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“APPLIED PHYSIOLOGY

A HANDBOOK FOR STUDENTS
OF MEDICINE

‘BY

ROBERT HUTCHISON, M.D., F.R.C.P.

PHYSICIAN TO THE LONDON HOSPITAL; ASSISTANT-PHYSICIAN TO THE HOSPITAL
FOR SICK CHILDREN, GREAT ORMOND STREET; LATE CHEMICAL ASSISTANT
TO THE/PROFESSOR OF PHYSIOLOGY, UNIVERSITY OF EDINBURGH, AND
DEMONSTRATOR OF PHYSIOLOGY, LONDON HOSPITAL MEDICAL COLLEGE

\ AUTHOR OF
‘FOOD AND THE PRINCIPLES OF DIETETICS,’ ‘LECTURES ON DISEASES OF CHILDREN’
JOINT AUTHOR OF ‘CLINICAL METHODS,’ AND JOINT EDITOR OF ‘AN INDEX
OF TREATMENT’

‘ Knowledge should be subservient to action’
BACON Vas

» 4
. .

LONDON AX
EDWARD ARNOLD (~\
1908 \

[All rights reserved]

PREFACE

Wirx the increasing complexity of the medical curri-
culum, and the growing inclination to specialism
amongst teachers, there is a tendency for the student
to keep his knowledge in water-tight compartments.
Physiology, for instance, is studied in the laboratory,
and clinical medicine in the wards, and too often one
finds that the student is incapable of applying his
scientific knowledge to his clinical work. This is to be
regretted, not only because it tends to lessen the interest
of the practical study of disease, but because it leads
to unsound and unscientific practice. For, beyond all
question, the medicine of the future will be based more
and more upon a sound knowledge of the normal
working of the human body; or, in other words, upon
Applied Physiology, and the best physician will be he
who combines such knowledge in fullest measure with
a wide practical experience at the bedside.

Inability to apply the teachings of physiology leads
also to this curious anomaly, that a man may have
been taught, and presumably still believe, certain facts
as true physiologically, and yet continue to act in his
clinical work upon an apparently quite opposite creed.
Such an attitude of mind, it need hardly be said, is

Vv

vi PREFACE

destructive of all sound medical thought, and makes for
purely empirical practice.

In the present book—the first, so far as the writer
knows, of its kind—an attempt has been made to apply
physiology to medicine in the same way as anatomy has
long been applied to surgery. Seeing that it is not
intended to be a substitute for physiological text-books,
but merely a companion to them, all descriptions of
methods have been omitted, and only the facts of
physiology dealt with, chief emphasis being laid upon
those which have a direct bearing upon clinical work ;
incidentally these bearings are pointed out.

The reader may be surprised at the small size of
the book, but when one deals only with the jfacts of
physiology, it is astonishing to find how little space they
occupy, and how few of them have as yet any direct
practical implications. It will be observed, too, that
there is no chapter on the muscular or nervous systems,
or on the special senses. These omissions are inten-
tional, for the writer is convinced that most of ‘ nerve-
muscle’ physiology, as ordinarily taught to students
is perfectly useless to the physician ; and, as regards the
nervous system and special senses, the time is not yet
ripe for writing their applied ‘physiology—clinically, one
can as yet hardly make use of more than their applied
anatomy. |

As the book is designed only for students, and not
for specialists, few references to original sources have
been given; but the writer feels that it is due to himself
to say that these have always been consulted, and that
the book really represents a very large amount of

PREFACE Vii

research in physiological literature, which has occupied
a fair amount of time for some years. He is indebted
to Dr. Leonard Hill and Mr. W. Rainey for kindly
revising the proofs.
R. H.
1908.

CONTENTS

CHAPTER

ay
It.

Ill.

IV.

. THE APPLIED PHYSIOLOGY OF THE CIRCULATION

THE APPLIED PHYSIOLOGY OF METABOLISM “
THE APPLIED PHYSIOLOGY OF BODY HEAT -

THE APPLIED PHYSIOLOGY OF THE BLOOD AND
HAMOPOIETIC ORGANS - :

THE APPLIED PHYSIOLOGY OF THE HEART -

'

. THE APPLIED PHYSIOLOGY OF RESPIRATION .
. THE APPLIED PHYSIOLOGY OF DIGESTION - -

THE APPLIED PHYSIOLOGY OF EXCRETION sf
INDEX : . ‘ : : ;

ix

PAGE

105
14]
177

295

270
291

Bas
ee

PLATE

LIST OF DIAGRAMS

IN COLOUR

II. DIAGRAM OF A LOBULE OF THE LUNG (AFTER STOHR)
III. THE RESPIRATORY CENTRE AND ITS CONNECTIONS

FIG,

$0

. ABSOLUTE NUMBER OF LEUCOCYTES PER CUBIC

MILLIMETRE AT DIFFERENT AGES > =

. DIFFERENTIAL PERCENTAGE COUNTS THROUGHOUT
LIFE (AFTER CARSTANJEN) : : ~—

SERIES OF VENTRICULAR SYSTOLES (AFTER WENCKE-
BACH) - : : . . :

. HEART SOUNDS - - - - ‘
. PULSE TRACING, SHOWING VENTRICULAR INTER-

MISSION (AFTER CUSHNY) - : ;
PULSE TRACING, SHOWING AURICULAR INTERMISSION
(AFTER CUSHNY) - - - : ;

. CHANGE IN SHAPE OF AN ARTERY DURING PASSAGE

OF THE PULSE WAVE~ - 3 3 ’
SPHYGMOGRAM OF RADIAL PULSE (MACKENZIE) -

. INFUNDIBULUM AT THE END OF COMPLETE INSPIRA-

TION AND EXPIRATION (HARRY CAMPBELL) ~~ -
xi

FACING PAGE
I. THE INNERVATION OF THE HEART (AFTER POWELL)

122
183
204

PAGE

88

89

118
138

138

139

145
148

184

xii
FIG,
10.
11.
12.
13.
14,

15.

16.
17.

18.

LIST OF DIAGRAMS

‘PULL’ EXERTED BY THE LUNGS BY MEANS OF THEIR
CONTRACTIBILITY - : - - -
CROSS SECTION OF THE RIGHT LUNG, SHOWING
DIRECTIONS OF EXPANSION (KEITH) : -
RIGHT LUNG FROM THE SIDE, SHOWING DIRECTIONS
OF EXPANSION (KEITH) - - - -
VERTICAL SECTION OF THE RIGHT LUNG TO SHOW
EXPANSION (KEITH) - . . -
VITAL CAPACITY (AFTER HUTCHINSON) - -
POSITION OF SHADOW DURING THE SWALLOWING
OF A MOUTHFUL OF MILK CONTAINING BISMUTH
CARBONATE (HERTZ) - - -
FUNCTIONAL DIVISIONS OF THE STOMACH - :
SEGMENTATION IN HUMAN. SMALL INTESTINES
OCCURRING SIMULTANEOUSLY WITH PERISTALSIS
(HERTZ) - : : : ; 4
AVERAGE TIME AT WHICH VARIOUS POINTS OF THE
COLON ARE REACHED AFTER A BISMUTH BREAK-
FAST (HERTZ) - : 3

PAGE
190
196
197
198

200

230
243

259

APPLIED PHYSIOLOGY

CHAPTER I

THE APPLIED PHYSIOLOGY OF METABOLISM

Tue future of medicine undoubtedly depends upon the
chemical physiologist. The scalpel, the microscope, and
the simpler application of physical and experimental
methods have, so far as we can perceive, nearly finished
their work, but the investigation of the chemical pro-
cesses of the body is just begun. The term ‘metabolism’
is used to embrace the sum of these chemical processes,
and as most diseases are, in the last resort, the ex-
pression of a perverted metabolism, it can easily be
understood how important a complete knowledge of the
subject would be to the physician. Unfortunately, how-
ever, we are constantly hampered by our ignorance in
this respect. Most of the intimate chemical changes
which go on in the organs and tissues are still utterly
beyond our ken. Some we guess at or catch glimpses of
from afar; it is only a few that we fully understand.
In the present chapter I propose to give a general sketch
of metabolism so far as our present knowledge permits,
and shall point out as one goes along the application of
1

2 APPLIED PHYSIOLOGY

the facts which have been ascertained to the problems of
clinical medicine—so far, at least, as such application is
at present possible.

Metabolism has two great purposes to fulfil: (1) the
maintenance unimpaired of the substance of the tissues ;
(2) the conservation of bodily energy. The former con-
sists in the replacement of the waste of tissue substance
which the stress and strain of vital activity entails; it
is therefore essentially anabolic in nature. The conser-
vation of bodily energy, on the other hand, is achieved
by the breaking down of food compounds and the libera-

tion of their potential energy in the form of heat and }

work, and is therefore preponderatingly katabolic.

We may regard these two aspects of metabolism
either from the point of view of the total amount of
chemical change which takes place (quantitative meta-
bolism), or from that of the intimate nature of the
chemical processes which they involve (qualitative meta-
bolism). As the former point of view is the simpler, it
will be best to consider it first.

QUANTITATIVE Mrrapoism.* ;
; ? KA
1. The Conservation of Tissue Substance. /

As protein is the only constituent of the food which is
able to repair tissue waste, it is obvious that this aspect
of metabolism when looked at quantitatively resolves

* In order to appreciate the relative mass of the various tissues
which compose the ‘ vital machine’ and take part in metabolism,
it should be remembered that, of the total body-weight, about 40 per
cent. is made up of muscle, 5 per cent. of blood, 2 per cent. of
brain, whilst the other internal organs and the skeleton make up
the remainder,

METABOLISM LL.

itself into the question, How much protein is required
to make good the daily destruction of tissue? This
question is one of such enormous practical importance
to the physician that a little space must be devoted to a
statement of the prevailing physiological views upon it.

How much Protein is required ?—If one attempts
to solve this problem by the simple method of estimating
the amount of nitrogen excreted daily, one is at once
met by the difficulty that ‘nitrogenous equilibrium’ can
be maintained on very varying quantities of protein.
The more protein the food contains, the more nitrogen
is excreted, and this goes on until the limits of the
digestive capacity are reached. If, again, one takes
the amount of nitrogen excreted during fasting as the
basis for constructing the diet sheet, it is found that if
this amount alone be supplied it is insufficient to
maintain equilibrium, and nitrogen is lost from the
body. At what point above this, then, is one to fix
the proper quantity? Despairing of any experimental
solution of this problem, the older school of physiologists
fell back on purely empirical observation. They esti-
mated the amount of protein actually consumed by
groups of individuals on freely chosen dietaries, and
took this as the answer to the question. It was in this
way that Voit arrived at the standard of 118 grammes,
which was long accepted as the proper amount of
protein for the diet to contain, and it was upon this
estimate that the prevailing ‘standard dietaries’ were
constructed. Within the last few years, however,
physiologists have begun to question the correctness of
the Voit standard. Investigation of the diets of many

4 APPLIED PHYSIOLOGY

individual vegetarians, and of vegetarian races, for
example, revealed the fact that health and activity
could apparently be maintained on much smaller allow-
ances of protein than the Voit standard postulated.
Finally there came the well-known experiments of
Chittenden, which showed for the first time on a suffi-
ciently large scale that, beyond all apparent doubt,
health and efficiency could be maintained for indefinite
periods upon a much smaller protein intake than
118 grammes. Chittenden fixes the protein optimum,
indeed, or the best amount for habitual consumption, at
about 60 grammes per day, which is not far above the
minimum upon which nitrogenous equilibrium can be
maintained. Any intake above this he would regard as
a luxus consumption.*

* It might seem that in human milk we would find a standard
which would furnish a guide to the proper proportion of protein
which the diet ought to contain.

An infant of six months, weighing 6°7 kilogrammes, and con-
suming an average quantity of breast milk (950 grammes), consumes
about 14 grammes of protein, and has a total energy intake of
594 Calories per day. This is about 2 grammes of protein per
kilogramme, and if an adult of average weight (70 kilogrammies)
consumed the same proportion of protein, he would require
140 grammes in his ‘diet, which is much above even the Voit
standard,

There is, however, another way of looking at the question: Of
the total Calories taken in by the infant, fifty-seven are derived
from protein ; and assuming the adult to require an intake of 3,000
Calories per day, and that the same proportion of these is derived
from protein as in the child, then the amount of protein the adult
should consume would only be about 70 grammes per diem, which
is approximately Chittenden’s standard. Which is the correct way
of looking at the question it is difficult to say. If the adult is to
take as much protein per unit of his body-weight as the child, then

METABOLISM 5

If Chittenden be right, there can be no doubt of the
far-reaching effect of his views; our dietary standards
would have to be revised, and vegetarianism would
become, not only uninjurious, but a system highly to be
commended on grounds alike of humanity, hygiene, and
economy. To consume a superfluous quantity of such
an expensive food constituent as protein is certainly not
only wasteful, but, from the great amount of work re-
quired for its digestion and the excretion of its end-
products, physiologically injurious as well. Chittenden,
indeed, is of opinion that many of the degenerative
diseases of later life, as well as many of the paroxysmal
neuroses, such as migraine, met with in younger
patients, are directly due to a luxus consumption of
protein.

Notwithstanding the apparently convincing nature of
Chittenden’s experiments, it will be well for the physician
to be cautious in applying their results in practice. It
is all very well for the physiologist to dismiss con-
temptuously the universal practice of mankind as having
been arrived at purely empirically, and as affording no
basis on which to establish rational rules of diet; but the
practical physician, whose art has taught him the safety
of a wise empiricism, cannot so lightly discard a rule
which has been adopted semper et ubique et ab omnibus.

even the Voit standard is too low. If, on the other hand, he is to
take only the same amount of protein in proportion to the total
energy value of his diet as the child, then Chittenden’s standard is
correct, It is true that the child is constantly laying up protein in
the body in the form of new tissue, but against this has to be set
the fact that the destruction of tissue in the adult is greater, owing
_ to the performance of muscular work.

6 APPLIED PHYSIOLOGY

It may be possible to live in apparent health on a low
protein intake for a long time, but can one do so with
impunity always? It may be true that a luxus con-
sumption of protein tends to produce disease, but may
an habitually low intake not predispose to diseases of
another sort? To take only two examples, our experi-
ence of the treatment of tuberculosis has shown the
value of a liberal meat diet in effecting a cure, and it has
been found in the Japanese Navy that a liberal protein
ration is a prophylactic against the ravages of beri-beri.
It may well be, in short, that the supply of a liberal pro-
portion of protein is necessary for the proper production
of these chemical compounds, which are one of the
means by which the body defends itself against invasion
by bacteria. Again, it may prove, when the reserve of
protein in the body is low—as it must be on an habitually
low intake—that any attack of acute fever will result in
too great inroads on the proteins of the fixed tissues,

_ with all the dangers which that entails. These are only ~

some of the considerations which must give us pause in
at once applying to practice the results of physiological
experiment. Time alone can show whether such objec-
tions deserve any weight. Meanwhile every practising
physician, by observing how patients who habitually
consume little protein resist the attacks of disease and
withstand it when attacked, can help to furnish the
data which are necessary for a final judgment in-the
matter. z

Storage of Surplus Building Material.—tIn any dis-

cussion of the conservation of matter in the body, two
influences must be considered: (1) the effect of growth,

re

METABOLISM 7

and (2) the influence of muscular labour. As regards
growth, physiology teaches that it can only take place
when protein is supplied in excess of the actual needs of
the body as measured by the output of nitrogen. In the
earlier period of life, therefore, a luxus consumption of
protein is actually necessary, a point which must be
borne in mind in constructing dietaries for the young.
On the other hand, experiment has also shown that,
once growth is completed, it is exceedingly difficult to
bring about a storage of protein in the body, except
when the muscles are being much exercised.* So soon,
moreover, as the period of exercise ceases the protein
gained is rapidly lost again. One cannot hope, there-
fore, to make an individual muscularly strong merely by
supplying him with protein; exercise must always be
taken at the same time. Convalescence from acute
disease is another event which permits of protein being
stored up, for in such circumstances the waste of
tissue which has taken place is rapidly made good by
retaining protein in the body, even although the amount
supplied in the diet be not very great. During preg-
nancy, too, protein is retained in order to take part both
in the formation of the foetus and in the hypertrophy of
the uterus and mamme.

As regards the influence of muscular labour, experi-
ment has clearly shown that the waste of tissue which
if causes is not really great, and there is therefore no
physiological reason for the consumption of an excessive

* The gain of protein in a fully-grown animal is attained by am

hypertrophy of cells already existing, not by the development of
new cells,

8 APPLIED PHYSIOLOGY

quantity of protein food during training merely to make
good wear and tear.

We may now pass on to consider the other great

* function of metabolism.
Tn,
2. The Conservation of Bodily Energy.

1. Expenditure of Energy.—By means of experi-
ments with the respiration calorimeter the daily ex-
penditure of energy in the body can be calculated |
without much difficulty. The chief items of expenditure
are these: (i.) internal work (heart, respiration, heat
production, secretion, excretion, etc.); (ii.) digestive
work ; (ili.) external or muscular work.

The expenditure of energy in the performance of
mental work cannot be calculated, and, indeed, external
work is the only item which can be estimated with any
accuracy.

(i.) By internal work is meant all the work which is
required for carrying on the chief vital processes of the
body, without which life would be impos@ible. The work
of the heart alone amounts to abo 0,000 kgm.
(183 Calories),* or about 64 foot-ton r day. “In
diseased conditions, in which the work of the circulation
is carried on with difficulty, this amount may be very
largely increased (see Chapter IV.), and may become so
great, indeed, that no margin of available energy is left
for any form of external work. A,-diliitent in such a
condition is thus inevitably condemned to a life of com-
plete inactivity. The work performed by the muscles
of respiration in elevating the chest amounts to about

* Allowing for heat produced as well.

METABOLISM 9

6,500 kgm., or 21 foot-tons, daily. Here, again, in
pathological conditions this necessary work may be
greatly increased in amount, and the daily output of
energy of the body proportionately raised.

Of all the items which fall under the heading of
internal work, heat production is, however, by far the
greatest. The mere performance of work by the heart
and the muscles of respiration involves the liberation as
a by-product of more than twice as much energy in the
form of heat as is actually required for the performance
of the mechanical work of respiration and circulation.
Whether besides this waste heat an additional quantity
is produced as a result of the mere vital activity of the
cells (apart from any work done) is a matter on which
physiologists are not all agreed, and we shall return to
its discussion later on (Chapter II.). The question is an
important one; for if heat results from the mere ‘living’
of the cells—if it be a by-product or excretion of. life as
such—then it is conceivable that cells of a low degree of
vitality may produce less heat, and therefore expend less
energy, than those. which are more ‘alive,’ and an
explanation would be found for the apparently greater
degree of economy in metabolism which some individuals
exhibit when compared with others. Some such explana-
tion, as we shall see, is almost necessary to account for
individual differences in nutrition.

(ii.) The item digestive work covers the expenditure
of energy required for the digestion and absorption of
the food. It is an item of no small importance, amount-
ing as it does in the case of an ordinary mixed diet to
about 150 or 200 Calories—i.c., about 6 to 8 per cent. of

10 APPLIED PHYSIOLOGY

the total intake of energy. It varies, of course, with the
bulk of the diet, for the manipulation of large masses of
food materially increases the amount of muscular work
to be done by the stomach and intestine. This has to
be taken into consideration in appraising the value of
some forms of purely vegetable diet which are apt to be
very bulky. Thus, it has been calculated that in the
case of a horse fed entirely upon hay 48 per cent. of the
energy of the food is expended in its digestion and
absorption. It varies, too, with the chemical constitu-
tion of the food. The digestion of proteins seems to
demand most work, then that of carbohydrates, whilst
that of fats requires least of all. Of common articles of
food, milk is that which entails the least digestive work.
Anything which increases the frequency or force of
peristalsis also raises expenditure under this head, and
part at least of the wasting effect of purgation or
diarrhoea is thus to be explained.

Gi.) By external (as distinguished from internal)
work is meant the work expended by the muscles in
performing not only the day’s task of labour, but that
required for locomotion and all the thousand ways in
which the skeletal as opposed to the visceral mus¢les
are brought into play. It is inevitably, therefore, a
heavy item.

It must be remembered, too, that all expenditure on
actual external work is unavoidably accompanied by an
increase of the work done by the heart and lungs as
well as by an increased production of heat. Physiolo-
gists differ as to exactly how much of the increased
expenditure of energy that muscular labour entails goes

METABOLISM 11

in the production of the outward task and how much in
increased internal work, but one may say approximately
that only about one-fifth should be put down to the work
itself, and four-fifths to internal expenditure. The human
body is therefore rather more economical than the best
steam-engine, which gives about 15 per cent. of its total
discharge of energy as work, and the rest as heat.

Practice, however, is of great importance in this con-
nection, for a man who is skilled in the performance of
any special piece of work certainly does it more economic-
ally and with relatively less increase of internal work
than one who is unskilled. One illustration will make
this clear. It was found by Hueppe, in comparing the
expenditure of energy by an untrained town-dweller and
an Alpine carrier in climbing, that in the course of a
six hours’ ascent the former expended 449 Calories in
work and 1,000 Calories in heat, whereas the latter
expended 884 Calories in work, and only 565 in heat.

Fatigue, pain, overheating of the body, and being in
bad health or ‘out of condition,’ are also all of. them
factors which increase the ‘expense’ of work. A man,
for instance, who is tired, footsore, and very hot, will
expend more energy in walking a given distance than is
really necessary to carry his body over the same space
under better conditions.

It must not be assumed from all this that human
labour is necessarily cheaper than that of a steam-
engine. Quite the contrary, of course, is the case. If,
for instance, a labourer works five days a week and earns
20s., of which he spends 5s. upon food, and has a total
daily intake of energy of 3,000 Calories, of which 500

12 APPLIED PHYSIOLOGY

are expended upon actual mechanical labour (exclusive
of increased internal work), then only one-sixth of the
sum expended on food is returned in work—.e., 10d.
worth a week represents the external work done, or
4s. 2d. worth, if one assumes that four-fifths have to be
added to this to allow for increased heat production. In
other words, only one-fifth of a man’s wages really go to
produce work if one regards him as a ‘hired machine.’
One pound of coal a day consumed in a steam-engine
would have produced more than as much work, assuming
that the combustion of the coal yields 3,000 Calories of
energy, and that the engine converts 15 per cent. of this
into work.

It will be obvious from this that the larger part of
a man’s earnings must always be spent simply in keep-
ing the machine ‘ alive,’ apart from whether it does any
work or not. If, on the other hand, one regards the
machine as merely a ‘ peripatetic residence for the soul,’
which has to be kept both alive and warm, then the
only waste in it is the heat given off from the surface,
and its efficiency from this point of view is advanced

to about 50 per cent. of the energy consumed, which’

is better than that of any human invention.” Ue

2. Income of Energy.—To balance its expenditure,
the body is dependent for its income of energy upon the
chemical constituents of the food.+ Of these, the pro-

* Thurston, ‘The Animal as a Prime Mover’ (Smithsonian
Report for 1896).

+ It is possible that the body may derive some energy from
sources other than food. Radiant heat—e.g., from the sun—may
‘ certainly be regarded as such a source, and there may conceivably
be others of which as yet we know nothing.

METABOLISM 13

teins, carbohydrates, and fats are alone of importance.
It is true that small amounts of energy are contained in
other ingredients of the diet, such as gelatin, but for
practical purposes only the three first named need be
considered. The energy yielded by a unit (1 gramme)
of each of these constituents in the body, expressed in
Calories, is as follows:

Protein... ee ..- 4*1 Calories.
Carbohydrate hy Rae i a
Fat hag ~A POA 2 os

Now, the total amount of energy expended by a man
of average weight doing a moderate amount of muscular
work is something between 2,500 and 3,000 Calories,
or the amount which would be produced by the con-
sumption of 1 pound of good coal; and it follows that, if
equilibrium is to be maintained, the total intake in the
form of food must equal this sum, and if it does not do
so chronic malnutrition and inanition result.

What proportion of the total energy required should
be supplied by each food constituent is an important
question in practical dietetics. «

We have already seen that protein should be regarded
as only accidentally a source of energy, its chief use
being to replace the loss of nitrogenous material in the
tissues, and that by far the largest proportion of the
body’s energy must be derived from carbohydrates and
fats.

Amount of Carbohydrate and Fat required.—As
to the proportion of the total intake of energy which
should be supplied by carbohydrates and fats respec-

14 APPLIED PHYSIOLOGY

tively, we have no clear physiological data to guide us.
So far as the tissues are concerned, indeed, the physio-
logical teaching appears to be that it is largely a matter
of indifference, but that, for the sake of the digestive
organs, it is best to derive our energy, not from one or
other exclusively, but in some measure from both. From
a medical point of view, however, it is not so certain
that fats and carbohydrates can replace each other in
the diet with indifference. Rickets, for example, is a
condition which seems to result from the consumption
of a disproportionate amount of carbohydrate and too
little fat. There is reason to believe, too, that a diet
which contains an excess of carbohydrates may pre-
dispose to diabetes by straining the sugar-assimilating
functions. On the other hand, when diabetes is once
developed, we are compelled to supply the greater part
of the patient’s energy in the form of fat.

Meanwhile it may be assumed that 50 grammes of
fat and 500 grammes of carbohydrate represent the
accepted standard for each ingredient; but it must be
borne in mind that these are capable of replacing each
other to a large extent, in accordance with the digestive’
peculiarities of the individual and the opportunities he
has of obtaining a supply of each ingredient.

The following balance-sheet, the expenditure side of
which is derived from observation of an actual case by
Von Noorden, whilst the income is approximately that
of the Chittenden standard, will serve to show in a
concise form the practical application of the study of
metabolism from its quantitative side. It exhibits a
surplus of income over expenditure, and it is assumed

METABOLISM 17

A patient on the Banting diet, therefore, must inevitably
suffer some loss of muscle besides his loss of fat.

The metabolic balance-sheet above described may be
regarded as a standard or average one for a man of
medium weight and doing a moderate amount of
muscular work. We have now to discuss how it is
affected by various external and internal influences.

1. Influence of Age and Sex.—The child, as some-
one has remarked, ‘is not merely a young city, but a
city of young inhabitants.’ In other words, owing to
their greater youth, the vital activity of the cells is
greater in childhood, and metabolism more intense.
The demand for food, therefore, apart from the necessity
for meeting the requirements of growth, is greater than
in the adult. Doubtless, too, the greater metabolic
activity of the child explains the immunity of childhood
from certain diseases—e.g., gout—which are common in
later life. In old age, on the other hand, respiratory
exchange and heat production are found to fall, so that
life may be maintained at this period on a very small
amount of food.

Sex appears to exert but little influence upon meta-
bolism if allowance be made for differences of weight and
build.

2. The ‘build’ of the body exercises considerable
influence upon metabolism. Tall people have a larger
surface in proportion to their bulk than short ; their
heat loss is therefore greater, and a larger sum of
energy in the form of food must be taken in to balance
it. This may explain why it is that tall persons are apt

2

18 APPLIED PHYSIOLOGY

to remain thin, for they need to produce so much heat
that there is no margin left for storage as fat.

Again, a man of large muscular development has a
more active metabolism than one whose weight is to a
ereat extent made up of fat; for muscle is a ‘ vital’
tissue, whereas fat is, comparatively speaking, ‘ dead.’
On the other hand, the mere carrying about of a stone
or two of fat increases considerably the mechanical task
of the muscles of locomotion in a stout man. There is
thus a sort of automatic check upon indefinite increase
of stoutness, for beyond a certain point the greater
expenditure of energy required for locomotion will use
up all the surplus intake in the form of food.

8. Influence of Work and Rest.—The large share of
the daily expenditure of energy in the body which is
due to external or muscular work has already been
pointed out, and it will readily be understood that
variations in the amount of work performed have more
influence upon the total turnover of energy than any
other single factor. It has been calculated that the
following amounts of energy must be supplied to meet
the requirements of varying degrees of muscular work i ;
the case of a man of about 10 stone weight (Magnus-
Levy) :

Calories.
At rest in bed ... Pa ide .»» 2,000
Resting indoors . - ba « 2,280
With light ied wake wr ... 2,600
With moderate muscular labour ... 8,100
With severe muscular labour ... «.¥ 13,500

The greatest economy of energy is attained by keeping

|

METABOLISM 19

an individual at complete rest in bed, for not only is
external work reduced to a minimum thereby, but heat
loss is also greatly curtailed. In these circumstances
the total turnover of energy is probably not more than
1,600 Calories per day in the case of an average patient,
an amount which could be supplied by 4 pints of milk.
If, on the other hand, a patient is allowed merely to be
up and moving about in the ward without doing any
real work, his turnover of energy is at once increased
about 10 per cent. It will readily be understood from
this how great an aid complete rest in bed is in cases in
which it is important to reduce a patient’s expenditure
of energy to its lowest terms.*

* Some practical, examples of the amount of energy expended
in different forms of exertion may be of interest. H.g., an hour’s
saunter consumes 137 Calories, or about $ ounce of fat; an hour’s
quick walk consumes 260 Calories, or 1 ounce of fat (Miiller), A
walk of four miles increases the expenditure of the body by about
275 Calories, which could be covered by the consumption of 1 ounce
of fat (Zuntz). A bicycle ride of nine and one-third miles expends
318 Calories of energy, or 14 ounces of fat (Zuntz). If a man of
70 kilogrammes weight takes to living up a stair 15 metres high,
and goes up four times a day, he does 4,200 kilogrammes of work
daily; but, as only 80 per cent. of the energy he expends actually
goes in doing the work, the increase in his metabolic turnover really
amounts to 14,000 kilogrammes, or 32°9 Calories daily. This equals
5°54 grammes of fat per day, or about 4 pounds of adipose tissue
per year (von Noorden),

Climbing expends twenty times more energy than walking on the
level ; 2.¢., to lift one’s weight one mile in a day is equivalent to a
walk of twenty miles,

A man walking against a strong wind for a mile expends an
amount of energy which would have raised him 8,202 feet, at a
cost of 1,200 Calories (about 44 ounces of fat).

Twelve per cent. more energy is expended when standing at
attention than when standing at ease (Miiller). ‘

,

20 APPLIED PHYSIOLOGY

From a therapeutic point of view, it is interesting to
note that massage has no appreciable influence upon
metabolism, and is therefore in no real sense a sub-
stitute for exercise.

As regards the best source from which to obtain the
increased amount of energy that hard work entails,
physiologists are now almost unanimous in recommend-
ing the carbohydrates and fats, for protein is only used
by the body when these are not available. Whether
fat or carbohydrate should be selected is chiefly a matter
of the digestion, but it is possible that when a rapid
output of energy is desired carbohydrate is preferable,
whereas for a more gradual expenditure over a long time
fat may have some advantages. Whatever the empirical
results yielded by a large meat diet in training may be,
therefore, there is certainly no scientific grounds for its
adoption.

Of the influence of mental work upon metabolism we
know very little, but there is some reason to believe that
it is accompanied by a diminution of general, and an
increase of cerebral metabolism, as manifested especially
by an increased elimination of phosphoric acid.* There
is thus some justification for the old belief that phos-
phoric acid is a useful ‘ brain-food.’ oe

4, Of the influence of such external conditions as
season, period of the day, and weather upon meta-
bolism we know but little. It would seem, however, as
if, contrary to general opinion, the metabolic processes

* See Mairet and Florence, ‘Le Travail Intellectuel et les

Fonctions de l’Organisme,’ Montpellier, 1907 (rev. in Brit. Med.
Jowrn., 1907, ii. 539).

METABOLISM 21

in the body are but little affected by them. It used to
be believed that metabolism was most active in early
spring, and that at this period every function was at its
highest degree of efficiency, a decline taking place as
summer advanced, with a gradual rise again in the
autumn. Later observations have shown, however,
that the demand for food, and presumably, therefore,
the activity of metabolism, is not less in summer than
in winter. The daily variations in metabolism, also,
would appear to be very slight if the influence of mus-
cular exertion and the taking of food be eliminated, but
there remains a certain amount of evidence to show that
metabolism is more active in the later part of the day
than in the earlier, the maximum being reached about
5 p.m., and the minimum about five o’clock in the
morning.* Medical experience would certainly seem to
show that ‘ vitality’ is less in the early hours of the
morning than at other times, and the need for stimulants
in asthenic conditions is then greater.

The influence of ‘weather’ upon metabolism is a
subject of great interest to the practical physician, but,
unfortunately, we have no accurate information about
it from the physiologist. Such observations as have
been made relate to the part played by such ingredients
of weather as heat and moisture, and will be referred to
in another chapter.

x 5. Of the influence of the nervous system on meta-

* For a comprehensive study of the whole subject, see H. D.
Marsh, ‘The Diurnal Course of Efficiency,’ Archiv. of Phil. Psychol.
and Scientific Methods, No. 7, July, 1906; New York, Science
Press (abst. in Brit. Med. Jowrn., 1907, ii. 1541).

22 APPLIED PHYSIOLOGY

bolism the physiologist has also little to tell us, although
from the clinical point of view there is evidence that
such an influence must be exerted in no small measure.
How else is one to explain the chronic malnutrition so
often met with in neurasthenic subjects, and which may
exist quite apart from any disturbance of digestion? In
the acute forms of neurasthenia, indeed, a patient may
emaciate rapidly even although he be taking a fair
amount of food. There is one way in which it is
obvious that nervous control can influence the amount
of general metabolism. The maintenance of ‘tone’ in
the muscles is one of the functions of the nervous
system, but ‘ tone’ involves chemical transformations in
the muscle akin to those which take place in contraction,
though doubtless less in degree. The greater the degree
of tone in the muscles, then, the greater their consump-
tion of energy, and it is noteworthy that in many neurotic
subjects there is evidence, from an exaggeration of the
tendon reflexes, of the presence of an abnormal degree
of ‘tone.’ On the other hand, flaccid paralysis of any
large number of muscles must lessen metabolism, just
as it has been found experimentally that poisoning with
curare does. These nervous influences upon metabolism
are apparently exerted through the medium of the
ordinary nerve fibres which are concerned in calling
into play the functional activity of the tissue concerned
(e.g., in the case of the muscles, the motor nerves, in
the case of glands the secretory), and not through any
special trophic fibres, for the existence of these—though
often assumed clinically—has never yet been proved
physiologically.

~ -_——— ooo

METABOLISM 23

It would almost seem as if the nerves which subserve
the physiological function of any organ or tissue exert
either a promoting influence on its anabolism or a
restraining influence on its katabolism, with the conse-
quence that when the nervous influence is withdrawn or
perverted rapid tissue destruction or alteration ensues.
It is perhaps in some such way as this that the influence
of emotional and mental states on local and general
nutrition is exerted, an influence which is shown locally
in the blanching of the hair from fear, and generally in
the promotion of fatness by cheerfulness (‘laugh and
grow fat’), and of leanness by anxiety. Again, ‘ consti-
tutional’ as opposed to muscular strength may perhaps
be due, in part at least, to a firm grip of the nervous
system upon metabolism. Medical experience, at all
events, would seem to show that a strong will and
a cultured mind make for strength and long life, whilst
a weak brain and will are often accompanied by a feeble
general vitality. |

6. Influence of Internal Secretions.—The term
‘internal secretion’ has come to be used in rather
a loose way, and in clinical medicine, at least, it is
often employed like the terms ‘reflex action,’ ‘ trophic
influence,’ and ‘toxin,’ as a sort of deus ex machindé to
explain pathological phenomena which would be other-
wise difficult of comprehension. It is, of course, in
a sense true that every tissue and organ produces an
‘internal secretion,’ inasmuch as the waste products
of its métabolism are turned into the blood-stream, and,
being diffused throughout the body, may conceivably
influence chemical processes in remote parts. It would

24 APPLIED PHYSIOLOGY

be more correct, however, to speak of such waste pro-
ducts as internal excretions, and to reserve the term
internal secretion for the products of glandular organs
which are not provided with ducts opening on to a free
surface. In any case, the fact that removal of an organ
is followed by certain derangements of metabolism is
no proof that the organ in question produces even an
internal excretion, for the changes observed might quite
as well be due to the blood being no longer deprived of
some of those constituents which should be taken out of
it by the organ removed. There is, therefore, a great
deal of loose thinking on the whole subject, and in
considering the influence of internal secretions on meta-
bolism it will be well to restrict ourselves to the more
exact connotation of the term indicated above.

Now, of internal secretions in the strici sense we
know for a certainty of one only—namely, the secretion
of the thyroid gland, the active constituent of which is
the iodine-containing compound known as ‘ iodothyrin.’
This is not the place in which to speak of the exact
chemical nature of this compound, and, indeed, but
little is known about it, but that it exerts a profound
influence upon metabolism there can be no question.
That influence may be described as one of stimulation
resulting in a great increase in the rate of oxidation
in the tissues. The increased elimination not only of
carbonic acid gas, but also of urea, which follows thyroid
feeding shows that both the fatty and nitrogenous
tissues are involved in the increase of katabolism which
it brings about. The pronounced effect upon the nitro-
genous tissues—presumably the muscles—is important

METABOLISM 25

clinically ; for were fat alone affected we would possess
in the thyroid an ideal remedy for obesity, but the
simultaneous destruction of fixed nitrogenous tissues
renders it a dangerous drug to employ for that purpose.
Considering the extremely minute quantity of iodothyrin
which is required to produce a profound metabolic effect,
one must regard it as one of the most potent of all the
agents at our command for influencing chemical changes
in the body, and the close resemblance of its action in
this respect to that of the poisons of many infective
processes renders it of the greatest interest to the
physician.

Further, the influence which the thyroid secretion
exerts upon metabolism explains fully the results
observed in disease of the gland. Myxcdema, for
example, is pre-eminently a condition in which meta-
bolic change has undergone a partial arrest, resulting
in the accumulation of an immature connective tissue
beneath the skin, the cells of which have not undergone
the normal process of division and maturation. In the
scalp, again, the development of young hairs is at a
standstill, and when the effete hairs fall out there are
no fresh ones to take their place, and the patient
becomes bald. Fat also accumulates in the body, and
from the lessened production of heat the patient has
a subnormal temperature and a constant feeling of
chilliness. In this way one could run through all the
well-known symptoms and signs of myxedema, and
show that they are all the result of a partial arrest of
metabolism brought about by the failure of the stimulus
which the thyroid secretion should normally supply.

26 APPLIED PHYSIOLOGY

Conversely, Graves’ disease is a condition characterized
by an increased rate of tissue metabolism, and many
pathologists believe that the essential fact in its etiology
is an over-activity of the thyroid gland. It is interesting
in the light of these facts to speculate on the question
whether variations in the metabolism of individuals
may not be due to a varying degree of activity of their
thyroids. Is the sluggish ang obese person one whose
thyroid is functionally rather inactive, and the alert
Spare man one whose metabolism is constantly being
stimulated by an exceptionally abundant outpouring of
iodothyrin? Again, is the tendency to accumulate fat
after the middle period of life to be ascribed to a natural
decline of thyroid activity about that time? It would
take us too far afield to consider these questions in
detail, but they are full of interesting suggestion to the
clinician.

Of the influence, if any, of the suprarenals on general
metabolism we know nothing. Even assuming that
adrenalin is a true secretion, its action is exerted upon
the vascular system, and not upon the tissues at large,
and upon the phenomena of Addison’s disease experi-/
mental physiology has not yet thrown any clear light. /

It is commonly assumed that the reproductive glands
exert a marked influence upon general metabolism.
Physiological experiments upon this subject have yielded
rather discordant results, but there is a considerable
amount of evidence to show that castration in either
sex results in a diminution of oxidation, and a tendency
to the accumulation of fat. This tendency is well shown
in many women after the menopause. Whether this is

METABOLISM QT

due to the direct withdrawal of an ‘ internal secretion’
(in the wider sense), however, or whether it is the
result of the change in disposition which the operation
is apt to bring about, is not yet determined. In favour
of the former hypothesis are some experiments which
seem to show that the administration of ovarian extract
is able to counteract the effects of ovariotomy in animals,
and to raise the oxygen cgnsumption again to its normal
level. Evidence is also accumulating that the develop-
ment of the secondary sexual characters, the changes
in the uterus which determine menstruation, and the
enlargement of the mammary glands during pregnancy,
are all the result of chemical influences.

More and more, then, is it becoming evident that no
organ lives to itself alone, but that the chemical changes
which take place*in each may be of the greatest import-
ance to metabolism as a whole, and to the normal
interchanges in others.

7. Influence of Personal Peculiarity.—A factor in
metabolism which is not often considered by the physio-
logist, but which is of the first importance to the
physician, is the question of personal peculiarity.
Putting aside such agents as differences of age and
build, and variations in the amount of body fat, by
which differences in the metabolic balance-sheet of
individuals can be explained, is there any reason to
suppose that the activity of metabolism is greater in
some persons than in others? As regards the quali-
tative side of metabolism, we shall see that individual
peculiarities are not only possible, but can actually be
- proved to occur; but even as regards the total turn-

28 APPLIED PHYSIOLOGY

over of energy in the body, there is a strong presumption
that such differences exist. It is tempting to suppose,
for instance, that the vital activity of the cells is greater
in some persons than in others. A feeble vitality of the
cells might explain the undoubtedly greater tendency to
obesity in some persons and families than in others.
From a physiological point of view such persons might
be regarded as very economical machines, their economy
being effected by a diminished output of heat. That a
lowering of general metabolism is attended by diminished
heat production is shown in the case of such diseases as
myxcedema and diabetes, in which the body temperature
is habitually subnormal; and it is conceivable that in
some individuals an unusually large fraction of the
energy set free by oxidation of the food is converted to
work, and an unusually small fraction to heat. It must
be admitted, however, that investigations into the
metabolism of obese individuals have not clearly estab-
lished the occurrence of such physiological economy,
though some distinguished physiologists, such as Cohn-
heim and Bouchard, have been believers in its possi-
bility. Meanwhile the question must be regarded as
still sub judice. Be |
Individual variations in muscular tone must also, as
already described, affect the total amount of metabolism.
A ‘highly strung’ person is one whose muscles are
- always in a high state of ‘tone,’ and are therefore
always consuming energy; such a one has brisk knee-
jerks, and is characterized by ‘energy’ which leads him
to perform muscular movements very quickly (and
therefore uneconomically), and also to be constantly

METABOLISM 29

executing superfluous movements (note how he is con-
stantly twisting and untwisting his fingers, clasping
and unclasping his hands, or walking up and down the
room instead of sitting in an easy-chair). In all these
ways energy is expended, and the balance for ‘ savings’
in the form of adipose tissue is reduced. It is in this
way that ‘temperament’ affects ‘physiological person-
ality’; or one might reverse the order of cause and
effect, and say, perhaps with equal truth, that it is the
possession of a protoplasm of unusual vital activity
which expresses itself inwardly by an active metabolism,
and outwardly by all the marks of the energetic
temperament. To the physician, at all events, the
metabolic peculiarities or physiological personality of
his patient is a factor of the greatest importance in
practice.

QUALITATIVE METABOLISM.
1. Proteins.

Physiologists are as yet only beginning the investiga-
tion of the chemical changes which proteins undergo in
the body, and of the facts already ascertained but few
are capable of application in medicine. This line of
research, however, is now being actively prosecuted, and
there is every reason to hope that the results which
it will yield will soon throw a flood of light on many
of the obscure disorders of metabolism met with in
disease. In the following paragraphs an attempt will be
made to trace the life-history of the proteins in the body
so far as present knowledge permits.

The protein of the food is first brought into solution

30 APPLIED PHYSIOLOGY

in the stomach, and its molecules are then split up in’
the intestine into finer fragments, nearly all of which are
amido-acids. It is in this form that proteins are absorbed,
and out of these fragments the specific body proteins are
again built up. It is not yet determined where this
reconstitution takes place. There is much reason to
believe, however, that the epithelial cells of the intestine
are mainly responsible for the rebuilding, and that the
proteins of the blood are the material that they produce.
On this view all the proteins of the food are ultimately
converted into serum proteins, which are in turn taken
to pieces by the cells of the tissues, and from the products
of their disintegration the special protein peculiar to any
particular tissue is finally formed. On the other hand,
there are some who believe that the amido-acids derived
from the original food-proteins are conveyed to the
tissues direct, and that it is from them that the specific
tissue-proteins are reconstituted. Whichever view be
correct, it is easy to understand how the initial picking
to pieces of thé protein molecule can enable the body out
of the manifold forms of food-protein to produce for
itself any kind of tissue-protein required. It must be /
remembered, however, that there are many different
kinds of protein contained in the food, and that the
nature of the amido-acids or ultimate fragments of which
these are composed is very variable; indeed, at least
twenty different kinds of amido-acids are already known.
One ought not, therefore, to speak of the food containing
so much ‘protein,’ as if the latter were always one
definite chemical compound. It may well prove to be
the case that it is not a matter of indifference to a patient

METABOLISM 31

what the kind of protein on which he is fed may be, but
that certain varieties, yielding particular forms of amido-
acids, may be peculiarly suitable or specially harmful
in particular pathological states.

Having once traversed the intestinal wall, it would
appear that protein is subjected to different treatment
according to the particular use which it is to serve.
That portion which is destined to serve as a source of
energy (or ‘ energy-protein,’ as we may call it) appears
rapidly to undergo a process of ‘ denitrification’ (possibly
in the liver), by which the nitrogen-containing part
of the molecule is split off, leaving the carbonaceous
moiety, which may contain 90 per cent. of the energy of
the original molecule, to be utilized, like fat and carbo-
hydrate, as a source of work and heat. The remainder, or
‘repair-protein,’ is conveyed to the tissues, and there enters
into the actual living substance of the cells, ultimately
replacing the molecules which are worn out in the vital
processes. The nitrogen-containing part of the ‘energy-
protein’ is speedily broken down by oxidation, and
eliminated chiefly in the form of urea and inorganic
sulphates; the repair-protein, on the other hand, is
broken down slowly, not by oxidation, but by a process
which seems more to resemble ferment action, and
eliminated largely in the form of kreatinin, uric acid, and
neutral sulphur compounds.

