the articles in this work dealing with the chemistry of the
urine and with the chemical processes of respiration and heat production,
both of which subjects constitute essential parts of the whole subject
of metabolism.

The metabolic changes which are undergone by the tissues must be
of two kinds, which are opposite in nature.^ For, on the one hand, the
complex molecules which constitute living tissue or hiojjlasm^^ are built

^ Hering, " Vorgtinge der lebenden Materie," Prag, 1888. A translation, by Miss F. A.
Welby, of this extremely important and interesting article will be foimd in Brain, London,
1897, vol. XX. p. 232.

^ I use the word hio2Jlasm as a synonym for living suljstance, I'ather than pj'otoplasm,
because the latter word has come to have a definite histological rather than a physiological
signification ; and, on the one hand, is used to include portions of cell substance which, for
aught we know, may not be actually living matter, whilst, on the other hand, it does not
include the living substance of the cell nucleus, which Avould be included in the expression
"bioplasm."



INTRODUCTORY. 869

up from non-living materials, furnished by the food ; and, on the other
hand, thej are broken down into simpler substances, which pass
away from the tissue into the blood, and ultimately from the body
with the excreta, or, as in the case of secretory glands, directly into
secretions. The building-up process, whereby fresh molecules of bioplasm
are formed, has come to be spoken of as an anabolic change {anabolism,
assimilation), and the breaking - down process as a katabolic change
(kataholism, dissimilation). It is clear that these two processes will
produce opposite effects upon the bioplasm, the one increasing and the
other diminishing its bulk. But, on the other hand, it is conceivable
that even within the same cell there may be, at the same time, both a
building up or anabolic change proceeding, so that fresh molecules of
bioplasm are being formed, and also a breaking-down or katabolic change,
affecting molecules which have been formed previously, and the net
result to the bulk of the tissue may be nil, provided that these two
processes balance one another ; that is to say, the bioplasm, although
undergoing active metabolic changes, and furnishing products of its
metabolism to the secretions or to the blood, is not altered in amount
(autonomous equilibrium). But although both processes are occurring
simultaneously, they nevertheless do not exactly balance one another,
there will be as the net result either a gain or loss of bioplasm, i.e. the
bioplasm of the cell will increase or diminish in amount. If every cell
were entirely composed of bioplasm, this would evidently involve an
increase or diminution in the bulk of the cell itself. But besides the
actual bioplasm, all cells contain in a variable proportion products of
the activity of their bioplasm; "formed material," in the sense of
Lionel Beale, as distinguished from " formative matter." If these
products remain within the cell, it may, in spite of the fact that kata-
bolic processes are proceeding '.within it more actively than anabolic
processes, still increase in bulk, even to a very large extent, but without
any corresponding increase, indeed even with an actual diminution, of
its bioplasm.

Various circumstances may determine the general direction of the
metabolism of a cell, whether upward in the direction of increased
anabohsm with increase of bioplasm, or downward in the direction of
increased katabolism with decrease of bioplasm. One such circumstance
is undoubtedly the amount and nature of the pabulum supplied to the
cell. Another is to be found in the general physical conditions of the
environment, such as variations of temperature, supply of water and of
oxygen, and the like. And in the case of many animal cells we may
well suppose (and indeed the point may be said to have been determined
for specific instances) that impulses derived from the nervous system
may set up respectively, according to their nature, or the nervous channel
along which they are conveyed, metabolic changes in either an anabolic
or a katabolic direction. Thus it has been suggested by Gaskell that the
heart nerves act upon its muscular substance, so as to produce respect-
ively anabolic changes (vagus fibres, inhibitory impulses) and katabolic
changes (sympathetic fibres, augmentor and accelerator impulses), accom-
panied by diminished activity in the one case, by increased activity in
the other. The possibility must, however, be also borne in mind that the
same nerve fibres may set up both anabolic and katabolic changes, as
when a secretory nerve is stimulated, provoking it may be for hours a
discharge of products of katabolism from secretory cells ; for it is in



870 METABOLISM.

such cases necessary to assume a continuous process of anabolism going
on at the same time within the same cells.