There are thus two main lines along which protein
metabolism proceeds, each with its own objects and
resulting in the formation of its own end-products.

The proportion of the total intake of protein which is
destined to follow each of these two possible lines depends

32 APPLIED PHYSIOLOGY

upon various circumstances. If the intake be greatly in

excess of the minimum required for the maintenance of |

nitrogenous equilibrium, the larger part is devoted to
early denitrification and utilized for energy produc-
tion. Much heat may be liberated in consequence of
this, which may, indeed, be harmful in cases in which
heat regulation is defective. Hence the importance of
avoiding large protein meals in fever. If, on the other
hand, but little protein is consumed, a large proportion
finds its way to the tissues. The amount and nature of
the other food constituents also exert a determining
influence in the matter. The gelatin, carbohydrates,
and fats of the food exert a shielding influence on the
protein, preventing it from undergoing the ‘ denitrifica-
tion’ process, and enabling a larger proportion to take
part in tissue metabolism than would otherwise be the
case. This shielding process is known to physiologists
as the doctrine of the ‘protein-sparers.’ The exact
mechanism of the sparing process is unknown to us, but
some idea of its possible modus operandi may be arrived at
by the use of a somewhat anthropomorphic simile. Let
us assume that into the neighbourhood of a cell there is
brought in solution an equal number of molecules of
protein, carbohydrate, and fat respectively. tt would
appear that the cell has least difficulty in ‘tackling’
(to use an expressive colloquialism) the molecules of
protein, possibly because they are most like itself, and
therefore least foreign to it, and in consequence more
molecules of protein are broken up than of either carbo-
hydrate or fat. If, however, instead of an equal number
of molecules of each kind reaching the neighbourhood of

METABOLISM 33

the cell, there is a great preponderance of those of carbo-
hydrate and fat, the ‘mass influence’ of these asserts
itself, the attention of the cell is, as it were, distracted
from the protein, and some of the latter safely runs the
gauntlet and escapes denitrification.

Whether or not this represents with any accuracy an
approximation to what actually takes place, there can be
no doubt of the importance of the influence of the protein-
sparers, and the way to ensure the least degree of degrada-
tion of protein to the purposes of energy production is to
take care that carbohydrates and fats reach the cells
along with it. Now, in vegetable foods proteins and
carbohydrates are so intimately mixed that this result
is achieved without difficulty, and hence it is that nitro-
genous equilibrium can be more easily attained on a
vegetarian diet than on any other. Similarly, if one
wishes to maintain life on as low an intake of protein as
possible, care should be taken that the protein food is
not mainly consumed at one meal, but that it is spread
over the day and mixed with non-protein ingredients.
In this way much more of it is likely to escape denitrifica-
tion, and be available for purposes of tissue repair.

It will be evident, then, that part of the protein which
is utilized for the production of energy is, so far as its
nitrogenous moiety is concerned, wasted, for carbo-
hydrate and fat would have served the purpose just as
_ weil. This, in point of fact, is the contention of those
who say that the ordinary protein-food standard is too
high. Indeed, they go further, and say that such pro-
tein is not only wasted, but is injurious, in so far as the
elimination of the urea and other products of its dis-

3

34 APPLIED PHYSIOLOGY

integration entails work upon the excretory organs. In
other words, the ideal they would have us aim at is the
utilization of protein—if that be possible—for repair
purposes alone.

Of the stages in the breaking-down of the repair-
protein we know very little, but there is reason to
believe that, like the preparation of food-protein for
assimilation, it consists in resolution by successive stages
into amido-acids. In normal circumstances these
undergo further destruction, and mere traces of them
appear in the urine, but in pathological states they may
be excreted in large amounts. The appearance of leucin
and tyrosin in acute yellow atrophy of the liver, and
the anomalies of metabolism which result in cystinuria
and alkaptonuria, are examples .of such imperfect
destruction.

2. Fats.

The assimilation of fat appears to be a much simpler
process than that of protein. The fat molecules of the
food, having been split up by digestion into fatty acids
and glycerine, are absorbed in that form by the cells of the
intestine, and apparently immediately reconstituted into
fat ; they then reach the general circulation by means of
the lymphatics. By the cells fat appears to be received
much more as a foreign body than protein is, and there
is not the same attempt to recast it into a substance
of uniform chemical composition. Hence it is that the
fat stored up may partake very largely of the chemical
characters of the fat absorbed. If, for instance, a fat
of low melting-point be given in large quantities, the fat
stored up is apt to be soft. This is, no doubt, the physio-

METABOLISM 35

logical explanation of the remark of an old nurse, quoted
by Lauder Brunton, that ‘ some fats are hard and some
soft, but cod-liver-oil fat is soon wasted.’ It is probable,
however, that after its storage in the tissues fat is gradu-
ally worked up into a chemical form peculiar to the
human body.

The functions of stored fat are stated to be two:
(1) to serve as a reserve of energy-forming material, and
(2) to diminish heat loss. Of the reality of the first of
these alleged functions there can be no question, but it
may be asked, How large a fat reserve is it advisable to
harbour in the body? There can be no doubt that in
the conditions of civilized life, with its regular three
meals a day, there is little advantage in the possession
of a large reserve of energy-forming material, although
in the case of a prolonged wasting disease such a reserve
must tend to lengthen the period during which a patient
can hold out. On the other hand, the presence in the
body of a large amount of fat has the obvious dis-
advantage that it increases the weight of the mass which
the muscles have to transport in locomotion, and in this
way must increase metabolic expenditure and restrict
activity. What the optimum amount of fat in the body
is we have no means of determining precisely.* It
probably corresponds to what is popularly known as the
‘ fighting-weight ’"—that is to say, the weight at which
. an individual is at his highest point of bodily strength
-and endurance, and this appears to vary very much in
different persons.

* In a well-nourished man fat makes up about 18 per cent. of
the body-weight.
38—2

36 APPLIED PHYSIOLOGY

Whether fat really restricts heat loss is not so certain.
Seeing that it is a highly vascular tissue, it is not quite
easy to see why it should, although it seems certainly to
be true that lean individuals stand cold badly. We shall
return to this point in another chapter.

In addition to its formation from the fat of the food,
body-fat is undoubtedly derived from carbohydrates—a
fact which is turned to account every day in the treat-
ment of obesity. The fat so derived appears to be richer
in palmitin and stearin and poorer in olein than fat
derived from fats in the food. Whether protein can be
used to form fat is a question which is still not definitely
settled. Certainly, the amount of fat so derived must
be very small. Were it otherwise, the results of the
Banting system of treating obesity would not be so
satisfactory.

Of the stages in the destruction of fat in the body we
know but little, but they are probably—in their initial

steps, at least—very similar to the cleavage into fatty —

acids and glycerine which takes place in digestion.
The possibility of the production of 8-oxybutyric acid
in the course of cleavage is of great interest in connection
with the pathology of diabetes. The stages in the} pro-
duction can be seen from the following formule:

0,H;(CH, > CH, oF CH, re CO,)3 — Glyceryl tributyrate, a
typical fat.

H(CH, - CH - OH — CH, — CO,) =8-oxybutyvric acid.

That fats undergo such a transformation as this in

diabetes a study of the chemical pathology of that
disease seems to show, and it is possible that the change

~

/

METABOLISM 37

is always going on to a less extent even in normal
metabolism.

8. Carbohydrates.

From the comparative simplicity of the chemistry of
the carbohydrates and the ease with which sugar can be
recognized, even in small amounts, it might have been
supposed that by this time we would have been well
informed as to the details of carbohydrate metabolism.
In spite, however, of the immense amount of work which
has been devoted to the subject, and the stimulus to
research which has been supplied by the ever-present
riddle of diabetes, we are still profoundly ignorant even
of the main outlines of the process. We know that
carbohydrates are all converted into glucoses by the
processes of digestion, but so soon as these disappear
into the wall of the intestine our uncertainties begin.
That sugar reaches the liver by the portal blood and
is there converted into glycogen* is well established, but
in what form it leaves the liver is still open to dispute.
According to the classical view, glycogen is reconverted
into sugar by the action of a ferment, and in that form
is transported to the cells. Opposed to this is the view
of Pavy, who strenuously denies that carbohydrates
leave the liver in the form of sugar, and maintains that
they are worked up into combination with nitrogenous
material to form proteins, and in that form are carried
to the cells. It might be thought that the dispute could
be settled by the experimentum crucis of estimating the
amount of sugar in the blood of the portal vein during

* The liver contains about 10 ounces of glycogen, and the
muscles rather less,

38 APPLIED PHYSIOLOGY

fasting, and comparing it with that in the blood of the
hepatic vein. Needless to say, this experiment has been
tried many times, but observers are not agreed as
to the result. The fact appears to be that a degree of
difference which would be quite sufficient to establish
the truth of the classical view once and for all is yet
within the limits of experimental error in the estimation
of sugar. Apart from this, however, it would seem
unlikely that all the sugar entering the body could be
transported in a protein form; for, after all, though
most proteins do contain a carbohydrate radicle, yet the
amount of this in the ordiiiary blood-proteins is but
small. At present, however, the dispute is still un-
settled, though the vast mass of physiological opinion
is in favour of the classical view. The point is of im-
portance to the clinician in the pathology of diabetes,
for, according to Pavy, one factor in the production of
that disease is a failure of the liver to perform its
normal function of converting sugar into other forms,
with the result that it passes unchanged into the blood
and leaks out through the kidneys.* According to the
prevailing view, on the other hand, diabetes is due to
a failure on the part of the cells to utilize sugar, a
failure, in its turn, is consequent upon defective - power
of glycogen formation; for it is only as glycogen that
carbohydrates can be utilized, or, as von Noorden puts
it, glycogen is the natural fuel of the cells, not glucose.
In the reason for this failure of glycogen formation the
riddle of diabetes resides.

* Tt should be remembered that in health the whole volume
of the blood contains less than 4 ounce of sugar in solution,

METABOLISM 39

It is interesting to note that it is only those sugars
which are directly fermentable by yeast which are
capable of conversion into glycogen, and of subsequent
utilization in the body. Unfermentable sugars, such as
cane-sugar and lactose, if they reach the blood-stream
as such, are excreted by the kidney. It is for this reason
that these sugars are unsuitable for administration
hypodermically in artificial feeding, and the same fact
explains the tendency for nursing women to suffer from
lactosuria ; for if lactose is reabsorbed from the mammary
glands, it cannot be burnt up in the body, but is excreted
in the urine.

It is further noteworthy that it is only those sugars
which contain three carbon atoms, or a multiple of that
number, which are capable of direct fermentation, and
therefore of conversion into glycogen. Those which con-
tain five, seven, or any other number of carbon atoms
cannot be so converted, and should they gain access to the
blood, are only with difficulty destroyed, and are apt
to be excreted in the urine. Now, sugars with five
carbon atoms (pentoses) commonly occur in certain
fruits, and hence pentosuria, as it is termed, is a not
infrequent consequence of the free consumption of such
foods.

Iti must be remembered that there is a limit to the
capability of the liver to convert soluble carbohydrates
into glycogen. If the amount of carbohydrates con-
sumed be excessive, the liver may not be able to keep
pace with the supply, with the result that some escapes
conversion, and passing into the general circulation is
excreted by the kidney. To this the term alimentary

40 APPLIED PHYSIOLOGY

glycosuria is applied. The limit of assimilating power
varies in different individuals and in the case of different
forms of carbohydrate. For starch, owing to its very
gradual digestion, no limit is known. For some of the
chief sugars the limit is as follows:

For glucose ... 150 to 200 grammes in one dose.
», levulose ... 140 to 160 Ax a
», cane-sugar 150 to 200 9 ”
» milk-sugar 80 to 120 ‘ "9

It will be observed that the assimilation limit is less
for lactose than for any other form of sugar. This may
perhaps be due to some of it escaping the action of the
ferment in the intestine, which should convert lactose
into glucose and galactose, with the result that it reaches
the blood as lactose, in which form, as we have seen, it —
cannot be utilized. It is a curious fact that even in
advanced cases of cirrhosis of the liver it is by no means
easy to produce alimentary glycosuria, except in the case
of levulose, and such ‘alimentary levulosuria’ may be
regarded as a sign of ‘hepatic insufficiency.’ The
reason for this is unknown. . /

That some of the sugar which enters the body is con-
verted into fat we are quite sure, but we do not even
know for certain where this transformation takes place.
The liver is generally regarded as the most probable site,
but it is not unlikely that the cells: of the connective
tissue possess the power of fat formation also. There is
some reason to believe, on clinical grounds, that this
power of converting carbohydrate into fat is not well
developed in certain individuals, and that from the

METABOLISM 4]

consequent imperfect assimilation of carbohydrates
various diseased states may arise. Some cases of
glycosuria in elderly subjects, for example, may be due
to sugar running off through the kidneys instead of
going to form fat. Such persons are only ‘ glycosurics’
because they are not obese.

That sugar can be formed in the body from sources
other than glycogen a study of the chemical phenomena
of diabetes has made quite clear, and it was at first
supposed that proteins were the source from which sugar
could be so derived. This view received confirmation
when it became known that most proteins contain a
carbohydrate moiety—usually glucosamin—in their
molecule. Subsequent investigation, however, has sug-
gested doubts as to whether proteins can be an important
source of sugar, and whether their glucosidal constitution
is an adequate explanation of it—for, in the first place,
the commonest and most usual proteins are those which
contain least of the carbohydrate element; and in the
second place, diabetics may continue to produce large
quantities of sugar even when fed on proteins, such as
casein, which contain no carbohydrate radicle at all. It
has therefore recently been suggested that the amido-
acid alanin—and possibly also glycocoll and leucin—
may be the source of the carbohydrate derived from
protein. At all events, there can be no question that
sugar can be formed in the body from proteins, and that
in severe cases of diabetes it may be as necessary to
limit the consumption of protein as it is to restrict that
of carbohydrates themselves.

Opinion has now veered round towards regarding even

42 APPLIED PHYSIOLOGY

fats as a possible source of sugar, though this view as
yet lacks actual confirmation. How important a solution
of the problem would be to the physician in affording
him guidance in the dietetic treatment of diabetes need
not be pointed out.

Relation of the Pancreas to Carbohydrate Meta-
bolism.— When first it was discovered that complete
removal of the pancreas resulted in permanent glycos-
uria, and when subsequent histological investigation
showed the almost invariable presence of lesions of the
islands of Langerhans in patients who had died of
diabetes, a great step forward in our knowledge of carbo-
hydrate metabolism had certainly been made. Up to the
present, however, the therapeutic results of this increase
of knowledge have been disappointing. Experience
showed that the administration of pancreatic extracts in
all: forms and in all ways, or even transplantation of the
gland, failed to exert any influence on the course of
diabetes. It would appear, then, that it is not by the
mere elaboration of an internal secretion that the
pancreas promotes the utilization of sugar. Nor,
apparently, is it by neutralizing some ‘toxin,’ for the
injection of the blood of depancreatized animals into
those of others does not induce the disease. The view
that the pancreas produces some secretion which activates
a ferment in the muscles, which ferment is the active
agent in glycolysis or the katabolism of sugar, has also
fallen into disrepute, and the two most probable solutions
of the puzzle are that the pancreas produces a ferment
which (1) either promotes the polymerization of sugar
into glycogen, or (2) restrains the disintegration of

METABOLISM 43

glycogen into sugar. Which of these will prove to be
the correct explanation time will doubtless show.

Puncture Glycosuria.— Since the time of Claude
Bernard it has been known that puncture of a point
in the floor of the fourth ventricle results in the appear-
ance of sugar in the urine. The glycosuria so produced
disappears when the liver has been emptied of glycogen,
and is apparently the result of a disturbance of the blood-
supply of the liver through its vasomotor nerves. A
similar resuli is sometimes observed in man in con-
sequence of injury to the central nervous system, but the
glycosuria which results is transient, and in that way
differs from true diabetes.

Phloridzin Diabetes.—In addition to its production
by removal of the pancreas and by puncture of the floor
of the fourth ventricle, glycosuria may also be produced
in animals by the administration of phloridzin, a gluco-
side derived from the thorn-apple. The glycosuria so
brought about resembles very closely that of true
diabetes, and is accompanied also by an acid intoxica-
tion identical with that found in the later stages of the
disease in the human subject. It has generally been
supposed, however, that phloridzin diabetes is brought
about by an action of the drug on the ‘renal filter,’
which it renders more permeable to sugar, and that it
has therefore nothing in common with true diabetes.
Opposed to this explanation is the fact that much more
sugar may be excreted in the urine after the administra-
tion of phloridzin than the amount present in the blood
will account for, and it would seem that the drug must

44 APPLIED PHYSIOLOGY

actually lead in some way to an increased formation of
sugar. Certain facts seem to suggest that fat may be
the source of the increased sugar formation, but this is
not yet clearly established.

If the kidneys be diseased, the excretion of sugar
under the influence of phloridzin is much less than
normally occurs, or may even be absent altogether.
Advantage has been taken of this as a test of the
glandular activity of the kidney in cases of suspected
renal inadequacy.

Metabolism of Uric Acid.—A knowledge of the
metabolism of uric acid is of special importance to
the physician because of its bearings upon gout. It
must be confessed, however, that, in spite of an
enormous amount of work which has been done upon
the subject, we are still very far from a complete under-
standing of it. Some facts, however, have been made
out beyond dispute, and these, with their clinical applica-
tions, must now be briefly set forth.

The first point to grasp clearly is that uric acid
metabolism goes on quite independently of general.
protein metabolism, and pursues special lines of its own.
The amount of protein in the food has therefore no
necessary connection with the metabolism of uric acid,
and in considering the pathology of gout this must be
constantly borne in mind. The disentanglement of uric
acid metabolism from general protein metabolism, indeed,
must be regarded as one of the most important advances
in chemical physiology, and when it has once been
thoroughly grasped by physicians will do much to
dissipate the rather confused thinking about gout and

METABOLISM 45

‘ soutiness’ which has hitherto prevailed in clinical
medicine.

Uric acid belongs chemically to the group of bodies
called ‘purins,’ which possess a common nucleus, the
purin nucleus, or ring, having the following formula:

Uric acid is trioxypurin :

HN—co ‘ Bd do CO

It is not very long since it was believed that uric acid
resulted from the breaking down of any protein in the
body, and as a corollary of this it was taught that in
gout, in which there is an excess of uric acid in the
body, any protein food is bad for the patient, and he
should consume as little of it as possible. It is now
known that the breaking down of proteins as such does
not give rise to uric acid, but that the latter is derived
from three possible sources.

1. From Purin Bodies contained in the Food.—This is
called ‘exogenous’ uric acid. The foods which contain
most purin are flesh foods and the internal organs of
animals (e.g., liver and sweetbreads), peas, beans and
lentils, oatmeal, asparagus, tea and coffee.

Of the purins taken in with the food part are destroyed
in the body—probably in the liver—with the production

46 APPLIED PHYSIOLOGY

of glycin and possibly of oxalic acid and allantoin, and
only a fraction appears in the urine. Of oxypurins
(hypoxanthin), about one-half; of amino-purins (c¢.9.,
those derived from nuclein), three-fourths; and of
methyl purins (caffeine), two-thirds, are destroyed in
this way. Whether gouty individuals have less capacity
for destroying purin than others has not been definitely
determined, but in any case the attempt to lessen the
amount of uric acid in the blood by feeding an individual
on a purin-free diet is undoubtedly rational therapeutics.
A diet of milk and vegetables was recommended to the
gouty so long ago as 1729 by Dr. George Cheyne, and
has since, under the title of a purin-free diet, been
widely advocated in this country by Dr. Haig.

2. Uric acid is also produced by the breaking down of
body tissues which contain amino-purins (e.g., adenin and
guanin) and oxypwrins (e.g., xanthin and hypoxanthin).
The two former are most abundant in nuclein, the two
latter in muscle. The uric acid so derived is spoken of
as ‘endogenous’ uric acid. It was at first supposed that
the destruction of leucocytes supplied the nuclein from
which most of the endogenous uric acid arose, and this
opinion gained confirmation from the large excretion of
uric acid in cases of leukemia. It is now known, how-
ever, that there is no constant relation between the
number of leucocytes and the excretion of uric acid, and
present physiological opinion is more in favour of re-
garding the muscles as the chief source of endogenous
uric acid.

The amount of endogenous uric acid varies consider-
ably in different individuals, but is singularly constant

METABOLISM 47

for the same individual under the same conditions as
regards exercise, eic. It might be supposed that the
gouty person is one who produces an unduly large
amount of uric acid, but this is apparently not the case.
It is probable, also, that a mere fraction of the uric acid
produced endogenously ever reaches the urine, but that,
as happens with urates taken in with the food, a con-
siderable part is destroyed in the liver; but this is a
matter very difficult to investigate at all accurately. In
any case, the amount of uric acid produced endogenously
is almost beyond our control, and so our knowledge of
its production in this way cannot be turned to account in
treatment. .

8. A third way in which uric acid may, perhaps, be
produced in the human body is by synthesis from other
substances which do not contain the purin-ring af all.
We know that it is so produced in birds and reptiles
from ammonium lactate, but there-is no reason to sup-
pose that any large production of it takes place by this
method in man. Otill, a small percentage may be
derived from lactic, tartronic, and f-oxybutyric acids,
and it may be that persons of the so-called ‘ uric acid
diathesis ’ have a special aptitude for forming it in this
way. The supposed synthesis from glycin and urea,
which at one time was so prominent in physiological
teaching, is now discredited ; for glycin and urea, when
administered to mammals, cause no change in uric acid
excretion, and glycin is probably rather a decomposition
product than a precursor of uric acid. The same may
be true of urea.

Quite as important in the pathology of gout as the

48 APPLIED PHYSIOLOGY

source of uric acid in the body is the form in which it
circulates in the blood. Now, it is a curious fact that,
although the administration of purins is followed by an
increase in their excretion, yet mere traces of purins can
be discovered in the blood in health. It has therefore
been suggested that they circulate in a combination—
possibly with proteins — which prevents them from
giving the usual reactions (just as iron is masked by its
combination in hemoglobin); and another thinkable
hypothesis to explain gout is that in the gouty indi-
vidual this combination is for some reason not formed,
and that uric acid circulates as urates, a form in which
it is with difficulty excreted.

Finally, it has been ascertained that in health the
subcutaneous injection of uric acid, or its excessive
ingestion in the form of purins, is accompanied by an
increased excretion in the urine; but prolonged examina-
tion of the urine in gout shows that the excretion of uric
acid is not greater than normal. It seems to follow from
this that the excess of urates in the blood in gout must
be due to diminished excretion, and not to increased
ingestion of exogenous, or increased production of endo-

genous, uric acid. ft
7%

CHAPTER II
THE APPLIED PHYSIOLOGY OF BODY HEAT

Hzat is to be regarded as a by-product of the metabolic
processes described in the last chapter. It is not a thing
which the living body manufactures, as if does a secre-
tion, for its own sake; on the contrary, life and heat
are inseparable, and so long as life exists in the body, so
long will heat continue to be produced. It is important
to make this clear, for there is still a tendency to regard
heat as something which is produced, as it were, by an
effort, simply in order to keep the body warm. So far
from this being the case, the ordinary processes of
metabolism result in normal conditions in the production
of considerably more heat than is really required to
maintain the body temperature at its usual level. It
has been calculated, indeed, that were it not for the fact
that heat is constantly being lost from the body, a man
of 10 stones in weight, with the usual metabolic turn-
over of 8,000 Calories, would reach boiling-point in
thirty-five hours! The greater the degree of ‘ vitality,’
_the larger, naturally, is the amount of heat produced.
Hence, any agent which tends to paralyze the proto-
plasm of the body cells brings about a diminished pro-
duction of heat. Alcohol and anesthetics are amongst

such agents, and it is a well-known fact that cold is
49 a

50 APPLIED PHYSIOLOGY

highly prejudicial to a person who is intoxicated. Seeing
that life always manifests itself by developing heat, we
need not be surprised to be told that there is really no
such thing as a ‘cold-blooded’ animal in the literal
sense, and that the creatures commonly so described
usually have a body temperature appreciably above that
of their surroundings. The real distinction, in fact, is
not between warm- and cold-blooded animals, but between
those whose temperature is constant and those in whom
it is not.

Now, the question naturally presents itself, What are
the advantages of having a constant temperature, or, in
other words, of being what is commonly called ‘ warm-
blooded’? ‘The reply to this is, that constancy of
temperature makes an animal more independent of its
surroundings. Extremes of heat and cold both tend to
paralyze living cells, and if the temperature of a man’s
body fell with that of his surroundings, all his vital
processes would become sluggish in cold weather. On
the other hand, when exposed to heat, it would be
necessary for him to adopt a voluntary sluggishness, as
otherwise his temperature might rise to a point at which
the vitality of his cells would become impaired. In the
process of evolution, therefore, when animals-ceased to
be aquatic, and came to live in a medium of varying
temperature, it became necessary to develop a mechanism
for maintaining the temperature of the body at a con-
stant level, and the animals which succeeded in doing
this in greatest perfection survived. Even yet we can
see in the Monotremata an example of creatures in which
the development of a heat-regulating mechanism has

/ BODY HEAT 51

been arrested at an early stage, with the consequence
that they can only to a small degree maintain their
activity, regardless of what the surrounding temperature
may happen to be, and in some cases at least, such as
Echidna, are compelled to resort to the device of hiberna-
tion and a suspension of all attempts at bodily activity
when exposed to great cold. Even in some-of the
higher mammals the heat-regulating mechanism is not
in proper working order at the time of birth, and such
animals perish from cold if separated from their mothers.
In the case of puppies, for instance, which of course
are born blind, the power of maintaining the temperature
of the body does not arise until sight is attained. Babies
who are born prematurely, also, are unable to control
their temperature, and would perish were it not for the
aid of an incubator or some other device for keeping
them warm. Even in normal infants the power of regu-
lating heat production and loss is very imperfect during
the first week; hence the importance of warmth to the
newly-born baby.

Now, although all the higher animals have developed
the power of maintaining their bodies at a constant
temperature, it is an interesting fact that the exact point
at which evolution has fixed it to be maintained is by
no means the same in all. In man it may be taken as
a temperature of 98°6° F., the range of internal tempera-
ture in health being from 96°8° F. to 100° F.; but in
most other mammals it is more nearly 102° F., whilst
in birds it is as high as 107° F. Why these differences
exist it is difficult to explain. All one can say is that
a temperature of 98°6° F. is the tune to which the

4—2

52 APPLIED PHYSIOLOGY

molecules of human cells ‘dance’ most actively. If the
temperature of the body falls below this point, their
movements become more sluggish; whilst if it rises
much above this point, they may dance more violently
indeed, but it tends to be a dance of death. Of the two
extremes, a low temperature would appear to be the
less dangerous, for whilst clinical observation shows
that recovery may ensue even when the temperature of
the body has fallen as low as 75° F., a rise of even
134° F. above the normal is but rarely survived unless it
be of short duration.

Although the heat-regulating mechanism succeeds in
keeping the mean temperature of the body very uniform,
slight daily variations do occur, the maximum being
reached about five o’clock in the evening, and the
minimum in the small hours of the morning. In cases
of fever these normal variations are sometimes exag-
gerated, and a ‘two-hourly’ chart may therefore exhibit
a rise of temperature which would be missed if the
thermometer is used only twice a day. The cause of
these daily variations is obscure, but it is certain that
they occur during both starvation and complete rest,
and it is probable that they result from the normal
daily fluctuations in metabolism to which reference has
already been made (p. 20). In people who pursue
nocturnal vocations the daily rhythm of temperature
may be inverted, the maximum being attained in the
early morning, and the minimum in the evening. §o
stereotyped, however, has the normal type of meta-
‘polism become through long habit that such inversions
of it are but rarely met with.

BODY HEAT 53

Even if one transposes day and night by a journey to
the other side of the world, the temperature rhythm
adjusts itself to the new conditions, so as still to show
the normal daily curve.*

There is a considerable amount of evidence, also, to
show that the temperature of the body is not quite
uniform all over the globe, but that it tends to be
somewhat higher in the tropics than it is in temperate
regions. This is probably owing to interference with
heat loss. The central temperature, however, is much
less affected by climate than that of the periphery of the
body.

TEMPERATURE-REGULATING MECHANISM.
The constancy of temperature of the body is attained—

1. By varying the heat loss (physical regulation).
2. By varying the heat production (chemical regu-
lation).

1. Physical Regulation.

In man the heat loss is regulated (a) naturally,
(b) artificially (¢.e., by clothes and artificial heating of
rooms).

(a) The Natwral Channels of Heat Loss are—

Percentage of
Total Heat Loss.

(i.) The skin ... a ee i aa
(ii.) The lungs ... 3 ala! a! :
(iii.) The excreta 7 OE

* Gibson, ‘The Effects of Transposition of the Daily Routine
on the Rhythm of Temperature Variation’ (Amer. Journ. Med.
Sct., 1905, exxix., 1048).

54 APPLIED PHYSIOLOGY

Of these, the skin alone is utilized for purposes of
regulating the temperature in man.
Heat is lost from the skin—

1. By radiation.

2. By conduction.
8. By convection.
4. By evaporation.

1. Radiation is by far the most important of these,
for 73 per cent. of the total loss from the skin, or
1,700 Calories, may be accounted for in this way.
Radiation is most active in cold, dry air, and the
greater the surface of the body relative to its mass, the ©
greater is the loss by radiation. Small animals, there-
fore, tend to lose heat more rapidly than large, which is
the chief reason why children should be warmly clothed.
It would appear that the amount of heat lost by radiation
cannot be varied much by natural means, for even such
a degree of dilatation of the surface capillaries as will
produce visible redness only serves to raise the surface
temperature of the skin 1°75° C. (Hale White).

2. Conduction.—Seeing that water is twenty-eight
times better as a conductor of heat than air, it will be
obvious that the greater the degree of moisture in the
atmosphere, the greater is the loss by this means;
hence the chilling effect of cold, damp air. Fortunately,
however, the human body is a bad conductor of heat.
Indeed, it may be compared to a mass of but moderate
conducting power containing a warm substance—the
blood—of almost constant temperature, and the tem-
perature of any point in the body depends upon its

BODY HEAT 55

nearness to the large bloodvessels and on the conducting
power of the intermediate tissues. Were it not for this
low conducting power of the body it would be impossible
to make use of the local effects of the cautery or of
freezing as we do. Fat is the tissue which is the worst
conductor of heat,* so that there is some reason in the
common belief that a thick layer of subcutaneous fat
serves as a blanket, which lessens heat loss.

Against loss of heat by conduction it is impossible for
the body to protect itself by natural means at all, but
clothes are of some avail against it (see p. 57).

8. Convection only comes into play when the body
is exposed to the influence of air in motion. Draughis,
for instance, produce their local chilling effects by this
means, and windg are: even more potent, the combined
effect of conduction and convection produced by a cold,
damp wind being one of the most chilling influences to
which the body can be exposed. |

4, Evaporation stands next to radiation in importance
as a mode of heat loss from the skin, 14°5 per cent. of
the total surface loss being accounted for in this way.
It has been calculated by Erasmus Wilson that the skin
contains twenty-one miles of sweat glands, from which
about 600 c.c. of sweat are evaporated daily, which will
produce a loss of about 350 Calories. During hard
exertion this loss is, of course, greatly increased. It has
been found, for instance, that stokers may lose 3 pounds

* For experiments on the conducting power of the different
tissues of the body, see Bordier, Archives de Physiol., 1898,
xxx. 17; also Charrin and Guillemonat (¢bid., p. 455).

56 APPLIED PHYSIOLOGY

of sweat by evaporation in less than an hour. That
complete cessation of evaporation can induce a rise of
temperature there can be little doubt. In belladonna-
poisoning, for example, in which sweat secretion is
entirely arrested, the temperature may rise to 104° F.

These various modes of heat loss present a different
degree of activity in different individuals. In tall thin
persons, for example, who have a large body surface,
radiation and conduction are very active, and evapora-
tion plays but a minor part. In short stout individuals,
on the other hand, who have a relatively small surface
and a bad power of conduction, the loss of heat by the
evaporation of sweat is much more often called for.

(b) Artificial Regulation of Heat Loss.

By the invention of clothes man has enormously
increased his power of withstanding cold. Thanks to
them, we live and move in a nearly constant atmosphere
of 91° F.,* whilst a naked man would have great
difficulty in maintaining his temperature at the normal
level if that of the surrounding air were even as high
as 80° F,

Locke + quotes with approval the answer given by the
Scythian philosopher to the Athenian who wondered
how he could go naked in frost and snow. ‘How,’ said
the Scythian, ‘can you endure your face exposed to the
sharp winter air?’ ‘My face is used to it,’ said the
Athenian. ‘Think me all face,’ replied the Scythian.

* Rubner, working with a thermopile, has shown that, if the
radiation of heat from the naked skin be taken as 100, with a vest
on it is 73; shirt and vest, 60; waistcoat, shirt, and vest, 46; and

coat, waistcoat, shirt, and vest, 33.
Tt ‘Some Thoughts concerning Education.’

BODY HEAT 57

The answer is really not a good one at all, for we can
only afford to expose the face because the rest of the
body is warmly clothed. Clothes regulate heat loss by
diminishing it, whereas the natural regulation of heat
loss by the skin is chiefly in the direction of increasing
it. Civilized man trusts to the former method to enable
him to resist cold, and to the latter to help him to
withstand heat.

Clothes should be so constructed as to lessen radiation
and conduction without interfering any more than can
be helped with evaporation. They will thus be of the
maximum utility in cold, and of the least inconvenience
in heat. The material of the clothes should therefore
be a bad conductor of heat. Count Rumford made
some interesting experiments* on the conducting power
of different materials, which are instructive from this
point of view. He placed a thermometer with its bulb
in a glass globe, the space between the thermometer
and the globe being filled with the material to be tested.
The instrument was heated to the temperature of boiling
water, and then plunged into a freezing mixture, and
the time taken for it to cool down to 85° F. noted.
The results were as follows:

When surrounded with— Seconds.
Twisted silk ... 4 aa 917
Fine lint ep “B sxe | ee
Cotton-wool ... Ra oss 2046
Sheep’s wool ... ae ive ete
Eider-down ... yO ass tai ee
Hare’s fur __... 1,312

* Phil. Trans., Roy. Soc., 1792, Ixxxii. 48,

58 APPLIED PHYSIOLOGY

Wool is therefore a better non-conductor than either
vegetable fibre or silk.

Equally important, however, to the material em-
ployed is the mode in which it is woven; for the air
enclosed between the different layers of clothing, and
entangled in its meshes, forms a warm envelope which
is a worse conductor of heat than any material of which
clothes are made, and which greatly interferes with
heat loss, besides being not readily removed even by
convection. Thus, too, garments which enclose a layer
of air between them are much more efficient in checking
loss than one garment, even though it be equal in
thickness to two. Clothes should therefore fit loosely.
They should also be loosely woven, so as to enclose as
much air as possible in the interstices of the material.
Here again the superiority of woollen garments is pro-
nounced, for 1,000 volumes of soft flannel contain
923 volumes of air, as against 723 contained in linen.
It is in accordance with this principle that ‘cellular’
clothing is made.*

The utility of clothes is greatly interfered with by
damp, for the moist air penetrates into the interstices
of the cloth and removes heat from the body by evapora-
tion. Wet clothes, indeed, are almost worse than none,
for they greatly increase loss by evaporation. Thus, it
has been calculated that, if the boots and stockings are
thoroughly wet and allowed to dry on the feet, they
remove as much heat as would have been required to

* It is noteworthy, too, that even in the lower animals the hair
stands on end in extreme cold, so as to enclose as large an amount
of air as possible. The production of ‘ goose-flesh’ in the human
subject is apparently a survival of the same device.

BODY HEAT ‘ 59

melt half a pound of ice or raise an equal weight of
water to boiling-point. This is a striking proof of the
danger of ‘ wet feet.’

Even in respect of damp, wool is the best clothing
material, for, being far more hygroscopic than vegetable
fibre, it can absorb much more water without feeling wet.
Again, when thoroughly wet, only 26 per cent. of the
pores in wool are closed and their air displaced, whereas
in the case of silk the percentage is 39, and in linen as
high as 56. Wool is also difficult to wet both on account

-of the natural oil which it contains and because of the
horny covering of its fibres. These advantages are well
illustrated in the case of Harris tweed.

As regards the amount of clothing which should be
worn, all that can be said is that it should be sufficient
to prevent ‘an abiding feeling of cold.’ As a rule, the
weight of the necessary clothes is from 6 to 12 pounds,
which may be easily doubled by the addition of an over-
coat and other outdoor apparel. Thus, in winter a man
may easily carry 18 per cent. of his weight on his back.
The lower animals are much more favourably situated
in this respect, for the weight of hair carried by a dog
weighing 9 pounds is only about 3 ounces.

Small animals should, for reasons already given, be
more warmly clothed than large. Infants, therefore,
require abundance of clothing, and the ‘ hardening’
plan so foolishly advocated even by such a profound
thinker as Locke* is opposed to all the teaching of
physiology.

* ‘Give me leave, therefore, to advise you not to fence too carefully
against the cold of this our climate.... Be sure let not his [the

60 APPLIED PHYSIOLOGY

2. Chemical Regulation.

In addition to the method of varying its heat loss, the
temperature of the body can be regulated by increasing
or lessening the amount of heat produced. As this
method, however, implies the production of variations
in the amount of metabolism, it is not used except in
emergencies, and for all ordinary contingencies variation
of loss is what is relied upon.

Metabolism in man is at its lowest point when the
surrounding temperature is somewhere between 60° and
68° F. If it falls below this, metabolism is quickened,
and more heat produced _to meet the demand. If, on
the other hand, the temperature rises above this, it is
difficult—indeed, almost impossible, except by curtailing
bodily activity—for the body to produce less heat, as it
is already producing as little as is compatible with the
full exercise of the vital powers, and it is accordingly
forced to keep its temperature down by increasing ‘the
amount of heat lost.

Muscle is the tissue which is chiefly called upon when
greater heat production is demanded. Even in a sta
of repose, 75 per cent. of the total heat production of the
body is derived from the muscles, and when the body is
in a condition of activity their share in the production
rises to 90 per cent. In normal conditions, therefore,
the effect of muscular exercise in raising the temperature

child’s] winter clothing be too warm. ... I would also advise his
feet to be washed every day in cold water, and to have his shoes so
thin that they might leak and let in water whenever he comes near
it’ (‘Thoughts concerning Education,’ 1690, p. 404).

BODY HEAT 61

of the body is quite marked. Jurgensen, for instance,
found that the work involved in sawing wood for six
hours raises the temperature of a healthy man 1°2° C.
above normal. Davy showed that walking for two or
‘three hours raised the temperature of the urine 0°8° C.
Clifford Allbutt found that Alpine climbing raised the
temperature of the mouth half a degree. Hobday has
taken the rectal temperature of omnibus horses, and
found that it is raised about 2° C. by hard work.*
These effects, however, are quite temporary, and in
about a quarter of an hour after the exercise has termi-
nated the temperature has again fallen to normal, but
they will serve to show what a valuable source of heat
muscular metabolism is.

When the body is exposed to cold, this source of heat
supply is drawn upon by throwing the muscles into
activity partly voluntarily (e.g., by moving about, stamp-
ing the feet, swinging the arms, etc.), and partly in
@ semi-invyoluntary way by the act of shivering. The
nerve mechanism which is made use of in throwing the
heat-generating apparatus into action will be described
immediately. |

The amount of heat which can be produced in this
way is very well seen in the table on page 62, which shows
the results which Rubner obtained from individuals
immersed in a cold bath.

The bath lasted one hour. For half an hour one
must halve the increased heat production.

Roughly it may be said that every fall of 1° C. in

* These examples are taken from Hale White’s Croonian Lectures
for 1897.

62 APPLIED PHYSIOLOGY

the surrounding temperature increases metabolism by
2 to 3 per cent. It will be seen from this how expensive
a method of regulating temperature increased heat
production is. So expensive is it, indeed, that feeble
individuals. are sometimes unable to produce enough
heat, and suffer a lowering of their body temperature
in consequence; and whenever in cases of disease one
finds a permanently subnormal temperature, one may
conclude that heat production is insufficient. Good
examples of such diseases are found in the case of
diabetes and myxedema.

Increased Heat Increased Combined
er geo Production Destruction _ Pei sry Effects, before
, Caused. of Fat. 7 and after.

59° F. | 407 Calories | 48 grammes | 9 grammes | 52 grammes
yt Pe Cy Re Lae - BOAT TB vgs
95° F. ae oF % Ue OF -%

The heat produced in the muscles in response to an
increased demand is distributed throughout the body by
the blood, and much of the glow felt after hard exercise
is really due not so much to increased heat production
as to better heat distribution. If the movement of the
blood is languid and the surface bloodvessels contracted,
as is the case with persons who suffer from what is called
a ‘bad circulation,’ the heat produced is not well dis-
tributed, and consequently such persons have difficulty in
maintaining their body temperature when exposed to cold.

‘We are not all blessed,’ says Lewes,* ‘ with the same

* The Physiology of Common Life,’ i, 436,

BODY HEAT 63

capacity for rapidly developing heat; we are not all
blessed with the same activity of the circulation. Yet
each is apt to make himself the standard. B. shivers,
and complains of the cold; thinks he must have the fire
lighted though it be June. C. is amazed that anyone
can possibly be cold on such a day; C.is quite warm....
The difference may arise from two causes: the heat-
producing capacity may be less, or the circulation
feebler. The stimulus of the external cold increases
the activity of the organic processes in one man, and
depresses it in another. That this is the real cause will
appear on examining the influence of cold on the various
classes of warm-blooded animals. One class—the hyber-
naters—is so incapable of resisting cold by an adequate
increase of its own temperature, that it falls into a
torpor; other classes are forced to seek external warmth
in nests and holes, as we seek it in warm clothing and
heated rooms; others, again, need nothing but their
own temperature. In spite of the active respiration of
a mouse, it needs a warm nest, and unless in active
exercise will perish if exposed to a temperature which
we should consider moderate; we, again, should perish
in a temperature which the cat or dog could endure
without uneasiness.

‘Among men there are some who resemble the mouse,
and others who resemble the cat. The slightest fall of
temperature causes the first to put on warmer clothing
or to light the fire, at which their robuster friends are
liberal in sarcastic allusions, spoken or thought, and are
somewhat impatient of this ‘coddling,’ These sarcastic
friends are the cats.

64 APPLIED PHYSIOLOGY

‘It is important to bear in mind, however, that this
inadequate production of heat does not always translate
itself by the expression of ‘‘chilliness”’; the effect of cold
is often totally unlike that of a chilly sensation. It
produces a vague uneasiness, a feeling of depression,
resulting from the lowering of the organic activity, and
many periodic forms of disease are probably connected
therewith. Without; positively ‘‘feeling cold,” the person
so affected need only enter a well-warmed apartment to
be at once aware of a reinvigorated condition.’

The immediate effect of a warm meal in raising the
temperature of the body is more apparent than real,
being due to stimulation of the circulation, with conse-
quent better distribution of the blood in the periphery.
Apart from this effect, however, food is undoubtedly an
important source of heat after it has had time to be
digested and absorbed. Of the chemical constituents of
the food, protein is the most rapid developer of heat,
probably owing to its speedy cleavage and the partial
oxidation of the nitrogenous part of its molecule already
referred to. Next to it in potency is carbohydrate,
whilst fat comes lowest in heating power.* These facts
have important bearings on the dietary suitable for’ hot
weather and warm climates. a |

Tue Nerve Mecuanism oF TEMPERATURE REGULATION.

Variations in heat loss from the surface of the body
are brought about through the medium of the vasomotor
and sweat-secreting nerves. The mechanism involved

* If the heat-generating power of protein be taken as 20, that of
carbohydrate is 10, and that of fat 7.

BODY HEAT 65

is a true reflex. When the skin is exposed to cold the
cutaneous vessels are reflexly contracted, and radiation
is lessened. When exposed to heat the vessels are
dilated, and sweat secretion begins. Thus both radia-
tion and evaporation are rendered more active. It is
important for adequate and instantaneous temperature
regulation that the nervous apparatus concerned should
be kept in good working order, and part of the good
effect of a morning cold bath is no doubt to be attributed
to its putting the vasomotor nerves ‘through their
drill.” It should be noted in this connection that the
cutaneous nerves are not tuned to appreciate actual
degrees of temperature, but merely a gain or loss of heat
from the skin. This explains why it is, for instance,
that when we go down into a ‘ tube’ railway in winter it
feels warm, but in the summer it feels cool, although the
temperature of the tunnel is really almost constant all
the year round. Mere sensation, therefore, is a most
fallacious guide to temperature, for which reason we
cannot trust to the hand in gauging the presence or
absence of fever in a patient, but have to fall back upon
the reading recorded by a thermometer.