Upon evidence founded mainly, but not exclusively, upon the investigation
of certain electrical and visual phenomena, Hering has concluded that in all
cases where either katabolic or anabolic changes are proceeding in any portions
of bioplasm, they tend to render the bioplasm more and more resistant to the
effects of the excitation which is producing the change (reaction) ; that in any
given cell the longer or more strongly metabolic changes of the one character
have been proceeding, the greater will be the tendency towards metabolic changes
of the opposite character, so that even if, as may happen, in consequence of the
action of an external stimulus (A), anabolic changes are proceeding at first more
rapidly than katabolic, so that the balance is in favour of the building up
or assimilation processes, the reaction which is thereby provoked will, after a
time, by increasing the katabolism of the cell, tend again to produce a condition
of balance. Only in this case the balance will be struck with the general
bioplasm of the cell in a condition above par, as compared with that from which
it was assumed to start (A — allonomous equilibrium). And, mutatis mutandis,
increased katabolic processes due to external stimuli are (D) assumed to produce
by reaction an increase of anabolism in adjacent portions of bioplasm, which
increase becomes eventually sufficient to balance the increased katabolism
induced by the stimulus, so that again the metabolism of the whole cell strikes
a balance as it were, but now in a condition below par, as compared with the
normal (D — allonomous equilibrium). Upon the cessation of the stimulus in
either case, the tendency, say, to increased anabolism being removed with the
stimulus, the opposite condition of increased katabolism, which was provoked
by the increased anabolism, will for a time prevail, and there will be a falling
off of the general assimilation of the cell, until what may be considered the
normal condition is again established, the two processes again exactly balancing
one another. And the same, mutatis mutandis, for the removal of a stimulus
which was producing a condition of increased anabolism. There is thus
assumed to be a sort of internal self -adjustment of metabolism in bioplasm.

It is a part of the theory of Hering that the anabolic and katabolic changes
in the bioplasm are the direct or indirect cause of many, if not of all,
physiological phenomena exhibited by living tissue, and that the prevalence
of one kind of change in any portion of bioplasm will tend to start a
change of the opposite kind in adjacent portions. But this is a subject
which we need not here specially concern ourselves with, since the most
important application of it to the explanation of physiological phenomena
concerns the effects produced by the stimulation of the retina by light, and
will be discussed in the article dealing with this question.

In connection with this subject, one other point must be borne in mind,
namely, the possibility, indeed probability, that many metabolic changes in the
body are not necessarily associated with the building up or breaking down of
bioplasm, but are effected outside the actual molecules of which the bioplasm
is composed, although under the influence of the activity of the bioplasm.
Such changes as these may be distinguished from the metabolic changes of the
bioplasm itself by the name of " contact changes," and they also involve both
the building up of complex materials and the subsequent breaking down of
such materials into simpler products associated frequently with oxidation.
Such contact changes are analogoiis to those which are produced by organised
ferments, such as yeast, outside the actual organism, although directly by its
activity, and they must be sharply differentiated from the changes which the
bioplasm itself is at the same time undergoing. This distinction will be
referred to again in a subsequent section.

The understanding of the metabolic processes presupposes an acquaintance
with the composition of the fo(i(lstuir8 and of the bodystufls, both of which



BALANCE OF NUTRITION.



871



have been dealt with in previous articles. So far as the bodystiiffs are con-
cerned (and to a somewhat less extent with regard to the foodstuff's), it cannot
be said that we possess an acquaintance so intimate as to enable us fully to
understand the changes which they undergo ; and as a consequence it will be
found that our knowledge of metabolism, in spite of the enormous amount of
work that has been done to elucidate it within the last five and twenty years,
is still in an unsatisfactory condition.

Balance of nutrition.— The first determinations that require to be
made in any inquiry into the metabolism of the body are those of its
incomings and outgoings.^ The incomings of the body consist of food
and oxygen ; the outgoings, of the various excreta, and of the carbon
dioxide and water lost by the lungs and skin. If the incomings of the
body exactly balance the outgoings, so that the animal neither gains nor
loses weight, the body is said to be in complete nutritive equilihrmm.

Sufficient information can be usually obtained regarding the balance
of metabolism of the body, if the nitrogen and carbon only are determined
in the ingesta and egesta.

As an instance of complete equilibrium in a man weighing 70 kilos.,
embracing both the nitrogen and carbon of the ingesta and egesta, the
following balance table may be given (Burdon Sanderson '^) : —



Incomings.


Outgoings.


Food.


N.


C.


Excreta.


N.


C.