The chemical regulation of temperature by increasing
heat production is also a function of the nervous system.
It used not to be believed that this was so. It was
thought that cold stimulated the activity of the cells
directly. That, of course, was an error. Cold is really
_ a depressant of vitality, and paralyzes the cells just as a
narcotic does. The clinical effects of cold, indeed, if it
be sufficiently severe actually to lower the temperature
of the blood, are wonderfully like those of an anesthetic

5

66 APPLIED PHYSIOLOGY

or of toxic doses of alcohol, and, as Watson says, ‘ there
is too much reason to believe that poor wretches who
have been picked up by the constables in the streets at
night during periods of hard frost have been supposed to
be drunk, when in truth they were only stupefied by cold.’

The nervous mechanism which calls out an increased
production of heat by the muscles, however, is not thrown
into action in a purely reflex way. In part it is a volun-
tary process, active movements being performed instinc-
tively in order ‘to keep one’s self warm.’ In part also
it is a subconscious ‘ psychical reflex,’ comparable to that
which leads to blinking of the eye on any sudden
menace to the cornea, and which leads to more or less -
involuntary shivering—+.e., slight but rapid muscular
contractions—and which can be more or less completely
inhibited by the will. Short of actual shivering, cold
seems, through nervous action, to raise the ‘tone’ of the
muscles, and therefore to increase the volume of heat
they produce (see p. 22). Kveryone feels more ‘strung
up’ on a cold day, and this is what is really meant when
a cold climate is spoken of as ‘bracing.’ It has, in =

a tonic effect very like that of strychnine.

Whether or not there is a special centre in the tiie
which presides over the function of heat production is a
point on which physiologists are not yet agreed, though
the bulk of opinion is opposed to such a conclusion, in
spite of the experimental and clinical evidence which
points to the existence of such a centre in the corpus
striatum. On the whole, it seems more probable that
the control is exerted through the medium of the
ordinary motor and vasomotor centres. There can be

BODY HEAT 67

little doubt that, in spite of the regulating mechanism,
the body becomes habituated to a certain level or balance
of heat production and loss, and takes a little time to
readjust matters when external conditions suddenly
change. Captain Parry, the Arctic explorer, tells us, for
instance, that when he and his men had been exposed to
a temperature of 13° I’. for some time, they complained
of the heat when the thermometer rose to 26° F., and
everyone knows how much more trying a cold day is in
the middle of summer than a day of the same tempera-
ture in mid-winter, even although the clothing be the same.

Similarly, persons who inhabit warm latitudes become
accustomed to losing much heat from the surface by
evaporation, and are out of practice, as it were, in pro-
ducing more heat to meet emergencies, and are therefore
prone to succumb to chills when they remove to colder
regions.

Alcohol in excessive doses and prolonged anesthesia
both paralyze the heat-regulating mechanism. A man
who is ‘dead drunk’ resembles a cold-blooded animal ;
exposure to cold produces not an increase but a decrease
in combustion, and his temperature steadily falls
(Pembrey). It is not surprising, therefore, that ‘death
from exposure’ chiefly occurs in the case of intoxicated
persons.

An anesthetized patient also cannot regulate his
temperature, and the importance of warm surroundings
in promoting recovery from prolonged operations and in
obviating ‘ shock’ is generally recognized.

‘Heat stroke’ and ‘heat exhaustion’ are probably
also due to a disturbance of the mechanism for regulating

5—2

68 _ APPLIED PHYSIOLOGY

temperature brought about by muscular. exercise—
especially when unsuitably clothed—in a hot and damp
atmosphere.

INTERNAL Heat-REGULATING MECHANISM.

In addition to the mechanism already described for
regulating the heat production and loss of the body in
accordance with variations in the temperature of its
surroundings, there must also be a means of regulation
in correspondence with variations in the temperature of
the blood which arise from within. The increased heat
production induced by hard exercise, for example, must
be met by some means of increasing heat loss, and we
know that this takes place by sweating. The mechanism
involved here is apparently not a reflex one, but is a
direct action of the temperature of the blood on the heat-
regulating centres. There is reason to believe that this
mechanism is less delicate and active than the reflex
one, and it is probable that disorders of it play a part in
the production of fever. Into the subject of fever, how-
ever, we can hardly enter, as it is purely a matter of
pathology, although one or two statements about it
which can be directly deduced from the teaching of
physiology may now be pointed out.

Fever.—In the first place, a permanent rise of tempera-
ture in the body cannot be due simply to increased heat
production, for, as we have seen, even hard exercise, in
which heat production is enormously increased, only
raises the temperature but a little, and for a short time.
Nor can diminished preduction alone be the cause of

Kors

BODY HEAT 69

fever, for in that case the rise of temperature of the body

ould be steady and progressive. It is probable, how-
ever, that diminished loss plays a large part in the
production of hyperpyrexia in which the rise of tempera-
ture is marked by those very characters. We may
conclude, then, on physiological grounds alone, apart
from the evidence of pathology, that in most cases fever
is due to a disturbance of the normal balance between
manufacture and loss of heat, or, in other words, to
a disorder of the internal heat-regulating mechanism.
What the nature of this disorder may be is uncertain, but
it has been suggested that the poisons which produce
fever lower the sensitiveness of the internal heat-regulat-
ing mechanism, so that (to compare it with a thermo-
stat) it is ‘set’ for a higher temperature than in health.

It is further of importance, in considering fever, to
distinguish between, the mere temperature of the body
and the total amount of heat which it contains. The
‘specific heat’ of the human body is high; ie., it takes
a considerable amount of heat to raise its temperature,
and the larger the mass of the body, the greater is the
amount of heat required. Other things being equal,
therefore, a given rise of temperature signifies a greater
amount of heat production.in a large body than in a
small one. ‘here is also every reason to believe that -
the specific heat of the body rises with an increase of its
temperature, or, in other words, the hotter the body
becomes, the greater is the amount of heat required
to heat it still more. It follows from this that a rise of
temperature from 104° to 105° F. is of relatively graver
significance than a rise from 99° to 100° F.

70 APPLIED PHYSIOLOGY

Seeing that the direct effect of heat upon the cells is to
stimulate and accelerate their katabolism—much as the
growth of plants is stimulated in a hothouse—it would
seem to be inevitable that, when the temperature of the
blood rises, tissue waste must be increased. A good
example of this is seen in the case of the heart, the rate
of contraction of which is increased by eight beats per
minute for every rise above the normal temperature of
1°F. Fever per se has therefore a destructive effect on
the cells of the body, whether it be primarily due chiefly
to an increased production of heat, to a diminution in
heat loss, or to a disturbance of the normal balance
between the two.

If it be desired to lower the temperature in fever, the
easiest means of doing so is to increase the amount
of heat loss, for this is more under our control than heat
production. Cold baths, for instance, act by removing
heat from the surface by conduction; sudorifics, by
increasing evaporation. On the other hand, we know of
but few drugs which diminish the amount of heat pro-
duced in the body. Alcohol in large doses appears to do
so, probably from its paralyzing effect upon the cells,
and quinine seems to have a similar action. Antipyrine
and other antipyretics of the same class appear to raise -
heat loss by dilating the surface bloodvessels, and so
increasing the amount of radiation from the body, whilst
at the same time they seem to have some action on the
heat-regulating centres whereby they overcome the dis-
organization of those centres which play a leading part
in the production of fever.

CHAPTER III

THE APPLIED PHYSIOLOGY OF THE BLOOD AND
HAMOPOIETIC ORGANS

GENERAL FUNCTIONS OF THE Boop.

From the earliest times of medical science the blood has
attracted to itself the most earnest attention of the
investigators of the secrets of life. Whole systems of
pathology have been built up upon supposed alterations
in its properties, and have subsequently fallen into
disregard, and yet in these latter days there is still no
field of research which is cultivated with more en-
thusiasm. Nor is the reason for this far to seek. Blood
is the one constituent common to all the organs and
tissues alike. It is the currency or medium of exchange
in the body, giving to every cell the substances necessary
for its life, and receiving back from it again the products
of its activity or waste. In this respect the blood, as it
flows ceaselessly along the bloodvessels, has been aptly
compared to the water in the canals of such a city as
Venice or Amsterdam, which brings to the doors of the
inhabitants the provisions necessary for their life, and
carries away the products of their handicraft, but which

is at the same time the recipient of their refuse and
71

72 APPLIED PHYSIOLOGY

sewage. Blood is thus an epitome of the results of the
metabolic exchange between the organs and tissues. . It
contains within itself representatives of all the soluble
constituents which play a part in the drama of cell life.
If any substance is being produced in excess it will be
found in the blood; if anything is in defect it is the
blood which will show it.

Not only is the blood the great medium of exchange: it
is also in a sense an organ which has had entrusted to it
one of the most important of all functions in the com-
munity of cells which we call the body—that, namely, of
defence. As pathologists penetrate more deeply into an
understanding of the means by which we are protected
from disease, these defensive functions of the blood
assume an ever-increasing importance, and the most
promising, though the most complicated, chapter in
modern bacteriology is that which deals with the anti-
toxic and bactericidal properties of the blood.

Add to all this the comparative accessibility of the
blood and the ease with which many of its changes can
be studied, even in the living subject, and one does not
wonder that ‘hematology’ has assumed such a ae
place in latter-day medicine.

We have spoken of the blood as a fluid mediate of
exchange, but that is only one aspect of it. In virtue
of the fact that it contains living cells, the blood is also
to be regarded as a tissue. Even here it is unique, for
the blood is a peripatetic tissue free from nervous control.
If in its capacity as a fluid it is to be regarded as a
mirror of metabolism, so in its quality as a tissue the
blood may be considered as a reflection of the mature

BLOOD AND HAIMOPOIETIC ORGANS = 73

red bone marrow. Is the marrow in defect? Then the
cells of the blood are also in defect. Is the marrow
diseased ? Do its cellular constituents no longer pre-
serve their due relative proportion to one another?
Then the microscopic picture of the blood faithfully
mirrors such disease and such alterations. It is be-
coming probable, indeed, that the blood is never itself
the seat of a primary pathological process, but simply
exhibits the consequeiices of disease in the marrow or
elsewhere.

We must now turn to a closer study of the properties
of the blood as outlined above, and we shall begin by
looking at it as a tissue containing living cells.

CELLULAR CONSTITUENTS OF THE BLOooD.

The cells which constitute the population of the blood-
stream are of three kinds: the red cells, the white cells,
and the blood platelets. We shall endeavour to trace
the origin, life-history, and fate of these separately.

The red cells in the adult—with their origin in the
foetus we are not concerned—arise in the red marrow of
the bones. They are produced from mother cells which
are at first colourless, but in which hemoglobin gets
deposited, and at first, like all cells, they contain a
nucleus. How the nucleus is got rid of—whether by
extrusion (as is most probable) or by absorption—has
been much discussed, but is a subject of little practical
interest. At any rate, by the time they reach the
general circulation they are non-nucleated, and for that
reason are by some denied the title of ‘cells’ at all.
Everything in them, indeed, seems to have been

rc: APPLIED PHYSIOLOGY

sacrificed to facilitate their function—that of taking up
and giving off oxygen. Their shape, for instance—that
of a biconcave disc—is such as to present the largest
possible surface compatible with their free movement in
the blood-stream. Collectively, therefore, they offer in
the lungs and in the tissues a large area over which
gaseous exchange can take place—an area which has
been not inaptly termed the ‘internal respiratory
surface.’* Further, they are enclosed in a smooth
membrane of great elasticity, which enables them easily
to wriggle their way through the most tortuous capillary
channels. This remarkable elasticity is a sign of health
in the corpuscle, and is lost in many diseases of the
blood in which the disc form gives place to various
irregularities of shape (poikilocytosis). Hach corpuscle
is stuffed full of hemoglobin, but the exact mode in
which this is disposed—whether it is partly in solution
in the corpuscle or loosely united in an amorphous form
to a stroma of nucleo-protein—is still disputed. In
addition, the red corpuscles contain a considerable
amount of lecithin and cholesterin, which probably form
a sort of waterproof coating to their walls. So long as
this impermeable membrane is in a living conditi n it
prevents the diffusion out of the contents of the
corpuscles, but if it be killed, diffusion begins, because
the plasma and the contents of the corpuscles are not
iso-tonic. Chilling seems to kill the membrane and

* Assuming that the body contains 34 litres of blood, with
5,000,000 red cells in each cubic millimetre, then the ‘internal
respiratory surface’ will amount to 2,500 square metres, or more
than 1,000 times the external body surface (Buckmaster).

BLOOD AND HA{MOPOIETIC ORGANS = %5

allow the passage outwards of hemoglobin, and this is
probably how blood pigment gets into the plasma in
cases of Raynaud’s disease. Hzemolysins also affect in
some way the permeability of the envelope without
necessarily dissolving the corpuscle.

The red cells are also fairly rich in salts of potash, a
recognition of which fact, indeed, has led some people to
recommend the treatment of pernicious anemia by the
administration of potassium compounds.*

Practically, then, one may regard a red corpuscle as
an elastic bag designed for the transportation of hemo-
globin, and whether it be really ‘alive’ or not is an
academic question still open to discussion.

The red cells make up by far the larger proportion of
the population of the blood-stream, amounting on an
average to 5,000,000 per cubic millimetre of blood. In
women, and in the earlier years of life in both sexes, the
number is somewhat below this. On the other hand, in
some ‘full-blooded’ individuals higher counts may be
obtained. The actual number of red cells and the
amount of hemoglobin in the blood apparently depend,
to a great extent, on the degree of muscular activity of
the body. In other words, the number of oxygen-carriers
is in proportion to the amount of oxygen needed. The
chief physiological condition which influences the number
of the corpuscles, however, is altitude, for numerous
observations have shown that with increasing elevation
above the sea-level the number of the red cells is
augmented, every 380 feet ascended causing an increase

of about 100,000 per cubic millimetre. The cause of

* Rumpf, Berlin. Klin. Woch., 1901, xxxviii. 477.

76 APPLIED PHYSIOLOGY

this increase, attempts to arrive at an explanation of
which have led to much controversy, cannot be discussed
here,* but it may be said in brief that, whilst in part the
increase is apparent only, and due to an altered distribu-
tion of the blood which is driven out of the abdominal
organs by the deeper respiration which life at high
altitudes entails, and also, perhaps, to a concentration
of it from increased cutaneous evaporation, yet most
observers admit that in part the increase is real and
due to a greater formation of red cells. The natural
teleological explanation of such increased formation is,
of course, that it is an attempt to compensate for the
ereater difficulty of oxygenating the blood experienced
at high elevations, more corpuscles being exposed to the
air to make up for less oxygen being taken up by each
individually. At all events, whatever the real explana-
tion is, many of the valuable therapeutic effects of
residence at high altitudes have been attributed to this
increased formation of blood. Unfortunately, however,
the number is soon reduced on return to lower levels.

A pathological increase in the number of red cells is
not common, and may be apparent only—the result of
stagnation of blood in the capillaries and its consequent
inspissation. On the other hand, all cases are not to be
so explained, and in the form of polycythemia associated
with splenic enlargement the evidence points rather to
an increased formation of red cells. It is interesting to
note that there would seem to be a limit to the extent

* For a full discussion of the subject, see Pacht, ‘ Ueber die
Veranderungen des Blutes im MHochgebirge,’ St. Petersburg
Med. Woch., 1901, xxvi. 548.

BLOOD AND HAMOPOIETIC ORGANS 17%7

to which the red cells can be augmented. Normally the
corpuscles make up about half the volume of the blood ;

if, then, their number were doubled, the blood would
become practically solid. For this reason it is difficult

to see how clinical estimations of 10,000,000 red cells

per cubic millimetre and upwards, such as are Oe.
recorded, can be really correct.

Ample provision has been made, in adult life at any
rate, to meet the demand for an increased supply of red
corpuscles which any abnormal destruction of them in
the blood-stream entails; for the red marrow of the long
bones, which under normal conditions is confined to their
extremities, can, if necessary, encroach upon and displace
the marrow fat until the whole interior of the bone
becomes a manufactory of red corpuscles. The best
example of such an extension of the blood-forming
territory is seen in pernicious anzmia, in which the
whole of the marrow of the long bones becomes red.
In young children such an extension is impossible, for
the whole of their marrow is red already. Perhaps that
is why young children stand loss of blood badly. On
the other hand, it would seem that sometimes the red
marrow is congenitally deficient or may disappear, in which
case a great diminution of red cells in the blood results.*

The function of the red cells, as we have seen, is
essentially a respiratory one. They carry oxygen from
the lungs to the tissues, and help in conveying back
carbonic acid from the tissues to the lungs. This they
are able to do in virtue of the fact that they contain

* For a report of such a case, see Muir, Brit. Med. Journ.,
1900, ii. 911.

78 | APPLIED PHYSIOLOGY

hemoglobin, to a consideration of which remarkable
substance we must now turn.

Hemoglobin is in many ways a unique compound.
It has the honour of possessing the largest molecule in
the body, and of being the only body protein which can
be easily obtained in a crystalline form. It consists of
an iron-containing pigment (hematin) united to a histon
termed ‘globin.’ It is to the fact that it contains iron
that it owes its power of taking up oxygen; the protein
part of the compound merely serves the humble function
of acting as a sort of lifebuoy to the heavy iron-containing
part of the molecule, and floating it along in the blood-
stream. Oxygen is, unfortunately, not the only gas
with which hemoglobin is ready to enter into partner-
ship. It has an inconvenient affinity for carbonic oxide,
nitric oxide, and other gases, and when it is united to
them its proper respiratory function is atan end. Hence
a patient poisoned by carbonic oxide really dies from
sheer inability to get oxygen conveyed from his lungs
to his tissues. Oxygen inhalation, which increases the
amount of oxygen dissolved in the plasma as opposed to
that in the corpuscles, may tide over the difficulty until
the gradual dissolution of the unnatural partnership has
taken place.

That hemoglobin is formed like the corpuscles in the
red marrow is probable, but not proven. It seems to be
deposited in the cells whilst they are still in their
nucleated condition, but by what intricate chemical pro-
cesses its complex molecule is built up is still a secret.
This, however, we do know—that hemoglobin is only
built up rather slowly, and that it takes some time, after

BLOOD AND HASMOPOIETIC ORGANS 79

a hemorrhage, for the new corpuscles to be loaded up
with it, so that one finds that the percentage of hemo-
globin in the blood remains low for a considerable time
after the red cells have reached their normal number.
Long before hemoglobin was known to contain iron, the
power of the latter metal as a remedy in some forms of
anemia was well known to physicians; but the natural
inference that such forms of anemia are due to a deficient
supply of iron in the food is not necessarily correct. It
would rather seem as if iron, arsenic, and some other
metals, have a direct power of stimulating the bone
marrow* to increased functional activity.

Hemoglobin is the mother of pigments in the body.
Bile pigment is its direct descendant, and so also is the
closely allied or iron-free pigment heematoidin, which is
met with at the site of old hemorrhages, such as apo-
plectic cysts.

Hzmatoporphyrin is another iron-free derivative of
hemoglobin, which is normally produced from the latter
in the body in small quantities. In patients who have
been taking sulphonal for a long time it is apt to be
produced in much greater amount, and gives to the
urine a deep port-wine colour, which is always a sign of
danger.

Hzmin, on the other hand, is a purely artificial deriva-
tive of hemoglobin never met with in the body, but of
great interest and importance as a test for blood in
medico-legal cases.

Methzemogilobin is met with in the urine in small

* See Stockman, Brit. Med. Jowrn., 1898, i. 881.

80 APPLIED PHYSIOLOGY

amounts in the rare and interesting disease metheamo-
globinuria. It probably owes its production to the
action of the acids of the urine on hemoglobin. It is
also produced from hemoglobin in poisoning with
chlorate of potash and antifebrin.

The duration of life of a red corpuscle is a point
upon which, unfortunately, we have no information, for
one cannot earmark one and trace its development, as
naturalists have done for fish, by passing a dated metal
plate through a fin. Transfusion experiments indicate
—though rather doubtfully—that the average length of
life is about three to four weeks. At all events, although
all the corpuscles in any given drop of blood appear
exactly alike, they must really be of different ages, and
presumably therefore of different degrees of vitality. In
accordance with this, one finds a great variation in the
resistance offered by different corpuscles to disintegrating
agencies, such as may be active in disease.

The ultimate fate of the red corpuscle is to be broken
down in the portal system, and got rid of in the form of
bile.* The spleen also seems to take a share in re-
moving the corpuscular débris from the blood (vide infra).
Whether a corpuscle is only destroyed when it is old
and effete, or whether some ‘ massacre of the innocents ’
also goes on, it is impossible to say with any assurance.

It would seem that the liver, spleen, and marrow
can retain the broken-down pigments of about 87 c.c.
(8 ounces) of blodd, but not more; and should the de-
struction of blood in the portal area be greatly increased,

* See Hunter, ‘ Pernicious Anemia,’ and Heinz, Beitr. z. Path.
Anat. u. Allgem. Path., 1901, xxix, 299.

BLOOD AND HASMOPOIETIC ORGANS 81

as it may be when various pathological agents are at
work, so much solid bile matter is formed that the
resulting viscidity of the bile may block the passages,
and hematogenous jaundice result (see p. 283).

The destruction of hemoglobin would appear to take
place to some extent independently of the red corpuscles
as a whole. It has been found, for example, that the
amount of it falls by about 7 per cent. during the day, as
a result, presumably, of the wear and tear of life, and
rises about the same amount during the night.’*

In persons who work by night this alternation is
reversed, whilst exercise increases the daily fall. In
these observations the number of corpuscles was not
affected; the variation is in the ‘ worth’ of each cell.
This helps to explain the undoubted aid which rest in
bed affords in the building-up of blood in anemic
subjects.

. White Cells.—Ever since the publication of Virchow’s
‘Cellular Pathology,’ the white cells, which make up the
second great tribe in the population of the blood-stream,
have been objects of the greatest interest to pathologists,
and in recent years have had devoted to them a greater
amount of research and a larger literature than any
other single set of cells in the body. Unfortunately,
however, many important points as to their origin and
life-history are still shrouded in obscurity. Unlike the
_ red corpuscles, the white cells are not all of one sort.
They differ in size, in the character of their nuclei, in
the staining reactions of their protoplasm, and in the
presence or absence of granules in the cell body, and

* Edgecombe, Brit. Med. Journ., 1898, i. 1650.
6

82 APPLIED PHYSIOLOGY

no doubt these morphological differences must mean
corresponding differences in function. As regards the
mutual relations of the different varieties of white cell,
investigators are at present divided into two camps. On
the one hand are those who assert that they are all
derived from a single type of cell, and that the non-
granular can develop into the granular forms; on the
other hand are those who maintain that, as regards the
non-granular and the granular cells, at all events, no
relationship exists, and that the one never changes into ~
the other. Into the merits of the controversy one cannot
enter here, but it is possible that, as in so many cases,
truth lies in a compromise between the two views, and
that whilst, if one goes far enough back, the two sets of
cells will be found to have a common origin, yet once
they have attained their distinctive features, and are
free in the blood-stream, no further transition occurs.

The varieties of white cell in normal blood may be
grouped as follows:

1. Non-granular :
(a) Lymphocytes (large and small), 283 per cent.
(b) Large mononuclears, 2 per cent. L
2. Granular : Fy
(a) Polymorphonuclear, with abundant nedagea
granulations, 70 per cent.
(b) Transitionals, with very few neutrophil granu-
lations, 1 per cent.
(c) Eosinophils, 3 per cent.
(d) Basophils, 0°5 per cent.

The morphological details exhibited by these different

=

BLOOD AND HEMOPOIETIC ORGANS 83 _

yarieties need not be described here, as they will be
found in any text-book, or, better still, can be learnt
from a personal study of stained films. We may deal,
however, with their place of origin and their function.

White cells are the special product of two tissues in
the body—(1) the red marrow of the bones, (2) the
adenoid tissue. ;

The red marrow is confined within the narrow limits
of the short bones, the ribs, and the ends of the long
bones. Adenoid tissue, on the other hand, is diffused
throughout the body, existing partly in substantial
masses, such as the lymph glands, the thymus, the
tonsils, Peyer’s patches in the intestine, and the Mal-
pighian bodies of the spleen, and partly in smaller
conglomerations to be found more or less in every tissue
and organ, probably including the bone marrow. It is
probable that the marrow is the sole seat of origin of the
granular cells, and that the adenoid tissue is the chief
breeding-ground of lymphocytes. Whether or not the
latter are also produced in the marrow, or, to put it
otherwise, whether or not the marrow, like other tissues,
also contains some adenoid tissue, is still disputed. In
lymphatic leukemia the red marrow becomes virtually
converted into a mass of adenoid tissue, with the natural
result that the granular cells disappear almost entirely
from the blood. Whether such a replacement of the
_ normal marrow is to be regarded as an invasion by
lymphocytes or a mere hypertrophy of already existing
adenoid tissue depends upon the view one takes as to
whether or not lymphocytes are a natural product of
the marrow.

6—2

84 APPLIED PHYSIOLOGY

The mother cells of the granular leucocytes in the
marrow are large clear cells with a single nucleus
(‘lymphoid’ cells). By the deposition of granules in
their protoplasm these become converted into granular
myelocytes in which the nucleus is still single, and
these are the cells so largely present in the blood
in myelogenous leukemia. The nucleus subsequently
becomes contorted or apparently subdivided when the
cell takes rank as a polynuclear leucocyte. It is believed
by some that the so-called ‘large lymphocytes’ met with
in the blood in the acuter forms of lymphatic leukemia
are identical with the original ‘lymphoid’ cells. Some
(e.g., Wolff) go so far as to regard the lymphoid cell as
the original parent from which all the cells of the blood
are derived, according to the following scheme:

Lymphoid cell.

Large lymphocyte. Erythrocytes. Myelocytes—
Small lymphocyte. (a) Basophil.
(6) Neutrophil.

Polynuclear leucocytes—
(a) With basophil granulation. g
(8) With neutrophil granulation. n?

In process of development, according to this view,
a gradual differentiation of function takes place on the
part of the blood-forming organs, in consequence of
which the lymphoid cells of the marrow confine them-
selves to the production of granular cells, whilst those
of the adenoid tissue become exclusively concerned in
the production of non-granular cells (lymphocytes).
The specialization, however, is never so complete but

BLOOD AND HAIMOPOIETIC ORGANS — 85

that, when a demand for a greater number of cells of
one type occurs, the lymphoid cells in any blood-forming
organ are able to produce that type.

The place of origin of the large mononuclears and of
the transitional cells derived from them is uncertain,
but it is probably in the bone marrow, though in part
also they may come from the lymph glands and the
spleen.

Various origins have likewise been described for the
eosinophils, but they, too, seem to arise from the
eosinophil myelocytes of the marrow.

The mast cells or basophils are probably also derived
from the bone marrow, and their number in the blood is
therefore increased as a result of the proliferation of the
marrow in leukemia.

It will thus be seen that the marrow is by far the
most important seat of blood formation, for not only
is it the sole producer of red corpuscles, but it also gives
origin to all the granular leucocytes, to the large mono-
nuclears, and probably also to some extent to lymphocytes,
whilst adenoid tissue can give rise to lymphocytes only.

The functions of the different forms of white
corpuscle have been as much disputed as their genesis.
Metchnikoff’s discovery of phagocytosis at once raised
the leucocytes to a position of great esteem as protectors
of the body against disease. They were regarded at first
- as ‘soldiers’ ready to rush out and destroy any invading
micro-organisms, and it became the fashion to speak of
them as if almost endowed with a sentient intelligence
and great discriminative powers. Further investigations
tended to throw doubt on the ability of the leucocytes

86 APPLIED PHYSIOLOGY

actually to destroy living organisms, and they were
degraded from the rank of ‘soldiers’ to that of a set
of mere ‘scavengers’ or ‘ undertakers’ who removed
from the field of action the bodies of micro-organisms
already killed by the blood or tissues. At the present
time the very important part played by the leucocytes
in the destruction of bacteria is generally admitted,
though it is now recognized that many fixed cells of
the body (e.g., endothelial cells and connective-tissue
corpuscles) have a similar property. Nor are all forms
of leucocytes to be regarded as phagocytic. The lympho-
cytes, the eosinophils, and the mast cells are not so
endowed. In addition to these duties, it must be remem-
bered that leucocytes produce ferments—e.g., fibrin
ferment, and possibly fat-splitting and tryptic ferments
as well. They also play an important part in the repair
of the body after injuries.

The abundance of lymphocytes in the neighbourhood
of the alimentary canal would lead one to suppose that
they may have some part to play in nutrition, possibly
in the absorption of proteins or in the carriage of fat or
glycogen. The greater number of lymphocytes in the
blood during the earliest years of life would also seem
to indicate that they may have nutritive functions. On
the other hand, they are increased like other white cells
in the neighbourhood of infections, and there is reason
to believe that in the lymph glands they inhibit the
growth of bacteria, although incapable of ‘ englobing’
them. It is thus possible that the lymphocytes aid in
the protection of the body. ;

The functions of the eosinophils are even less under-

BLOOD AND HAMOPOIETIC ORGANS — 87

stood. It cannot be doubted that the coarse granules
which they contain must be intimately concerned in
some way with the functional activity of the cell, and
if we knew the nature of these granules we might be
nearer to a comprehension of the work of the cell as
a whole. But, unfortunately, we do not know the nature
of the granules. They have been variously supposed *
to consist of (1) fat, (2) protein, (3) hemoglobin or a
derivative of it, (4) nucleo-albumin, (5) defensive secretory
granules. Some people have asserted that the granules
are rich in phosphorus and iron; others have denied
that they can find any evidence of iron in them at all.
Nor is any light thrown upon their functions by the fact
that their number in the blood is increased in such
_ diverse conditions as asthma, some skin diseases, and
helminthiasis. If we know little of the eosinophils, we
know nothing of the basophils at all. They are so
extremely scanty in normal blood that one cannot
attribute to them any important function.

The total number of white cells in the adult blood
varies between 10,000 and 7,000 per cubic millimetre,
and is by no means the same in every one.

Assuming the total number of leucocytes in a cubic
millimetre of blood to be 7,500, the proportion of this
made up by the different varieties is as follows:

Polymorphonuclears - ... 5,000
Lymphocytes wae si ... 2,000
Large mononuclears exe ave) =), oO)
Eosinophils oe iets ae

* See Howard and Perkins, Johns Hopkins Hospital Reports,
1902, x, 249.

88 APPLIED PHYSIOLOGY

It has been calculated that there are about 25,000
million leucocytes in the whole blood, which if gathered
together would make up a solid organ about as large as
the thyroid.*

At birth the total leucocytes number 17,000 per cubic
millimetre, but have fallen by the end of a year to
14,000, and by the end of three years have reached
the adult standard. The excess in the earlier years is
entirely due to an increased number of lymphocytes.

z r
a m
Bb 8. gh) Bom
ss = > 3 -
= fl a ol e ©
20,000 -— o
15000
\
10.000 4 ¥— OCF
7,500 tise" 7
a a be”
5,000 poor oe Cag ies
4998 a A
2.000 a) SW ae sd oe B

AT DIFFERENT AGES.

A, Polynuclears ; B, Lymphocytes. /

The relative numbers of the different forms present at
different ages will be found in graphic form in Figs. 1
and 2.

A distinct increase in the number of leucocytes can
usually be observed a few hours after a meal, which is
sometimes due to an increase in the polynuclear cells,
and at others to an augmentation of uninuclears. The

* Muir calculates that all the white cells in the blood put
together would not suffice to form more than an ounce of pus.

BLOOD AND HASMOPOIETIC ORGANS — 89

mechanism and meaning of this physiological leuco-
cytosis is obscure, and it does not seem to be of much
importance. Its occurrence must be borne in mind,
however, when one is estimating the leucocytes in
disease, and the time of the blood examination chosen
so as to avoid it.

The average duration of life of a leucocyte is quite
unknown, but it is almost certainly much less than that
of a red cell, and may not amount to more than a few

4
z £* e ses: eessetctrseee2e eee P=
o5:% ot~nesfsse
: eon O82
BEBPanteeneolsSrriHZsosss >
ztntanrtnon ao flake sSVranwrnd

72%} 1p

sB%4 |

64%! POLY NUCLEARS,

6 Ca t 4 c= ~ a en . a

<ax ‘i Ps a al ~~ 7 + a No mR

52 44 at a

48% f

*,

44% ts

40%-3+-

36% ¢ ‘ i

32%* ~ ate, pon, LYMPHOCYTES |

pte : “aT “ ie ai tx Bi bas PP AMR a

20% HF Fy

= 2 ANSITIONALS & LARGE MONONUCLEARS

Bx “he ‘ ome e bel 3 Pre | <2 ot Jel, | Le

pen FR ma lp OS et S

elite LAY con, T_ Ss EOSINO

Fic, 2.—DIFFERENTIAL PERCENTAGE COUNTS THROUGHOUT LIFE.
(AFTER CARSTANJEN.)

days. Hence any theory of immunity which is based
upon the ‘ education’ of individual leucocytes in dealing
with bacteria must be regarded as very unlikely to be
correct.

Leucocytes probably perish everywhere. We know,
indeed, that many of them are destroyed under patho-
logical conditions at the seat of infections, and subse-
quently are themselves ‘englobed’ by mononucleated
phagocytes, thus falling victims to the same fate which

90 APPLIED PHYSIOLOGY

they themselves inflict upon bacteria. That the spleen
is largely concerned in their destruction under normal
conditions, or, at all events, in the removal of their
débris from the blood, there is little reason to doubt
(vide infra).

The Blood Platelets.—There are some who would
deny to the platelets the right to be regarded as cellular
constituents of the living blood. They have been
variously supposed to be simply ‘chips’ off leucocytes,
portions of extruded nuclei, or a mere ‘ precipitate ’
from the plasma, not found in its natural circulating
condition. One of the most recent investigators* of
them, however, concludes that they really are cells with
a nucleus and protoplasm, and possessed of the power
of amceboid movement, and that they certainly are not
degeneration products, but are probably independent.
elements of the blood.

On the other hand, Buckmaster+ regards them as
pure artefacts. In any case, their function is as obscure
as their origin, although it has been suggested that they
are in some way concerned in the process of coagulation,
and their number in the blood appears to be increased
in those diseases in which there is a marked tendency
to clotting. So far no one has attributed to them any
definite rdle in pathology, and they cannot be considered
of much interest to the clinician.

* Deetjen, Virchow’s Archiv, 1901, clxiv. 239.
t ‘The Morphology of Normal and Pathological Blood’ (John
Murray 1906), p. 182,

~ BLOOD AND HASMOPOIETIC ORGANS = 91

Tur Buoop PLAsMA.

The plasma, or fluid in which the corpuscles float,
consists essentially of certain proteins dissolved in a
solution of sodium salts. It contains in all about 10 per
cent. of solid matter, of which 8 per cent. is made up
of proteins. These proteins belong partly to the albumin
and partly to the globulin group. In the former are
serum albumin, in the latter serum globulin and
fibrinogen. Whilst one speaks of them in this collective
fashion, there can be no doubt that there are really
several albumins and several globulins present. The
proportion of serum albumin to serum globulin is in
man about 44 to 8, but the exact proportion varies
considerably in different animals. In the cold-blooded
animals, for instance, it is chiefly globulins which are
present. Of the part played by the albumins and
globulins respectively we know nothing, but one cannot
believe that it is a matter of indifference which pre-
dominates. Bunge has suggested that globulin is the
form in which protein circulates in the body for nutritive
purposes, whilst the albumin is the more constant basis
of the plasma; but this has not yet been proven. Nor
do we know whence the proteins are derived. They can
hardly be built up directly from the protein of the
food, for they are apparently regenerated even during
starvation. It has been suggested that they are
‘secreted’ by the blood corpuscles, but it is quite as
likely that fixed cells in the body are able to help in
their production. Modern theories of immunity compel
us to believe that the blood may contain bodies, pre-

92 APPLIED PHYSIOLOGY

sumably of a protein nature, thrown off by the fixed
cells, which act as protectives against infection, and,
reasoning from analogy, it seems not unlikely that the
normal proteins of the blood may have a similar
origin.

The salts of the plasma are chiefly the chloride,
carbonate and phosphate of sodium, the two latter being
responsible for the reaction of the blood, a matter
which must now be considered more closely.

From a strictly chemical point of view the blood is
really an acid fluid, for the phosphates and bicarbonates
which it contains are really acid salts, inasmuch as they
- still contain hydrogen atoms replaceable by a base.*
The blood is generally regarded as alkaline, however,
because its chief salts are alkaline to litmus, and it will
be convenient still to speak of it as alkaline. Quanti-
tatively considered, the alkalinity of the whole blood is
equal to 300 milligrammes of NaOH per 100 c.c., and this
degree of alkalinity is maintained with extraordinary
constancy, although a slight rise in it can be detected
after meals. In disease the alkalinity is probably never
increased, but it is occasionally diminished when large
quantities of acid are entering the circulation—e., in
diabetic coma, and also in anemia. The mechanism
by which this constancy of reaction is maintained is
interesting. Alkaline compounds entering the blood are
apparently partly excreted by the kidneys, carrying with
them a certain amount of water, so that they act as
diuretics, and partly turned out of the blood-stream into

* It is interesting to note that the blood is really neutral by
physical methods of investigation.

BLOOD AND HAMOPOIETIC ORGANS = 93

the lymph spaces of the tissues.* Free acids or acid
salts are neutralized partly by the alkaline sodium
phosphate (Na,HPO,) of the blood, which they convert
into sodium acid phosphate (NaH,PO,), and which is
voided in the urine, and partly by the sodium carbonate
of the plasma with ‘the liberation of CO,, which is
eliminated by the lungs. If there be more acid than
can be dealt with in this way, the excess appears to lay
hold of ammonium carbonate (probably in the liver),
diverting it from its usual fate of being turned into urea,
and converting it into an ammonium compound of the
corresponding acid which is excreted by the kidney.
A surplus of ammonium salts in the urine is therefore .
an indication of the entry into the circulation of acid
compounds, one of the best examples of which is to be
found in diabetic coma, in which aceto-acetic acid is
excreted in such combination in enormous quantities.
So perfect is this mechanism that the reaction of the -
blood remains largely independent of the amount of
acid entering the circulation. Thus, even a dose of
2 drachms of the official HCl has no effect on the reaction
of the blood. On the other hand, an ounce of dilute
lactic acid when given in one day reduced the alkalinity
by one-fourth, whilst 2 drachms of tartaric acid reduced
it one-sixth (Freudberg).t |

The relative proportion of phosphoric and carbonic
acids in the blood depends very much upon the com-
position of the diet. The chief mineral constituents of

* Hence it is that if bicarbonate of soda be given in large
quantity for some time—e.g., in diabetes—dropsy is apt to result.
+ Vurchow’s Archiv, 1891, exxv. 566,

we

94 APPLIED PHYSIOLOGY

animal food are phosphates; those of vegetable foods,
carbonates. The blood of herbivorous animals is there-
fore rich in the latter, that of carnivora in the former,
and the acids formed in the tissues will form bicarbonates
in the blood of the herbivora, and acid phosphates in
that of carnivora. Now, acid phosphates hold earthy
phosphates in solution, and bicarbonates dissolve earthy
carbonates. Hence the urine of carnivorous animals is
rich in phosphates of lime and magnesia, that of the
herbivora in calcium and magnesium carbonate.

The molecular concentration of the blood is isotonic
with a 0°9 per cent. solution of common salt, and it
tends to maintain this degree of concentration with great
constancy. It takes a very large loss of fluid from the
body to render the blood appreciably more viscid, but
this does sometimes occur, as, for instance, in the case
of choleraic diarrhea.

In addition to its saline ingredients, the plasma also
contains, as one would expect, traces of various soluble
substances on their way to and from the cells. Chief
amongst these are urea, sugar, and fat, but many other
substances are represented in traces. The exact amount
of these ingredients must naturally vary greatly from
time to time. Sugar, for instance, normally amounts to
about 1 part per 1,000, but may rise above this after an
excessive consumption of carbohydrates. Fat is usually
present to the extent of 0°75 per cent., but after a meal
rich in fat this amount may be greatly exceeded. Where
the body fat is being utilized as food also, the amount in |
the blood on its way to be consumed may rise consider-
ably. Thus, it may be very high in cases of cesophageal

“
BLOOD AND HASMOPOIETIC ORGANS 95

obstruction, in which no food can reach the stomach,*
and in diabetic coma it may be present in such quehtity
that the blood serum becomes milky.

The most striking thing about the composition of the
plasma is its great constancy. The blood maintains in
a wonderful way a uniform standard of composition.
This it does by means of two mechanisms—viz., excretion
through the kidney and excretion into the lymph spaces
of the tissues. Hemorrhage, for instance, does not con-
centrate the blood, for fluid is instantly withdrawn from
the tissues to make good the loss. Nor is the blood
necessarily more watery in conditions of dropsy, for the
excess of fluid is got rid of into the tissues. t

Injection of saline solution into a vein does not dilute
it, for the excess is immediately excreted through the
kidneys, and, above a certain point, into the tissues also.
As a matter of fact, if ? litre of normal solution is
injected into a vein, only a slight fall in the specific
gravity of the blood is noticeable, and it only lasts for
about half an hour (Schmalitz {).

In the same way it is impossible permanently to
increase the proportion of any of the mineral constitu-
ents of the plasma, for the kidney immediately excretes
any surplus.

The total amount of blood in the body is about one-
twentieth of the body-weight, or on an average 34 litres
(about 6 pints). In health this amount is probably as

* Boninger, Zeit. f. Klin. Med., 1901, xlii. 65.

7 Askanazy, Deut. Arch. f. Klin. Med., 1897, lix. 885; also
Hammerschlag, Zeit. f. Klin. Med., 1892, xxi. 475.

t Deut. Arch. f. Klin. Med., 1891, xlvii, 145.

96 APPLIED PHYSIOLOGY

constant as the composition of the blood itself, variations
depending only on variations in the capacity of the
vascular system. In chlorosis the total volume of blood
is increased, and the constant tension of the vessels is
believed to be the cause of the vascular murmurs in that
disease. In no form of anemia is the total volume of:
the blood constantly diminished.*

Clotting.—The power of the blood to clot is one of
its most convenient attributes. Were it not for this, we
should all be liable to bleed to death.from any trivial
wound of a bloodvessel.

Much ingenious experiment has been expended in
attempts to explain the true inwardness of clotting and
what really happens when it takes place, but it cannot
be said that we are even yet completely informed on all.
details. It is generally agreed, however, that clotting
is due to the conversion of the soluble globulin called
fibrinogen into insoluble fibrin, and that this change
takes place under the influence of a ferment called
thrombin, which, however, is not present in the living
blood as such, but is liberated by the breaking down of
white corpuscles, and possibly of platelets. Thrombin
belongs, apparently, to the nucleo-protein class, and ~
exists as a ‘zymogen’ (prothrombin) which only be-
comes active in the presence of soluble salts of lime.

It is difficult to say what the rate of clotting of blood
outside the body is, as it varies greatly according to the
method employed to determine it. It seems certain,
however, that the rate is very variable, not only in

* See Lorrain Smith, Trans. of the Path. Soc. of London, 1900, ©
li, part 311.

BLOOD AND HZMOPOIETIC ORGANS 97

different individuals, but in the same individual at
different times, and this must be borne in mind when
attempts are made to estimate the coagulation time
clinically.

To the question, Why does the blood not clot inside
the living vessels? it may be replied that such an occur-
“rence is apparently prevented (1) by the active move-
ment of the blood, (2) by the absence of free fibrin
ferment, (8) by an influence—not understood—exerted
by the lining of the living and healthy vessel. It has
recently been suggested that the absence of clotting in
the living body is due to the constant neutralization of
fibrin ferment (plasmase), produced by leucocyte dis-
integration by an antibody or thrombase.*

If these conditions are not fulfilled, clotting can and
does occur. If the blood stagnates for a time, as it may
do in the interior of a dilated heart, for example, clotting
may occur; or if anything injures the leucocytes and
causes them to break down, fibrin ferment is liberated,
and clotting ensues. This has been taken advantage of
in the treatment of aneurysm. By the introduction of a
coil of wire into the sac, separation out of leucocytes and
platelets is brought about and clotting is promoted. If,
again, the wall of a vessel becomes diseased, it may lose
its power of preventing clotting, and actually promote
the process just as a foreign body does. Hence clotting
is not infrequent in atheromatous vessels. The fact that
the presence of calcium salts favours the coagulation
of blood has been turned to therapeutic account. In
.patients who are the subject of jaundice the blood tends

* Buckmaster, loc. cit., p. 217.
7

98 APPLIED PHYSIOLOGY

to clot very slowly, and prior to operations in such cases
surgeons often administer calcium chloride in full doses,
with, it is stated, very satisfactory results. The same
drug is also useful in preventing hemorrhage in scurvy.
Albumoses appear to have a power of inhibiting coagula-
tion. Ina fluid secreted by the mouth of the leech this
is made use of to prevent clotting in the bites, for such
fluid is found to contain an albumose, and it is so efficient
in its action that serious hemorrhage may take place
from the bites of leeches applied medicinally. There
is an impression amongst some clinical observers that
the administration of ammonia salts also tends to lessen
the coagulability of the blood, and such salts have been
given in cases of threatened thrombosis. I am not
aware, however, of any direct experimental evidence in
support of such a belief. Gelatin, on the other hand,
promotes coagulation, and has been largely used by
subcutaneous injection to increase the clotting power of
the blood in cases of aneurysm.

Clotting may be regarded as the death of the blood,
for the serum which is squeezed out of the clot is, as
compared with the plasma, de-vitalized. If injected into
another animal, its constituents are broken down and
excreted, the output of urea being raised. Thus serum
can be regarded as a food. After the injection of plasma,
on the other hand, no rise in nitrogenous output can be
observed.