Proteids . lOOgrms.
Fat . . 100 ,,
Carbohydrates 250 ,,


15-5


53
79
93


Urine
Faeces
Eespiration


14-4
1-1


6-16

10-84

208-00




15-5


225




15-5


225



We may also have a condition in which the body either gains or
loses weight, and in which consequently the incomings and outgoings do
not exactly balance one another, but during which, nevertheless, the
niiroge7i which is taken into the body, and that which leaves the body,
may strike an exact balance, while the other elements which compose
the food and excreta, and especially the carbon, hydrogen, and oxygen,
may not be similarly balanced. When the nitrogen of the food exactly
balances the nitrogen excreted, the body is said to be in nitrogenous
equilihrmm. Under these circumstances we may assume that the living
material of the tissues (which is essentially composed of nitrogenous
substance) is neither diminished nor increased in amount ; whereas, if
at the same time the other constant elements of the food — the carbon,
hydrogen, and oxygen— are met with in diminished or increased quantity
in the excreta, we may assume that substances in the body other than
the living tissues are either becoming laid on, or becoming diminished

1 For tlie methods of determining these may be consulted, C. Voitin Hermann's "Hand-
buch," 1881, Bd. vi. S. 6 et seq., and numerous papers which have appeared since then
chiefly in the Arch. f. d. ges. Physiol., Bonn (by Pfluger, Zuntz, and their pupils), and in
the Ztschr. f. Biol., Munchen (by Voit and his pupils). See also v. Noorden, "Grundriss
einer Methodik der Stoffwechsel-Untersuchungen," Berlin, 1892. For the methods of deter-
mining the respiratory products, see article "Chemistry of Respiration ").

" " Syllabus of Lectures on Physiology," 1879,



872



METABOLISM.



in amount. These substances are mainly the fats, to a much less
extent the carbohydrates, whereas the substances which form the
actual tissues are composed of proteids and nucleo-proteids.

The following is an instance of a balance table ^ of a man weighing 70
kilos., showing nitrogenous equilibrium only, some of the carbon of the ingesta
(mostly representing stored fat) not reappearing in the excreta : —



Incomings.


Outgoings.


Foodstuffs.


N.


C.


Excreta.


N.


C.


Proteids . 137gi'ms.
Fat . . 117 .„
Carbo-hydrates 352 ,,


19-5


1
!- 315-5


Urine
Fseces
Eespiration


17-4
2-1


12-6

14-5

248-6




19-5


315-5




19-5


275-7



Whether the material which forms the bioplasm of the tissues has an
essentially diiferent molecular constitution during life from that which is met
with in it after death, is not certainly known, but is extremely probable. This
is obviously a point which is difficult of determination, because we cannot
investigate the material composing bioplasm without previously killing it.
All we are able to do is to determine, as far as possible, the changes which the
tissues undergo, by investigating the products which they give off during life.
Our knowledge of these products has led some physiologists to the conclusion
that the substance of living material is composed of unstable cyanogen or
aldehyde compounds, whereas it is well known that dead proteid yields bodies
of an amide nature.-

Composition of foodstuffs. — The most important general fact that
we need concern ourselves with in this place regarding the composition
of foodstuffs is that, with ordinary mixed diet, they are composed in
certain not very definite proportions of three chief kinds of organic
material, namely, 'protdch, carhohydrcdes, and fats\ in addition to
which, v:ater and salts are a necessary part of the food. The most
general proportion of these three primary varieties of foodstuffs
to one another in ordinary diet is found to be about one part of
proteid material to from four to six parts of non-proteid, while the non-
proteid constituents stand to one another in about the proportion of one
part of fat to from five to ten parts of carbohydrate, this ratio having
been arrived at by investigating the composition of freely chosen diets
of persons in various occupations and stations of life. At the same time,
it must be pointed out that departures from these proportions are by no
means unfrequently met with, and especially is this the case with
certain races of mankind, e.g. some of the Asiatic races, where a very
much larger proportion of non-proteid material is ordinarily taken with
the diet than is the case with Europeans ; whereas, on the contrary, in
parts of South America and Australia, where meat is plentiful, the pro-
portion of proteid to non-proteid may be far larger than that above given.



^ C. Voit, Hermann's "Handbuch," Bd. vi. S. 513.
here given is from Neuraeister, "Lehrbuch," Jena, 1897,
- Cf. Halliburton, this Text-book, vol. i. p. 38.



The table in the simplihed form
Anfl. 2, S. 344.



COMPOSITION OF FO OD STUFFS. 8 7 3

On the whole, however, the above proportions are found to be fairly well
maintained, the ratio of carbohydrates to fats in the diet varying more
than the proportion of proteid to non-proteid material. As a general
rule, it will be found that with the more wealthy classes there is a
relatively greater amount of proteid and fat as compared with carbo-
hydrates : whereas with the poorer classes the carbohydrates increase in
proportion, and the proteids and fats diminish. With a diet composed
of vegetable matter alone, the proportions are liable to be considerably
modified, since, in order to obtain a sufficient amount of proteid from
most vegetables, a much larger proportionate amount of carbohydrate
food is inevitably consumed. On the other hand, since with flesh food
the amount of proteid necessary for carrying on the metabolic processes
of the body is much more easily obtained than from vegetable food,
and since flesh food invariably contains a considerable amount of fat,
the proportion of proteid and fat to carbohydrate is apt to be much
greater than the normal when the diet is mainly composed of animal
matter.