Serum contains all the constituents of plasma except

fibrinogen, and in addition it holds in solution the pro-
ducts of disintegration of leucocytes; and amongst the
bodies interesting to the pathologist which have been

BLOOD AND HASMOPOIETIC ORGANS = 99

recognized in it are antitoxins, agglutinins, precipitins,
ferments, opsonins, and cytotoxins. It would be trans-
gressing on the domain of pure pathology to consider
most of these in any detail, but a word may be said
about precipitins, which are assuming some importance
in legal medicine.

If some human ascitic fluid be injected into the peri-
toneal cavity of a rabbit, there develops in the blood
serum of the latter a substance (precipitin) which causes
a turbidity when added to diluted human blood, but
which has no effect on the blood of other animals. The
nature of the precipitin is unknown, nor do we know
how it is that it causes a precipitate in human blood
(possibly this is due to an agglutination of protein mole-
cules), but it is obvious that we have here a specific test
for human blood which is of great delicacy. The test
has already been widely employed in forensic medicine in
Germany, and has been the means of bringing about
conviction in cases of suspected murder.

The Spleen.—The spleen is usually classed in text-
books of physiology amongst the ductless glands. If by
a ‘gland,’ however, one means an organ with secretory
functions, then the term is hardly applicable, for whatever
its part in the economy of the body, the spleen certainly
does not secrete. Indeed, physiology can tell us almost
nothing definite about the spleen, except that it is not an
- organ which is essential to life, and that was already
known more than a hundred years ago.* All other
statements about this organ are more or less conjectural,
and it is for this reason that the part it plays in patholegy

* See the collected works of William Hewson, F.R.S.
7—2

100 APPLIED PHYSIOLOGY

is so ill-understood, and that diseases of the spleen are
the despair of the physician.

The spleen is often regarded as a blood-forming organ.
In man, however, there is really no evidence that it can
form red cells. Richly endowed as it is with adenoid
tissue in the form of the Malpighian bodies, there is no
doubt that it helps in the manufacture of lymphocytes,
but that is the only blood-forming function which can be
assigned to it. There is more reason for regarding
it as playing a part in the destruction of the blood; but
it is still open to question whether it does so actively or
whether it merely removes from the blood-stream the
débris or corpuscles which have been broken down
elsewhere. It is uncertain, in other words, whether the
spleen is an active agent in hemolysis or whether it is
only a blood-filter. Injection of poisons, such as chlorate
of potash, which disintegrate the blood corpuscles, causes
the spleen to enlarge, and’ the enlargement is in direct
proportion to the amount of blood destruction.* Similarly,
if bacteria or pigment particles be injected into the
vessels they are found to accumulate in the meshes of
the spleen. It would seem, therefore, as if the filter
function of the organ can be definitely established, and
it is believed that this explains its enlargement in such
diseases as malaria and enteric fever, in which blood
destruction is increased. On the other hand, there are
difficulties in the way of this view. The spleen is not
constantly enlarged in pernicious anemia, and yet most
pathologists are agreed that in that disease blood destruc-
tion is greatly increased. The subject is still further

* Jawein, Virchow’s Archiv, 1900, clxi. 461.

vee. 3s

BLOOD AND HAIMOPOIETIC ORGANS 101

complicated by the fact that splenic anzemia can be cured
by the operation of splenectomy, which would appear to
indicate that the spleen in that disease is playing an
active role in the production of anemia. The only con-
clusion which these considerations justify is that we are
still much in the dark as to the part played by the spleen
in hemolysis, although the balance of evidence is in
favour of the view that it serves at least as a filter in
removing effete corpuscles from the blood, whether or not
it can also give them the coup de grace. In any case its
duties cannot be very important, or they must be capable
of being performed vicariously by other organs, for
removal of the spleen does not seem to lead to any
impairment of health.* Even here, however, we want
more light. What, for instance, would happen to a
spleenless man if he took malaria or enteric fever ?

A slight enlargement of the lymphatic glands has been
noted after removal of the spleen, but neither constantly
nor to any striking degree. Probably this is com-
pensatory—an effort to replace the lost adenoid tissue.
The blood shows at first an increase of lymphocytes—
most likely as a consequence of the hypertrophy of the
glands, and later on a considerable rise in eosinophils,
the meaning of which is quite obscure. It cannot be
said that these observations throw any great light on the
functions of the organ.

As the spleen is practically a sponge filled with blood,
its volume varies with fluctuations in the general blood-
pressure. Such variations, however, are devoid of

* For the results of splenectomy in man, see Harris and Herzog,
Annals of Surgery, 1901, xxxiv. 111.

102 APPLIED PHYSIOLOGY

clinical significance. When the discharge of blood from
the splenic vein is interfered with, the organ becomes
passively overfilled. This is probably the reason for the
enlargement of the spleen which occurs in cirrhosis of
the liver. Oncometer tracings show that the spleen
exhibits independent rhythmical contraction, apparently
by means of the muscular tissue in its capsule and
trabecule. In consequence of this it has been looked
upon as endowed with a propulsive power as regards the
blood in the portal circulation, and has even been spoken
of as the ‘portal heart.’ The thickening of the capsule
and trabecule of the spleen, which undoubtedly occurs
when the portal circulation is obstructed, has been
regarded as evidence of an attempt on the part of the
‘portal heart’ to overcome the obstruction by hyper-
trophy. |
The Thymus.—The only thing we know with certainty
about the functions of the thymus is that, like adenoid
tissue generally, it is a place where lymphocytes are
born. Beard,* indeed, regards the thymus as the start-
ing-point of all adenoid tissue in the body. In his view,
lymphocytes are first formed by a tonsil i
primitive epithelial cells of the embryonic thymus, and
until the latter appears there are no white cells in the
blood. Later on secondary depots or colonies of adenoid
tissue are started in various parts of the body by

lymphocytes which have emigrated from the thymus,

and when these have been fairly established the thymus

itself disappears. With its disappearance, however, as

he justly remarks, adenoid tissue no more vanishes from
* Lancet, 1899, i. 144.

et ea ee

BLOOD AND HAMOPOIETIC ORGANS 103

the body than the Anglo-Saxon race would disappear
if the British isles became submerged. Most writers
are agreed* that the thymus attains its maximum
development relative to that of the body as a whole between
the second and fourth years of life, and it is interesting
to note that it is after this period that the lymphocytes
of the blood undergo a diminution in number. It
would appear as if more lymphocytes were wanted in the
earlier years of life, and that the thymus existed in order
to manufacture them; but why they are wanted we do
not know. Excision of the gland throws little light on
the matter, most experimenters having found after it a
diminution of red cells and an increase of white. Nor
do we even know whether the presence of the organ in
the first years of life is essential to existence or even to
health. I know of only one case in which the thymus
was absent in an infant,t and in that case the child lived
until it was six months old, but as one kidney was absent
also, this case is of little value as evidence. ;

Physiology and pathology are here alike at fault.
Neither has succeeded in showing that the thymus is
more than a mere mass of adenoid tissue.

The lymphatic glands are, like the thymus, important
birthplaces of lymphocytes, and when they take on
increased functional activity, as in lymphatic leukemia,
there ensues a great rise in the lymphocytic population
of the blood-stream.

In addition to this they seem to help, at least, in the
protection of the body against invasion by bacteria or

* Bonnet, Gaz. des Héopitaux, 1899, lxxii. 1321.
+ Reported by Alfred Clark, Lancet, 1896, ii. 1077.

104 APPLIED PHYSIOLOGY

their poisons. Placed, as they are, like sentinels at the
points of convergence of the lymphatics, they entangle
micro-organisms in their meshes and prevent their
onward passage. That they are able directly to destroy
these is unlikely, for the lymphocytes are not phagocytic,
and it is well known to surgeons that organisms can lie
latent in lymph glands for a long time and come to life
and dangerous activity again if the gland be opened into.
In the meantime, however, the growth of the germs has
been restrained, probably by means of a chemical
influence exerted by the cells of the gland.*

* See Manfredi, in Virchow’s Archiv, 1899, clv. 885.

ee ne

CHAPTER IV
THE APPLIED PHYSIOLOGY OF THE HEART

The Beat of the Heart.

Tue tendency of all recent physiological investigation
has been to magnify the importance and independence
of the heart muscle. It is now believed that the beat of
the heart takes place independently of nerve influence,
and as a consequence of the automatic contractility
which the cardiac muscle possesses in virtue of its com-
paratively embryonic and undifferentiated form.* The
beat or contraction starts, as might be expected, in that
part of the heart wall which possesses these character-
istics in the greatest degree—i.e., in the muscle at the
mouths of the great veins. Thence the contraction is
conducted from muscle cell to muscle cell, sweeping over
the auricles and producing their systole, and is trans-
mitted to the ventricles by means of the auriculo-ven-
tricular bundle of fibres which crosses the auriculo-
ventricular groove. t

* This is sometimes spoken of as the ‘myogenic’ theory of the
heart’s action, as opposed to the ‘ neurogenic’ theory, which supposes
the necessity of a local nerve apparatus to maintain the contractions
of the heart.

+ A full anatomical description of the auriculo-ventricular bundle

in man will be found in a paper by Keith and Flack (Lancet,
105

106 APPLIED PHYSIOLOGY

The force with which the fibres contract seems to
depend largely upon the pressure in the interior of the
heart, or, in other words, on the extent to which it is
filled during diastole. If, for example, the heart ‘ misses
a beat,’ and in consequence of that the left ventricle
becomes overfilled, the next systole is unusually power-
ful, and is felt as the ‘thump’ so often complained of by
patients with palpitation.

Although, as has just been pointed out, the normal
contraction starts at the venous ostia, yet it must be
remembered that the whole of the heart muscle possesses
the power of originating stimuli, and a contraction set
up in the ventricles will pass back to the auricles. In
cases of disease this abnormal mode of cardiac contrac-
tion sometimes occurs. The capacity of transmitting a
wave of contraction is spoken of by physiologists as the
conductwity of the heart muscle, and we shall see later
on that alterations in conductivity explain many of the
alterations in cardiac rhythm which can be observed in
disease. The ventricles respond to the contraction wave
by a simultaneous and cogjadihated shortening of all
their fibres—not by a peri ic wave—by which
ventricular systole is produced These fibres are co pl
circular and partly longitudinal in arrangement. The

1906, ii. 359). The muscle’ fibres which make up its ramifica-
tions are of the Purkinje type, and possess a lower degree of con-
ductivity than the more highly developed fibres of the heart wall.
If the bundle is destroyed by disease, the propagation of the wave
of contraction is ne “ae and a condition of ‘heart-block’
results. In such a case the ventricles take on an independent
action, and contract sbythmically at arate of 28 to 36 beats per
minute.

THE HEART 107

contraction of the circular fibres results in considerable
diminution of the diameter of the base of the heart (the
clinical importance of which we shall see immediately),
whilst the total length of the ventricles is not increased,
owing to the fact that the transverse thickening of the
circular fibres of the wall is neutralized by the contrac-
tion of the opposing longitudinal fibres.*

The result is that the walls of the heart approach
nearer to the septum, and in consequence the blood is,
as ib were, ‘wrung out’ into the aorta and pulmonary
artery. It must not be supposed, however, that the ex-
pulsion of the contained blood takes place the moment
the ventricular wall enters into contraction. During
an appreciable interval—‘ the presphygmic interval ’—
which varies in the human heart from seven to ten-
hundredths of a second, the muscle of the wall is engaged
in compressing the contained blood in order to get up a
pressure sufficient to overcome the resistance in the
aorta and pulmonary artery, and it is only when a
sufficient degree of pressure has been attained that the
semilunar valves fly open and the blood is expelled.
Thus one might divide the period of systole into (1) a
compression time, during which pressure is brought to
bear on the contained blood, and (2) an expression
time, which is occupied by the expulsion of the blood
into the aorta and pulmonary artery.+ It is during the

* For a very interesting description of the functional anatomy of
the musculature of the heart the reader should consult a paper by
Dr. Arthur Keith in the Jowrnal of Anatomy and Physiology, 1907,
vol. xlii.

+ See Martius: ‘Der Herzstoss des Gesunden und Kranken
Menschen.’ Volkmann’s Samml. Klin. Vort. 1894, Inn, Med.,
No. 34, p. 171.

108 APPLIED PHYSIOLOGY

former of these periods that the apex-beat is produced.
The greater the resistance offered to the escape of blood
from the ventricles, the more prolonged is the com-
pression period required, and the longer, therefore, the
systole.* Hence the slow systole of aortic stenosis and
high arterial pressure. It is now generally believed
that the systole never succeeds in expelling the whole of
the blood contained in the ventricles; a fraction is
always left behind. If the systole is feeble, this fraction
is increased, and may be so great as to retard the whole
current of blood through the heart, in consequence of
which all the signs of back pressure may result even in
the absence of any valvular defect. To this condition
the term ‘ systole catalectic ’ is sometimes applied.+
After their contraction, the walls of the ventricles
rebound in diastole. Whether this is due merely to an
elastic recoil of the compressed columne carnex and
musculi papillares, or whether there is an ‘active’
retraction of the muscle fibres, is disputed; but, at all
events, the force of the recoil is sufficient to produce a
degree of negative pressure in the ventricular cavities.
It is still denied by some physiologists that this is /of
sufficient degree to aid in the filling of the ha it
seems to playa larger part in some conditions of disease.
One cannot explain the diastolic murmur met with in
some cases of mitral stenosis, for instance, unless on the

* Even when the aortic pressure is high, the compression time
does not seem to be much prolonged so long as the heart muscle is
healthy. As Hill points out, this is equivalent to saying that the
heart can meet great demands on its powers without any appreciable
loss of time (Schifer’s ‘ Physiology,’ ii. 20).

+ Graham Steell.

ea ic. ante

-
ee ee

THE HEART 109

assumption that there is a considerable degree of suction
exerted by the ventricles during diastole.*

If the ventricle is unable to empty itself completely at
each systole, any negative suction which it can exert is,
of course, abolished. This may be an additional reason
for the laboured action of a dilated heart. The part
played by the negative pressure in the mediastinum in
promoting expansion of the heart during diastole is also
of considerable importance, and will be considered in
another chapter.

The Apex-Beat.

The apex-beat is normally felt in the fifth intercostal
space at a point (in the adult) about 43 inches from the
mid-sternal line. The apex-beat is not felt with equal
ease, however, at all periods of life. Up to the age of
twenty or thereabouts it is always palpable in normal
conditions, even when the subject lies on his back; but
beyond that age it can only be made out at all easily in
about half the individuals examined. The reason for
this is that the ease with which the apex-beat can be
determined depends upon the extent to which the heart
and chest wail are in contact—i.e., upon the size of the
heart relative to that of the thoracic cavity. Now, the
ratio of the heart to the chest is greatest in young
subjects, hence the ease with which the apex-beat
can be made out in such cases. For this reason, too,

* Stacey Wilson, ‘The Diastolic Expansion Movement of the
Ventricles as a Factor in Compensation for Disease of the Mitral
Valve,’ Brit. Med. Jowrn., 1900, ii. 895.

110 APPLIED PHYSIOLOGY

an hypertrophied heart always displays a strong apex-
beat.

The exact way in which thé apex-beat is produced has
been much discussed, but everyone is agreed that it does
not result from the heart knocking up against the chest
wall as the fingers knock on a door, for the simple reason
that the heart and chest wall are always in contact. We
have seen that the apex-beat is synchronous with the
‘compression ’ period of the systole, and it is really due
to the hardening and change of shape of the heart as it
contracts upon its contained blood, but before the ex-
pulsion of the latter begins. Hence one finds that the
apex-beat always precedes the thrill felt over the aortic
orifice in aortic stenosis, for the thrill occurs as the blood
escapes into the aorta from the ventricles; and thus the
apex-beat really occurs before the diminution in size of
the ventricle begins, and the old difficulty of explaining
how the beat could be felt though the ventricle was
getting smaller is seen not to exist. An hypertrophied
heart produces a forcible apex-beat, but in dilatation the
beat, though diffusely felt, owing to the large surface of
heart in contact with the chest wall, is less forcible,
because the left ventricle does not completely empty
itself, and so the diminution of the volume of the heart
during the ‘expulsion time’ is not so pronounced.
There is, then, no necessary relation between the ease
with which the apex-beat can be appreciated and the
force of the heart; the latter can be judged from the
pulse alone.

It should be noted that when the right ventricle is so
much dilated as to bulge into the epigastrium the im-

Mita 1 PE as is

"Le =.

regis sy) ve

THE HEART 111

pulse which it communicates is not synchronous with
the apex-beat, but is diastolic in time, and really due
to the filling of the chamber and not to its contrac-
tion. During systole in such a case the epigastrium
recedes.

Tracings of the apex-beat will be found in any work
on physiology, but clinically they are of little interest.

The Pericardium.

The pericardium corresponds to the tunica adventitia
of the arteries, and is to some extent a protection to the
heart. It has been argued that it tends to prevent
dilatation of the heart under sudden strain (acting like
the outer case of a football or the netting round an
indiarubber spray bag), but this can only be true of
extreme emergencies.* Certainly a sudden paralytic
dilatation of the heart sufficient to cause its arrest does
not seem to be prevented by the pericardium. Nor does
free movement between the surface of the heart and the
inner aspect of the pericardium appear to be essential to
the unhampered action of the former, for clinical observa-
tion shows that, provided the heart muscle has escaped
damage in the process which leads to the pericardial
adhesion, little, if any, hypertrophy of the heart ensues.
As the space inside the pericardium is strictly limited,

it seems not unlikely that great enlargement of one side
- of the heart must interfere with the action, and especially
with the filling, of the other. Thus, for example, the

* See Theodore Fisher, ‘Dilatation of the Heart,’ Lancet, 1902,
i. 1594,

112 APPLIED PHYSIOLOGY ‘

great overdistension of the right heart in asphyxia may
help to explain the emptiness of the left.

There is probably but little room for lateral movement
of the heart inside the pericardium. The change in
position of the apex-beat when an individual moves over
on to his side—a change which may amount to some
inches—is believed by physiologists to be due to the
heart rolling over inside the pericardium under the
action of gravity, so that a different part of its wall
comes into contact with the chest. It is doubtful, how-
ever, if this can be regarded as a complete explanation,
for ‘fixation of the apex-beat’ is believed by many good
clinical observers only to occur when the pericardium
itself is adherent to the chest wall, but not when the
heart and pericardium are alone adherent to one
another.

Dee SO rea as

The Valvular Mechanism of the Heart.

If the blood contained in the heart is always to be
driven on in a definite direction, it is obvious that the
orifices between its different chambers and at its entrances
and exits must be provided with valves. The tendency
amongst clinicians in the past—a tendency due partly to
the introduction of the stethoscope as an instrument of
observation and partly to an almost exclusive study of
the naked-eye pathology of the heart—has been to attach
an undue importance to the membranous valves as
guardians of the orifices. At all events, this is in-
disputably true as regards the auriculo-ventricular
valves. It is doubtful, as MacAlister has said,* if these ~

* Brit. Med. Jowrn., 1882, ii. 821.

=

THE HEART 113

would be alone sufficient to prevent the reflux of blood
into the auricles in two cases out of three were it not
that, as has been already stated, the diameter of the
base of the heart undergoes such a marked diminution
during systole in consequence of the contraction of the
circular muscle of the ventricular wall. In other words,
fhe muscular contraction of the ventricle is quite as im-
portant in preventing a backward flow of blood as is an
intact condition of the auriculo-ventricular valves. One
need not wonder, then, that mitral incompetence so often
results simply from disease of the muscular wall. The
closure of the aortic and pulmonary orifices, on the other
hand, is entirely brought about by the semilunar valves,
but it is well known that even extreme cardiac dilatation
does not lead to any regurgitation at these situations.
Recgnt investigations by Keith* tend to show that the
backflow of blood into the vene cave is also prevented,
to some extent at least, by a series of muscular arrange-
ments in the heart which are of too intricate an
anatomical nature to be described here. Enough has
been said, however, to show that the valvular mechanism
of the heart is as largely muscular as membranous in
character, a conclusion which is quite in harmony with
the results of clinical observation.

Sounds of the Heart.

_ It is generally agreed that the first sound of the heart
is the product of at least two factors: (1) the tone
produced by the contraction and vibration of the muscle

* Proc. of Anat. Soc. Gt. Brit. and Irel., 1902, Nov. p. ii. (issued
with vol. xxxvii. of Jowrn. of Anat, and Physiol.).

114 APPLIED PHYSIOLOGY

substance of the ventricles, (2) that which results from
the stretching of the auriculo-ventricular valves. One
gays advisedly the stretching of the valves, for the sound
is not due, as was once supposed, to the driving together
of the membranous flaps, but to their sudden tension
between the fibrous ring round the mouth of the auriculo-
ventricular orifice on the one hand and the papillary
muscles on the other. ‘The flaps of the mitral and
tricuspid valves are at no period of the cardiac cycle in
anything approaching to a horizontal position. On the
contrary, they are always more or less vertical, and the
contraction of the musculi papillares merely serves to
counteract the tendency of the cusps to float up owing
to the constriction of the base of the heart during
systole. Hence it is that the valves are suddenly made
tense by being pulled on at both their extremities like
a sheet well shaken, and the characteristic flapping
sound results. Hither the muscular or the membranous
element of the first sound may come to predominate in

‘conditions of disease. If the ventricular wall is hyper-

trophied, the sound is low and booming from an emphasis
of the muscle element; if, on the other hand, the
muscle is thin and atrophied, the predominance of the
membranous factor imparts to the sound a high-pitched ©
and slapping character. When the ventricular systole
is feeble and inefficient, both the muscular contraction
and the stretching of the valve are so much reduced
that the first sound becomes very faint, or may even
be inaudible.

The second sound, on the other hand, is due entirely
to the tension of the semilunar valves, and its loud-

THE HEART 115

ness depends solely upon the pressure in the aortic and
pulmonary systems. Increased loudness of this sound,
therefore, always indicates an increased arterial or
pulmonic blood-pressure. The sound produced in the
left ventricle is always louder than that of the right,
and both attain their maximum intensity between the
ages of twenty and forty. The pulmonary second sound
is louder than the aortic up to the age of puberty ; there-
after the aortic second becomes progressively the louder.

3 Second. Ventricular Systole. ‘| 8; Second. Ventricular Diastole.

Compression : F Auricular
Pees 3 heeeemicn Timo, Systole,
gs Second. Lg im 5 denna yy Second,

All valves | Auriculo- ven-
closed;| tricular valves
apex-| closed, blood
beatpro-| being expelled;
duced recession of

apex

First Opening Second
sound of sound
semilunar

valves

The Work of the Heart.*

The total work of the heart is the sum of that done
by its different chambers. The work of the ventricles
_ consists chiefly in overcoming the pressure in the aorta
and pulmonary artery, and, to a much less extent, in
imparting to the expelled blood the necessary velocity.

* Benno Lewy, ‘Die Arbeit des Gesunden und des Kranken
Herzens,’ Zeit. f. Klin. Med., 1897, xxxi. 321.

8—2

116 APPLIED PHYSIOLOGY

About 7 per cent. of the total work is also expended in
overcoming resistance in the heart itself. Assuming
that the volume of blood expelled from each ventricle is
approximately 60 c.c., the total work of a cardiac
cycle amounts to 0°2 kgm. (or 12 foot-pounds). At a
rate of seventy beats per minute this means 252 litres
of blood distributed to the organs every hour, and
implies a work of 815 kgm., or 20,000 per day (about
140,000 foot-pounds). In normal circumstances an in-
crease in the rate of the heart does not indicate an
increase in its work, for the output per systole is pro-
portionately lessened. The peculiarity of the heart is,
not that it does a great amount of work, but that it does
it incessantly. This cannot be due altogether to any
peculiarity of its muscle, for the diaphragm also works
continuously, and does 376 kgm. per hour. Prob-
ably all the voluntary muscles could do as much work
as the heart were it only possible for the digestive
organs to keep them supplied with a sufficiency of
potential energy in the form of food.*

Great as the normal energy of the heart is, its reserve
power is greater still. Even moderate muscular work
demands a fourfold output of cardiac energy, and the
total reserve power has been estimated at thirteen times
the normal output during rest. In conditions of disease
the work of the heart is enormously augmented, largely
from increased resistance in driving the blood through
its own chambers (e.g., in mitral stenosis). In disease,
too, all such factors as number and duration of systoles
are of importance.

* Lewy, op. cit.

THE HEART 117

In a case of aortic stenosis, for example, in which 0°7
of the opening is obstructed, as happens when two of the
cusps are completely adherent, the heart does 1,000 kgm.
of work at sixty beats per minute, but at seventy beats
it does 1,150 kgm. Further, the fluid tension to
which the wall of the heart is subjected increases with
the radii of curvature of the cavity. Hence a dilated
heart must put forth more energy in order to expel its
contents than one of normal ventricular capacity, and
for that reason it hypertrophies.*

In addition to this, the mere overfilling of the left
ventricle must always lead to an increase of its work
during systole, for although the systole is prolonged in
such circumstances, yet the prolongation never extends
to more than 20 or 80 per cent. of the normal time.t
Hence the blood must be expelled more rapidly—.e.,
more work must be done.

It has been calculated that if a lesion is so bad as to
require 7°7 times as much energy as usual to com-
pensate it—i.e., a heart 7-7 times heavier than normal—
the maintenance of the circulation is impossible.

In normal circumstances the different chambers of
the heart transmit equal volumes of blood in the same
time. Were this not so, of course, the circulation would
- come to a standstill, and the usual cause of death from
- heart failure is inability on the part of one or more
. chambers of the heart to fulfil its duty in this respect.
Iiyven in health, however, the law may be temporarily

* See Hill in Schifer’s ‘ Physiology,’ ii. 40.

t See von Frey, Deutsch, Arch. f. Klin. Med., 1890,
xlvi. 398.

118 APPLIED PHYSIOLOGY

disregarded, and unequal volumes of blood transmitted ;
but the balance is always speedily rectified by an extra
effort on the part of the heart.

Physiological Properties of Heart Muscle.

The starting of the cardiac systole is due to the
excitability of the heart; the propagation of the systolic
wave, as we have seen, to its conductivity ; the expul-
sion of the contained blood to its contractility; and the
regularity of the contractions to its rhythmicity.

The properties of excitability and rhythmicity will be

20 e02
2
ees Bed

3
3
4 ’
72 '
a
2]
Aa
a

gna 1 tty 20 i 20 1
P abcd
Fie 8.—SERIES oF VENTRICULAR SYSTOLES (AFTER WENCKEBACH.)

p to a= Refractory period ; at a, b, c, and d lessening degrees of
stimulation will induce contraction.

further discussed when we come to consider the rhythm
of the heart (p. 130). ys

As regards the property of contractility, » two pecu-
liarities must be emphasized. ‘The first is that the
contractions of the heart are always maximal—i.e., if a
stimulus is strong enough to excite the heart to contract
at all, the latter always responds with all the strength
of which it is capable at the moment. The advantages
of this, as pointed out by Wenckebach, are (1) that it
makes the heart independent of the strength of the
stimulus, and (2) that while weak stimuli produce the

THE HEART 119

full effect, strong ones are unable to produce an excessive
contraction.

The second peculiarity of the contraction of the heart
is that it abolishes for a time (the refractory period) all
the other properties of the heart muscle, including the
power of further contraction. This ensures a period of
rest to the heart, and makes it impossible for it to pass
into a tetanic condition (Fig. 3).

The property of conductivity is exercised through
the muscle fibres themselves, and not through nerves.
The advantage of this is that, even although the heart
be extensively diseased, conduction can still go on so
long as the muscle cells are connected to each other,
which would hardly be possible if conduction were
dependent on a comparatively small number of nerve
fibres.

It should be pointed out, further, that the physio-
logical properties of the heart muscle are all independent
of each other, so that one may be diminished or even
abolished altogether without affecting the other.

The question must now be discussed, Does the heart
wall possess, in addition to these properties, the quality
of tonicity? By this one means does the volume of the
heart and the capacity of its chambers tend to be kept
always somewhat reduced in consequence of a slight
tonic contraction of its muscle fibres, or, what comes to
much the same thing, as a result of their elastic
resilience? ‘To this question physiology now furnishes
an affirmative reply, and various clinical facts render
the existence of tonicity undoubted. It will be obvious
that tonicity must oppose dilatation of the heart from

120 APPLIED PHYSIOLOGY

pressure on the inner aspect of its wall during diastole.
Now, the degree of resistance offered to such dilatation
appears to vary considerably in different individuals.
In other words, the ‘ tone’ of the heart seems to be by
no means constant. That is probably why one man
gets cardiac dilatation as the result of a degree of
exertion which is borne with impunity by another. The
toxins of some diseases, too, such as diphtheria and
influenza, appear to lower heart tone, and predispose to
dilatation; and the same is true of some poisons, such
as muscarine. Considerable variations in the tone of
the heart may, and probably do, occur unobserved.
Thus a degree of relaxation sufficient to double the
output would only mean an increase in diameter of the
heart of 2 centimetres—an increase inappreciable by
percussion.*

On the other hand, the most valuable property of
digitalis as a drug appears to be its power of increasing
the ‘tone’ of the heart muscle and so of opposing dila-
tation. The possible relation of such tone to nervous
influence will be discussed later. |

Tonicity resembles in a minor degree an active con-
traction of the heart, and we shall see later (p. 137) that
contraction suspends the other functions of the heart
muscle whilst it is taking place, and for some time after-
wards. Similarly, when tone is increased, conductivity
and excitability are diminished, and when tone is
diminished these are increased.t Now, diminution of

* See Hensen, Deutsch. Arch. f. Klin. Med., 1900, Ixvii. 436.
+ See a very suggestive paper by Gossage, Med. Chir. Trans.,
1906, vol. xe.

THE HEART 121

tonicity is one of the commonest events in cardiac
disease, and, probably in consequence of this, increased
excitability and conductivity of the heart muscle are
common occurrences in disease too, and are mainly
responsible for some of the chief forms of irregularity
of the heart’s action.

The Nervous Control of the Heart.

The maintenance of the heart’s action is a matter of
such transcendent importance to the organism that, as
we have seen, it has been made to depend upon the
intrinsic qualities of the heart muscle. On the other
hand, the dependence of every organ upon the heart for
a due supply of blood, and the necessity for frequent
variations in the rate and force of the blood-stream and
the height of the general blood-pressure, make it essential
that the heart should be ‘connected up’ with all other
parts of the body by nervous communications. As a
matter of fact, this is very carefully provided for, and the
heart is accordingly played upon by more reflex influences
than almost any other organ in the body.

These nervous influences act upon the various physio-
logical properties of the heart muscles, either intensifying
or lessening them. Thus they may:

1. Accelerate or lessen the rate of stimulus production,
and so increase or lessen the rate of the beats.

2. Accelerate or lessen the rate of conduction of the
contraction, and so accelerate or retard the beats.

3. Increase or diminish the excitability of the muscle,
and so affect the strength of the stimulus required to
produce a beat.

122 APPLIED PHYSIOLOGY

4. Increase or diminish contractility, and so affect the
force of the beats.

If one remembers that each of the physiological
properties of the heart muscle can be affected inde-
pendently by nervous influences in a positive or negative
direction, and reflects upon the different permutations
and combinations of disturbances of the heart’s action
which may be so produced, one will readily understand
how complicated the control exercised by the nerves of
the heart in health really is.

Efferent Impulses.

The paths by which these influences reach the heart
are shown in detail in Plate I.

It will be observed that two sets of efferent fibres pass
to the heart from the nervous system :

1. Inhibitory fibres contained in the vagus.

2. Accelerator or augmentor fibres which run in the’

sympathetic system.

The inhibitory fibres are inimical to the exercise of
most of the physiological functions of the heart muscle.
They lower its excitability, its conductivity,* and/ its
contractility, but not, apparently, its tonicity.+ In other
words, the influences which they convey are opposed
to those molecular changes which manifest themselves
in the discharge of function—i.e., they restrain kata-
bolism. For this reason the vagus has been described

* Muskens (Amer. Journ. of Physiol., 1898, vol. i., p. 486) regards
as the chief effect of the vagus.

+ Gaskell, however, believes that the vagus does lower tonicity
(Schiifer’s ‘ Physiology,’ ii. 215).

Te
“s

THE HEART 123

by Gaskell as the ‘anabolic nerve’ of the heart, and he
has compared it to a vaso-dilator.

The vagus control is in constant action, but varies
sreatly in different individuals and in the same individual
at different times. It keeps the heart slightly ‘reined
in,’ as it were, and conserves its energy, for after a period
of increased vagus control the vigour of the heart is
augmented. Putting aside the results of physiological
experiment, clinical observation* has clearly shown that
when the vagus influence is removed the rate and force
of the heart-beat are both increased, but the former
more notably than the latter. There are limits, how-
ever, to the increase of rate observed as the result of
vagus lesions in man. In no such case have the heart-
beats amounted to more than 160 per minute. Pulse
rates above this, therefore, cannot be due to vagus
paralysis alone. The increased rate is observed when
either vagus is destroyed, but, of course, rather more
markedly when the influence of both has been with-
drawn. Nor has cardiac dilatation been observed in
such circumstances, not even when the lesion has been
present for many months. This is to be explained by
the independence of the ‘tone’ of the heart of nervous
influences. ,

The influence of the sympathetic nerve upon the
heart is exactly opposed to that of the vagus, and is
directed to increasing the force and frequency of the
beats. For that reason it is spoken of as the accelerator
or augmentor nerve. It is probable, however, that these

* See a collection of twenty-four cases by Martius, ‘Tachycardie,’
p. 87 (Stuttgart, 1895).

124 APPLIED PHYSIOLOGY

two influences are separate and travel by different
fibres, for on stimulating the sympathetic one some-
times produces a mere increase in rate, whilst at other
times one gets an augmented output and rise of blood-
pressure. Gaskell has described the effects of the
sympathetic on the heart, as a whole, as a ‘ katabolic’
one, for it tends to increase those chemical changes
which lead to the beat, and he compares it to a vaso-
constrictor. The right sympathetic seems to exert more
influence than the left.

Curiously enough, we know much less of the action
of the sympathetic, both clinically and physiologically,
than of the vagus. It was even long disputed whether
or not the sympathetic had a constant tonic action. It
is now generally agreed, however, that it has.* Indeed,
its action seems to be at least as continuous as that of
the vagus. The normal heart rate, in fact, appears to
be determined by the influences reaching it through the
vagus and sympathetic channels, and between these
there is, as it were, a constant struggle for supremacy
going on. All the physiological evidence, however,
points to the fact that an increase in the rate of the
heart is always due to a diminution of vagus tone, and
not to an increased action of the sympathetic. It might
seem natural to suppose that cases of palpitation
characterized by increased force and frequency of the
beats were produced by an increase of the sympathetic
influence; but this would appear not to be the case.
The mere fact that such attacks may cease very abruptly
would negative such a view, for experimental stimulation

* See Reid Hunt, Amer. Jowrn. of Physiol., 1899, ii. 895.

THE HEART 125

of the sympathetic always shows that the heart con-
tinues to beat rapidly for a long time after the stimu-
lation has ceased. Even emotional increase in the
heart’s rate, then, is apparently due_to_a temporary
diminution of Vagus fone, and the same is true of the
acceleration observed during swallowing and as the
result of inspiration. At the same time such temporary
suspension of vagus control could not exert such an
immediate and marked influence upon the rate of the
heart were it not for the constant action of the sympa-
thetic, which merely waits, as it were, for the oppor-
tunity afforded by the relaxed control of the vagus in
order to assert its influence. Conversely, when the
heart has been slowed by increased vagus action, the
sympathetic limits the slowing, and enables the heart
to return more quickly to its normal rate. This action
is probably of importance in counteracting influences
which tend to cause reflex slowing, such, for example,
as injury to the abdominal viscera. It therefore
minimizes shock.

The accelerator centres and nerves would appear to
be very resistant to influences such as a low blood-
pressure, extreme asphyxia, and certain drugs, which
quickly depress other nerve centres. This is fortunate,
for they are thus, in virtue of their tonic activity, in a
state to aid the heart in an emergency when it most
needs help.

The degree of control exercised by the nervous system
over the heart probably varies at different ages. This
certainly seems to be so in the case of the inhibitory
fibres, at any rate. These appear to be almost inactive

126 APPLIED PHYSIOLOGY

at birth,* but their tone increases up to twenty-five to
thirty-five years, and from this time lessens again, and
is very slight in old age. Atropine, which acts by
paralyzing the ends of the inhibitory fibres, has thus
very little effect on the heart at the extremes of life.
This may be one reason why children stand large doses
of belladonna so well.

Afferent Impulses.

The course of the afferent nerves from the heart to
the nervous system is not so well known as that of the
efferent. In man they appear to be both in the vagus
and in the rami communicantes of the upper dorsal
nerves.t The vagus fibres which constitute the de-
pressor nerve are those with which we are best ac-
quainted, though these probably belong, in man at least,
to the root of the aorta rather than to the heart itself.
The name ‘ depressor’ is applied to these fibres because
of the great lowering of general blood-pressure which
stimulation of them brings about. They appear to be
thrown into action when the heart is struggling against
an aortic pressure which is rather too great for it’ to
overcome, and their stimulation appears to be attended
by the production of pain, which may manifest itself in
some cases in the form of the disease known as angina
pectoris. Normally, however, the heart, like most of
the internal organs, appears to be but poorly endowed

* Cushny, ‘A Textbook of Pharmacology,’ first edition, 1900,
p. 280,

{ See Ferrier’s Harveian Oration on ‘The Heart and Nervous
System,’ Brit. Med. Journ., 1902, ii. 13386.

THE HEART 127

with sensibility, except, perhaps, to states of abnormal
tension within its cavities. The insensibility of the
heart was first demonstrated by Harvey in the case of
the son of Viscount Montgomery, whose heart had been
exposed by destructive ulceration of the overlying chest
wall. Harvey related as follows* :

‘I found a large open space in the chest, into which
I could readily introduce three of my fingers and my
thumb: which done, I straightway perceived a certain
protuberant fleshy part, affected with an alternating
extrusive and intrusive movement; this part I touched
gently. Amazed with the novelty of such a state, I
examined everything again and again, and when I had
satisfied myself, I saw that it was a case of old and
extensive ulcer, beyond the reach of art, but brought
by a miracle to a kind of cure, the interior being in-
vested with a membrane and the edges protected with
@ tough skin. But the fleshy part (which I at first sight
took for a mass of granulations; and others had always
regarded as a portion of the lung), from its pulsating
motions and the rhythm they observed with the pulse

. | saw was no portion of the lung... but the
apex of the heart! covered over with a layer of fungous
flesh by way of external defence, as commonly happens
in old foul ulcers. The servant of this young man was
in the habit daily of cleansing the cavity from its accu-
mulated sordes by means of injections of tepid water,
after which the plate was applied, and with this in its
place the young man felt adequate to any exercise or

* William Harvey, Collected Works (Sydenham Soc., 1847), on
Generation, p. 388. .

128 APPLIED PHYSIOLOGY

expedition, and, in short, he led a pleasant life in perfect
safety. Instead of a verbal answer, therefore, I carried
the young man himself to the King, that His Majesty
might with his own eyes behold the wonderful case:
that in a man alive and well ke might, without detri-
ment to the individual, observe the movement of the
heart, and with his own hand even touch the ventricles
as they contracted. And his most excellent Majesty,
as well as myself, acknowledged that the heart was
without the sense of touch; for the youth never knew
when we touched his heart except by the sight or sensa-
tion he had through the external integument.’

Cases such as this belong, of course, to the curiosities
of medicine, but the insensitiveness of the heart to
punctured wounds is a well-established clinical fact.

The nervous mechanism of the heart may be brought
into action in various ways.

1. Psychical and emotional influences may so
stimulate the cardio-inhibitory centre as to lead to
instant and fatal arrest of the heart’s action. A number
of classical examples of such cases are mentioned by
Balfour.* pi

‘Sophocles, at the age of ninety, died suddenly of joy on being
crowned as the first tragic poet of the age. Philippides, the comic
writer, died a similar death. Chilon, of Lacedemon, died in the
arms of his son, who had borne away the prize at the Olympic
games. The famous Fouguet died of joy on being set free by
Louis XIV. The niece of Leibritz died suddenly of joy at finding
a box containing ninety thousand ducats beneath the philosopher’s
bed. ... It seems more natural that terror and grief should be

* ‘Diseases of the Heart,’ third edition, 1898, p. 267.

ee Wed Meter

THE HEART 129

more hurtful than joy, and though this does not appear to be the
case, yet these emotions have in their turn been fatal to many.
Philip II., King of Spain, enjoys the unenviable notoriety of having
frightened two of his counsellors to death. One of his Ministers
of State died suddenly on being sharply rebuked for a hesitating
answer. Another, the Cardinal Espinoza, died a few days after
being sternly told, “ Cardinal, know that I am master.” ... In
the end of last century Prince George Louis of Holstein, having
removed the body of his wife from one coffin to another of more
costly materials, desired his valet to read him some pages from a
pious book, and, kneeling at the side of the coffin, he burst into
tears and died. And a few years ago there occurred in France an
even more startling instance of the fatal effect of overwhelming
emotion. Dr. Deleau, a celebrated aurist, only forty-four years
of age, leaning over his dying daughter to receive her last farewell,
himself fell dead as if struck by lightning.’

Even in the more prosaic records of clinical medicine
death from a ‘ broken heart’ is not unknown,* and it is
thanks to the play of emotional influences on the in-
hibitory mechanism that

‘A merry heart goes all the day;
Your sad tires in a mile-a.’

2. The nervous mechanism of the heart may also
be affected reflexly by impulses arising either in the
skin or in the internal organs. A good example of
reflex inhibition of the heart from stimulation of the
skin is seen in some cases of death from so-called
‘cramp’ on plunging into cold water. On the other
hand, gastric irritation is one of the commonest causes
-of that temporary diminution of vagus control which
manifests itself in ‘ palpitation’; and many similar
instances might be multiplied.

* See Schrotter, ‘ Verhand. d. 17th Cong. f. Inn. Med.,’ Weisbaden,
1899, p. 23.
9

130 APPLIED PHYSIOLOGY

What the advantage to the organism of many of the
disturbances of the heart brought about by nervous
influences may be it is often hard to say, but probably
we shall not be far wrong if we regard most of them as
essentially protective and compensatory in their nature.
In particular, they seem to be designed to mitigate
the effects of sudden rises of blood-pressure, especially,
perhaps, on the heart itself; for all rises of arterial
pressure seem to induce a slowing and enfeeblement of
the heart’s action, whilst, conversely, sudden falls of
pressure are attended by a more frequent and powerful
heart-beat. In this way, too, the heart itself is protected
from undue strain.

8. The ability to exercise any voluntary control over
the nervous mechanism of the heart is a phenomenon of
the rarest occurrence. The best example of it is the
classical case of Colonel Townshend, recorded by Dr.
George Cheyne,* who, when on his death-bed, was able
to throw himself at will into a state of suspended anima-
tion, in which the heart’s action became imperceptible.
There are other cases on record as well, in which the
heart’s rate could be voluntarily increased, and in all
such instances there has been an unusual | degree of
control over the involuntary muscles. +

The Rhythm of the Heart.

The maintenance of the regularity or otherwise of the
rhythm of the heart depends upon two factors: (1) the

* “The Case of the Hon, Colonel Townshend,’ ‘The English
Malady,’ fourth edition, 1734.

t See Reid Hunt, Amer. Jowrn. of Physiol., 1899, ii. 895.

en ro

THE HEART 131

condition of the muscle wall; (2) the influence of the
nervous mechanism. _ .

Rhythmicity and Excitability.

What it is in the fibres of the heart muscle which
endows them with the property of regular rhythmical
contraction, or rhythmicity, we do not know. In the
last resort it must depend upon some peculiarity in their
metabolism, possibly the building up of some ‘ explosive’
compound, upon the disintegration of which the starting
of a contraction ensues, the normal intervals between
contractions representing the time required for the
formation of this compound. From this point of view
the heart muscle might be compared to a gun, which
is always fired off as quickly as it can be loaded. To
pursue this analogy, the ‘rhythmicity’ of the heart
corresponds to the rate of loading; its ‘ excitability’ to
the ease or otherwise with which the trigger can be
pulled.*

The more excitable the heart, the less the stimulus
which is required to produce a contraction. A very
excitable heart, therefore, is like a gun with a ‘hair-
trigger,’ and any abnormal stimulus can readily prompt
it to produce extra beats. Increased excitability—a

* In the text the myogenic origin of the rhythmical contraction
of the heart has been adopted, but the reader is reminded that
many physiologists believe that the production of the stimulus to
rhythmical contraction resides in the intrinsic-nervous mechanism
(neurogenic theory). The question is one of no direct clinical
interest, but the pros and cons of the two theories are well stated
in a paper by Gossage on ‘The Automatic Rhythm of the Heart’
(Brit. Med. Jowrn., 1907, ii. 1818).

9—2

132 APPLIED PHYSIOLOGY

condition of ‘irritable weakness ’—is a common occur-
rence in disease.

Alterations in Rhythm.

Alterations in rhythm may be induced either by
abnormal conditions of the muscle substance or by the
intervention of nervous influences, and clinically it may
be impossible to say which of these factors is at work.

A discussion of the rhythm of the heart involves a
consideration of—

1. Its rate.

2. The relative duration of systole and diastole.
8. The regularity of the beat.

4, The synchronism of the two sides of the heart.

1. The rate of the heart-beat is due primarily to the
excitability of the less differentiated muscle of the sinus
venosus, but it is also dependent upon the degree of con-
trol exercised by the inhibitory fibres of the vagus. The
greater rate of the heart in young subjects is probably
due to a feebler influence of the vagus in early life
(see p. 125), and the same may be true of the differences
in the rate of beat in different individuals. On the
other hand, alterations in the heart muscle may be a
cause of a more frequent beat. Fever seems to affect
the excitability of the heart directly, as well, perhaps, as
through the nervous centres, and the same is probably true
of the chemical products produced by muscular exercise.

The initial increase in the heart-rate which exertion
induces, however, must be due largely to mechanical
influences.

5
+
- Fi

THE HEART 133

‘The first effect of powerful general muscular action
is to drive the blood along the veins towards the heart,
and the right auricle and ventricle are at once distended.
To pass on the blood through the lungs as fast as it
arrives, the right heart must act more frequently and
powerfully, and the stimulus to this exists in the
increased pressure on its inner surface. For a time
there is accumulation in the pulmonary circulation, and
while this is the case there is dyspnoea and shortness of
breath and panting; but when the individual is vigorous
the circulation in the lungs and system becomes equal-
ized, and he gets his second wind, as the term is.’ *

All sudden alterations in the general blood-pressure
immediately affect the heart through its nervous con-
nections. Thus, on standing up the blood-pressure tends
to fall, but the heart beats more rapidly to make up for
it, The difference in rate between the horizontal and
erect postures, indeed, may amount to 8 or 10 beats
per minute, or 500 to 600 beats per hour. One can see
from this how great rest is afforded to the heart by
maintaining the horizontal position. In slow walking a
pulse of 60 per minute goes up to about 100, in quick
walking to 140, and on running to about 150 (Mac-
kenzie). On the other hand, conditions of high blood-
pressure are attended by a slowing of the heart which is
partly reflex, and partly the result of prolongation of the
‘compression period’ of the systole from the obstacle
offered to the expulsion of the ventricular contents.

Persistent acceleration of the heart from diminution
of vagus inhibition seems sometimes to occur as the

* Broadbent, ‘ The Pulse,’ p. 77.

134 APPLIED PHYSIOLOGY

result of nervous shock. A soldier in South Africa, for
instance, was suddenly startled by the explosion near
him of a 4°7 gun. His heart immediately began to beat
very rapidly, and continued to do so for some months.
Vagus acceleration, however, can never, as we have seen,
lead to a rate of more than 150. Attacks of ‘ paroxysmal
tachycardia,’ in which the beat runs up temporarily to
200 per minute or more, must have another origin than
that, and seem to be due to a sudden loss of tone in the
heart leading to temporary dilatation, in which so little
blood is expelled at each systole that the total number of
beats must be greatly increased if the circulation is to go
on.* The opposite condition of bradycardia, or diminu-
tion in the heart’s rate, may also be due either to
diminished excitability of the muscle itself or to in-
creased vagus inhibition. The former is the cause of
the very slow pulse sometimes observed during conva-
lescence from enteric fever or pneumonia.+ The latter
occurs, as we have already seen, when the vagus is
stimulated by a high blood-pressure, and also occasion-
ally under emotional influences. A slow beat from
change in the heart muscle can easily be distinguished
clinically from one due to increased vagus inhibition by
the administration of adose of atropine. In the former
case the rate will not be accelerated; in the latter case
it will.

* Mackenzie has suggested (‘The Study of the Pulse,’ p. 126)
that paroxysmal tachycardia is really due to a long-continued series
of premature systoles.

Martius, ‘ Tachycardie’ (Stuttgart, 1895).

+ Dehio, ‘Ueber die Bradycardie der Reconvalescenten,’ Dewt.
Arch. f. Klin. Med., 1894, lii. 74.

s)

THE HEART 135

Of alterations in rate due to augmentor impulses we
know nothing, but it seems not unreasonable to suppose
that the rapid and forcible beat of excitement may be
induced in that way.* Experiment, however, has shown
that stimulation of the accelerator does not raise the
heart rate above 120 per minute.

2. In health, no matter how fast or how slowly the
heart may be beating, the relative duration of systole
and diastole remains unaltered. If the cardiac muscle
is diseased, however, or if nervous influences are at work,
the normal relative duration of the different phases of
the cardiac cycle is often disturbed. Such disturbance
can be recognized at the bedside by changes in the
spacing of the heart sounds. In early life irregularity of
rhythm is chiefly due to occasional prolongation of the
diastole. In later life the occurrence of premature
systoles is a more potent source of varying rhythm.

The following alterations may occur :

1——_2—__-1—_-2__1—2_ Normal.

1 2 1 2 1 2 Prolongation of systole (pen-
dulum rhythm).
1—2 1—2 1—2 Shortening of systole.

|
bo
_
bo

1 Prolongation of diastole (brady-
cardia).
1—2—1—2—_1—_2—_1—2—-1—2—_ Shortening of systole and dia-
stole (tic-tac rhythm).
i—2——_-1——_-2—-1——-2—-_1_ Shortening of diastole (tachy-
cardia),

(a) The systole may be unduly prolonged from in-

* Determann, ‘Ueber Herz-und Gefiissneurosen, Volkmann’s
Samm l. Klin. Vort., 1894, Inn. Med., Nr. 80, p. 1.

136 APPLIED PHYSIOLOGY

creased resistance to the outflow from the heart, as in
aortic stenosis, or it may be unusually short from
diminution of the resistance to be overcome, or from
incomplete contraction of a dilated ventricle.

In the former condition the time between the first and
second sounds will be prolonged, and the heart assumes
on auscultation a pendulum rhythm. In the latter
state of affairs the interval between the two sounds is
unusually brief.

(b) Prolongation of the diastole occurs in bradycardia,
shortening of it in palpitation with increased frequency
of action, and in dilatation of the ventricle. In the
latter case one gets a tic-tac or foetal rhythm on auscul-
tation. Shortening of the diastole is always of serious
significance for the heart, as it is only during that phase
of the cycle that rest and restoration of the fibres can
take place.

8. Variations in the regularity of the beats are
also frequently met with, and occur, indeed, in many
persons throughout life without affecting the circulation.

As we have already seen, the regular beat of the heart —
depends upon a proper degree of excitability in the
auricle which initiates the systole, the wave of contrac-
tility so started being propagated to the ventricles by
the conductivity of the muscle fibres, the ventricles in
their turn then passing into systolic contraction. Now,
it must not be supposed that the muscle substance of
the ventricles is equally excitable and responsive to the
auricular stimulus at all periods of the cardiac cycle.
During their systole, and for a short period after it, the
ventricles are irresponsive to stimuli, this constituting

THE HEART 137

the ‘refractory period’ of the physiologists. Should
the auricular stimulus happen to arrive during this
period, the ventricle will fail to respond, with the result
that the heart ‘ misses a beat.’

The arrival of the auricular stimulus at the wrong
moment may be due either to (1) undue excitability of
the auricles, so that they pass prematurely into con-
traction again before the ventricles have had time to
complete their systole.* This is the chief cause.
(2) To alterations in the conductivity of the heart
muscle, either in the direction of increase, so that the
auricular impulses reach the ventricles too soon, and
whilst they are still refractory ; or of diminution, so that
some of them never get there at all, and the ventricles
are not ‘fired off.’ (8) The excitability of the ven-
tricles themselves may be raised, so that they occasion-
ally go into contraction whilst waiting for the auricular

signal, with the result that when the latter arrives they

are incapable of responding.
These ventricular ‘ extra-systoles’ are commonly in-
efficient, and do not expel enough blood to reach the

wrist, so that we arrive at the apparent paradox that

intermittence of the pulse is sometimes due to extra
heart-beats.t Their occurrence, however, can be told by

* Gaskell points out that the fact that the conductivity of the
heart muscle is diminished immediately after a contraction will
tend to counteract the effect of extra systoles of the auricle, for the
impulse so produced will be conducted slowly to the ventricles, and
its effect largely neutralized, the ventricular contractions being
more regular than those of the auricles (Schifer’s ‘ Physiology,’
ii. 195).

t+ Wenckebach, ‘Zur Analyse des Unregelmissigen Pulses,’ Zeit.
f. Klin. Med., 1899, xxxvi. 181.

138 APPLIED PHYSIOLOGY

the appearance of a feeble first sound immediately after
the second (Fig. 4). On the other hand, the excita-
bility of the ventricles may be lowered, so that they fail
to respond to all of the auricular contractions, again
with the result that some beats are dropped.

an ~— — WwW — ~— —_—_ =" _—_ ~—/

6-—-—-~— _— _ _~

Fia. 4.

a = Normal heart sounds ; } and c = sounds heard when extra-systoles
are occurring.

Now, inasmuch as the variations in the excitability
and conductivity of the heart upon which those irregu-
larities of rhythm depend may be brought about either
through disease of the heart muscle or from nervous
influences, it will readily be understood that the clinical
interpretation of irregularities of the pulse is often a

it

l 73 176! 2m! 76 | 152 loz V6! ze! 79! 4

4
fo _
Fic. 5.—Putsz TRACING, SHOWING VENTRICULAR INTERMISSION.
(Arter Cusuny.) (THE FIGURES REPRESENT ONE-HUNDREDTHS
OF A SECOND.)

The intermission, 152, is exactly twice the length of the preceding
pulse, 76.
matter of no small difficulty. We are aided, however,
in arriving at an idea of the nature of the irregularity in
any particular case by the fact that ventricular inter-
missions during which the auricle continues to beat

THE HEART 139

regularly must always be as long as twice the ordinary
pulse interval (Fig. 5). Those of auricular origin
may be of this length, but are not usually so; for the
irritability of the auricle increases so fast during quies-
cence that it is not likely to wait so long before passing
again into contraction (Fig. 6). On the other hand,
all intermissions less than two beats in duration are not
necessarily due to disease in the auricular fibres, for
some of them may be brought about by excessive vagus
control, which actually stops the heart for a moment.
This form of intermission, however, is abolished by
atropine, and can be recognized by that peculiarity.*

loa! 9! i589 | 98 o@ 98 94 97.
Fic. 6.—Putsn TRACING, SHOWING AURICULAR INTERMISSION,
(AFTER CUSENY.)

The intermission, 158, is much less than twice the length of the
preceding pulse.

As a matter of clinical experience, irregularity of the
heart seems specially prone to occur when the auricle is
diseased.+ Such irregularity proceeding from the auto-
matic contractile fibres is of more serious import than
that due to alterations in conductivity or lowered ven-

* Cushny, ‘On the Interpretation of Pulse Tracings,’ Jowrn. of

Hixper. Med., 1899, vol. iv., p. 327, and Brit. Med. Jowrn.,
1900, ii. 892,

+ Radasewsky, Zeit. f. Klin. Med., 1895, xxvii. 381.

140 APPLIED PHYSIOLOGY

tricular excitability. The former has been likened to a
man who stumbles because he is lame, the latter to one
whose gait is irregular because he is on rough ground.
The first may be described as ‘arhythmia,’ the second as
‘ pararhythmia’ (Wenckebach).

4, The last form of irregularity of the cardiac rhythm
(allorhythmia) is that due to a want of synchronism in
action between the two auricles or two ventricles
respectively, or between the two sides of the heart
as a whole. A want of complete synchronism in the
action of the ventricles is believed to be the clinical
explanation of reduplication of the first sound, the
tension on the mitral and tricuspid valves reaching its
maximum at different moments. Such want of syn-
chronism can best be explained by local alterations in
conductivity in different parts of the heart, alterations
which might very well be the result of disease affecting
the muscle of one ventricle more than that of the other,
or to local variations in nervous control.*

The former is the more likely cause, for the normal
synchronism of the ventricles appears to be maintained,
not through nervous, but through muscular connections,
and to be independent of nerve cells. Further, it is
apparently managed by the ventricles themselves, and
not by the auricles.

* Engelmann, Arch. f. d. Ges. Physiol., 1896, lxii. 548.
t Porter, ‘The Co-ordination of the Ventricles,’ Amer. Jowrn. of
Physiol., 1899, ii. 127.

CHAPTER V
APPLIED PHYSIOLOGY OF THE CIRCULATION

Ir might seem at first sight that our knowledge of the
circulation must be more precise and susceptible of more
direct clinical application than that of any other depart-
ment of physiology; and to some extent, indeed, this is
true. It must be admitted, however, that when one
comes to apply this knowledge at the bedside, many gaps
are discoverable in it. This is due partly to our still
imperfect comprehension of the physical laws which
govern the circulation of fluids in a closed system of
tubes, and partly to our ignorance of the extent to which
such laws are applicable to the conditions which obtain
in the living body. The problems presented by dis-
orders of the circulation, moreover, are rendered still
more difficult by the complicated nature of the checks,
adjustments, and compensations which are exhibited in it
under the sway of nervous influences, the precise nature
and mode of action of which we are still far from fully
comprehending even in health, to say nothing of disease.
Much attention, however, is now being devoted to the
exact study of disorders of the circulation by physical
methods, which the invention of instruments of pre-

cision has rendered possible, and there can be no doubt
141

142 APPLIED PHYSIOLOGY

that the results of such study will add much to our
knowledge both of physiology and pathology. Mean-
while an attempt will be made here to indicate the
applications of the chief facts about the circulation on
which physiologists are generally agreed.

The Arterial Circulation.

The arteries are both propulsive and conducting tubes.
Their function in the circulation is to assist the heart
in driving the blood into the capillaries, to induce a
continuous flow in the latter, and to maintain a ‘head
of pressure’ sufficient to allow any part of the body
to become flushed with blood when its arterioles are
dilated.

The driving power of the arteries is due to their
elasticity, and the elastic element in the arterial coat
is most abundantly _present and most widely diffused
throughout the wall in the large arteries}/ The blood
which is expelled from the heart at each systole of the
left ventricle distends the aorta and stretches to some
extent its elastic wall; part of the force of the ventricle

is thus converted from an actual into a potential form, —

and is again liberated in the recoil of the arterial wall
during disastole, thus maintaining a continuous ‘squeeze’
on the contained blood, and causing the flow of the latter
to be constant instead of intermittent, whilst distributing
the work of the heart over more than twice the time

occupied in its contraction. If the elasticity of the

arteries be impaired through disease of their walls, the
work of the heart is increased, and enlargement of if
follows ; at the same time the flow of blood approximates

Py Hes) re

‘THE CIRCULATION 143

more to an intermittent stream, and the pulse wave is
propelled more rapidly throughout the body. It is for
this reason that, in cases of aortic incompetence which
are secondary to aortic atheroma, the ‘delayed’ pulse
characteristic of incompetence due to rheumatic endo-
carditis is not observed. It should be noted, also, that
the distensibility of the elastic coat of the arteries is
greatest when the pressure within them is moderate.
In conditions of high tension a greater degree of force
is required to stretch them, and hypertrophy of the
heart results, whilst any increase in the pulse volume
raises the tension within the arteries far more than it
would do at a lower pressure, and so tends to rupture
them.

In the smaller arteries the muscular element pre- .
dominates over the elastic fibres, for it is in the smaller ~
arteries that the power of actively regulating the amount
of blood-flow to any part resides. This stop-cock action
of the arterioles will be more fully considered under the
head of blood-pressure, and is largely controlled by the
vasomotor nerves, but it may be pointed out here that
the muscular wall has a certain amount of independent
action. Thus, the muscular coat of the small arteries
reacts to a stretching force of contraction* just like
unstriped muscle elsewhere. Hence any permanent
increase in the volume of the blood may be expected
to lead to hypertrophy of the muscular coat, and in con-
ditions of plethora this actually occurs. The muscular
coat also contracts to cold or great degrees of heat, an
action which is constantly taken advantage of in the

* Bayliss, Jowrn. of Physiol., 1902, vol. xxviii. 220.

144 APPLIED PHYSIOLOGY

arrest of hemorrhage. Some drugs also—e.g., ergot—
cause a direct contraction of the muscle fibres, whilst
others—e.g., the nitrites—cause them to relax.

In addition to their muscular elements, the arteries
possess an outer fibrous coat which is purely protective,
and an inner endothelial lining which is designed to
lessen friction. Underneath this is a delicate layer of
connective tissue which, although it does not bulk largely
under the microscope, is of great importance in disease,
for in it many of the pathological processes which affect
the arteries have their starting-point.

The Arterial Pulse.

The pulse is of such extreme clinical importance that
a thorough knowledge of its mode of production and
physiological characters is essential to the physician.
It is necessary at the outset to clear the mind of two
misconceptions about the pulse, which are still very
prevalent: (1) It is not due to the transference of a
wave of blood along an artery, but to the transference
of a wave of pressure; (2) it is not due to a change in
size or distension of an artery, but to a change in its
shape. a

The blood discharged from the left ventricle during
its systole is accommodated in the large vessels imme-
diately beyond the heart, and merely raises the pressure
throughout the smaller arteries without actually dis-
tending them, the rise of pressure being transmitted
along the columns of blood contained in the arteries
in the form of the wave called the ‘ pulse.’ To suppose,

THE CIRCULATION 145

as some do, that the actual 4 ounces or so of blood
which is expelled at any given systole rushes straight
along the arteries and produces a ‘swelling of them,’
and that this is the pulse, is erroneous, though it may
be admitted that such a misconception need not make
& man a worse physician. On the other hand, one can
hardly feel a pulse intelligently unless it be clearly
realized that it indicates merely a change in shape of
an artery from an oval to a circular form—along with
a certain amount of straightening out, like a slack wire
suddenly put on the stretch—and not a real increase in
circumference of the artery (Fig. 7). The proof of this,

cs

Fie. 7.—SHOWING THE CHANGE IN SHAPE OF AN ARTERY FROM
AN OVAL TO A CIRCULAR FORM DURING THE PASSAGE OF
THE PULSE WAVE.

as Broadbent pointed out, is readily demonstrated by
placing the foot on a leather fire-hose (which of course
cannot change in calibre), when a pulse will be felt at
each stroke of the pump.

Of the characters of the pulse studied at the bedside,
one group—its frequency, regularity, and equality—are
entirely cardiac in origin, and are merely convenient
indications of the way in which the systole is being
_ performed. ,

Of these features the frequency need alone be referred
to here, as variations in regularity and equality have

been dealt with in considering the heart.
10

a

146 APPLIED PHYSIOLOGY

The average frequency of the pulse varies with age as
follows :

Foetus Ae 3 ... 180-140.

Q-l year... oe ei 1 OR

1-2 years ... ane .-- 115-120.

BES cas “ye nee .-» 105-110.

RO ae ai .» 95-100.

ot i eae “ss Se <i
RO cli wpa “Ap oad «| |
Adults ee a .- 70-80.

In old age it tends to quicken again a little. As
a general rule the pulse tends to be slower in tall and
big men than in short and small. It is quicker in
women than in men. Muscular effort quickens the
pulse considerably; mental effort slightly. On slow
walking it may run up to 100 per minute, and on quick
walking to 150. Exposure to cold renders the pulse
less, and response to warmth more frequent. A cup of
hot milk or a plateful of hot soup raises the pulse five
beats for half an hour; large quantities of cold water
may reduce it ten beats. Cold dry meals nave a
influence, but warm meals result in quickening.

Kvery sensation of burning, pressure or nauséa in the
stomach or of distension in the intestine (especially
the rectum) raises the rate. It is in this way that
| indigestion or flatulent distension of the bowels causes
‘ circulatory excitement’ and sleeplessness.

The volume of the pulse, or the height to which it
appears to rise under the finger, indicates the increase
in pressure within the artery during systole, or the

THE CIRCULATION 147

‘pulse pressure.’ The degree of this increase depends
upon the volume of blood thrown into the aorta by the
left ventricle, and the amplitude of the pulse is usually
a guide to the amount of this volume. If, however, the
diastolic pressure within the artery be very low, as it
is, for example, when the arterioles are dilated, a com-
paratively small output on the part of the heart may
cause a considerable relative rise in the systolic pressure,
and so make the pulse appear one of large volume, and
the ‘ pulse pressure’ high. Further, if the radial artery
be of small size, or if its muscular coat be contracted,
the pulse volume may appear small, even although the
systolic pressure within the artery rises very considerably.
In such a case a sphygmometer is a useful corrective to
the indications furnished by the finger.

The force with which the pulse wave is transmitted
indicates the energy of contraction of the left ventricle.
A forcible pulse is usually one of large volume, but an
ample pulse is not necessarily forcible if it be the result
of a low diastolic pressure within the arteries; nor is
a small pulse necessarily a weak one, for its want of
volume may be due to contraction of the arteries or to
the output of the ventricle being small owing to its
being imperfectly filled, as happens, for example, when
the total volume of the blood is reduced by hemorrhage.

The tension of the pulse will be considered when we
_ come to deal with blood-pressure. |

The Sphygmogram.—lIf one analyzes a pulse wave as
depicted by the sphygmograph, it will be found to consist
of an upstroke (called the ‘primary’ or ‘ percussion’

wave), an apex, and a downstroke. On the downstroke
10—2

148 APPLIED PHYSIOLOGY

are two secondary waves, the upper called the ‘pre-
dicrotic’ or tidal wave, and the lower the ‘dicrotic’
wave (Fig. 8). ;

Physiologists seem to vary in their interpretation of
the meaning of the predicrotic wave, but it would appear
that it indicates the true summit of the pulse wave, and
that the primary wave is merely the result of instrumental
error, and due to the sudden jerking upwards of the lever.
of the sphygmograph.*

If the tension in the artery rises very slowly, as it
does in aortic stenosis, the lever is not jerked upwards

Fic. 8.—SpHyGMoGRAM oF Raprat Putse. (MACKENZIE.)

E = Period of systole when aortic valves are open; G@ = Ventricular
diastole ; s = pulse wave due tosystole ; » = aortic notch ; d = dicrotic
wave ; p= wave due to instrumental defect.

so abruptly, and in that case the predicrotic wave comes
to form the apex of the pulse curve, whilst the tidal
wave is represented by a notch on the ascent; this is
termed the ‘anacrotic pulse.’ a

The most probable explanation of the dicrotic wave is
given by Mackenzie as follows: + ‘ The semilunar valves

* This view, though supported by Mackenzie, is not universally
accepted. Lewis, for instance, as a result of a recent careful study
of the subject (Jowrn. of Anat. and Physiol., 1906-7, xli. 187),
concludes that, in the great majority of cases, the primary and

predicrotic waves are both genuine, and are of central origin.
+ ‘The Pulse,’ p. 20.

THE CIRCULATION 149

are so delicately constructed that they readily respond
when the pressure on one side rises above that on the
other. As soon as the aortic pressure rises above the
ventricular the valves close. At. the moment this
happens the valves are supported by the hard, con-
tracted ventricular walls. The withdrawal of the
support by the sudden relaxation of these walls will
tend to produce a negative pressure wave in the arterial
system. But this negative wave is stopped by the sudden
stretching of the aortic valves, which, on losing their firm
support, have now themselves to bear the resistance of
. the arterial pressure. This sudden checking of the
negative wave starts a second positive wave, which is
propagated through the arterial system as the dicrotic
wave.’

This is not the place to describe all the modifications
of the pulse curve which may occur in various states of
health and disease. It must suffice to point out some of
the more general clinical applications which follow from
the exposition which has been given of the way in which
its different parts are produced.

The ascent of the curve will obviously be abrupt in
proportion as the output from the left ventricle is large,
its contraction forcible, and the pressure in the arteries
low. All these conditions concur in sthenic’ fever, and
they are also present to an extreme degree in most cases
of aortic incompetence, both of which. conditions are
therefore characterized by a sudden rise of the pulse.

On the other hand, the ascent will be gradual in pro-
portion to the resistance which the heart experiences in
expelling its contents into the aorta. Narrowing of the

150 APPLIED PHYSIOLOGY

aortic orifice, therefore, and cases in which the diastolic
pressure within the arteries is high are characterized by
a pulse wave of gradual ascent.

The apex of the curve will be well or ill sustained, and
the downstroke gradual or abrupt, in accordance with the
ease with which the blood can escape through the arte-
rioles into the capillaries. When the arterioles are con-
tracted, therefore, the apex is blunt and the pulse ‘ well
sustained’; when they are dilated, it is pointed and the
pulse ‘ collapsing.’

The predicrotic wave will be well marked when the
artery tends to flatten itself slowly between the beats,
and so allows the lever to rest upon it for a moment
before collapsing. A well-marked predicrotic wave is,
therefore, a sign of a high diastolic pressure in the
artery. The dicrotic wave, on the other hand, is best
marked when the pressure tends to fall rapidly after the
pulse, so allowing the secondary rebound from the aortie
cusps the opportunity to make its presence felt, which it
could not do in a full vessel. A ‘dicrotic’ pulse is,
therefore, usually met with in cases of low pressure due
to rapid escape of blood into the capillaries, especially
when combined with a short, sharp systole. Its presence,
however, is not incompatible with high systolic pressure,
provided the latter be of ventricular origin.

The pulse wave travels along the arteries at the rate of
about 80 feet per second. Owing to the elasticity of the
sreat vessels, part of the work of the heart is spent in
distending them, and this causes a delay in the trans-
mission of the wave of pressure, so that the pulse is not
synchronous with the heart-beat, but follows it at an

haa

vg
Ca.

{

THE CIRCULATION 151

appreciable interval. It is for this reason that the
radial pulse cannot be used in timing heart murmurs.
The less elastic the arteries are, the less is the delay in
the transmission of the pulse, and in cases of extensive
atheroma the delay may for this reason be very slight.
The actual time occupied by the pulse wave in passing
any point—e.g., under the finger laid upon it—depends
upon the resistance it has to overcome from in front. If
the arterioles are contracted the resistance is great, and
the pulse passes slowly, and in clinical language it is
spoken of as a long pulse; on the other hand, if the
arterioles be dilated so that blood escapes easily into the
capillaries, the wave sweeps on rapidly and the pulse is
short. In other words, a ‘long’ pulse is characteristic
of high tension in the arteries, and a ‘ short’ pulse of low
tension.

We may sum up the characters of the standard or
typical pulse of the adult male in the words of Broad-
bent,* as follow:

‘Tt will have a frequency of seventy-two beats
per minute, will be perfectly regular in time, and
the beats will be of equal force.... The individual
pulse waves reach the finger nearest the heart with a
definite stroke, which can scarcely be described as
sudden, still less as sharp; they have sufficient vehe-
mence to be felt by all three fingers, unless decided
pressure is made on the vessel, but they can be arrested
without difficulty by one finger, the beat feeling then
both more sudden and more vehement. The wave of
expansion or distension of the artery does not instantly

* ‘The Pulse,’ p. 46.

152 APPLIED PHYSIOLOGY

drop, but subsides gently and without perceptible
dicrotism.

‘The sphygmogram corresponding to this description
will have a nearly perpendicular rise, a moderate eleva-
tion, a rounded summit, and a gradual, almost unbroken
fall.’

The great differences in the frequency, volume, force,
and tension, and the character of the wave, in the
pulse of different individuals are matters of common
knowledge, and it is of interest to ask whether differences
of pulse are indicative of differences in physical or mental
constitution. It is instructive, on this point, to learn the
opinion of such an experienced observer as Broadbent.
‘Speaking generally,’ he says,* ‘I have found physical
strength, energy, and endurance impartially associated
with small, low-tension pulse, and with large arteries
and high tension, and the reverse. I can say the same of
intellect, perseverance, courage, and force of character
generally; they appear to be absolutely independent of
circulatory conditions. It is, indeed, clear that the
circulation is not the determining influence in the pro-
duction of the differences which are found to exist in
respect of bodily or mental energy. The circulation is
the servant, and not the master; and, physiologically, it
is tissue activity which conditions the blood-supply, and
not the blood-supply which conditions the tissue change.
In disease, again, the modifications of the circulation
which are observed are more frequently effects than
causes, and the pulse is an index not so much of a
more or less rapid movement of the blood, to be taken

* «The Pulse,’ p. 48.

THE CIRCULATION 153

into account as a factor in the morbid processes, as of
the state of the nervous system and of the body generally
which has determined its rate and character.’

The Capillary Circulation.

As the whole aim and end of the circulation is to
convey material to and from the tissues, the passage of
blood through the capillaries is, in a sense, the most im-
portant part of the circulatory process. Unfortunately,
however, the attention of physiologists has been until
lately so much concentrated upon the arteries that we
are still very far from being conversant with all the facts
relating to the capillary circulation.

In what follows an attempt will be made to indicate
briefly the present state of our knowledge on the subject,
and its application to clinical medicine.

The capillaries are only about 4 to 1 millimetre in
length, but they form a network so dense that it would
hardly be possible to stick a pin into any part of the
body without injuring one of them. Notwithstanding
this, the capillaries are by no means always full of blood,
as is shown, for instance, by the great increase in redness
of the skin when one applies a blister to it. They con-
sist, anatomically, of a single layer of endothelial cells,
which, although they appear to be of the simplest
structure, are possibly endowed with important selective
and other properties. In health this layer is so thin
that it forms a mere hair line, but in disease it may
become considerably thickened.

The appearance presented by the blood as it circulates
through the capillaries must be so vividly present to the

154 APPLIED PHYSIOLOGY

mental eye of anyone who has ever looked at the web of
a frog’s foot through a microscope that it calls for no
description, but some of the conditions on which the
character of the flow depends must now be considered.

The velocity of the capillary flow varies greatly—
0°5 to 25 millimetres per second being given as the
extremes by some observers—and is constantly changing
from time to time. It depends upon several factors,
amongst which the energy of contraction of the heart
and the pressure in the veins are of great importance.
If the heart be contracting feebly, or if the back pressure
in the veins be increased (and in most cases of cireula-
tory failure these two factors co-operate), the blood flows
so slowly through the capillaries that it becomes sur-
charged with carbonic acid, and the patient is cyanosed.
Dilatation of the arterioles, which supply any part of
the body, quickens the flow through the corresponding
capillary area. This happens atthe outset of inflamma-
_ tion. On the other hand, there is no constant relation
between general blood-pressure and the rate of the flow.
The viscosity of the blood is another factor of great
importance, but of which little is yet known. In the
tarry blood of cholera the viscosity is often so great that
it will not flow through the capillaries at all. “In poly-
cythemia, again, which raises the viscosity considerably,
the capillary flow is so much impeded that the ex-
tremities of the patients are usually cold or dusky.
Whether changes in the capillary wall may retard the
flow is not certainly known, but retardation from such a
cause has been postulated to explain the high blood-
pressures sometimes met with in pathology.

Sli a's Av

THE CIRCULATION 155

The pressure of the blood in the capillaries is only
second in importance to the rate of flow, and upon it in
large measure the amount of lymph transudation de-
pends. The pressure in the capillaries is surprisingly
high, being often, according to Hill, above 100 millimetres
of Hg. The capillary wall is so slender that it would be
unable to withstand such a pressure were it not sup-
ported from without by the ‘tension’ of the tissues.
The degree of this tension varies. greatly in different
localities, being greatest in the lower limbs, and where
it is low increased transudation from the capillaries, or
even rupture of them from the strain of internal pressure,
is apt to occur. This is the reason for subconjunctival
dropsy and occasional ecchymosis as the result of the
high tension of chronic renal disease, for the ‘tension’ of
the subconjunctival tissue is very low.

The pressure in the capillaries depends more upon
the venous than upon the general arterial pressure.
When the small arterioles are contracted the capillaries
are thereby shielded to some extent from the high
arterial pressure, and if the contraction be extreme the
capillary pressure may fall to zero. On the other hand,
if the pressure in the veins be raised it tells directly back
upon the capillaries, and the transudation in them is
increased. This is often a factor in the production of
dropsy, and it is taken advantage of to increase local
transudation in Bier’s method of treatment. Dilatation
of the arterioles raises the capillary pressure, and if the
dilatation be local and the general blood-pressure high,
the capillary blood-pressure in the area concerned may
rise very greatly. This is the reason why hemorrhage

156 APPLIED PHYSIOLOGY

from the capillaries of the brain so often occurs in cases _
of high arterial pressure, for the cerebral arteries being
unprovided with vasomotor nerves, there is no method
of shielding the intracranial capillaries from the effects
of the general rise.

The action of gravity may increase the capillary
pressure very markedly. Thus the pressure in the
finger is more than twice as high when the hand is
hanging by the side than when it is raised to the level
of the top of the head. It is for this reason that raising
the hand relieves the pain and throbbing in an inflamed
finger so noticeably.

The most important function of the capillaries is to
permit of an interchange between the blood and the
tissues, and two opposing views have long been held by
physiologists as to how this takes place. The upholders
of the mechanical theory, first propounded by Ludwig,
maintain that the physical processes of diffusion, osmosis,
and dialysis (which may be spoken of collectively as
‘transfusion ’) are sufficient to explain all the facts; on
the other hand, Heidenhain and the ‘vital’ school
invoke a special secretory power on the part of the cells
forming the capillary wall, and look upon lymph 4s a
secretion of the capillaries, just as milk is a secretion of
the mamme or urine of the kidneys. The problem is
one which is, perhaps, more of abstract physiological
interest than of direct concern to the physician, but it
may fairly be said that at present the views of the
mechanical school tend to hold the field.

On neither hypothesis has a complete explanation yet
been given of the chief anomaly of lymph production—

THE CIRCULATION 157

dropsy. We know, indeed, that this must be due to an
over-production of lymph, and not to a diminished
absorption of it from the tissues, for ligature of the chief
vein of a limb does not lead to its becoming edematous,
but the parts played in the increased production by
alterations in (1) capillary pressure, (2) permeability of
the wall, (3) tissue-tension, and (4) composition of the
blood respectively, have not been unravelled, and it is
possible that in different cases each of these is responsible
in different degree. We know still less of the opposite
condition of diminished lymph formation, or whether,
indeed, that ever occurs at all, although more knowledge
on this head might explain some anomalies of nutrition
which at present puzzle us. There appears to be no
doubt that the permeability of the capillary wall varies
in different localities. It is least in the limbs and
greatest in the liver. This may explain how it is that
ascites may be present in mitral stenosis without there
being any evidence of dropsy elsewhere. It is possible,
too, that the permeability of the wall is increased as the
result of the action upon its cells of certain poisons
which fail to be excreted in disease of the kidneys, and
this may play a part in the production of renal dropsy.

The Venous Circulation.

The veins resemble the arteries in their essential
structure, but contain relatively less muscular and
elastic tissue, and a stronger external fibrous coat, which
enables them to withstand the influence of gravity.
They attain their maximum distension at a much lower

158 APPLIED PHYSIOLOGY

internal pressure than the arteries, and when the
pressure within them is much increased they easily be-
come overdistended, and lose their elasticity. Hence
it is that when the arterial pressure is brought to bear
upon a vein by the establishment of a communication
between it and an artery the vein becomes varicose
(aneurysmal varix).

The flow of blood in the veins is determined by the
following factors: (1) the vis a tergo of the arterial
pressure ; (2) the vis a fronte of the ‘thoracic pump’;
(3) the ‘squeeze’ exerted by the contraction of the
muscles, and by the ‘tissue-tension,’ which, thanks to
the veins being provided with valves, drive the blood
always towards the heart. Gravity would exert a very
great retarding effect on the flow were it not for the
valves with which every vein subjected to its action is
provided, but if these fail to act the flow is greatly
impeded, as happens in cases of varicosity.

The influence of the vis a tergo will depend upon the
degree to which the potential energy exerted by the
force of the arterial pressure is obliterated by the peri-
pheral resistance in the capillaries. If, owing-to high
viscosity of the blood or great contraction of the arte-
rioles, the potential energy of the arterial system be
greatly reduced, the velocity of the flow in the veins will
be proportionately diminished, and in cases of heart-
failure these factors help to bring the circulation to a
standstill.

The influence of the vis a fronte exerted by the
thoracic pump is almost as important as that of the
arterial pressure, but will be fully dealt with when

\
ate me

THE CIRCULATION 159

we come to consider the relation of respiration to the
circulation.

The squeezing of the veins by contraction of the
skeletal muscles is also a factor of great importance
in promoting the venous flow, and is one of the chief
reasons why muscular exercise so powerfully promotes
the circulation. Whilst one is standing this factor is
in abeyance, and the venous flow in the legs is sluggish ;
whereas during walking the veins are constantly being
massaged by the contractions of the muscles of the legs,
and the return of blood from them is brisk. It is for
this reason that much standing tends to produce varicose
veins, whilst walking does not. The military plan of
‘marking time’ when standing tends to counteract the
tendency to stagnation of blood in the veins of the legs.

The pressure exerted by the ‘ tone’ of the skin and
tissues is only second in importance to the more active
squeeze effected by the muscles. Where this tone is
low, as in the scrotum, overdistension and varicosity of
the veins easily occurs, and it used to be a recognized
method of treating varicose veins in the leg to excise
a large area of skin on the back of the calf, in order
to increase the pressure on the veins by forming a
natural ‘ elastic stocking.’

Blood-pressure.

Blood-pressure signifies the degree of fluid-pressure
present within the vessels, putting their walls on the
stretch. As commonly used, the expression refers only
to the arterial blood-pressure, and as this is the sense in

160 APPLIED PHYSIOLOGY

which it is always employed in clinical work, it will be
used with that meaning in what follows.

The advantages of having a certain amount of fluid-
pressure within the arteries are these :

1. It ensures a ‘head’ of pressure by which any
sudden demand for an increased supply of blood on the
part of an organ or tissue can be immediately met.

2. It ensures an adequate degree of transudation of
lymph for the nourishment of the cells.

3. It accommodates the amount of their contents to
the size of the arteries, so that a considerable loss of
blood can take place without the pressure falling to a
dangerously low level.

It is obvious that the arterial pressure must always be
at least high enough to overcome the resistance of the
arterioles, and so ensure a steady flow of blood through
the capillaries. The fraction of the total arterial pressure
which is necessary for this purpose may be spoken of as
the ‘essential’ element in blood-pressure, whilst the
margin above this, which maintains a ‘ head of pressure’
sufficient to meet the varying demands of the tissues, is
the ‘functional’ element (Janeway). About 50 milli-
metres of mercury is the amount of the pei ;
pressure; the remainder (70 millimetres or more) is
functional and variable.

In considering arterial pressure, one has always to
distinguish between the pressure during the pulse wave
or systolic pressure, and the pressure between the waves
or diastolic pressure. Most clinical sphygmometers
record the former, and it is systolic pressure that is
ordinarily referred to when one speaks clinically of a

3
.

:

s

THE CIRCULATION 161

patient’s ‘ blood-pressure.’ This distinction between the
systolic and diastolic pressure has already been pointed
out when the pulse was described, and it was then seen
that the systolic pressure depends mainly upon the left
ventricle and the diastolic pressure upon the degree
of contraction. of the peripheral arterioles. An estima- |
tion of the former, therefore, gives us most information
about the heart ; an estimation of the diastolic pressure
about the tone of the arterioles. Information on both
of these points is of great use clinically, but whereas we
have many other means of ascertaining the efficiency of
the heart, we have none of estimating the degree of peri-
pheral constriction ; it is, therefore, to be regretted that
our clinical methods of measuring diastolic pressure are
not more perfect.

The factors concerned in maintaining blood-pressure
are :

1. The Force and Output of the Left Ventricle.—
If the force fails or the output per beat diminishes,
blood-pressure falls.

2. The peripheral resistance, which is made up of
the opposition offered to the passage of the blood by the
tonic contraction of the small arteries, by the friction
produced in the capillaries by the viscosity of the blood,
and by the ‘ tissue-tension.’* Variations in the degree of

* Under the term ‘tissue-tension’ may be included not only
the elastic pressure exercised on the vessels from without, but the
~ atmospheric pressure, and all casual mechanical pressures the
result of posture, etc. That these, collectively, are a considerable
factor in making up the sum total of the ‘peripheral resistance’
there can be no doubt. The infiuence of external pressure, for

11

162 APPLIED PHYSIOLOGY

the peripheral resistance are the most potent cause of
individual and pathological variations in blood-pressure,
especially of diastolic pressure.

8. The Elasticity of the Arterial Wall.—Without
this there would be no diastolic pressure at all, and the
flow would correspond to that through rigid tubes —
i.e., the pressure would be alternately very high and
reduced to nil. In the rigid arteries of advanced
atheroma an approximation to this state of things
actually obtains.

4. The Volume of Blood in Circulation. — This
factor is not of so much importance as might be ex-
pected, owing to the action of compensating mechanisms.
If the total volume of the blood is lessened—e.g., by
hemorrhage — blood-pressure is temporarily lowered;
but it is quickly restored again by the power of the
bloodvessels to contract down and accommodate them-
selves to the amount of blood they contain, whilst at the
same time fluid tends to be withdrawn from the tissues.
It follows from this that venesection is but of temporary
use as a means of lowering tension. Conversely, if/the
amount of the circulating blood be increased—eg., by
transfusion—the blood-pressure is only raised for a short
time, and to a comparatively slight degree ; for the excess

example, has been shown by Crile, who found that, by enclosing a
patient in a pneumatic rubber suit into which air can be pumped,

the blood-pressure could be controlled to the extent of 25 to 60 milli-
metres of Hg. He makes use of the pneumatic suit in order to —

produce an artificial peripheral resistance in cases of shock, in

which the general vasomotor centre is completely paralyzed (see _

* Blood-pressure in Surgery’).

a

THE CIRCULATION 163

of fluid is quickly drained off into the lymph spaces
or accommodated in the large veins of the abdomen.
Transfusion, therefore, may raise a depressed blood-
pressure to the normal level, but it cannot do much
more than this, and, like venesection, its effect tends to
be very transient.

There is but very little difference between the pressure
in the large arteries near the heart and that in the
smaller peripheral arteries. It is only when the
arterioles themselves are reached that a rapid and
notable fall of pressure occurs. Hence it is immaterial
which artery is selected for the clinical estimation of the
blood-pressure, and the brachial, which is the artery
usually chosen, will afford quite a trustworthy indication
of the aortic pressure.

Variations in Blood-pressure.

The general arterial blood-pressure tends, like the
body temperature, to be maintained at an extraordinarily
constant level, and such variations as do occur are more
in an upward direction than a downward—.e., abnor-
mally high pressures are much commoner than abnor-
mally low ones. It would appear, indeed, that the
normal degree of pressure is pretty near the minimum

at which life can be constantly sustained, and every
_effort is made to uphold it.

The normal systolic pressure in a healthy young adult
male is about 120 millimetres Hg, and the diastolic
pressure about 100. In women they are about 10 per
cent. less, and in children the systolic pressure may be

11—2

164 APPLIED PHYSIOLOGY

as low as 90 millimetres Hg, with a diastolic pressure of
about 80. As age advances pressure tends to rise, on
account of lessened elasticity of the vessels. /

It must be noted, however, that the blood-pressure
differs from the body temperature, and resembles the
pulse rate in that it is not necessarily the same for all
healthy individuals of the same age. In some persons
and families the pressure tends to be habitually low;
in others it is always above the normal, and, just as in
the case of the pulse, there is no constant mental or
physical peculiarity which one can associate with these
differences. Seeing, however, that a high arterial
pressure must tend to determine a relatively large
amount of blood to the brain, owing to the uncontracted
cerebral arteries offering the path of least resistance
(see p. 175), one might expect an habitually high arterial
pressure to be favourable to the performance of mental
work. Families in whom such habitually high tension
is discernible are often ‘ gouty,’ and it is interesting in
this connection to remember that gout has been described ~
as the ‘disease of the intellectual’—the dominus mor-
borum, et morbus dominorum. ps

There appears to be a slight diurnal variation of
pressure in health in the direction of a rise in the
morning and a fall at night, corresponding to the
morning fall and the evening rise in temperature and
pulse rate.

Rest tends to lower pressure, whilst exercise increases
it at first, but ultimately lowers it. Thus, a man may
start out for a walk with a systolic pressure of 125,
which during the first half-hour may rise to 140 or 150;

THE CIRCULATION 165

but as he continues his walk, and the peripheral arteries
dilate, it drops to 100 or less. Sudden or violent effort
raises the pressure abruptly (though briefly), and is a
fertile cause of apoplexy in persons whose tension is
abnormally high. Mental work also raises the pressure
considerably, and those who use their brains much are
often the subjects of high tension. Excitement is an
even more potent elevator of blood-pressure, and
explains the frequency with which cerebral hemorrhage
is associated with anger; hence the expression ‘ apo-
plectic with rage.’ The possible disturbing influence
of excitement should always be borne in mind when
making blood-pressure observations on patients. Posture
is also of considerable influence, the pressure being
about 10 millimetres less when lying down than when
standing up. This will be referred to again when we
come to speak of the effect of gravity on the circulation.

Cold contracts the peripheral arteries, and raises the
pressure, so that the first onset of cold weather in winter
is apt to be attended by a crop of apoplexies. Warmth
has the opposite effect. Hence during a spell of hot
weather an arterial pressure may appear quite normal
which in ordinary conditions would exceed the upper
physiological limit (Oliver).

A meal has much the same effect on pressure as
exercise, raising it at first, and causing a fall later.
. Sleep has the reverse effect, the pressure falling during
the first few hours and then rising gradually up to the
time of waking.

The effect of all these influences is a transient one,
for, as has been already pointed out, the mean blood-

166 APPLIED PHYSIOLOGY

pressure tends to be maintained at a. very constant

level; but they are of sufficient importance to make it .

necessary to exclude them when making blood-pressure
estimations in patients.

Regulation of Blood-pressure.