For the determination of the value of the chief organic materials of the
foodstuffs in nutrition, the most important point to be ascertained regarding
their composition is the amount of nitrogen and carbon in each. In round
numbers, this may be stated as follows : — Proteids contain 15 to 17 per cent.
JST, and 50 to 55 per cent. C ^ ; animal fats, on an average, 76 "5 per cent. C ; and
carbohydrates, such as starch and sugar, 40 to 45 per cent. C. Since the amounts
of proteid fat, and carbohydrates in all the ordinary foodstufls has been accur-
ately determined," and is given in the form of tables, it is not difficult, if the
amounts of each which are ingested are carefully weighed, to determine by
calculation the total JS" and C of the ingesta. For very accurate work,
however, it is necessary to make direct determinations of the N and C in
the food taken; this is effected by ordinary chemical methods (that of the
nitrogen usually by Kjeldahl's method).

The amoimt of flesh or fat which is at any time becoming lost or laid on
can be easily approximately determined by an examination of a balance table,
for the nitrogen in the urine represents metabolised proteid, the amount
of which is arrived at by multiplying the numbers of grms. of nitrogen found
by 6*25 (since proteids contain 16 per cent. W). Since any excess or deficit
of proteids represents flesh lost or laid on, the amount of such loss or addition
can be directly obtained by taking each gramme N in excess or deficit to
represent 30 grms. flesh (since flesh contains about 3 '4 per cent. jSJ") (Voit).
And, after reckoning off the carbon which the proteid metabolised would contain
(53 per cent.), any further excess or deficit of carbon in the ingesta would
represent the carbon of fat lost or laid on, and the amount of this may he
approximately obtained by multiplying the number of grms. of carbon in the
excess or deficit by 1'3 (since fat contains about 76"5 per cent, carbon). Thus,
in the balance table on p. 872, the man under observation retained 39 "8 grms.
C, representing 52 grms. fat laid on.

The following table (from Bunge) gives the percentage composition of
some of the chief foodstuffs ; the remainder in each case is mainly water with
a variable amount of salts — the numbers are taken from Konig. They are
given in inverse order to the proportion of proteid they contain : —

^ Argutinsky determined the percentage composition of beef, completely divested of fat
and dried, to be as follows :—C 49-6, N 15-3, H 6-9, + S 23-0, ash 5-2 {Arch. f. d. ges.
Physiol, Bonn, 1893, Bd. Iv. S. 345).

- Konig, "Chemie der menschl. Nahrungs-u. Genussmittel," Berlin, 1882, Aufl. 2.



874



METABOLISM.



Foodstuff.


Proteid.


Fat.


Carbohydrate.


Apples


0-4




13


Carrots






1-1


0-2


9


Potatoes .






2


0-1


20


Human milk






2


4


6


Cabbages .






3-3


0-7


7


Cow's milk






3-4


4


5


Rice .






8


0-9


77


Maize






10


4-6


71


Wheat






12


1-7


70


White of eggs






13


0-3




Fat pork .






15


37




Yolk of eggs






16


32




Fat beef .






17


26




Fish (pike)






18


0-5




Lean beef .






21


1-5




Peas .






23


1-8


58



Heat value of foodstuffs. — A most important determination to be

made regarding any diet is its caloric (calorific) value. This is arrived at
by multiplying the number of grammes of its several organic constituents
by a number, determined by exact experiment, representing the amount
of heat produced by the oxidation of 1 grm. of the carbohydrate, fat, or
proteid to water and carbon dioxide and to urea. Such calorimetric
experiments were first carried out systematically by Frankland,^ who
determined the caloric value of various articles of diet, and his results
have since been extended and confirmed or amended by various
observers,^ using improved calorimetric methods.

According to Eubner, the average caloric value of the proteid of the
aliment is 4124 calories, i.e. 1 grm. proteid oxidised to urea yields 4124
grm. degrees (or 41 kilogram-degrees) of heat ; of the fat, 9321 calories
(9-3 kilogram-degrees) ; and of the carbohydrate (starch), 4116 calories
(4-1 kilogram-degrees). Applying these numbers to Volt's diet (see
next page), we obtain in round numbers — ■

105 grms. assimilated proteid x 44 = 430

56 „ fat X 9-3 = 520

500 „ carbohydrate x 44 = 2050



Online LibraryE. A. (Edward Albert) Sharpey-SchäferText-book of physiology; (Volume v.1) → online text (page 121 of 147)