The constancy of the arterial blood-pressure is attained
by the control exercised over it by the general vaso-
motor centre, which exerts a continuous tonic influence
upon the muscular coat of the arterioles. By the agency
of this centre and its nervous connections the general

blood-pressure is kept fairly constant, whilst at the ~

same time the varying local needs of the organs or
tissues for an increased blood-supply are provided for, as
will be described more fully when we come to speak of
the distribution of blood in the body. .

When the pressure in the arteries tends to rise very

high, the heart is slowed through the influence of the
vagus, the reflex being probably started by the pressure
of the blood in the left ventricle; and at the same time
its output is lessened, and thus the high pressure tends
to be counteracted. The diminution of output may in
these circumstances become so great that the ventricle
does not completely empty itself at each systole, with
the result that blood is dammed back into the lungs,
and thence into the veins, and all the symptoms of back
pressure result. Hence in conditions of high tension
one may get all the clinical signs of heart failure without
there being any defect of the mitral valve.

If the rise of arterial pressure be very abrupt—as,

7 1

THE CIRCULATION - + GF

for example, during sudden muscular effort—and if the
heart tends to be overwhelmed by it, the depressor
fibres of the vagus come into action, and the vasomotor
centre is reflexly inhibited, with the result that the
blood-pressure suddenly falls and the heart is relieved.

Seeing that such efficient arrangements exist for
counteracting abnormally high blood-pressure, it is
difficult to understand how a continuously abnormal
degree of tension can exist unless there be some de-
rangement of the compensating mechanism. Abnormal
lowering of the blood-pressure is not so easily compen-
sated for, but it is noteworthy that anemia of the
medulla stimulates the general vasomotor centre, and
in this way a fall of blood-pressure from hemorrhage
is counteracted. When the pressure is low, too, the
action of the heart is more rapid, and the total output
of blood from it in a given time greater, and this also
tends to raise the pressure again towards the normal
level.

Distribution of Blood in the Body.

Intimately associated with blood-pressure is the
question of the distribution of the blood in the body.
We have seen that the existence of blood-pressure is in
part the result of the necessity for accommodating the
vascular ‘bed’ to the volume of the circulating blood.
The capacity of the vascular system is so great that it
could accommodate one-half or one-third as much blood
as it already contains, and the volume of the blood can
be increased by this amount without the pressure in the
aorta being affected, for the vessels simply relax in order

168 - APPLIED PHYSIOLOGY

to make room for the increased quantity. In conditions
of true plethora, and in chlorosis, the total volume of
the blood may be increased to this amount, and the
vasomotor centre accommodates the vascular area to
it without affecting the pressure.

On the other hand, if the vasomotor centre be
paralyzed the vascular bed is so much widened that
the blood simply accumulates passively in the most
dependent part of it, or in the large splanchnic area.
In these circumstances the return of blood to the heart
becomes less and less, and finally the circulation may
come to a standstill, even although the heart is still
quite fit to maintain it were it only supplied with blood.
This is what happens in surgical shock and in the
‘collapse’ which often comes on in acute disease; and
the indication in such cases is not to stimulate the
heart, but artificially to increase the peripheral resistance
(see footnote, p. 162). |

In the distribution of the blood as a whole there is
a reciprocal action between the splanchnic system and
the more peripheral parts of the circulation. When
blood is wanted at the periphery the splanchnic vessels
are contracted by the vasomotor centre and the normal
level of the blood-pressure maintained. This happens,
for instance, when the cutaneous vessels are dilated by
heat, and if the compensating mechanism be not in
good working order, the blood-pressure may fall so low
that the individual faints. Many cases of ‘ collapse’ in
hot weather are brought about in this way. On the other ~
hand, when more blood is wanted in the splanchnic system,
the peripheral vessels contract to make up for it; hence

ae

THE CIRCULATION 169

the occurrence of cold feet in many persons or a general
feeling of coldness during the early stages of digestion.

The splanchnic system may be described as the
‘resistance-box’ of the circulation (Hill), by means of
which variations in the systemic blood-pressure are
regulated, and examples of its operation have already
been given. In addition to this, the circulation possesses
two regulating ‘reservoirs’ in the liver and lungs. As
Stolnikow has pointed out, the liver acts as a blood
reservoir on the systemic circulation, so that the right
heart may take a greater or less volume of blood from
the great veins without materially modifying the systemic
pressure. ‘The lungs play a similar part to the left
heart, acting as a reservoir in which blood may be
stored if the left heart for some reason diminishes its
output, and, conversely, contains a reserve of blood upon
which the left heart draws when its output increases
(Brodie). Overfilling of the pulmonary and hepatic
reservoirs are prominent features among the ‘back-
pressure’ signs of a failing heart. |

Local variations in blood distribution are controlled
by the tissues or organ concerned themselves. By means
of afferent impulses the tonic constriction normally
exerted on the arterioles of the part by the vasomotor
centre is cut off, the arterioles dilate like stop-cocks
which have been suddenly turned on, and the general
arterial pressure drives more blood into the dilated area.
In the case of organs in which a sudden and very
copious blood-supply is often demanded vasodilator
nerves are present as well, by means of which an active
dilatation of the arterioles is brought about.

ee

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170 APPLIED PHYSIOLOGY

This local control of the blood-supply is apt, as might
be expected, to become deranged with resulting disease.
Sometimes, for example, as in the syncopal stage of
Raynaud’s disease, the arterioles pass into a state of
spasm, and the blood-supply to the part is entirely cut
off, so that it goes white and cold. A similar state of
things on a larger scale occurs in the condition known
as ‘intermittent limp.’ On the other hand, a permanent
dilatation of the arterioles is the cause of the local capillary
congestion known as erythromelalgia. In neurasthenic
subjects the local control of the circulation by the vaso-
motor system seems to be peculiarly feeble, and many
of the symptoms of which they complain, such as throb-
bings and flushings, and probably many more obscure
symptoms as well, are the result. |

_) That the veins of a part as well as its arteries are

subject to nervous control there can be little doubt. In
no other way could one explain, for example, the spasm —
of veins which seems to be the cause of the asphyxial
stage of Raynaud’s disease. Both the inflow and outflow
of blood, therefore, can be regulated through the nervou

system. A

The Influence of Gravity upon the Circulation.

The pressure effects exerted by the influence of gravity
on the contents of the bloodvessels may be spoken of as
the hemostatic pressure, as opposed to the hemodynamic
pressure which results from the action of the heart. The
actual pressure at any point of the vascular system is
equal to the sum of these two (see Scheme). In aman
of 6 feet the hydrostatic pressure of a column of blood,

_ THE CIRCULATION 173

be suddenly set up in the erect position the blood may
settle down into the most dependent parts by hypostasis,
and the heart stop owing to its being no longer kept
filled with blood. This has already been referred to
when the mechanism of shock was described (p. 168).

The less the hemodynamic pressure, the more pro-
nounced is the effect of the hemostatic pressure. Hence
sudden changes of position are most dangerous in those
whose arterial blood-pressure is low.

Influence of Respiration upon the Circulation.

Owing to the negative pressure within the thorax
(p. 190), the heart and part of the large veins are really
placed in a partial vacuum, which has the effect of
helping to fill the heart during diastole. By the act
of inspiration this suction effect is greatly increased,
whilst at the same time blood is squeezed out of the
large abdominal veins into the inferior vena cava. As
a result the current of blood in the large veins is
accelerated, and the right heart more rapidly filled.
At the same time the pathway for the blood through
the lungs is opened up, and the escape of blood from
the right side round to the left is greatly facilitated. It
can readily be understood from this what a great aid the
action of the respiratory pump is to the proper carrying
on of the circulation. If, however, the action of the
respiratory pump be interfered with, as it is, for example,
in emphysema, the circulation is apt to become laboured,
and the large veins engorged with blood. One conse-
quence of the orthopncea of cardiac disease is to facilitate

174 APPLIED PHYSIOLOGY

the action of the pump as an auxiliary in maintaining
the circulation. In cases of pericardial effusion the
heart, instead of being placed in a vacuum, is subjected
to a constant positive pressure which interferes greatly
with its proper filling; hence the large veins become
overdistended, whilst the output of the left ventricle
falls. |

Owing to the aspiration of blood into the chest at each
inspiration, a certain degree of ‘ pooling’ of it takes place
in the lungs at the commencement of the act, and in
consequence the output from the left heart is diminished
at first, and the arterial blood-pressure falls. So soon,
however, as the blood has had time to find its way round
to the left ventricle the output rises again above the
average, and the blood-pressure rises in proportion. If
there be any obstruction to the free entry of air into the
lungs, the amount of blood which can be accommodated
in the thorax is all the greater, and in such circumstances
the output from the left ventricle may fall so low that
the pulse disappears for a time. This result is all the
more likely to ensue if the peripheral arterioles be dilated,
so that blood can readily pass out of the arteries into
the veins—i.c., in conditions of low arterial pressure.
Such a temporary disappearance of the pulse during
inspiration is spoken of clinically as the pulsus para-
doxus.

The Cerebral Circulation.

The circulation in the brain is so peculiar, and at the
same time its disturbances are of such clinical importance,
that it demands a special description. The peculiarity

Baad

THE CIRCULATION (ae

consists in two points: (1) the cerebral arteries alone of
all systemic arteries in the body are not under the direct
control of the vasomotor centre; (2) the circulation
takes place in a rigid, enclosed space.) Sébing that the
cerebral arteries are not endowed with vasomotor nerves,
they do not participate in any general constriction of the
arteries brought about by the vasomotor centre. On
the contrary, as the blood-pressure throughout the body
tends to rise as the result of such constriction the blood,
choosing the path of least resistance, passes through
the intracranial cavity in increased amount.

General vasoconstriction, therefore, increases the
amount of arterial blood which the brain receives, and
cerebral hyperemia is a necessary concomitant of high
blood-pressure, and may explain some of the symptoms
of the latter.

Seeing, again, that the skull forms a rigid box,
and that its contents are incompressible, this increased
amount of arterial blood can only be accommodated by
the squeezing out of a certain amount of cerebro-spinal
fluid or of venous blood.

If a foreign body—such, for example, as a blood-clot—
be introduced into the intracranial cavity, room can
only be found for it at the expense of a certain amount
of blood—i.e., the brain becomes to a greater or lesser
degree anemic. If the anemia increases to such a
degree as to affect the arterial flow through the medulla,
the vasomotor centre experiences its effects, and responds
by constricting the arterioles throughout the body, with
the result that the general blood-pressure rises and
more arterial blood is squeezed through the brain to make

-

176 APPLIED PHYSIOLOGY

good the deficit. Hence it is that clinically cerebral
compression is marked by increased blood-pressure, and
this increase of pressure must be regarded as essentially
conservative in its action, and designed to compensate
for the cerebral anemia which compression causes. It
is therefore not lightly to be interfered with—e.g., by
venesection.

The intracranial tension or pressure of the brain
against the skull wall is, as Hill has pointed out, purely
circulatory in origin, and is the same as the cerebral
capillary or venous pressure, and varies with every
change of pressure in the aorta or superior vena cava ;
but, like capillary pressure generally, it is more sensitive
to an increase of tension in the veins than in the arteries
(see p. 155). It is for this reason that an abrupt rise of
venous pressure—such, for example, as occurs when any .
effort is made with the glottis closed—may easily rupture
a weakened cerebral capillary. This is the explanation
of the frequent occurrence of apoplexy during straining
at stool.

CHAPTER VI
THE APPLIED PHYSIOLOGY OF RESPIRATION

The Air Passages.

THE nose is an organ whose function it is to protect the
lungs in the same way as the mouth protects the
stomach. It ‘cooks’ the raw external air, if one may
use the expression, and renders it fit to enter the lungs.
It is enabled to do this by the tortuous course of its
airway, and by its succulent mucous membrane s0
richly supplied with nerves, vessels, and glands. As the
air enters the nostrils, any large particles of foreign
matter which it contains are entangled by the vibrisse,
which like sentinels guard the entrance to the nasal
cavities. The current of air then sweeps upwards and
backwards in a curved direction to pass over the
superior and middle turbinated bodies. In its course it
is further purified from foreign particles by the layer of
viscid mucus which covers the lining membrane, and
which catches particles of dust and bacteria as a
_ fly-paper catches flies. At the same time the air is
moistened and warmed. It is moistened by the evapora-
tion of the watery secretion produced by the glands
embedded in the mucous membrane, and it has been
calculated that the nose yields up to the inspired air in
177 12

178 APPLIED PHYSIOLOGY

this way as much as 2 quarts of water in the twenty-
four hours. It is warmed by passing over the highly
vascular mucous membrane, the surface of which is
increased by the projection of the turbinates, just as the
surface of a radiator by which one warms a room is
multiplied by its projecting metal bars. How efficiently
the warming is carried out may be judged from the
result of experiments, which show that air entering the
nose at the freezing-point is warmed to a temperature of
81° F. by its passage through the nose alone.

But the nerves of the nose have also a protecting part
to play. The sense of smell is no doubt primarily
protective rather than esthetic. It warns us of the
presence of gases which might be injurious to the lungs.
Nor is the common sensibility of the nose without its
uses. Stimulation of the branches of the fifth nerve in
the nasal mucous membrane has been found to induce a
reflex contraction of the bronchial muscles,* and go
prevent the entrance of air into the lungs. It can easily
be understood that in many circumstances—as, for
example, when irritating fumes have been inadvertently
inhaled—this may be a real source of protection tothe
lungs.t Sometimes, on the other hand, this reflex
mechanism becomes unduly sensitive, and brings about
spasm of the bronchial muscles on quite inadequate
provocation, and it is in this way that some cases of
asthma are caused.

* See Dixon and Brodie, Jowrn. of Physiol., 1908, xxix. 97,
and Trans. of the Path. Soc. of London 1903, liv. 17.

+ See Mackenzie, Amer. Journ, of Med. Sciences, 1883, lxxxvi.,

106; also Riegel and Edinger, Zevt. f. Klin. Med., 1882, v. 413.

~

Ok oe Cea acs eens |

ae ¥ a4

RESPIRATION 179

As the air leaves the posterior nares, its course turns
sharply downward, and the stream impinges on the
posterior wall of the pharynx; and it is here, perhaps,
more than anywhere else that particles of dust are most
likely to get entangled. It is not to be wondered at,
then, that the inhalation of dust is apt to produce a
pharyngitis.

The functions of the nose in respiration, then, are
(1) to free the air to a large extent of suspended particles
and micro-organisms; (2) to warm it; (8) to saturate it
with moisture; (4) to advertise us of the presence of
noxious gases, and, by a reflex mechanism, to prevent
the entrance of irritating fumes into the lungs.

The disadvantages of mouth-breathing will now be
apparent, for the buccal cavity is not primarily designed
to fulfil the above requirements for the modification of
the air before its entry into the lungs. It is true that
the warming process is almost as efficiently carried out
by the mouth as by the nose,* but the absence of a
sufficient apparatus of secreting glands renders it almost
impossible for the mouth to moisten the air sufficiently
without its mucous membrane becoming dry and irritated
in the process; hence the parched, cracked tongue
produced by the stertorous breathing of apoplexy and
the dry morning throat of the nocturnal mouth-breather.
Dust and micro-organisms, too, are less perfectly removed
- by the mouth, and, reaching the bronchi, set up irrita-
tion there. This probably explains the frequent associa-
tion of bronchitis with adenoids and other causes of
nasal obstruction.

* Kayser, Pfliiger’s Archiv, 1887, xli. 127.
12—2

180 APPLIED PHYSIOLOGY

The Trachea and Bronchi.—The trachea and large
bronchi are wide tubes kept permanently patent by
hoops of cartilage. Scattered through their wall are
numberous bands of elastic fibres, chiefly longitudinal
in direction, which permit of a certain amount of stretch-
ing as the lungs move up and down in respiration, or
when the head is thrown back. The free ends of the
hoops of cartilage are connected by unstriped muscle
fibres, the function of which it is difficult to understand.
Embedded in the wall of these tubes are numerous
mucous glands, the secretion of which moistens the
surface of the mucous membrane, and entangles such
particles of dust as have escaped capture in the nose.
Lining the tube is a layer of stratified ciliated epithelium,
the cilia of which are constantly engaged in maintaining
an upward current in the mucus poured out on the
surface, so that particles of foreign matter are floated
away from the direction of the lungs. The removal
of such particles is also facilitated by the existence in the
submucous coat of masses of adenoid tissue, the cells
from which wander into the tube and lay hold of
intruding bodies, and carry them off to be dealt with in
the lymphatic glands. As the bronchi break up’ after
entering the lungs, the hoops of cartilage become re-
placed by smaller plates, which allow of partial collapse
of the tubes during expiration; and as the breathing
surface is approached these disappear altogether, neither

cartilage nor glands being found in the walls of the

bronchioles, which measure only half a millimetre in
diameter. As the cartilage disappears, however, the
muscular layer in the wall becomes more pronounced,

ara.

RESPIRATION 181

and can be seen to consist of two layers—one circular,
the other longitudinal. The function of the circular
layer in controlling the entrance of gases into the air
cells, and the inconvenience it may give rise to in the
shape of asthma, have already been pointed out. The
longitudinal layer probably aids in producing the
contractility of the lung (vide p. 188). It is believed,
too, by some that the asthmatic attacks which sometimes
supervene in the course of chronic bronchitis are due to
the inflammatory products which infiltrate the bronchial
wall, affecting the delicate longitudinal fibres more than
the circular, with the result that the action of the latter
is unopposed and spasm supervenes.*

Each bronchiole terminates in a ‘ lobule,’ which may
be regarded as the ultimate pulmonary unit,t or a lung
in miniature, shut off by a fibrous covering and endowed
with its own vessels, nerves, and lymphatics, and capable
of becoming the seat of disease independently of the
other lobules by which it is surrounded. In the interior
of the lobule the bronchiole subdivides into still smaller
divisions (intralobular bronchioles), the terminal branches
of which end in the narrow alveolar ducts, which expand
in turn into the comparatively wide infundibula lined by
their air cells. This sudden widening out of the air
passage is believed to aid in the production of the
‘ inspiratory sound ’ heard in ausculting the lungs, eddies
being set up in the passage of the air from the narrower
to the wider cavity.

When the lungs expand during inspiration the infun-

* Aufrecht, Deut. Arch. f. Klin. Med., 1900, Ixvii. 586.
{ See Ewart, ‘The Bronchi,’ etc. (Lond.), 1889.

182 APPLIED PHYSIOLOGY

dibula are enlarged, whilst the alveoli lining them are
widened and flattened out. Keith’s observations* show
that the infundibula in the anterior and superficial parts
of the lungs are larger and more easily distended than
those which occupy the deeper and posterior parts,
and it is to this, perhaps, that their greater liability to
suffer from the overdistension of emphysema is to be
attributed.

The alveoli, or air cells, are the respiratory units.
Their walls contain a large quantity of elastic tissue, to
which the contractility of the lungs is due. They also
contain a dense network of capillaries, the meshes of
which are no larger than the diameter of the individual
twigs. In these the blood is spread out and separated
from the air in the alveoli only by the walls of the
capillaries and bya single layer of endothelial plates, not
even provided with nuclei, and through which inter-
change between the blood and the lungs can readily take
place. In the meshes of the capillary network, however,
where interchange does not occur, one finds smaller and
nucleated cells, from which the larger plates appear to
be continually renewed. It has been calculated that the
total area of the alveolar surface of the lung amounts to
no less than 90 square metres, or 100 times the body
surface, from which one can realize how perfect the
arrangements for bringing the blood and the air into
proximity are. Here, however, as in all the organs of
the body, ample provision has been made for accidental
contingencies, and the fact that life can be maintained

* ‘Why Does Phthisis Attack the Apex of the Lung?’ (London
Hosp. Gaz., 1904, x. 99).

Nt | passage.

ig

Al

PuaTE i].—DIAGRAM OF A a si OF THE poe =
(AFTER STOHR). -
’

RESPIRATION 183 °

even when one lung has been completely destroyed, or
rendered temporarily useless by disease, shows that a
much smaller alveolar area than this is sufficient to allow
of efficient oxidation of the blood.

Bloodvessels, Nerves, and Lymphaties of
the Lung.

Each lobule is supplied by a branch of the pulmonary
artery, which accompanies the bronchiole and divides
with it, ending by pouring its blood into the capillary
network in the walls of the alveoli. From the margin
of that network the purified blood is taken up by a branch
of the pulmonary vein, and ultimately returned to the
lefé auricle. The lobular branches of the pulmonary
artery are therefore ‘end arteries, and so liable to
become the seat of embolic infarction—a process often
met with in cardiac disease. |

The balance of evidence is opposed to the view that
the pulmonary bloodvessels are possessed of vasomotor
nerves.* Hence, perhaps, the ease with which they
become the seat of passive engorgement when there
is any obstacle to the onflow of blood into the left heart,
and enable the lungs to act as a reservoir for the
pulmonary circulation in much the same way as the liver
serves the systemic. There can be no doubt, also, that
such passive congestions play a large part in the diseases
of the lungs. By the expansion of the lungs during
inspiration the alveolar capillaries are opened out and

* See Brodie, ‘The Pulmonary Circulation,’ Lancet, 1902, i. 803.

184 APPLIED PHYSIOLOGY

the circulation through the lung facilitated; during
expiration, on the other hand, the pulmonary circulation
is much more difficult (Fig. 9). This is one reason
why a patient whose circulation is embarrassed tends

SN

B

A

Fia. 9. :

/

These diagrams represent an infundibulum, A, at the end of a complete
inspiration, and B, at the end of a complete expiration. 6 = alveolar
wall ; a = bloodvessels of the same. It will be seen that the amount
of blood in the lungs varies directly with the amount of air, and that
the pulmonary bloodvessels are most dilated and the resistance to the
right heart least at the end of a full inspiration ; while, contrariwise,
the vessels are most contracted and the resistance to the right heart
greatest at the end of a eomplete expiration. (Harry Campbell.)

instinctively to keep his chest as much as possible in
the position of inspiration.

The absence of a vasoconstrictor supply to the pul-
monary arteries also implies that suprarenal extract

RESPIRATION 185

(which acts only on the terminals of such nerves) can be
of no use in checking hemorrhage from the lungs.

In addition to the pulmonary set of vessels, each
lobule is provided with a branch of the bronchial artery
for the nourishment of its own tissues. Free anasto-
mosis between the pulmonary and bronchial sets occurs
at the edges of the alveoli, which render the latter liable
to become the seat of congestion, both in obstruction to
the return of blood through the pulmonary veins, as, for
example, in mitral regurgitation, and when there is a
damming back of blood in the vene cave, as occurs
when the lungs themselves are the seat of the obstruc-
tion—e.g., in emphysema. In both events bronchitis
will be apt to ensue.

The pulmonary pleura is supplied by the bronchial
arteries, and the parietal pleura by the internal mammary
and intercostals, whilst the venous blood is carried away
by the azygos veins. The latter are very imperfectly
provided with valves, and hence when the pressure in
the right heart is raised the venous radicles in the pleura
readily become congested, and effusion (hydrothorax)
results.

Unlike the pulmonary vessels, those of the pleura are
supplied with vasoconstrictor nerves, which renders them
susceptible to the action of adrenalin. Advantage has
been taken of this fact by Barr in the treatment of
- pleural effusion.

There are two sets of lymphatics in each pulmonary
lobule. First, a central set which accompany the branch
of the pulmonary artery and pass direct to the bronchial
glands at the root of the lung; the flow of lymph in

186 APPLIED PHYSIOLOGY

these is promoted by the pulsation of the adjoining
artery. Secondly, a peripheral set which run in the
fibrous tissue between the lobules, and often into the
lymphatic plexus of the pleura. The flow in these is
kept up by the respiratory movements of the lung.
It will therefore be most active where these movements
are freest—e.g., in the lower and anterior parts of the
lung, and most sluggish where expansion is least—e.g.,

at the apices. Thi Ips to determine the greater
liabilit the apices to become the seat of tuberculosis. _

Both of these are in communication with the air cavities
by means of stomata, and are provided with valves,
so that any foreign particles which have successfully run
the gauntlet of the arresting mechanisms of the nose and
air passages are finally conveyed either to the bronchial
glands or pleura.

It is in this way that disease of these parts is so often
set up. Tubercle bacilli, for instance, get lodged in the
bronchial glands, and set up there a local tuberculosis,
which may become the starting-point of a general infection;
or particles of dust pass from the alveoli to the pleural
cavity, and are thence taken up into the costal pleura,
and may thus excite a pleurisy by purely mechanical
means.* A consideration of these facts still further
emphasizes the importance of keeping the nose and

other protective mechanisms of respiration in a healthy _

condition.

The respiratory movements favour absorption from
the pleural cavity, acting like a ‘ pleural pump’ through
the stomata, and as these movements are more extensive

* Grawitz, Berlin. Klin. Woch., 1897, xxxiv. 621.

RESPIRATION 187

in the erect position, the absorption of a pleural exudate
may be favoured by allowing a patient to get up and
move about. A very large effusion, however, may stop
the action of the ‘pump,’ and in such a case removal of
part of it by aspiration may restart the mechanism, and
be followed by spontaneous absorption of the remainder.

Compared with that of most other organs, the
lymphatic supply of the lungs is peculiarly abundant,
a circumstance which, whilst it undoubtedly predisposes
to rapid toxic absorption from the pulmonary surface,
also facilitates the speedy absorption of fluid or inflam-
matory exudates which have been poured out into the
alveoli. As the lung expands during inspiration the
stomata in the alveoli open up, and absorption is made
much easier. In accordance with this, one finds that
the clearing up of a pneumonic exudate often goes on
much more quickly if the patient is allowed to get up and
move about a little, for that ensures deeper breaths than
when he is lying in bed. It has been pointed out* that
there is much less variation in respiratory pressure
at the apices of the lungs than elsewhere. The blood
and lymph flow are thus not so well promoted in these
regions, with the result that they are apt to be less well
nourished than the rest of the lungs. The bearing of
this upon the special liability of the apices to become the
seat of tuberculosis has already been pointed out.

The nerves of the lobule are derived from branches of
the vagus, which supply motor twigs to the muscle of the
bronchioles and sensory fibres to the alveoli. The
broncho-constrictor fibres of the vagus are of great

* Hofbauer, Zeit. f. Klin. Med., 1906, lix. 38.

188 APPLIED PHYSIOLOGY

interest, for there is no doubt that reflex stimulation
of them is the cause of asthma. As has been already
mentioned, reflex constriction of the bronchioles can be
best obtained by exciting the nasal mucous membrane,
but it can also be induced by impulses from other
organs—e.g., the siomach. Certain drugs have a marked
effect on the apparatus. Muscarin, for example, stimu-
lates the nerve endings, and may induce an artificial
asthma, whilst the inhalation of chloroform or ether, or
the injection of atropin, abolishes the effect of the vagus
and leads to bronchial relaxation.

The Mechanics of Respiration.

The lungs may be compared to two elastic bags
partially distended with air and enclosed in a closed box,
the thorax. They are only prevented from collapsing
altogether by the pressure of the atmosphere (amounting
to 15 pounds to the square inch), which can reach their
interior through the air passages, but is prevented from
pressing on their outer surfaces by the resisting chest
wall. When the chest wall is perforated, the lung on
that side at once falls in to about one-fifth of its original
bulk.* _

This tendency of the lungs to collapse—their ‘con-
tractility,’ as it may best be called—is the result mainly
of the large quantity of elastic tissue in the lung
substance, but in part also, perhaps, of the tonicity of
the muscular fibres in the walls of the bronchi, and has
been described by some writers as ‘ pulmonary tone.’f

* See Salter, Lecture on Dyspnea, Lancet, 1865, ii, 111.
+ Samuel West, Med. Chir. Soc. Trans., 1898, Ixxxi. 278.

RESPIRATION 189

It is easily overcome by too great an inflating strain, as
happens in some forms of emphysema, and for this
reason artificial inflation of the lungs by bellows is
dangerous; and it is also diminished when the lung is
floated up by fluid in the pleura or when it is the seat of
acute congestion. The normal ‘lung note’ obtained on
percussing the healthy chest depends on a proper ‘tone’
in the lungs, and when that is diminished, as happens,
for example, in the upper part of the lung when there is
an effusion into the pleural cavity or where the lung is
the seat of acute congestion or miliary tuberculosis, a
more resonant and even tympanitic percussion note is
obtained (Skodaic resonance).

The surface of the lung is bound to the chest wall by
an ‘atmospheric ligament,’ which acts in the same way
as a rubber sucker (Keith). This permits of the lung
gliding freely over the interior of the thoracic wall with-
out the bond being broken. The weight required to
separate the visceral from the parietal pleura over both
lungs amounts to about a ton, which is far greater than
any force the inspiratory muscles can bring to bear.
Hence by no muscular effort can the pleural bond be
broken.

The contractility of the lungs causes them to exert a
certain ‘pull’ on the chest wall and on the mediastinum
(Fig. 10). A sort of ‘ tug-of-war,’ indeed, goes on between
the two lungs, with the mediastinum and its contents as
the rope, so that if one lung becomes collapsed—e.g., in
pneumothorax—the other, being no longer opposed, pulls
over the heart and other mediastinal organs to its own
side. It is mainly in this way that displacement of the

190 APPLIED PHYSIOLOGY

heart is produced in cases of pneumothorax and pleural
effusion.

The ‘pull’ of the lungs on the chest wall entails a
slightly negative pressure (amounting to about 6 milli-

Fie. 10.

The arrows represent the direction of the ‘ pull’ exerted by the lungs
by means of their contractility.

metres Hg) in the pleural cavity and on the heart.*
This favours the effusion of fluid (hydrothorax) when

* The following table exhibits approximately the variations in
the intrathoracic pressure under different conditions:

Milligrammes
Hg.
Normal inspiration ... ~ bis bad - 10
Normal expiration ... oe es aks a A
Deep inspiration... bes re ie - 40
Deep expiration ay ~ 0
Deep inspiration with air eae omit? - 100

Deep expiration with air passages closed + 100

RESPIRATION 191

the pleural bloodvessels are passively congested. As
fluid is poured out, the contractility of the lung is
gradually able to assert itself, and the organ continues
to recede pari passu with the encroachment of the fluid.
As it does so the negative pressure gradually diminishes,
but it requires a large effusion to produce a really positive
pleural pressure. Hence the necessity for aspiration in
removing small effusions. If one lung collapses, the
other, being no longer pulled on from its mediastinal
side, contracts up to a considerable extent, and the
healthier it is—i.e., the greater its ‘tone’—the more
does it do so. Hence if a healthy man becomes suddenly
the subject of a pneumothorax, he loses not only the
lung of the affected side, but a large part of the other as
well, and his dyspnoea is proportionately great.

During forcible expiration the intrathoracic pressure
becomes positive, with the result that the two layers of
the pleura are squeezed tightly together, and even
although the lung be penetrated by a punctured wound,
pneumothorax may not result. This point has been
graphically put by Sir James Barr:* ‘I do not know
if any of you have encountered a man who was making
indiscriminate use of a knife. I have, and for a short
time I got the worst of the conflict. If you should meet
such an individual, you can deal with him as you think
best, but if you find him making a lunge for your chest,
_ I would strongly advise you to let your breath out before
he does it for you. In this way the knife or dagger has
another inch to travel before it reaches your chest, and
you establish a positive pressure within your thorax

* The Bradshaw Lecture, 1907.

192 APPLIED PHYSIOLOGY

which prevents the two pleural surfaces from separating.
After the injury keep the wounded side as much as
possible in a state of expiration, and do not on any
account take a deep inspiration.’

Respiration is a process in which the whole body wall
participates. In textbooks of physiology it is usually
stated that inspiration alone is a muscular act, that
expiration takes place as the result of elastic recoil; but,
as Keith has shown, all the muscles of respiration are
involved in both phases. During inspiration the in-
spiratory muscles overcome those of expiration; during
expiration the reverse takes place. This view is in con-
formity with the well-recognized principle that in per-
forming any movement active relaxation of one set of
muscles has as much to do with it as the active con-
traction of their opponents. Inspiration, however, is an
opposed act, the opposing forces being the contractility
of the lungs, the elasticity of the chest wall, and, to
some extent, the force of gravity. Expiration is an
unopposed act. Hence the thorax is in a position of

expiration after fainting or death, and in great weakness |

if is inspirations alone which are delayed. Expiration
follows inspiration at the usual interval. The opposition
to be overcome during inspiration is considerable, and
involves, it has been calculated, a muscular strain
equivalent to raising a weight of 100 pounds, not count-
ing the contractility of the lungs. This has to be raised
eighteen to twenty times per minute. Where inspiration
has to be repeated very frequently, as in many conditions
of disease, the expenditure of muscular energy may be-
come very great. It is inadvisable, therefore, to add to

~ Secegtibenanye 5

RESPIRATION 193

it in any way, as, for example, by placing a heavy
poultice on the front of the chest.

The elevation of the ribs is effected partly by the
scaleni and intercostals, partly by the diaphragm. The
normal condition of the latter is one of “arched tension,’
it being held up partly by its attachment to the peri-
cardium, partly by the pull exercised on it by the
elasticity of the lungs. It is the tension of the
diaphragm, indeed, which retains in the lungs their
supplemental air. As long as the ribs are fixed the
diaphragm cannot be pushed upwards, but if the
abdominal muscles pull the lower ribs inwards, then
the tension of the diaphragm is relaxed, and the
abdominal viscera, under the pressure of the abdominal
muscles, can drive it upwards and expel the supple-
mental air.

The mode of action of the diaphragm is peculiar, and
has important bearings in disease.* The diaphragm is
to be regarded as a digastric muscle which takes origin
from the vertebre behind, and is inserted into the lower
six ribs. Its central tendon rests upon the liver, which
acts as a sort of fulcrum, over which the muscle passes.
As the diaphragm contracts, the liver tends to be pushed
forwards and downwards; but its movement in this
direction is frustrated by the anterior abdominal wall,
with the consequence that it forms a fixed point, over
which the ribs are pulled up. If the abdominal muscles

are badly developed, however, or if they have become
partially atrophied from practical disuse, as happens,

* Keith, ‘The Anatomy of Glénard’s Disease,’ London Hosp,

" Gaz., 1902, ix. 55.
13

194 APPLIED PHYSIOLOGY

for instance, in women in whom the normal function of
the abdominal muscles has been largely usurped by the
support given by corsets, then the descent of the liver
and the organs lying beneath it is unopposed, and a dis-
location downwards of the abdominal viscera takes place,
a condition known in clinical medicine as Glénard’s
disease. It might be supposed, from a study of the
anatomical relations of the diaphragm, that it would
tend to pull the ribs inwards quite as much as to elevate
them ;* but such an action is prevented partly by the
resistance offered by the comparatively solid mass of the
liver, partly by a fixation of the ribs by the intercostal
muscles. As a matter of fact, when the latter are
paralyzed, as happens, for example, when there is a
transverse lesion of the cervical cord or when the ribs
are already much raised, as in emphysema, a recession
of the ribs along the line of attachment of the diaphragm
can be observed to take place.

The slight descent of the central tendon of the
diaphragm, which takes place during inspiration, pulls
down the heart with it, and so provides a still larger

space into which the lungs can expand. This descent

of the diaphragm is aided in the vertical position by the
action of gravity, but in the case of a patient lying on
his back the liver has got to be pushed upwards instead
of downwards, and so the easy descent of the diaphragm
is impeded. It is for this reason, in part, that patients

whom the respiration is embarrassed prefer to sit
up in bed. An accumulation of fluid or gas in the

* Gerhardt, ‘ Ueber Inspiratorische Einziehungen am Thorax,’
Zeit. f. Klin. Med., 1896, xxx. 87.

=

RESPIRATION 195

abdomen will also offer a mechanical obstacle to the
descent.

The degree to which the ribs and the diaphragm
respectively take part in elevating the chest determines
whether the respiration will be mainly ‘costal’ or
‘abdominal’ in type.* The better developed the abdo-
minal muscles are, the more easily can the diaphragm
elevate the ribs, and the more ‘thoracic’ the type of
respiration. Abdominal respiration is the type in men.
In women, on the other hand, the elevation of the upper
ribs takes place more freely. In part this is only apparent
—the mass of the mamme magnify the apparent move-
ment, as a writing style exaggerates the movements
of a lever—but in part also it is genuine. It is now
generally admitted that the occurrence of this type of
breathing in women is due to the wearing of corsets.

Under diseased conditions it would seem as if the
different parts of the chest wall attained a certain inde-

pendence of action, so that one side, or even part of the
chest, may move more than the rest, the air seeming to
be sucked into some parts of the lung and prevented
from reaching others. Thus rest is ensured to diseased
parts of these organs.

The result of the combined action of the muscles of
inspiration is that the chest is enlarged downwards,
forwards, and outwards, and a vacuum formed within

* Whether respiration is costal or abdominal in type depends
also upon the order in which the different parts of the body wall
come into action. If the wave begins in the abdomen and passes
upwards, the type is abdominal; if it begins above and passes
down, the type is costal.

138—2

196 APPLIED PHYSIOLOGY

it. In normal circumstances this vacuum is filled partly
by blood which enters the large venous trunks and right
heart, but mainly by air which rushes into and inflates
the lungs. Should there be any obstacle to the entrance
of air, the vacuum in the alveoli tends to be filled by the
transudation of fluid. It is in this way that cedema of
the lungs is produced in laryngeal or tracheal obstruc-
tion. If the chest wall is very soft, ii may be unable to

Fic. 11.—Cross Section oF THE Rieut Luna, SHOWING
DIRECTIONS OF EXPANSION. (KEITH.)

withstand the atmospheric pressure on its outer surface
when the internal pressure is lessened by inspiration,
and it will then sink in at its softest parts. It is in this
manner that the chest deformity of rickets is produced.
As the greatest increase in the capacity of the thorax
during inspiration occurs in its lower part, it will readily
be understood that the expansion of the lungs is freest
in their lower and lateral portions; indeed, they cannot

RESPIRATION 197

expand either upwards, inwards, or backwards. It is
probably for this reason that the friction sound of
pleurisy is usually best heard over the antero-lateral
aspect of the chest wall. The expansion of the apices,
on the other hand, is relatively feeble, and can only

Fie. 12.—Rieut LUNG FRoM THE SIDE, SHOWING DIRECTIONS
OF EXPANSION. (K&ITH.)

take place indirectly and chiefly through the diaphragm
- allowing descent of the lung as a whole, and some writers
have ascribed to this fact the liability of the apices to
become the seat of tuberculous deposits (Figs. 11, 12,
and 18).

In forced inspiration all the muscles which can in any

198 APPLIED PHYSIOLOGY

way help in raising the chest wall are called into play,
and the expenditure of muscular energy becomes very
great, equivalent, it has been calculated, to raising a
weight of 800 pounds. In forced expiration the abdo-
minal muscles are largely made use of to press up the
liver and other viscera against the under surface of the

“a

diaphragm, which has been relaxed by the pulling down
of the lower ribs. Hence the capacity of the chest is
lessened both laterally and vertically.

The air which is still left in the lungs after the fullest
expiration, and which is only displaced when the chest
wall is opened, is termed ‘residual.’ It amounts to
about 100 cubic inches for the two lungs. When the

RESPIRATION 199

lungs are overdistended, however, as in emphysema,
it is greatly increased. The volume of air which we
ordinarily use for breathing, and which passes out and
in at each breath, is about 20 cubic inches. This is
called the ‘tidal air.’ For the most part, however, it
does not go straight into the alveoli, but only into the
upper air passages, the renewal of the air in the lungs
themselves taking place by a process of diffusion, whilst
the composition of the alveolar air remains fairly con-
stant. |

The tidal air is sufficient for the ordinary purposes of
life, but, when an emergency arises, we are able to get
an increased supply of oxygen by taking into the lungs
by a full breath another 100 cubic inches of air which is
termed complemental. By a forced expiration an equal
quantity can be expelled in the wake of the tidal air,
and this is termed supplemental. Were it not for these
reserves of capacity every extraordinary effort would
entail great dyspnea and the risk of premature death.
‘Every man,’ says Sibson, ‘has much more lung than
he requires in the quiet pursuits of life ; he requires less
when he lies down, sleeps, or is depressed; but more
when he walks, runs, wrestles, or is roused by passion.
The lung that is used is an ever-varying quantity... .
The more the lungs are used, the more is their capacity
nursed. The man that under one training is the feeble,
narrow-chested, sickly mechanic, is under another the
active, full-chested, and healthy sailor.’

The tidal air supplies only enough oxygen to last us
a few seconds ; if the breath is suddenly held, discomfort
begins to be experienced after the lapse of that time.

200 APPLIED PHYSIOLOGY

Even the supplemental air only gives another two
minutes’ supply, for the most expert pearl-divers cannot —
stay longer under water than that.

The complemental capacity of the lungs is made use
of by a man who fills his chest preparatory to swimming
under water ; the supplemental by a singer in sustaining
a prolonged note.

If the chest be filled as completely as possible, and

Complemental
Vital :
Capacity si
Reserve
Residual

Fig. 14.—D1acram oF Vita Capacity. (AFTER HurTcHInson.) ;

then squeezed as empty as the expiratory muscles can
squeeze it, the volume of air expelled is the measure of
the vital capacity. The vital capacity is thus a gauge of
the efficiency of respiration or of the vital activity of the
lungs. In health it amounts to about 225 cubic inches,
but varies greatly with age, size of chest, etc. Tall
people have a greater vital capacity than short,* and,

* For every inch of stature between 5 and 6 feet, 8 additional
cubic inches of air are given out by a forced expiration.

RESPIRATION 201

curiously enough, broad-chested persons are not neces-
sarily well endowed in this respect. Disease affects it
very markedly, especially phthisis. Thus a man below
fifty-five whose capacity is only 193 cubic inches is
probably the subject of disease of the lungs. Curiously
enough, both pleure may be entirely adherent all over
without in any way limiting the respiratory capacity.

The vital capacity also varies greatly with posture.
Thus in the same man it was:

260 cubic inches when standing.

955 _,, a », sitting erect.

230 —sé4,; ms », lying supine.

yy) re me a » prone.
—HuvtTcHINSON.

This shows how it is that patients with dyspnea
cannot breathe when lying down. The diminution of
vital capacity as age advances is due to an increasing
difficulty in completely emptying the lungs on account
of thoracic rigidity.

The Nervous Mechanism of Respiration.

The mechanical part of the respiratory process is
controlled by an elaborate nervous apparatus, the head-
quarters of which are situated in the respiratory centre
in the medulla. This centre consists of two lateral
halves either of which is apparently able to act inde-
pendently of the other, for it is quite common for a
patient with disease of the lungs—e.g., pleurisy—to
breathe on one side only. There would also appear
to be independence of action as regards those parts of

202 APPLIED PHYSIOLOGY

the centre which control the diaphragm and the ribs
respectively, so that one or other of these can be thrown
out of action without interfering with the other. Thus
it is possible for a patient with localized peritonitis to
breathe with his ribs only, part or the whole of the
diaphragm being kept motionless. It is probable that
a like independence is possessed by the different groups
of cells in the centre which innervate the muscles which
act upon the individual ribs, so that even a limited
portion of the chest wall can be thrown out of action
if the need arises without disorganizing the rest.

On the other hand, it seems to be impossible to mark
off any part of the centre as being specially connected
with inspiration or expiration respectively.

Much discussion has raged over the question whether
the centre can act spontaneously or whether it must
always be prompted by influences coming to it from
without. The truth would appear to be that whilst the
centre is possessed of power of spontaneous action, such
power is very rarely put into exercise; probably, indeed,
never at all even in conditions of disease, unless, perhaps,
the last gasping breaths of life are to be regarded” as
evidence of such activity. a

The respiratory centre can be powerfully influenced
by two distinct agencies: (1) nervous stimuli, (2) the
composition of the blood. We shall consider these
separately.

1. The chief afferent nerves which act upon
the centre are the vagi. As regards these, matters
seem to be so arranged that each phase of respiration
prepares the way for its successor. Collapse of the

ACT

RESPIRATION 203

lungs excites in the vagi impulses which lead to an
inspiration ; distension of the lungs arouses nerve cur-
rents which prompt the centre to an act of expiration.
Divide the vagi, and the respiration becomes slower and
deeper ; apply a powerful stimulus to the upper end,
and the inspiratory movements are greatly increased.
This controlling action of the vagus is no doubt often
disturbed in disease. Irritation of the fibres of the
vagus, for example, appears to be the cause of the
rapid respiration which comes on in pneumothorax,
for it disappears when the nerve is divided (Traube).
If, again, the air passages are in any way obstructed,
as may happen, for example, in stenosis of the larynx,
the respirations—though the need for air is urgent—are
very slow, the reason being that the lung can only be
slowly expanded with air, which takes a long while to
get past the obstruction, and during all that time the
reflex inhibitory action of the vagus in inspiration is
steadily in action.

The vagi, though the most constantly active, are by
no means the only afferent nerves which can influence
the respiratory centre. Stimulation of the nasal branches
of the fifth nerve produces expiratory efforts (sneezing),
and stimulation of the superior laryngeal has a similar
but even more powerful effect (coughing). Both of these
reflex effects upon the centre are protective in nature,
and lead to the expulsion of irritating foreign bodies
from the nose and larynx respectively. The temporary
arrest of respiration which is necessary during the act
of swallowing is secured by the action of the glosso-
pharyngeal, which, when stimulated in the throat,

204 APPLIED PHYSIOLOGY

induces a temporary cessation of the breathing move-
menis.

Irritation of the splanchnic also seems to induce an
arrest of respiration, as is familiar to anyone who has
been ‘ winded’ by a blow on the upper part of the
abdomen. This mechanism seems to be brought into
play in lessening the diaphragmatic movements in painful
affections of the viscera in the upper part of the abdomen.
Further, all sensory nerves appear to be able to influence
the centre. This reflex action, indeed, is perhaps the
first we make use of on entering the world, for our first
breath is, in part at least, brought about by the action
of cold air on the skin of the trunk, and if it is at all
delayed the accoucheur puts the reflex into more power-
ful action by dashing cold water on the chest and
abdomen.

Similar methods of reflexly stimulating the respiratory
centre through sensory nerves are constantly used in
disease. In collapse of the lung in young children, for
instance, frequent and vigorous ‘ spanking’ is constantly
resorted to in order to induce re-expansion of the alveoli
by the deep breaths which crying necessitates. In cases
of narcotic poisoning, too, the respiratory centre is kept
awake by flicking the patient with wet towels or applying
a strong faradic current to the skin.

None of the vital centres, in fact, is more intimately
in touch with the whole body than that which presides
over respiration. Nor need this cause surprise when
one remembers how important it is that our breathing
should be able to respond at once to the most varying
demands for oxygen which the emergencies of life call

RESPIRATION 205

forth ; whilst at the same time it controls the voice, which
is one of the chief means by which the emotions are
expressed. That the most diverse causes may induce
an attack of asthma is a pathological consequence of the
wide ramification of the connections of this centre.

Not only do constant afferent impulses pour into the
respiratory centre from below, it is also under very direct
control from the upper regions of the brain. This control
is partly unconscious and continuous in nature; in part
it is intermittent and under the dominion of the emotions
and will. The nature of the unconscious control is not
clearly understood, but when it is withdrawn the centre
tends to take on a rhythmical action (Cheyne-Stokes
respiration). The voluntary and emotional promptings
are no less important, though only intermittently asserted.
The exact centre in which such impulses arise has not
been localized, but it is probable that it is situated in
the cortex. It has been shown, for example, that in
cases of hemiplegia there may be partial paralysis or
inco-ordination of the respiratory movements on the
affected side,* whilst the influence of the emotions on
respiration is a commonplace of ordinary observation.
We speak, for instance, of ‘holding our breath’ in
suspense, or of ‘gasping’ with astonishment, and so
slight are the causes sufficient to set emotional dis-
turbances in action that when one wishes to count a
patient’s respirations it is inadvisable to let him know
that one is doing so, or the process is almost sure to be
quickened. .

* Grawitz, Zeit. f. Klin. Med., No. 26, and Stirling, <bid., 1896,
No. 30, p. 1.

206 APPLIED PHYSIOLOGY

It is an interesting fact that whilst voluntary or
forcible breathing soon produces a feeling of fatigue,
he equally powerful breathing of hard exercise does
not. The physiological explanation of this apparent
anomaly may, perhaps, be that voluntary breathing
involves the use of the brain cortex, whereas the in-
voluntary breathing of exercise does not, and it is well
known that the sense of fatigue, though referred to the
muscles, is really experienced in the brain.

The efferent impulses from the respiratory centre
travel along the vagi, the phrenics, and the intercostal
nerves. Those which proceed by the vagi innervate the
posterior crico-arytenoid muscles, and so cause the
glottis to open more widely during respiration. Inter-
ference with these fibres is the cause’of the ‘abductor
paralysis ’ so common in cases in which there is pressure
upon the recurrent laryngeal nerve. The separate route
pursued by the fibres for the diaphragm and the inter-
costals respectively enables one or other of those portions
of the breathing apparatus to be paralyzed without the
other. Thus a patient who has sustained a crush of
the cord below the level of the fifth cervical roots can
breathe for a time by his diaphragm alone. BY.

If, again, the phrenic nerve be in any way y injured
or degenerated, the patient can breathe—in a sort of way,
at least—with the intercostals, although the imperfect
expansion of the lower parts of his lungs is very apt to
lead to troublesome complications.

Division of one vagus in man does not appear to lead
to bad results. On the other hand, a case is on record
in which the left vagus was included by mistake in a

>.

‘hae Mp al

RESPIRATION 207

ligature of the common carotid. In this case the
respiration stopped from stimulation of the inhibitory
fibres in the superior laryngeal, and death resulted.

2. In addition to its susceptibility to nervous influences,
the respiratory centre responds with marvellous delicacy
to variations in the composition of the blood which
circulates through it. Should an excess of venosity in
the blood indicate the necessity for a fuller and freer
interchange between the blood and the air, the respi-
ratory movements are at once increased in frequency
and depth. This is the prime cause of the exaggerated
breathing of dyspnea. Experiments tend to show that
even the chemical products of muscular fatigue can
exercise this effect, and that it is by this means that
deeper breathing and a fuller supply of oxygen are
ensured during exercise. If, too, the blood which
reaches the centre is unduly warm, the activity of the
latter is increased. This may explain in part the rapid
respiration of fever. Certain drugs have a similar
influence, and strychnine is constantly used in clinical
medicine in order to produce such effects. On the other
hand, some agents, such as alcohol and opium, ulti-
mately depress the centre, and may end by paralyzing
it, and so lead to death.

Whether the nervous or chemical method of stimu-
lation plays the greater part in determining the normal

quiet rhythmic action of the respiratory centre is not
- yet determined, but the trend of recent physiological
Opinion is in favour of attaching more importance to
the effect of the condition of the blood and less to
nervous influences than was the case a few years ago;

208 APPLIED PHYSIOLOGY

and it is significant that the mode of starting of the
first breath after birth, which was so long a fruitful
source of discussion, is now pretty generally attributed
to the effect upon the respiratory centre of the accumu-
lation of carbonic acid in the blood rather than to the
action on the centre of stimuli from the surface of the
body. That the latter can be powerful aids in stimu-
lating the centre to action, however, the good effect of
‘spanking’ a newly-born infant which is disinclined to
breathe effectually proves.

We have spoken hitherto as if there was only one
respiratory centre, and that wholly given over to the
superintendence of inspiration. It is probable, however,
that there is an expiratory centre as well, and that it
comes into play in the performance: of forced expiration.
It may be excited reflexly, as in the act of coughing, or
by voluntary effort when it is desired to increase the
intrathoracic pressure, as in straining; and it would
seem also to react to peripheral sensory stimuli, and to
excessive venosity of the blood. Unlike the inspiratory
centre, however, it is not rhythmically active, for it
must always be remembered that the act of respiration
consists in a series of inspirations only, the expiratory
part of the process being, in normal conditions, purely
physical.

The inverted type of breathing observed in young
children suffering from pneumonia is perhaps due to
stimulation of the expiratory centre.

a

RESPIRATION 209

The Chemistry of Respiration.

1. Pulmonary Respiration,

The general principles of the chemical side of respira-
tion are easily understood, though the details are in
many points still involved in obscurity. The essence
of the process consists in the conveyance of oxygen to
the tissues and the removal of carbonic acid from them,
The lungs thus play a double part. They absorb oxygen
from the air just as the stomach and intestine absorb
nutritive constituents from the food, and they excrete
carbonic acid just as the kidneys excrete urea. Disease
may result from a disorganization of either of these
functions: on the one hand from failure of the lungs
to absorb sufficient oxygen, and on the other hand from
an inability on their part to excrete carbonic acid.

We may now look at some of the practical bearings
of this interchange between the lungs and the air in
greater detail. |

If one compares the composition of the air as it
enters and leaves the lungs, one gets such a result as
the following :

Inspired Air. Expired Air.
Oxygen ... 20°96 percent. 16°03 per cent.
Nitrogen ... 79 per cent. 79 per cent.
CO, .. 0°04 percent. 4:4 per cent.*

- In addition, the expired air is saturated with water

* Variations in ‘respiratory exchange ’—.e., the total consump-
tion of oxygen and excretion of CO,—usually discussed under
-* Respiration,’ are really the expression of variations in metabolism,
and are considered under that subject.

14

210 APPLIED PHYSIOLOGY

vapour; but so, probably, is the inspired air before it
reaches the alveoli, thanks to the moistening influence
of the upper air passages already described.

A comparison of the composition of inspired and
expired air does not, however, give us an accurate idea
of the actual composition of the air when it comes into
relation with the blood in the alveoli, for the following
reason: The air in the passages from the nose to the
alveoli is not really changed during respiration, but
comes out again the same in composition as it went in.
The air which has actually been in the alveoli, therefore,
is, as it were, diluted by this purer air when the total
output of a breath is collected, and the latter does not,
therefore, really represent the composition of the air as
it actually left the alveoli themselves. Seeing that the
volume of air in the air passages is about 140 c.c., and
the total air taken in and sent out again at one breath
is about 500 c.c., it will easily be seen that a considerable
fallacy is introduced if the composition of the expired
air be taken as representing that of the alveoli. As a
matter of fact, if the alveolar air be collected separately, as
it can be, it is found to contain much more CO, and less
oxygen than ordinary expired air, the oxygen amounting
to only 18 or 14 per cent., and the CO, to 5 or 6 per
cent. Further, this method of analysis has shown that
the partial pressure of CO, in the alveoli is constant.

It will be seen from this that the essential fact of
respiration is that the blood gives up carbonic acid to
the air in the lung and receives back oxygen from it.

When one comes, however, to ask how this exchange
is effected, one finds oneself involved in a maze of con-

RESPIRATION 211

troversy. Is the process a purely physical one, in which
the epithelium of the alveoli which separates the air
from the lung acts merely as a permeable membrane,
or have the epithelial cells themselves something to say
in the process? Are they able actively to pick up oxygen
out of the air, and to excrete CO, from the blood, irre-
spective of such considerations as the tension of these
gases? In other words, is the process a purely physical
one, or is it—to use the only available word—in part at
least vital? This question is one, if need hardly be
said, of great theoretical importance; it is one of the
fundamental problems of physiology which goes to the
root of our conceptions of living function. But it has
also practical bearings. For if the epithelial cells of
the alveoli really do play an active part in the process
of exchange in the lungs, it is conceivable that the dis-
order of this exchange and the imperfect purification of
the blood which results from it, as seen in acute disease
of the lungs, may be due, in part at least, to disorganiza-
tion of the alveolar epithelium. Asphyxia would then
be the result of an inability of the epithelium of the air
cells to excrete CO,, just as uremia is the result of a
failure of the renal epithelium to excrete the constituents
of the urine. That such interference with function does
occur in acute disease there is some experimental evidence
to prove. Lorrain Smith,* for example, concludes that
_an interference with active absorption through the lung
epithelium is an integral part of many conditions of
disease directly or indirectly associated with the lungs.

Meanwhile it is interesting to note that most physiolo-

* Jowrn, of Phystol., 1897-98, xxii. 307.
14—2

212 APPLIED PHYSIOLOGY

gists are coming round to the view that the part played
by the epithelium of the lungs is an active and not
merely a passive one, and cannot yet be explained by
the ordinary physical laws as we see them in operation
in non-living matter. As E. H. Lewes said nearly fifty
years ago:* ‘Physical laws reveal only one part of the »
mystery. Respiration is not a simple physical act. It
is the function of a living organism, and as such receives
a, specific character from that organism. No sooner do
we cease to regard the exclusively physical aspect of this
function—no sooner do we fix our attention on the
organism and its influence, than the theory raised on
the simple laws of gaseous interchange suddenly totters
and falls.’

One hundred volumes of arterial blood yield sixty
volumes of gas of the following composition :

Oxygen sae ee ... 20 parts.
Nitrogen iby: Be oi | eee
Carbonic acid ... sl ae; ee

Of the oxygen less than one volume is in solution in
the plasma. ‘The rest is combined with hemoglobin in
the red cells. Arterial blood is, however, not saturated
with oxygen. It is only about nine-tenths saturated, and
under ordinary conditions not more than one-third of
the combined oxygen is used. There is, therefore, a
considerable margin of oxygen to draw upon in
emergencies. Thanks to this, a very considerable
proportion of the hemoglobin in the blood can be

* ‘The Physiology of Common Life,’ 1859, i., 378.

RESPIRATION 213

saturated by a foreign gas, such as carbonic oxide, with-
out any symptoms of want of oxygen arising. On the
other hand, where the amount of hemoglobin in the
blood is greatly reduced, as, for example, in anemia,
there is no margin of oxygen-carrying power to draw
upon when oxidation in the tissues is increased, and
dyspnoea results upon slight exertion; and if 70 per
cent. of the total blood be removed the deficiency of
oxygen is enough to cause death.

If the tension of oxygen in the inspired air is in-
creased, the proportion of dissolved oxygen in the blood
is also increased. This is specially true when, owing to
disease of the lungs, the normal oxygenation of the blood
is interfered with. Physiologists who studied the subject
on perfectly healthy animals came to the conclusion
that oxygen inhalation would be of little use in disease,
for they found that even when the amount of oxygen in
the atmosphere was doubled the uptake of it was only
slightly affected.*

We have here, however, an example of the danger of
the premature application of the results of physiological
experiment directly to the problems of disease. As a
matter of fact, an increase in the oxygen tension in the
air breathed does result in a considerable increase in the
amount of oxygen which enters the blood in conditions
of partial asphyxia, and the treatment of such con-
‘ditions by oxygen inhalation has justified itself by its

* Thus, when air is breathed, arterial blood contains 184 per cent.
combined QO, by vol., and 0°6 per cent. dissolved O, by vol.

When pure oxygen is breathed, arterial blood contains 18°7 per cent.
combined O, by vol., and 3 per cent. dissolved O, by vol.— Ha.panz.

214 APPLIED PHYSIOLOGY

results.* The matter has been put very clearly by
Pembrey :

‘The normal animal does not increase its respiratory
exchange when it breathes oxygen instead of air, for its
metabolism is regulated by the needs of its tissues and
not directly by the amount of oxygen absorbed in the
lungs. In the case of some diseases, during which the
blood, owing to diminished absorption of oxygen in the
lungs, is abnormally venous, the breathing of pure
oxygen would increase the percentage of oxygen in the
alveolar air, and thus enable the blood in the lungs to
take up more oxygen. In these cases breathing oxygen
under pressure greater than that of oxygen in the air
would, for a similar reason, be effective, and would also
increase the amount of oxygen simply dissolved in the
plasma. It would appear, therefore, that there is strictly
no contradiction in most of the experimental and clinical
results, for in the normal animal breathing ordinary air
the arterial blood is almost saturated with oxygen, and
without doubt contains as much or more oxygen than
the tissues need. This is certainly not the case in some
diseases, during which the patients have derived benefit
from breathing oxygen.’ f pe

At the same time it must be remembered that the
phenomena of asphyxia are, to some extent, due to the
presence in the blood and tissues of an excess of CO,,
and this, of course, oxygen inhalation can do nothing to
remedy. Nor can it be expected to be of use where the

* See Michaelis, ‘Ueber Sauerstoff Therapie,’ Zezt. f. didit.

wu. phys. Therapie, 1900, iv, 122.
{ Schifer’s ‘ Physiology,’ i. 736.

RESPIRATION 215

difficulty in respiration is due to a breakdown in the
circulation and a failure of the regular transportation >
of oxygen between the lungs and the tissues.

The carbonic acid in the blood is distributed equally
through the corpuscles and plasma. It is to a small
extent in solution, but for the most part combined with
alkali in the plasma and corpuscles, and perhaps also to
some extent united in some fashion to the hemoglobin.
It is the alkalinity of the blood which gives it its chief
power as a CO, carrier, for sodium carbonate (Na,CO,) is
able to take up one molecule of the gas, forming sodium
bicarbonate (NaHCO.). There seems to be a constant
struggle going on between the proteins of the blood and
CO, for the possession of the sodium carbonate of the
plasma, and it depends upon the relative mass of each
present which prevails. Should any stronger acid get
access to the circulation and lay hold of the existing
alkali, the carriage of CO, is greatly interfered with.
Until recently it was believed that this took place in
diabetic coma owing to the presence in the blood of
large quantities of oxybutyric acid; but the observations
of Pembrey have rendered it doubtful whether the
sodium carbonate is sufficiently neutralized in that
condition to interfere seriously with the transport of
CO, from the tissues.

On the subject of ventilation a study of the chemistry
of respiration throws disappointingly little light. We
do not even know, to begin with, what the effects of
‘fresh’ air are due to, or wherein the evils of ‘ vitiated ’
air consist. Analysis has failed to tell us to what
ingredients the different effects on health and vitality

216 APPLIED PHYSIOLOGY

produced by the air of different localities is to be attri-
buted; yet upon such effects the undoubted benefits of
‘change of air’ largely depend. Dalton even held the
view that chemical experiment could not distinguish the
air of Manchester from that of Helvellyn. This opinion,
though shared by other chemists, cannot any longer,
however, be regarded as accurate. Francis Jones,* for
example, found that on the same days, when the air in
the centre of Manchester contained on an average
4526 parts of CO, in 10,000, that of Alexandra Park,
three miles distant, contained 3°1186 parts, and when
the air of Manchester contained on an average 4°255
parts CO,, that of Arnside, near the Lake District, con-
tained only 8°2387. Still, such comparatively small
differences as these can scarcely explain the difference
between town and country air.

All that physiology clearly teaches on this subject,

* ‘The Air of Rooms’ (Manchester: Taylor, Garnett, Evans
and Co.), 1900. Some of the results of Dr. Jones’s experiments
may be summarized here: The air of a room always contains more
CO, than the external air, even when it is well ventilated. The
writer concludes that a certain amount of CO, is in some way
retained by the walls, and is constantly passing back into the room,

The amount of CO, is always high during fogs and in snowy
weather, and is greater in winter than in summer. The air of a
room is always purest at the floor, less pure 3 feet above, and most
impure at the ceiling.

When a coal fire is in use for heating and the electric light for
lighting an inhabited room, the air is purer than by any other
method of heating and lighting, and this is the only combination
which will keep the CO, in the air of the room below 10 paris
per 10,000.

A room heated by a gas fire contains more CO, than one heated
by a coal fire.

a ae > wed

“it oe “a

RESPIRATION 217

indeed, is that either an excess of CO, or a deficiency of
oxygen is injurious. The former acts as a narcotic
poison, but it does not begin to exert its effects until
3 per cent. is present, an amount which is never reached
even in a very ‘stuffy’ room. It is to deficiency of
oxygen that the effects of breathing a limited quantity
of air and the phenomena of asphyxia are due, but here,
again, it is not until the proportion of oxygen is reduced
to about 10 per cent. that any bad symptoms manifest
themselves. Reviewing the whole subject, even such a
careful and experienced worker in this department as
Professor Haldane is able to come to no more satisfactory
conclusion than that the headache, lassitude, etc., which
are experienced in a badly ventilated room are not due
either to want of oxygen or to the presence of an excess
of CO,, but that they are partly the result of heat and
moisture, and partly, perhaps, produced reflexly through
the olfactory nerves.*

An interesting point in connection with this bien is
that much-breathed air is more injurious to healthy,
vigorous animals than to those which are feeble and
exhausted. If, for example, a sparrow is confined in a
bell jar for a matter of two hours it will still be alive
and fairly vigorous. A second sparrow now introduced,
however, dies at once. It would thus appear as if an
animal can accommodate itself to oxygen starvation,
probably by a general lowering of its metabolism, but in
part also, perhaps, by an increased power of absorbing

* Hale White’s ‘System of Pharmacology.’ The proportion of
CO, in an inhabited room should not exceed 12 parts per 10,000
during daylight, and 20 parts per 10,000 when gaslight is used.

218 APPLIED PHYSIOLOGY

oxygen.* This may possibly be the reason why the
Kast-End Jew who is accustomed to overcrowding
from infancy appears to suffer so little in health
from it.

The limit of height at which respiration can still be
carried on is another practical question to which no
definite reply is forthcoming. We know that Whymper
on Chimborazo reached a height of 20,517 feet, and Sir
Martin Conway in the Himalayas got as high as
22,600 feet, but it is probable that even higher altitudes
than these could be reached if time were given for the
subject to become accustomed to them. It is an interest-
ing fact that the higher one goes the more easily oxygen
appears to enter the blood, perhaps because of the
greater mobility of its molecules at reduced pressures.
No doubt some of the benefits derived from residence
in the high altitude health resorts are to be thus
explained.

An impetus has recently been given to the study of
the effects of increased atmospheric pressure on the body
by the use of caissons in engineering operations, and by
the observance of cases of ‘ caisson disease.’ The result
of breathing compressed air is naturally to cause the
blood to take up a much larger proportion of dissolved
gas, especially of nitrogen. When the pressure is
relieved nitrogen is liberated in the blood-stream in the
form of bubbles which may block some of the smaller
capillaries. It is to such blockage that the symptoms
of caisson disease are now believed to be due. As two

* See Haldane and Lorrain Smith, Jowrn. of Phystol., 1897-98,
xxii. 231.

RESPIRATION 219

French writers on the subject have put it, ‘ Payment is
only made on coming out.’

The effect on the lungs of breathing compressed air
is to cause them to expand downwards, the liver and
diaphragm being depressed so as to occupy the space
obtained by the compression of the gases in the stomach
and intestine. At the same time, the circumference of ©
the chest is increased and the number of respirations
lessened. By frequent repetition of exposure to com-
pressed air these effects may become permanent.

In medicine, compressed-air baths have been used in
the treatment of emphysema. Favourable results have
been reported in many cases, results which, when one
considers the state of the lungs in emphysema, it is very
difficult to explain. One would have expected, indeed,
that their effect would have been to aggravate the con-
dition, for what is emphysema but overdistension of the
lung? In the subjects of this disease, however, the
physical effects of compressed air on the lung seem to be
exactly the reverse of those produced in health, the
diaphragm being raised instead of lowered, and the
circumference of the chest diminished, not increased.
The explanation of this apparent paradox is not forth-
coming.

2. Tissue Respiration.

In the days of Priestley (1772) it was held that
respiration and combustion were identical processes, that
compounds carried to the lungs were burnt up there by
oxygen, and carbonic acid formed from them, just as
happens in the combustion of a candle. When this

220 APPLIED PHYSIOLOGY

simple view was disproved, physiologists shifted their
ground, and declared that the combustion process took
place, not in the lungs, but in the blood. Finally, and
in comparatively recent years, the correct notion was
arrived at, as the result of indisputable experiments, that
the utilization of oxygen and the production of CO, take
place in the tissues themselves. In other words, the
tissues control their own respiration. Supply a man
with more oxygen, and you do not necessarily ‘ burn up’
his tissues one whit, though a candle under similar
circumstances will be consumed faster. The cells simply
ignore the excess of oxygen, even if it does not actually
lessen their vitality, as the experiments of Paul Bert
would seem to indicate. The acceptance of this view
has modified profoundly some of our fundamental
pathological notions. In consequence of it we no longer
believe that the high temperature of fever is the result
of an increased ‘combustion’ in the lungs, and that a
free supply of food must necessarily be injurious under
such conditions. It implies, too, that the regular
practice of ‘deep breathing,’ which is so much vaunted
by some professors of personal hygiene, is no substitute
for exercise. The latter alone can really increase the
oxidation processes in the body.

In the lymph which actually bathes the cells there is
almost no free oxygen. Indeed, its presence in even
small amount seems to exercise a depressing influence
on cell activity. Itis for this reason that, at pressures
of even 5 atmospheres of air, oxygen, instead of being
a stimulant, is actually poisonous to the tissues after
long exposures.

RESPIRATION 221

Some Special Respiratory Acts.

The mechanism of sneezing and of coughing have
already been described. Of the latter it need only be
said further, that although primarily protective in its
nature, and designed to bring about the expulsion of
irritating bodies from the upper air passages, it may
also be excited by peripheral stimuli in various parts of
the body. Thus, irritation of the gastric branches of the
vagus is said to produce a ‘ stomach’ cough, and of its
auricular branch an ‘ear’ cough. In persons who are
unduly sensitive to cold, a hard dry cough may be
excited by getting into bed between cold sheets, or when
exposed to a draught.

Curiously enough, irritation of the interior of the
trachea does not seem to excite cough. Perhaps that is
why a tracheotomy-tube can be worn so comfortably.
The bronchi appear to be less sensitive than the larynx,
but more so than the trachea. Foreign bodies in them
sometimes excite cough, sometimes not. The same is
true of the lung substance. Disease of it does not
necessarily lead to coughing. Coughing may also be
excited by irritation of the pleura; hence the cough of
pleurisy and the paroxysm of coughing which often
comes on in aspirating the chest. Even a ‘uterine’
cough has been described, although its real existence is
somewhat doubtful. When such peripheral irritations
exist, the cough which they excite is useless, and its sup-
pression by opium justifiable.

Sighing is a deep inspiration intended to make up
for a temporary depression or a cessation of breathing.

222 APPLIED PHYSIOLOGY

When the mind is much preoccupied, the breathing
becomes feeble, and this has to be compensated by a
few deep inspirations, which take the form of ‘ sighs.’
It is the result, therefore, of a spell of ‘breathless
attention.’

‘The philosopher brooding over his problem,’ says
Lewes,* ‘will be heard sighing from time to time,
almost as deeply as the maiden brooding over her forlorn
condition. All men sigh over their work when their
work deeply engages them; but they do not remark
it, because the work, and not their feelings, engages their
attention, whereas during grief it is their feelings which
occupy them.’

A similar sighing respiration has been noted as the
result of the depression of the respiratory centre from
the excessive use of tobacco.

Hiccough is the result of a spasm of the diaphragm,
which produces a sudden inspiration, the inrush of air
being as suddenly checked by closure of the glottis,
which produces the characteristic sound. It is often
the result of gastric irritation, and is a common phe-
nomenon in many conditions of disease. yy

eZ

Sobbing is another alteration of respiration, consisting
in an inco-ordination in the different parts of the pro-
cess. It consists in sudden inspirations, in which the
glottis opens a little too late, the inrush of air producing
the familiar sound. It is comparable to the crowing
sound produced in laryngismus stridulus.

* ‘The Physiology of Common Life,’ i. 899.

Se ee

RESPIRATION 223

Yawning consists of a slow deep inspiration per-
formed with the mouth widely open, and succeeded by
a slow expiration accomplished with a gaping mouth
and contracted glottis, which produces the well-known
sound. It is apparently the result of a fatigue of atten-
tion, and therefore appears most readily when the brain
is easily exhausted, as in the subjects of anemia. The
stretching of the limbs which accompanies it is believed
to be an attempt to overcome the stasis of blood in the
muscles, and to drive it to the brain.

Laughing and crying are, like sobbing, results of
disordered action of the respiratory centre brought about
by emotional influences.

The peculiar rhythmical form of breathing which goes
by the name of Cheyne-Stokes respiration is probably
due to periodic variation in the automatism of the
respiratory centre. This periodic variation shows itself
when the influence of higher regulating centres is
removed, as may happen, for example, in uremic
poisoning, and perhaps also simply as a result of a
lowering of the activity of the respiratory centre itself.
When the sensitiveness of the respiratory centre is
lowered, it does not respond to the stimulus normally
given by an excess of carbonic acid in the blood until
this has reached an unusual degree. A series of deep
inspirations is then initiated, which result in very
perfect ventilation of the lungs, and the carbonic acid
is so thoroughly removed that a period of apnea sets
in until enough of it has accumulated to stimulate the
centre once again. That this explanation is correct
seems to be proved by the fact that Pembrey has been

224, APPLIED PHYSIOLOGY

able to abolish the apnoeic period by causing a patient
exhibiting Cheyne-Stokes respiration to inhale carbonic
acid.

Rhythmical respiration is often accompanied by similar
periodic variations in the control exercised over the blood-
vessels by the general vasomotor centre and over the
pupil by the pupil centre, and even by rhythmical
increase and diminution of the activity of the brain
cortex as manifested in consciousness.

It is noteworthy that in sleep, when the higher centres
are presumably less active, the respirations readily take
on a rhythmical character, particularly in childhood,
when the control of the lower centres is presumably not
well developed.

See

CHAPTER VII
THE APPLIED PHYSIOLOGY OF DIGESTION

Digestion in the Mouth.

Tue object of digestion in the mouth is to convert the
food into a mechanical form in which it can be easily
swallowed. By means of the teeth the solid part of the
food is broken up and reduced to a state of fine division,
in which form it is easily attacked by the gastric juice.
It can therefore be readily understood how imperfect
chewing, brought about either by bolting the food or by
a defective dental apparatus, impedes gastric digestion,
and by allowing the entrance of lumps of food into the
stomach which irritate its walls is a frequent cause of
gastritis.

By means of the saliva dry food is moistened, and the
bolus which results from chewing is lubricated with
mucus and rendered fit for swallowing. That the mere
moistening of the food is one of the chief objects of
salivary secretion is shown by the experiments of
Pawlow, which have demonstrated that a much larger
secretion of saliva is called out by the introduction into
the mouth of dry substances than by those that are

moist.
225 15

226 APPLIED PHYSIOLOGY |

The ingredients of mixed humah saliva are water,
mucin, ptyalin, a trace of globulin, and certain salts, of
which the chief are sodium chloride, sodium phosphate
(NazHPO,), along with earthy carbonates and phos-
phates, and a trace of sulphocyanide of potassium.
Its alkalinity is due to sodium phosphate, but there
is not a trace of sodium carbonate present.* The
production of gastric flatulence can therefore hardly
be due, as has been suggested by some, to the
liberation of CO, from a highly alkaline saliva by
the gastric juice. The alkalinity is greatest before
breakfast. Salivary calculi result from the separation
out of the lime-salts in the gland ducts. The meaning
of the presence of sulphocyanide of potassium—of all
salts !—in the saliva has given rise to much speculation,
and attempts have been made—without much success—
to show that variations in its amount are of diagnostic
value in disease. It has also been suggested that it
may play the part of an antiseptic, but this is apparently
not the case,+ and we are still really quite in the dark as
to its significance.

The ptyalin of the saliva plays a considerable part
in the conversion of the starch of the food into ) dextrins,
but its powers in this direction are chiefly exerted in the
stomach, where it remains active for a much longer time
than used to be supposed. It is most active in a neutral
medium, any degree of acidity being specially inimical to

* See Chittenden and Richards, Amer. Journ. of Physiol., 1898,
i. 461.

+ See Nicolas and Dubief, Jowrn. de Phys. et Pathol. Gen.
1899, i. 979.

:
{
;

DIGESTION Q27

it. Hence the taking of acid fluids—e.g., wines—along
with starchy food is apt to interfere with the digestion of
the latter, although to some extent this is counteracted by
the more profuse flow of saliva which acids call out.
Tannin is also a powerful inhibitor of ptyalin, which
explains part, at least, of the unfavourable effect of
strong tea upon digestion. It is interesting to note that
the activity of the ptyalin of the saliva is diminished in
most cases of dyspepsia, and in dilatation of the stomach
it may be entirely absent. On the other hand, in cases
of diabetes it is unusually powerful.*

The secretion of saliva is called out reflexly through
the medium of cranial and sympathetic fibres, which are
the nerves of secretion. Not all stimuli are capable of
exciting secretion—in other words, it needs a ‘ specific’
stimulus to do so, but the range of these is very wide.
Psychical impressions—such as the mere sight or smell
of food—are powerful stimuli, and may literally ‘make
the mouth water.’ Very dry substances, again, as has
already been pointed out, call out a profuse secretion,
in order to moisten them and wash them out of the
mouth. Acid and acrid substances, too, which, if not
neutralized or diluted, would be injurious to the mouth
and stomach, strongly excite the glands. In the action
of all of these the essentially purposive nature of the
salivary reflex is clearly shown forth. Of the two sets
of secretory nerves, the cranial fibres produce a more
watery flow, and the sympathetic one which is richer
in mucin. The latter comes specially into play under

* ‘The Activity of the Saliva in Diseased Conditions of the
Body,’ Aitchison Robertson, Jowrn. of Pathol., 1900, vii. 118.

15—2

228 APPLIED PHYSIOLOGY

the influence of emotion, with the result that the saliva
then becomes sticky, and the tongue may ‘ cleave to the
roof of the mouth.’ On the other hand, if the chorda
tympani be paralyzed, as itis in some cases of facial nerve
palsy, the saliva is more scanty. Division of the secretory
nerves leads after a time to the appearance of a steady
flow of saliva, spoken of by physiologists as a ‘ paralytic
secretion,’ which may last for some days. It has been
suggested that the ptyalism met with in cases of bulbar
paralysis is of this nature, but against such an explana-
tion is its long persistence.

The secretory nerves of the salivary glands are sus-
ceptible to the influence of certain drugs. Atropine, for
instance, paralyzes the terminals of the cranial fibres,
and diminishes the flow; whilst pilocarpine, by stimu-
lating them, exerts an opposite effect. Hence dryness
of the mouth is one of the unpleasant consequences
of the exhibition of atropine, whilst pilocarpine is used -
as a remedy in cases of diminished salivary secretion
(xerostomia).

The salivary glands also possess a degree of excretory
power for some substances. We know that certain
drugs, for instance, are so excreted. Chlorate of potash
is a case in point: when swallowed in solution it is
partly excreted by the saliva, and may thus exert a —
local effect upon the mouth. It is useful in this way in
cases of stomatitis. Again, ‘a bad taste in the mouth’
is probably due, in some cases at least, to the excretion
of abnormal substances by the salivary glands.

DIGESTION 229

Deg lutition.

The bolus which is formed by mastication and in-
salivation is pushed by the tongue to the back of the throat.
The cavity of the mouth is then closed by the approxi-
mation of the dorsum of the tongue to the palate by
the palato-glossal muscles, whilst the nose is shut off

- by the elevation of the soft palate by the levator palati

and palato-pharyngeal muscles. This stage of deglutition
may be interfered with by paralysis of the tongue—e.g.,
in bulbar paralysis—or of the soft palate, when fluids
tend to regurgitate into the nose—e.g., in post-diph-
theritic paralysis. Food is prevented from entering the
larynx during deglutition by the larynx being drawn up
towards the base of the tongue, and by its posterior wall
being pulled forwards away from the back of the pharynx.
The bolus of food therefore glides over the posterior wall
of the epiglottis, which explains how it is that destruc-
tion of the epiglottis by disease has no effect on degluti-
tion—a fact which was inexplicable on the old theory
that the epiglottis shut down on the top of the larynx
like a lid. Normally, respiration is reflexly inhibited
whilst the food is passing over the top of the larynx, but
if a breath be involuntarily taken during the process, food
enters the larynx, and coughing and ‘choking’ result.
In the case of fluids, the contraction of the pharyngeal
muscles is sufficient to force them rapidly through the
cesophagus until the cardiac orifice is reached, after
which their progress becomes much slower, and they
merely trickle into the stomach (Fig. 15). Hence, when
corrosive liquids are swallowed, it is found that the

230 APPLIED PHYSIOLOGY

cesophagus may escape injury except at the cardiac
orifice, which is much longer in contact with them.

The process of deglutition in the case of well-chewed
and thoroughly insalivated solids is very much the same
as that of fluids, but if lumps of dry food are swallowed,
they traverse the cesophagus very slowly, and may,

rh 5” a 4
Fie, 15.—To sHow Position oF SHADOW aT INTERVALS OF ONE

SECOND DURING THE SWALLOWING oF A Moururun or Minx
CONTAINING BismuTH CARBONATE. (HERTZ.)

indeed, stick there for some minutes. It has been
suggested (Hertz) that the feeling of pressure in the
chest experienced after a hurried meal may be due to
distension of the cesophagus caused by the presence of
solid lumps of food, which only pass very slowly down-
wards.

a ed

4)
‘
i] i
e
i
=
:
4
~.

f

°

DIGESTION 231

The swallowing reflex is started by the contact of
food with the back of the tongue, the superior laryn-
geal being the afferent and. the recurrent laryngeal the
efferent nerve concerned. Loss of the swallowing reflex
always indicates a bilateral lesion, as destruction of
either both superior or both inferior laryngeals is neces-
sary to bring it about. The unstriped muscle of the
lower part of the esophagus is to a large extent auto-
matic in its action, and independent of the nervous
system. Thanks to this it is still possible to introduce
food into the stomach even when voluntary swallowing
is impossible and the deglutition reflex abolished; for
if a tube be passed into the upper thoracic region of the
cesophagus, any food introduced through it will be passed
on by the unstriped muscle. Advantage is taken of this
in ‘nasal’ feeding. If the vagus nerves be divided, a
condition of paralytic dilatation of the esophagus ensues,
and it is probable that this may also occur as the result
of disease affecting the nerves. ‘That a reverse peri-
stalsis in the cesophagus is possible seems to be proved
by the occurrence of rumination in some subjects.

Digestion in the Stomach.

Experiments on animals, as well as the results of
gastrectomy on patients, have shown that the stomach
is not actually essential to life. On the other hand,
there can be no doubt that it is not really a superfluous.
organ, but is of great use in so preparing the food as to.
protect the intestine from possible injury. |

The uses of the stomach are apparently these: (1) To

232 APPLIED PHYSIOLOGY

act as a reservoir, from which the intestine may be
eradually supplied; (2) to sterilize the food to some
extent; (8) to regulate its temperature; (4) to help to

reduce the food to a fluid form; (5) to aid in the stimu-

lation of pancreatic secretion.
These may now be briefly considered.

1. By acting as a reservoir the stomach enables us
to take food in considerable quantities at a time—.e., it
renders meals possible. The practical convenience of
this does not need to be pointed out. The capacity of
the stomach varies considerably in different individuals
and in the same individual at different periods of life.
Roughly it may be put down in the case of liquids at
2 to 4 pints, and in the case of solids at about 2 pounds.
If it be remembered that the total amount of solid food
required daily amounts to about 3 pounds, it will be
evident that it is hardly possible to take all our food

at one meal without seriously overburdening the

stomach. Again, were it not for the reservoir action
of the stomach, there would tend to be a waste of food
by putrefaction, owing to the intestine being supplied
with it more rapidly than it could be digested and
absorbed. a

2. Another function which the stomach fulfils is that
of partially sterilizing the food by the antiseptic action
of the hydrochloric acid of the gastric juice. This
action, however, is not a powerful one, and some organ-
isms, such as those that form acids, seem to escape it
altogether, and there is reason to believe that the same
is true of some, at least, of the commoner pathogenic

DIGESTION 233

organisms, notably the tubercle bacillus. Hence the
possibility of acquiring tuberculosis by drinking milk.
The sterilizing power of the stomach varies greatly,
according to the stage of digestion and the nature of the
food. It reaches its maximum towards the end of diges-
tion, when hydrochloric acid is present in the free state,
whilst it is much less, or even in abeyance altogether, in
the earlier stages, when only combined acid is present.
Foods rich in protein, by combining with much of the
acid, lessen the germicidal power of the gastric juice.
Over the growth of organisms in the intestine the
stomach seems to exert but little control. Even when
the secretion of gastric juice is entirely arrested, or the
stomach is excised, no increase in the amount of intestinal
putrefaction occurs.* Increased decomposition in the
bowel can therefore hardly be regarded as the cause of
the diarrhoea which is apt to occur in cases of achylia.

8. The regulation of the temperature of the food
is one of the minor, but none the less important, functions
of the stomach. In this respect it acts as a protector of
the intestine, which appears to be more sensitive to
extremes of temperature than the stomach itself. As
ordinarily taken, the temperature of food may be con-
sidered to vary between 5° C. and 50 to 60° C. It
requires only about ten minutes for a pint of liquid at
50° C. (122° F.) to be brought down to the body tempera-
ture after it has been swallowed, but considerably longer
for a similar quantity at 5° C. (41° F.) to be raised to the

* Schlatter, Lancet, 1898, i. 146, and Filippi, Deutsch. Med.
Woch., 1894, XX., No. 40,

234 APPLIED PHYSIOLOGY

same point.* Hence cold fluids are more apt to escape ~
over into the intestine imperfectly warmed, and may thus —
excite diarrhea. The best temperature for food is that
of the body, for it then stays the shortest time in the
stomach. This should be remembered in cases such as
those of atonic dyspepsia, in which it is important that
the food—and especially its fluid constituents—should be
passed on out of the stomach as quickly as possible.

4. By reducing the protein constituents of the food
to a soluble form, the stomach helps to prepare them —
for more complete digestion in the intestine. In study-
ing this process one has to do with the three physio-
logical properties of the stomach: (a) sensibility, (6)
secretion, (c) motility; and for the sake of clearness it
will be well to take these up separately, especially as the
disorders of gastric digestion can be traced in every
instance to a disturbance of one or more of these
functions.

Sensibility.

Normally the stomach does not appear to be sensitivein
the ordinary sense, or, at all events, any sensations which —
proceed from it fail to reach the seat of conscio a
It would appear, however, that the degree of anesthesia —

_ of the stomach varies in different persons, for some, at
least, are able to discriminate between hot and cold
liquids when introduced by the stomach tube.t It is .

noteworthy that in such cases the sensation is referred, _

* See Mueller, Zeit. f. Didt. und Phys. Therapie, 1905, Ba. viii.
Heft 11.

+ Neumann, Archi f. Verdawwngskrankh., 1907, xiii. 81.

DIGESTION 235

not to the stomach itself, but to the skin of the epi-
gastrium, just as pain is in cases of gastric hyperesthesia
and gastralgia. There can be little doubt, too, that in
everyone centripetal impulses reach the lower centres
from the stomach, which are concerned in producing the
‘sensation ’ which we call appetite, and it is possible that
anorexia is due to a subnormal state of gastric sensibility.
On the other hand, it is also possible that in certain
states of the nervous system the centripetal impulses
from the stomach actually penetrate as far as the seat of
consciousness, and are ‘felt’ as pain, or, at least, as
vague discomfort. It would appear, too, that pain can
be produced even in an otherwise normal stomach by
any excessive or irregular contraction of its muscular
coat, just as it may be so produced in any other hollow
viscus, and many cases of dyspeptic pain are probably
thus brought about. Again, traction on the cardiac or
pyloric ends of the stomach affects the nerves of the
subserous connective tissue, and is extremely painful.
It is probably to this that the pain which may result
from the presence of gastric adhesions owes its origin.

Secretion.

The secretion of gastric juice is not the result of
mechanical stimulation of the mucous membrane of the
stomach by the contact of food, as was once supposed,
but of the action of nervous impulses reaching the
stomach through the vagus. Mechanical stimulation is

_merely followed by a flow of alkaline mucus, which is
designed to protect the delicate lining membrane, and

236 APPLIED PHYSIOLOGY

it is in consequence of such direct stimulation that irri-
tating and unsuitable foods may set up gastric catarrh.

The stimuli which can excite a flow of juice are either
(1) psychical or (2) chemical. The mere sight or smell
of food, or the agreeable taste of it in the mouth, given
the presence of appetite, is sufficient to start an active
flow of juice whilst the stomach is still empty. It is not
the mere mechanical act of chewing, but the relish of
the food which originates the reflex. Hornborg,* for
instance, has observed in the case of a boy with a gastric
fistula and occlusion of the cesophagus that the chewing
of indifferent substances, such as indiarubber, failed to
cause gastric secretion.

The juice thus poured out—to which Pawlow has
given the name of ‘ appetite juice ’—is of great value
in starting the process of digestion, and it has been
suggested that the favourable results in some cases of
dyspepsia of giving frequent small meals rather than
a larger quantity of food at longer intervals are to be
attributed to the greater quantity of ‘appetite juice’ which
is thus obtained. Be this as it may, the realization of
the value of the ‘ appetite juice’ is of the first importance
to the physician, and should encourage him _ to make
every effort to promote the appetite of patients with
feeble digestion by attention to the esthetic qualities
and flavour of their food, as well as by the administration
of exciters of appetite such as bitters.

* Skandinaw. Archw f. Physiol., 1904, xv. 248,

t Seeing that bitters promote a flow of gastric juice by acting
upon the nerves of taste, they should always be administered in
solution if their full effect is to be obtained, and not swallowed
in the form of a tabloid, capsule, or pill.

DIGESTION 237

‘It appears to me,’ says Pawlow,* ‘that... instinct
has often made out a brilliant case when brought before
the tribunal of physiology. Perhaps the old and
empirical requirement that food should be eaten with
interest and enjoyment is the most imperatively empha-
sized and strengthened of all. In every land the act of
eating is connected with certain customs designed to
distract from the business of daily life. A suitable time
of day is chosen ; a company of relatives, acquaintances,
or comrades assemble. Certain preparations are carried
out (in England a change of raiment is usually effected,
and often a blessing is asked upon the meal by the oldest
of the family). In the case of the well-to-do a special
room for meals is set apart; musical and other guests
are invited to while away the time at meals—in a word,
everything is directed to take away the thoughts from
the cares of daily life, and to concentrate them on the
repast. From this point of view, it is also plain why
heated discussions and serious readings are held to be
unsuitable during meal-times.’

The above quotation shows the importance attached
to the ‘appetite juice’ by the distinguished Russian
physiologist even in a state of health, and in abnormal
conditions it is of still greater importance to bear it in
mind. In cases, for instance, in which it is necessary to
introduce food directly into the stomach through an
cesophageal tube or a gastrostomy wound, care should
be taken, whenever possible, to call out a flow of ‘ appetite

* «The Work of the Digestive Glands,’ English translation, 1902,
p. 133 (Griffin and Co., Limited).

238 APPLIED PHYSIOLOGY

juice’ by introducing substances into the mouth before
the meal is given.

In this connection it is of interest to ask, What is
appetite, and can the physiologist give any explanation
of it? The reply is that the nature of the state of
feeling we call ‘appetite’ is still very obscure. One
thing is certain—namely, that it is not the same as
hunger. Hunger is the cry of the tissues for food, or, as
it has been put, ‘the expression of the caloric require-
ments of the tissues,’ and may be experienced even when
the stomach is quite full, as happens, for example, in the
case of a patient who has a fistula high up in the
intestine.

Appetite, on the other hand, is apparently more
dependent on sensations derived from the stomach itself,
and may be quite absent in cases of gastric disorder, even
although the patient be in a state of hunger. It has
been suggested, as already pointed out, that the sensa-
tions from the stomach on which appetite depends are
of a subconscious nature, and that a depression of them
may give rise to abolition of appetite (anorexia), whilst —
their exaltation may produce an excessive desire for food
(bulimia). SY.

How long the flow of ‘appetite juice’ lasts in normal
feeding it is impossible to say, but very soon the second
or chemical method of excitation comes into play. This
is brought about by the action of certain chemical con-
stituents of the food on the nerves of the stomach. Not
all nutritive substances are able to excite the gastric
nerves. The most powerful are the extractives of flesh,
dextrins, milk, and water.

DIGESTION 239

A consideration of these facts shows that the long-
established custom of beginning dinner with soup is
justified, and should also be a guide to us in selecting
suitable foods for administration by forced feeding.

On the other hand, some foods, such as bread, starch,
and white of egg, do not excite a flow of juice at all,
whilst fat tends actively to restrain the secretory activity.
The former foods are therefore indicated where one
wishes to excite gastric secretion as little as possible,
whilst the administration of fatty substances is justified
in cases in which secretion is already excessive. Some
_ drugs, such as bicarbonate of soda and bismuth, appear
also to have the power of inhibiting the secretion.

The proof which physiology has now furnished that
gastric secretion is entirely dependent upon nervous in-
fluences, and is not the result of mechanical stimulation
by the food, is of great interest to practical medicine,
for it makes it easier to understand the large part which
disturbances of the nervous system play in the pro-
duction of functional dyspepsia.

The gastric juice, then, which is required for the
digestion of an ordinary meal is the result of the com-
bined action of these two sorts of stimulus, and the flow
of it begins even before food has actually entered the
stomach, and continues actively during the first hour or
so of digestion, and then undergoes a gradual decline.
The composition of the juice appears to be fairly con-
stant in the same individual, but varies in different
persons, even although the food be the same. In other
words, when more hydrochloric acid is required it is
obtained by increasing the total quantity of juice

ED
Se

\

240 APPLIED PHYSIOLOGY

secreted, and not by the outpouring of a more acid
juice. The time at which free HCl appears varies with
the composition of the food; the richer the latter is in
protein, the longer is the appearance of uncombined acid
delayed, for protein has a high acid-binding power. It
is for this reason that foods rich in protein are recom-
mended in cases in which the production of HCl
tends to be excessive. If free HCl appears early it
disappears soon, and the later it appears the longer it
lasts, but the average duration of its presence is probably
about one and a quarter to one and a half hours. It is
of interest clinically to know that after an ordinary
Ewald’s test-breakfast, free HCl is always quite evident
in an hour (Penzoldt). The stomach is always and at
all times acid to litmus, although at the beginning and
end of digestion the reaction is very feeble.

The total acidity of the stomach contents an hour
after a test-breakfast (Hwald’s) varies from 0°11 to 0°26
per cent. in different individuals, and the proportion of
free HCl from 0°07 to 02 per cent. These differences
are apparently due to individual peculiarities. The pro-
duction of acid seems to be greater in young and healthy
subjects than it is in the old, and in 40 per cent. of
persons above the age of fifty free HCl is absent
altogether (Seidelin),* a fact which should be borne
in mind a propos of the diagnostic value of the absence
of free HCl in cases of carcinoma.

It will be obvious from the above description that
abnormalities of gastric secretion may arise in several
ways: (1) The total amount of juice produced may be

* Abst. in Archiv f. Verdawungskrankh., 1904, x. 426.

DIGESTION 241

too great (hypersecretion); (2) the total amount of
juice may be normal, but the percentage of HCl which
it contains too high (hyperchlorhydria); (8) there may
be errors in the time-rate of the secretion—e.g., it
may be poured out too fast if the glands are irritable or
overexcited, or it may be produced too slowly.

The experiments of Pawlow appear to show that in
the dog, at least, there is a certain adaptation of the
composition and strength of the gastric juice to the kind
of food which has to be digested. For example, for
bread-protein five times more pepsin is poured out than
for protein in milk, and for flesh-protein 25 per cent.
mors than on that of milk. It is doubtful, however,
whether such variations occur in man,* although pos-
sibly if one particular kind of food is taken for a
long time such an adaptation may be arrived at, and a
‘ digestive habit’ for that form of diet established.

Motility.

1. Tonicity.—In the empty stomach there is normally
a slight degree of tension present which keeps up a
pressure within it, which has been estimated in man as
equal to a manometric pressure of about 4 to 5 centi-
metres of water.f This is due in part to a slight tonic
contraction of the muscular coat, and in part also,
perhaps, to the contractile pressure exerted by the

* See Penzoldt, Dewts. Archi f. Klin. Med., 1894, liii. 209,
and Schiile, Zeit. f. Klin. Med., 1895, xxviii. 461, and 1896,
xxix. 49.

t+ See Dobrovici, Archiv f. Verdawungskrankh., 1907, xiii. 78;
also Moritz, Zeit. f. Biologie, 1895, xxxii. 313.

16

242 APPLIED PHYSIOLOGY

elastic tissue in the wall of the stomach, which forms
two layers—one in the muscularis mucose, and the
other and more definite layer between the submucous and
muscular coats. In chief measure, however, the tension
within the empty stomach is not the result of such
factors as these, but is due simply to pressure exerted
upon the stomach from without by the abdominal wall
and by other viscera, especially the liver. Thus, the
intragastric pressure is lowest when the individual is
lying upon the right side, when the weight of the liver
is taken off the stomach ; and it is worth noting that this
is the position which it is best to adopt if vomiting be
urgent, as in sea-sickness. It is of interest, too, to
observe that, contrary to expectation, the intragastric
tension is not increased in pregnancy, a fact which has
important bearings upon some of the theories which
have been advanced to explain the occurrence of vomit-
ing in that condition.

After food enters the stomach the intragastric tension
in the fundus rises to a pressure of 10 to 12 centimetres
of water, and if enough food be taken to raise the
pressure to 20 centimetres, the feeling of distension
becomes painful. This, however, is nothing compared
with the pressure which may be exerted upon the
stomach by pressure from without, for it has been found
that forced expiratory efforts with the diaphragm fixed
and depressed may raise the pressure within the stomach
to that of 830 centimetres of water, and such is the
‘squeeze’ brought to bear upon the organ in the act of
vomiting.

The rise in intragastric tension after the taking of

DIGESTION 243

food is probably due to a slight active contraction of the
wall, which is reflexly brought about and is designed to
resist the mechanical pressure of the contents. Failure
of this reflex contraction has been alleged to play a large
part in the development of ‘atonic dilatation’ of the
stomach, by allowing the fluid pressure of its contents
to exert its distending effect unopposed.*

hincter ardri pylorici

Transverse Band or

§

Fie. 16.—FuncTIonaL Divisions oF THE STOMACH.

2. Active Movements.—F rom the point of view of its
active motility, the stomach may be divided into two
distinct parts—(1) the fundus, (2) the antrum (Fig. 16).
‘These are separated from each other by a muscular con-
striction—the transverse band—situated a little to the
left. of the pyloric orifice, and no mixing of the contents

* See a paper by Agéron, Archiv. f. Verdawwngskrankh., 1905,
xi. 460.

16—2

24.4. APPLIED PHYSIOLOGY

of the two parts occurs. The fundus serves the function
of a reservoir, in which the food is gradually mixed with
the gastric juice and slowly squeezed on into the pyloric
end. It is not the seat of any very active churning
movements, and as each bolus of food is swallowed it
is received into the centre of the accumulated mass,
where the gastric juice only slowly reaches it, thus
affording the saliva time to act.

‘These observations show that the order in which the
chief courses of a dinner are arranged is physiologically
suitable, as the part containing most carbohydrate comes
last, and so remains for a time in the fundus, where
salivary digestion can continue, whilst the part rich in
proteids passes quickly to the pyloric end of the stomach,
where peptic digestion begins early and salivary digestion
soon becomes impossible. The great importance of
thorough mastication and the consequent efficient im-
pregnation of the food with saliva is at once explained
by these facts. When a farinaceous meal is bolted, only
a very superficial layer ~ef the masses of food can be
digested by the saliva. The carbohydrate is then very
liable to undergo bacterial fermentation with the pro-
duction of flatulence and all its unpleasant results. This
is prevented when salivary digestion can occur, as dextrin, _
the first product of the digestion of starch, is less easily
decomposed by bacteria than starch, and maltose and
dextrose, the final products of salivary digestion, are —
soluble and readily diffuse into the pyloric end of the —
stomach, where the presence of hydrochloric acid prevents .
the occurrence of bacterial decomposition’ (Hertz).

The movements of the pyloric end of the stomach are

DIGESTION — 245

much more forcible and active than those of the fundus.
It is here that the food is mixed with the gastric juice,
rubbed down to a more or less fluid consistency, and
gradually expelled into the duodenum. The mechanism
by which this takes place is as follows (Cannon): Whilst
food is present in the stomach constriction waves are
seen continually coursing over the antrum towards the
pylorus. The fundus meanwhile serves as an active
reservoir for the food, and squeezes out its contents
gradually into the pyloric portion. The stomach is
emptied by the formation, between the fundus and
antrum, of a tube (‘pre-antral’ or ‘middle’ portion, in
Fig. 16), along which constrictions pass* at regular
intervals of fifteen to twenty seconds. The contents of
the fundus are pressed into the tube, and the tube and
antrum slowly cleared of food by the waves of con-
striction. The food in the pyloric portion is first pushed
forwards by the running wave, and then by pressure of
the stomach wall is returned backwards through the ring
of constriction, being thus thoroughly mixed with gastric
juice. Finally, when the solid food has been thoroughly
triturated by the constrictions, the pylorus opens and
allows the contents of the antrum to escape.

It will be readily understood from this description that
the stomach is much more likely to be affected by
mechanical injuries at its pyloric end than at the fundus,
- and it is perhaps for this reason that this portion is most
often the seat of an ulcer. Seeing, too, that the pressure
is highest at this end of the organ, it is important in

* The waves of constriction can be seen very well, in cases of
congenital pyloric stenosis, coursing from left to right.

246 APPLIED PHYSIOLOGY

performing gastro-enterostomy that the opening should
be made as near the natural pylorus as possible, so that
the expulsive effect which results from the ‘systolic’
contraction of this part of the organ may be taken
advantage of.

The movements of the stomach are apparently
myogenic in origin, or, at least, dependent upon a
purely local nerve mechanism, for they continue even
when all its nerves are divided, but there is no doubt
that the vagus can exert both a stimulating and an in-
hibitory influence upon them.* On the other hand, the
sympathetic appears to be incapable of exerting any
effect in either direction. It has been found experi-
mentally that emotional states—such as rage, fear, or
distress—inhibit the movements of the stomach, and
in accordance with this is the well-recognized influence
of such states in the production and maintenance of
dyspepsia. It is stated by Moritz} that the movements
of the stomach are not affected by electrical stimulation.
On the other hand, it has been shown that they are con-
siderably strengthened by massage. If these observa-
tions are correct, they have important bearings: on the

therapeutics of ‘atonic’ dyspepsia. ee:

What is the stimulus to the movements of the
stomach? To this question physiology is not able to —

furnish a clear reply. The presence of free HCl seems

to increase the activity of the movements; but that it is
not their sole cause is shown by the fact that they may

* See Page May, Brit. Med. Jowrn., 1902, ii. 779.
+ Zeit. f. Biologie, 1895, xxxii. 313.

DIGESTION 247

take place quite efficiently when no gastric juice is
secreted at all, as in cases of achylia. Probably the
mere presence of food is in itself an exciter of the
movements. There is equal doubt as to the agent
which unlocks the pylorus and allows the food to escape
into the intestine. According to some, free HCl is also
the active agent in this process. This, however, is un-
likely for several reasons. In the first place, as has just
been pointed out, the discharge of the stomach contents
into the intestine may take place quite quickly when no
free HCl is present at all. In the second place, observa-
tions on patients with gastric fistule show that free HCl
tends to inhibit the opening of the pylorus rather than
to favour it,* and there is some clinical evidence for the
belief that the presence of an excess of acid may cause
pyloric spasm. In the third place, there is no doubt
that the presence of acid in the duodenum prevents the
pylorus from opening until it has been neutralized. It
would be very unlikely, surely, that the presence of acid
on one side of the pylorus should open it, and on the
other should cause it to close. On the whole it seems
more probable that the pylorus opens when the waves of
contraction in the stomach become strong enough, pro-
vided it be not reflexly inhibited by distension of the
duodenum or the presence in the latter of an acid
reaction or of fat. Warmth, internal or external, and
the presence of alkalies in the stomach seem to unlock
the pylorus; hence, probably, the usefulness of poultices,
hot liquids, and alkalies in relieving gastric pain. On

* See v. Pfungen, Centralb. f. Physiol., 1887-88, i. 220,
277.

ie

248 APPLIED PHYSIOLOGY

the other hand, the presence of insoluble lumps of food
in the stomach seems to excite a powerful contraction of
the pylorus, which expresses itself as ‘stomach - ache.’
The result is that such undissolved lumps are retained
in the stomach for more prolonged digestion and attrition.
The presence of an ulcer or fissure in the near neighbour-
hood of the pylorus would seem to be capable of inhibit-

ing the relaxation of the latter, which normally occurs

when peristaltic waves reach it. In this way the outlet
may be blocked and dilatation of the stomach result.

The rate at which different substances leave the
stomach seems to depend upon many different circum-
stances, chief of which is the mechanical form and con-
- sistence of the substance in question. Fluids begin to
pass out of the stomach almost at once, warm fluids
sooner than cold. ‘Slops’ begin to pass out almost as
soon, and even solids may begin to be discharged in less
than half an hour. These observations show the im-
portance of attending to the mechanical form of the food
in cases in which the stomach has difficulty in emptying
itself.

The chemical composition of the food, however, is not
without influence upon the rate of its discharge. _ Some
observations by Cannon* are of interest in this con-
nection. As the result of experiments in the Harvard
Physiological Laboratory, he states that ‘it was proved
that when carbohydrates, proteins, and fats of the same
consistency are fed separately and in equal amounts, they
do not leave the stomach at the same rate. Fats remain
long in the stomach. Their discharge into the small

* Amer. Journ. of Med. Sciences, 1906, cxxxi. 563.

sibs

ea ee
Te ia

4 — as
a Lh

DIGESTION 249

intestine begins slowly, and continues at about the same
rate as their absorption or their passage onward into the
large intestine. Carbohydrates begin to leave the
stomach soon after their ingestion (within ten minutes).
They pass out with rapidity, and at the end of two hours
reach a maximum amount in the small intestine, almost
twice the maximum for proteins, and two and a half
times the maximum for fats, both of which maxima are
reached only at the end of four hours. Proteins
frequently do not leave the stomach at all during the
first half-hour, and, occasionally, not for an hour. The
initial departure of proteins from the stomach, therefore,
is much later than that of carbohydrates, and the rate of
discharge slower than that of either carbohydrates or
fats. ‘The pylorus evidently permits the carbohydrates
not digested by the gastric juice to pass quickly into the
intestine, where they are digested, and retains the
proteins, digested in the stomach, there to undergo
digestion. When proteins are fed first, and carbo-
hydrates later, the proteins occupy the pyloric end of
the stomach, and the carbohydrates lie mainly in the
cardiac end. Under these circumstances the presence of
the proteins near the pylorus causes a characteristic
slow discharge, which thereby checks the carbohydrate
departure. If, on the other hand, the carbohydrate is
fed first, it passes on at once to the small intestine for
further digestion and absorption, and the protein remains
to undergo the changes produced by the stomach. It
would seem from these experiments that the American
breakfast, in which the cereal precedes the meat, has a
rational and physiologically economic arrangement; and

250 APPLIED PHYSIOLOGY

the ancient English custom of eating the pudding before 7
the meat is likewise more defensible than the modern

order of the dinner menu.’

The cardiac orifice is normally in a state of tonic con-
traction,* which is aided by the fibres of the diaphragm,
which embrace the end of the cesophagus, as well as by
the oblique entry of the latter into the stomach. Division
of the vagus causes relaxation of this tonic contraction.
It is possible that such a diminution of vagus control
during life may play a part in the regurgitation of food
or the escape of gases into the cesophagus, which is the
cause of some forms of flatulence.

The cardiac orifice, like the pyloric, is controlled by a
special nerve centre situated in the medulla. Stimulation
of this centre causes contraction of the longitudinal fibres
which pass from the lower end of the cesophagus and
spread out over the stomach. A horse is unable to vomit
because the longitudinal fibres of its cesophagus wind
round spirally in the neighbourhood of the cardia
instead of running straight on to the stomach, as in
most mammals.

/ /
Ae
/
4

Absorption from the Stomach. ~~

The absorptive power of the stomach is surprisingly
small, and in this fact one may see a provision for the
protection of the body, for it allows of the neutralization
or rejection of injurious substances before they have
time to enter the blood. Alcohol is of all substances

* Sinnhuber, abst. in Archiv. f. Verdawungskrankh., 1904,
x. 93.

itmkcrge eg rtele

DIGESTION 251

that which the stomach absorbs most readily, which
explains to some extent the rapidity with which it exerts
its effects. Peptone, sugar, and salts are also absorbed
to some degree. On the other hand, water, curiously
enough, is scarcely absorbed at all. Hence, in pyloric
stenosis the tissues may suffer from water starvation
unless water be administered by other routes—e.g., the
rectum.

There is reason to believe that the process of absorp-
tion by the stomach partakes much more of the nature
of a mere physical osmosis than is the case in the
intestine, and it is accompanied by the pouring out of a
good deal of secretion. It is in this way, perhaps, that
a mixture of alcohol and sugar, such as is found in
sweet wines and malt liquors, may cause ‘ acidity.’

The Gases of the Stomach.

The stomach usually contains a small amount of
gas, which consists of a mixture of nitrogen and CO,,
the latter being present in the same proportion as
oxygen in atmospheric air, whilst the nitrogen is present
in the same proportion as it is in air. It is believed that
the nitrogen is derived from swallowed air, the oxygen
of which has been absorbed by the bloodvessels of the
gastric mucous membrane, whilst the nitrogen escapes
absorption because the blood is saturated with it already.
The CO, is probably transfused from the blood. Evans*
has brought forward evidence, derived from a study of
the gas contained in the swim-bladder of fish, in favour

% Brit. Med. Jowrn., 1897, i. 649.

252 APPLIED PHYSIOLOGY

of the view that some of the nitrogen may also be
derived from the blood. This has important bearings
on the subject of gastric flatulence.

The Physiology of Vomiting.

The act of vomiting is preceded by an abundant flow
of saliva, which, along with air, is swallowed. There
follows a series of spasmodic contractions of the dia-
phragm, during which the entrance to the larynx re-
mains closed, so that the air is forced into the stomach.
Thus the intra-abdominal pressure is raised, whilst that
in the thoraxis lowered. The cardiac orifice then opens,
and the csophagus is shortened by contraction of its
longitudinal fibres.

Meanwhile, as observations with the X-rays have
shown, the cavity of the stomach itself, after the
development of a series of strong waves of peristalsis,
becomes separated into two parts by a constriction at
the entrance to the antrum (see Fig. 16), the cardiac
portion relaxes, and the contents of the fundus are
forced up by the pressure brought to bear upon them by
the diaphragm and abdominal wall (see p. 242). O¢eca-
sionally antiperistaltic waves occur from the pylorus
towards the cardia.

The stomach, therefore, does not play an entirely
passive role in the act of vomiting, and one can easily
understand how, for example, sutures in its wall might
be torn out in the course of the act. That it is able,
even by its own contraction, to empty itself of its con-
tents is shown, too, by the possibility of vomiting taking

ie

DIGESTION 253

place even when all the abdominal muscles are paralyzed.
That the pylorus does not remain tightly closed during
the whole process is indicated by the clinical facts
that bile, gall-stones, and intestinal worms may all be
vomited.
_ The simultaneous contraction of the diaphragm and
the abdominal muscles, which is peculiar to vomiting,
raises enormously the intra-abdominal pressure, and
forces blood up into the heart. The blood-pressure is
thereby increased, and the feeling of faintness which
precedes the act of vomiting is relieved. This explains
the great relief which immediately follows vomiting in
cases of sea-sickness; and, indeed, the tendency to vomit-
ing which is exhibited in all cases of cerebral anemia
must really be regarded as a conservative measure
which is calculated to increase cerebral blood-pressure.

The complicated mechanism by which vomiting is
brought about is controlled by a special centre situated
in the medulla in the neighbourhood of the calamus
scriptorius, and close to the respiratory and vasomotor
centres. Destruction of this centre renders vomiting
impossible, whilst the application to it of a dilute solu-
tion of apomorphine excites the act in an extreme
degree. |

The proximity of the respiratory and vomiting centres
explains how it is that irritation of the former, as in
dyspnoea, often induces nausea or even actual vomiting
as well. On the other hand, it has been found that the
induction of apnoea—i.e., the temporary inhibition of the
irritability of the respiratory centre—can arrest the act
of vomiting for a time, a fact which is often acted upon

254 APPLIED PHYSIOLOGY

unconsciously by patients who seek to stop vomiting by
the taking of a series of deep breaths.

The vomiting centre can be excited either directly or
reflexly. The former mode of excitation occurs in the
vomiting of cerebral anemia or hyperwmia, in intoxica-
tions—e.g., uremia—in cases of intracranial disease,
and in the vomiting of psychical origin. Reflex irrita-
tion of the centre can be brought about by stimuli
reaching it from many peripheral sources.

Duodenal Digestion.

In the duodenum the chyme discharged from the
stomach meets the bile and pancreatic juice. The mix-
ture of the two latter forms a yellowish-green fluid of a
specific gravity of 1010, and of a neutral or slightly

‘ alkaline reaction.* The addition of the acid chyme to

this throws down a precipitate which consists of mucin,
bile acids, and bile pigments, but which does not contain
pepsin; and if there be sufficient chyme to give it a
decidedly acid reaction, digestion goes on just as in the
stomach, and this undoubtedly must happen to a con-
siderable extent when the stomach produces an excess
of acid. Asa rule, however, beyond the first few inches
of the duodenum, there is no free mineral acid present,
and it may be for this reason that duodenal ulcers are
only met with for a short distance beyond the pylorus.
Pure human pancreatic juice, as derived from a
fistula,t.is a clear fluid of specific gravity 1007, alkaline

* Boas, Zett. f. Klin. Med., 1890, xvii. 155.
t Glaessner, Zeit. f. Physiol. Chemie, 1908-4, xl. 465,

8

DIGESTION 255

in reaction, and containing 15 per cent. of protein
(chiefly albumin) and 6 per cent. of ash. About 500
to 600 c.c. of it are produced in twenty-four hours.

It is not yet determined whether there is a psychical
or ‘appetite’ production of pancreatic, as there is of
- gastric, juice, but the chief flow is reached about three
hours after the taking of food, and is the result of a
chemical stimulus exerted on the pancreas by the
substance secretin, which is produced by the action of
acids upon the cells lining the upper part of the in-
testine. That the presence of acids is not essential for
the production of the stimulus, however, there can be no
doubt, for the secretion may still go on in cases in which
the production of hydrochloric acid by the stomach is
entirely arrested, and Pawlow has shown that fats are
also capable of calling out a flow of the juice.

The pancreatic juice contains a proteolytic ferment
(trypsinogen), which is converted into trypsin by mixture
with the enterokinase of the intestinal juice. Unless
enterokinase be present, trypsinogen is inactive, which
explains the fact that the pancreas does not digest itself.
In addition to trypsinogen, the juice contains the fat-
splitting ferment (lipase) and a diastasic ferment, which
converts starch to maltose. Both of these are present in
the fresh juice, though the action of the fat-splitting
ferment is intensified by the presence of bile and
_ intestinal juice.

Absence of pancreatic juice from the intestine inter-
feres to some extent with the absorption of protein, but
to a greater extent with that of fat, although the split-
ting up of fat seems still to go on to a considerable

256 APPLIED PHYSIOLOGY

extent,* probably as the result of bacterial action. The
presence of large quantities of fat in the stools should
therefore suggest pancreatic disease or blocking of the
duct.

From its action in digestion bile is entitled to rank as
a secretion. Its properties as an excretion will be con-
sidered in another chapter (p. 282).

The chief use of bile in digestion consists in the power
it possesses of increasing the breaking up and absorption
of fat, which resides, as Starling says,} ‘in its power of
serving as a vehicle for the suspension and solution
of the interacting fats, fatty acids, and fat-splitting
ferment.’ This is due to the peculiar physical properties
of the bile salts along with those of the lecithin and
cholesterin which they hold in solution. Hence it is not
surprising that when bile fails to enter the intestine the
loss of fat in the feces is greatly increased,{ and part
of the pale colour of the stools in jaundice is due to
this cause. In such cases fats should be withheld from
the diet.

The antiseptic power of bile in the intestine has prob-
ably been exaggerated, but if free bile acids are present,
as they are when acid gastric juice is entering the
intestine freely, a certain degree of antiseptic power
is exerted. On the other hand, the increased amount of
intestinal putrefaction which undoubtedly occurs in

* Vaughan Harley, Jowrn. of Pathology, 1896, iii. 245; see
also Krehl’s ‘ Clinical Pathology,’ English translation, p. 280.

T ‘Recent Advances in the Physiology of Digestion’ (Constable),
1906, p. 117.

{ Mueller, Zeit. f. Klin. Med., 1887, xii. 45.

DIGESTION 257

cases in which bile is prevented from escaping into
the bowel is due to the unabsorbed fat favouring putre-
faction.

The frequency with which biliary obstruction is asso-
ciated with constipation has led to the belief that bile
acts as a stimulant to peristalsis, but of this there is as
yet no experimental proof.

The stimuli to the discharge of bile into the
intestine are apparently the same as those of pancreatic
secretion—acids and fats. Proteins also call out an
increased secretion of bile, probably because they lead
to a large production of acid in the stomach. Starches
have very little influence ; hence it may be that restric-
tion of starchy foods and an increase of the amount
of meat in the diet are useful in cases of ‘ biliousness ’
in which bile production is believed to be defective.

Intestinal Digestion.

The importance of the succus entericus as a digestive
agent has been greatly enhanced in recent years since it
became known that by means of enterokinase it ‘activates’
trypsinogen, and since the discovery in it of the ferment
‘erepsin,’ which, though not able to attack proteins
(except, apparently, casein), has the power of splitting up
proteoses and peptones with the formation of amines and
diamines. It is believed that this part of its action
’ is not exerted in the lumen of the intestine, but in the
actual cells of the villi, and its importance in the picking
to pieces of the protein molecules of the food and their
reconstitution into body proteins has already been

referred to (p. 80). 2

258 APPLIED PHYSIOLOGY

In addition to these ferments, intestinal juice contains
a series which invert the various sucroses (cane-sugar,
lactose and maltose) into dextrose and levulose, the
existence of which has long been known, and by means
of which it completes the work already begun by the
saliva and the pancreatic juice.

The stimuli which lead to the production of normal
intestinal juice have not yet been clearly made out,
though here again secretin is believed to play a part.
Mechanical stimuli lead to the production of a very
watery secretion which has little or no digestive
power, and the object of which, apparently, is to wash
away the source of irritation. It is in this way, seem-
ingly, that solid indigestible oe as well as some
purgatives, excite diarrhea.

Intestinal Movements.

The intestine exhibits two forms of movement: (1)
Movements of rhythmical segmentation (which occur at
the rate of about seven per minute in man), the
object of which is to ensure thorough mixing of the
contents of the gut, but which have no translatory effect
(Fig.17). These movements are most vigorous in hunger,
the small amount of material left in the intestine being
searched again and again for nutriment until it has all
been absorbed, just (to quote a German writer) as one
may peel an apple, eat it, and then nibble the peel. An
exaggeration of these movements in nervous subjects is
the cause of borborygmi, which, as is well known,
are most troublesome when the stomach is empty.

DIGESTION 259

(2) Peristaltic movements which propel the contents
of the gut downwards, every such movement consisting
in a contraction of the gut above the point of stimulation
and relaxation of it below that point (Starling’s ‘ Law of
the Intestines ’).

The peristaltic contractions are the result of a local
nerve mechanism (Auerbach’s plexus), but they are also,
apparently, under the influence of the central nervous
system, especially through the medium of the splanchnics,

Bak. ¢
Gig. oA

Fic. 17.—D1aGRamM or SEGMENTATION IN HuMAN SMALL INTESTINES
OCCURRING SIMULTANEOUSLY WITH PERISTALSIS. (HERTZz.)

which appear to exert a slight tonic inhibition of them.
Thus paralysis of the solar plexus induces an exaggerated
peristalsis with diarrhoea, and ‘nervous diarrhea’ is
probably brought aboutin this way. On the other hand,
irritation of the splanchnics induces colic and constipa-
tion, as happens in lead-poisoning or in cases of intra-
abdominal inflammation.*

* See Largiel Lavastine, abst. in Archiv f. Verdawungskrankh.,
1908, ix. 417.

17—2

260 APPLIED PHYSIOLOGY

It must not be supposed that a peristaltic wave
traverses the intestine steadily from one end to the
other. On the contrary, as it has been graphically put,*
the contents ‘are moved in an irregularly pendulum-
like fashion downwards, somewhat like a walker who
always takes two steps on and one back, then several
forwards, then stands. still for some time, and then, as
if he had forgotten something, runs back again, but
finally, although naturally much later than one who
walked right on, he arrives at his goal.’

The time taken by food to traverse the small in-
testine seems to vary considerably. In a patient with
a fistula at the lower end of the ileum it was foundt
that green peas appeared from two and a half to five
hours after they had been eaten, and continued to be
passed up to the seventeenth hour. MHertz,{ as the
result of experiments on men in whom the progress of
a ‘bismuth meal’ was watched by aid of the X-rays,
concludes that the average rate at which the contents
of the small intestine travel is about 1 inch per minute.
Progress through the large intestine is much slower
(see Fig. 18). y

Inco-ordination of peristalsis, by which relaxation in
front fails to coincide with contraction behind, results
in colic. Strong mechanical irritation results often in
a local tetanic contraction (enterospasm) and in a peri-
staltic wave. Local inflammation of the gut (enteritis)

* Griitzner, Archiv f. d. Ges. Phystol., 1898, xxi. 492.

+ Neucki, MacFadyen, and Sieber, Archiv f. Haper. Path. und
Pharmak,, 1891, xxviii. 311,

t Guy’s Hospital Reports, 1907, lxi. 889.

DIGESTION 961

does not in itself lead to peristalsis, but exaggerates
greatly the sensitiveness of the bowel to other stimuli.
Antiperistalsis has not been clearly proved to occur
in the small intestine experimentally, although it has
been observed to take place in a case of intestinal

lo & of Ne
mer day, 4a
Orns hewn wit bur grersel

Fig. 18.—AveRAGE TIME AT WHICH VARIOUS POINTS OF THE
CoLON ARE REACHED AFTER A BISMUTH BREAKFAST TAKEN
AT 8 aM. (HERTZ.)

fistula in man.* It may, perhaps, occur in pathological
conditions.

Sensibility of the Intestines.

The intestine would appear to be insensitive to all
ordinary stimuli. Intestinal pain arises either from

* Busch, Virchow’s Archi, 1858, xiv. 140,

262 APPLIED PHYSIOLOGY

(1) traction upon the nerves which run beneath the
parietal peritoneum (the visceral peritoneum is insen-
sitive), or (2) from violent contraction of the muscular
coat, producing local anemia, which stimulates the
nerves of the bowel.

Thus, the separation of adhesions which do not
involve the abdominal wall is painless, but if they
exist between the intestine and abdominal wall their
separation produces pain. The pain of colic or of
violent peristalsis is probably produced in the second
method by an overcontraction of. the muscular coat, and
resembles the pain of ‘ cramp.’

Absorption.

Absorption of the soluble products of digestion is
carried out almost entirely in the small intestine; that
of water in the colon. Observations on cases of fistula
at the lower end of the ileum have shown that by the
time the contents of the bowel have reached that point
87 per cent. of the nutriment of the food has already
entered the blood. It can readily be understood from
this that in cases of diarrhea due entirely to disease/of
the colon a patient’s nutrition does not spr
suffer. Even when the passage of the food through the
small bowel is accelerated, as in enteritis, absorption
is not interfered with so much as one might expect,
owing, apparently, to the enormous provision made for
it by the great length of the ileum. It is only, indeed,
in cases of severe disease of the intestinal mucous

membrane, such as amyloid degeneration, or where the
lymphatics leading from the bowel are blocked, as in

DIGESTION 263

tuberculosis of the mesenteric glands, that any great
arrest of absorption seems to occur.

The importance of the colon in the absorption of water
is very great. As the contents of the ileum pass into
the cecum they contain only from 5 to 10 per cent. of
solid matter, and as they amount to something like
+ to 1 pint in the twenty-four hours, the activity with
which water is absorbed in order to convert them into
solid feces must be very considerable. It is not difficult
to understand, therefore, how, in a case in which the
contents of the bowel are discharged from an artificial
anus without passing through the colon, the patient
may easily come to suffer from a defective absorption
of water.*

In addition to water, the colon absorbs some forms
of sugar very readily—peptone to an appreciable degree,
but fats very slightly. Those facts have an important
bearing upon the question of rectal alimentation. _

As the result of the combined action of the small and
large intestines, ii may be taken that the nutritive
constituents of an ordinary mixed diet are absorbed to
the following extent :

Proteins ie .- 92 per cent.
Fats ... eee oe 944 9
Carbohydrates ... OCR ss

But the exact amount of absorption varies greatly with
the composition of the diet.
The fate of the protein and carbohydrate absorbed

* See Monier-Williams, ‘The Importance of the Colon,’ Brit.
Med. Journ., 1906, 787.

264 APPLIED PHYSIOLOGY

from the intestine has already been described (pp. 80 and

87) ; the fat, after being reconstituted in the cells covering _
the intestinal villi, enters the lacteals, and thence passes
to the thoracic duct, forming with the lymph the milky
fluid termed ‘chyle. The composition of the chyle
discharged from wounds of the thoracic duct in man
varies considerably with the amount of fat in the diet,
but as a rule it contains about 92°5 per cent. of water,
8 to 4 per cent. of protein, 0°5 per cent. of salts, and
2 to 8 per cent. of fat.*

It is a somewhat viscid fluid, and readily coagulates
on standing. As much as 6 litres of it have been dis-
charged from a wound of the duct in the course of a day,
and it can readily be imagined how in such circum- -
stances a patient emaciates rapidly and suffers severely
from thirst.

Bacteriology of the Bowel.

Bacteria of all sorts are, of course, constantly being
swallowed with the food. Of these a certain number
are destroyed in the stomach, but a considerable quantity
run the gauntlet of the gastric juice, and reach the
intestine. The number and variety of these will
naturally vary considerably with the character of the
diet, and also, it would seem, with the locality in which
the individual happens to live.t That their presence is
not essential to normal digestion is shown by the fact
that animals can be reared on sterile food, and also that

* Carlier, Brit. Med. Journ., 1902, ii. 175; and Veau, Gaz. des

Hép., October 80, 1906 (?), p. 1205.
{ Bruini, Archw f. Verdawungskrankh, 1905, xi. 162.

DIGESTION 265

the feces of many animals in Arctic regions are free
from them. Nor is the number or character of the
bacteria in the feces very different in animal and
vegetable feeders,* or whether the diet be an ordinary
mixed or a purely vegetarian one.

The characteristic organisms of the small intestine
are those which produce acids from carbohydrates; that
of the large intestine, the Bacillus coli. Putrefactive
bacteria are not found to any extent in the ileum, and
the contents of the latter, even at its lower end, contain
no putrefactive products such as leucin, tyrosin,
indol, or skatol.t Hence they are also devoid of fecal
odour.

In the ileum bacteria are present in greatest number
at the lower end—the restraining power of the gastric
juice being apparently still operative higher up {—and it
is interesting to remember that it is just this part of the
bowel which is most subject to infective disease.

The acids produced by the acid-forming bacteria tend
constantly to be neutralized by the alkaline secretion
of the pancreas and intestine, but in spite of that the
activity of acid production is sufficient to give the con-
tents of the ileum a slightly acid reaction, which tends
to restrain putrefaction. Hence a diet which contains
much" carbohydrate is one on which little intestinal
putrefaction can occur.§$

In the colon putrefactive organisms get the upper

* Levin, abstract in Archw f. Verdawuwngskrankh, 1904, x. 530.
+ Neucki, ete., loc. ctt.

{ Lorrain Smith and Tennant, Brit. Med. Jowrn., 1902, ii. 1941.
§ Backman, Zeit. f. Klin, Med., 1902, xliv, 458.

266 APPLIED PHYSIOLOGY

hand, and the contents of the bowel acquire a fecal
odour; and the more watery the contents, the greater
is the degree of putrefaction. For this reason, if the
contents of the ileum be hurried into the colon very
rapidly and retained there, the stools may become very
offensive. This takes place in cases in which there is
catarrh limited to the small intestine.

The gases of the intestine consist chiefly of nitrogen,
hydrogen, carbonic acid gas, sulphuretted hydrogen, and
marsh gas. Of these, the last four are produced by
bacterial action—carbonic acid by fermentation of carbo-
hydrate in the small intestine; H,S from proteins; and
marsh gas and hydrogen from cellulose, and chiefly by
bacteria present in the colon. CO, is also produced by
the action of acids on the pancreatic and intestinal
juices. The possible source of nitrogen in the alimentary
canal has already been discussed.

The gases of the intestine no doubt help to promote
peristalsis by their mechanical pressure on the wall of
the bowel, but sulphuretted hydrogen appears to act as a
chemical _ stimulant also, Sulphur apparently owes its
laxative properties to the production from it of H,§,
whilst the constipating action of bismuth may be due in
part to its power of fixing that gas. CO, seems also to —
stimulate peristalsis when present in excess; hence,
perhaps, the spontaneous action of the bowels which
sometimes occurs in asphyxia.

Movements of the Colon.

When the intestinal contents enter the colon a strong
general contraction takes place along the cecum and

DIGESTION 267

ascending colon, forcing some of the food onwards; a
moment later antiperistaltic waves begin, which drive
the food back again into the cxcal pouch, thus churning
the contents up and exposing them to the absorbing
wall. It is here that the absorption of the remains of
the nutritive constituents of the food takes place, as well
as that of most of the water, for the contents of the ¥
transverse colon are usually nearly as solid as those of
the sigmoid.

As material accumulates in the transverse colon, deep
waves of constriction appear one after the other and
carry the material into the descending colon, leaving
the ascending and transverse portions free for the occur-
rence of antiperistalsis.

The occurrence of antiperistalsis as a normal process
in the upper part of the colon makes clear the signifi-
cance of the ileo-cexcal valve, which is competent for the
amount and character of the material normally dis-
charged from the ileum. It can be overcome, however,
by large injections of fluid from below, which has been
proved both experimentally* and by observations on
patients with a fistula of the ileum,t as well as by
accumulated instances of the vomiting of enemata.t

Fig. 18 shows the average rate at which the colon is
traversed by a bismuth meal according to the observation
of Hertz.§

* Griitzner, Pfliiger’s Archiv, 1898, Ixxi. 492.

tT See Neucki, etc., loc. cit.

t See Mohroof, Indian Med. Gaz. 1902, xxxvii. 394.
§ Loe. cit.

268 APPLIED PHYSIOLOGY

Defecation.

In evacuating the large intestine the material in the
lower part of the descending colon is first expelled by
the combined action of peristalsis and pressure by the
abdominal muscles and diaphragm. The material
higher up is then carried down into the cleared area
and the process of evacuation repeated.

During the straining which normally accompanies the
act of defecation, the diaphragm descends to its lowest
point, carrying with it the hepatic and splenic flexures
of the colon. The hepatic flexure, indeed, may nearly
reach the level of the umbilicus, so that the ascending
colon is compressed to an almost globular form (Hertz).
The transverse colon also descends from about an inch
above to an inch below the umbilicus.

As feces are forced into the rectum and anal canal,
afferent impulses are set up which produce strong peri-
. Staltic contractions, involving the whole length of the
colon.

In normal circumstances the stool passed to-day is
probably derived in chief measure from the food of the
day before yesterday. Ya

The functions of the colon as an organ of excretion
will be considered in another chapter (p. 287).

Reviewing the whole trend of recent work on the
physiology of digestion, and considering its bearings
upon practical medicine, one is struck by the great
delicacy and complexity of the processes by which the
digestion of the food is accomplished, and one ceases to

DIGESTION 269

wonder that a mechanism so constituted should easily
become deranged. One is impressed, too, by the increas-
ing importance attached by physiologists to the part
played by the nervous system in the inception and co-
ordination of the various muscular and chemical func-
tions of the organs concerned, which amply justifies the
view long held by physicians, that functional disorders of
digestion are really manifestations of an affection of the
nervous centres.

Experiment has made clear to us how it is that dis-
order of one section of the alimentary apparatus may
throw out of gear the working of other sections, and how
healthy intestinal digestion is dependent upon a normal
state of the stomach, and that in its turn upon the
efficient carrying out of the preliminary processes of
digestion in the mouth; and it follows from this that, in
trying to cure disturbances in one part of the alimentary
canal, we must often direct our treatment to the part
which lies above it. The cure of gastritis by attention ©
to the teeth, and of some forms of chronic diarrhea by
- the administration of hydrochloric acid, are instances in
point. At the same time, one cannot help being im-
pressed, from the physiological point of view, by the
liberal provision made in the digestive tract for the
supplementing of defective action of one part by a more
vigorous exercise of function by others, and the lesson of
this to the physician is one of hope and encouragement.

CHAPTER VIII
THE APPLIED PHYSIOLOGY OF EXCRETION

Mucx discussion has taken place as to the difference
between a secretion and an excretion, and as to whether
certain organs are to be regarded as secretory or excre-
tory in function. The simplest way of looking at the
matter, for clinical purposes at least, is to define as an
excretion any waste matter which is discharged from the
body and is incapable of being further utilized, and to
regard any organ which is responsible for getting rid of
such matters as excretory in function, whether it merely
picks them out of the blood or builds them up from
simpler compounds before getting rid of them. From
this point of view the excretory organs of the body, and
the waste substances which they cisehar ey may be
arranged as follows:

Organ. Excretion.
Kidney exe ... Waste products of nitrogenous metabchian
soluble mineral matters, and water.
Liver ... sat ... Waste products of the red blood corpuscles.
Lung ... sas ... Waste products of ‘carbonaceous’ meta-
bolism and water.
Intestine ay ... Unabsorbed residues of food and of the

digestive juices, and some less soluble
mineral matters—e.g., calcium and iron.
270

EXCRETION 271

The skin is commonly spoken of as an organ of excre-
tion, but, as we shall see later, it is very doubtful whether
it is right to regard it as such in any but an accidental
way.

Excretion by the Kidney.

It is admitted by physiologists that we are still very
much in the dark as to the mechanism by which the
kidney produces the urine, but we know it to be an organ
of excretion in the strict physiological sense, for, with
the exception of hippuric acid, all the ingredients of the
urine are already present in the blood. Hence, in
disease of the kidneys the urinary constituents may
accumulate in the body.

Opinion has long been divided between the relative
merits of the ‘vital’ theory of urine production pro-
pounded by Bowman and the so-called ‘mechanical’
theory of Ludwig, nor can the controversy be regarded
as even yet finally closed. Perhaps the view which finds
most favour at the present day is that which attributes
to the glomeruli the function of separating out water
and mineral constituents (except phosphates), and per-
haps some foreign ingredients, such as sugar, whilst
regarding the cells of the convoluted tubules as respon-
sible for picking out of the blood the specific organic
components of the urine, such as urea. Whether any
-reabsorption of water takes place during the passage of
the urine along the tubules is still disputed. The strictly
mechanical theory of filtration through the glomeruli,
however, has been generally abandoned since evidence
has accumulated to show that the cells covering the

272 APPLIED PHYSIOLOGY

glomeruli are capable of some selective action. The
proteins of the blood, for instance, are not excreted by a
healthy kidney, whilst ‘ foreign’ proteins, such as egg
albumin and peptone, are. Good examples of such
selective excretion of foreign proteins are also seen in
human pathology in the excretion of hemoglobin by the
kidney in paroxysmal hemoglobinuria, and of the so-
called ‘Bence Jones’s albumose’ in myelopathic albu-
mosuria, and a study of the urine in these diseases is
alone sufficient to disprove any purely mechanical filtra-
tion theory of urine production.

It cannot be said, however, that the clinician is acutely
interested in the physiological theories of renal function,
for when disease affects the kidney the organ usually
suffers as a whole, and it is but rarely that the glomeruli
or the tubules are either solely, or even preponderatingly,
involved. In scarlatinal nephritis, it is true, the glom-
eruli are sometimes much more disorganized than the
tubules, and such cases are characterized by the produc-
tion of a scanty and concentrated urine, which is evidence,
so far as it goes, in favour of the view that the glomeruli
are chiefly concerned in the production of water. / It is
interesting to note that the epithelium which 1 covers the
glomerulus is more differentiated than that which lines
Bowman’s capsule, and, in harmony with this, it shows
a different reaction in disease. Like all highly differ-
entiated epithelia, it is very vulnerable, and its cells
readily necrose, a process which can be well observed in
a, kidney which has been damaged by the excretion of
the poisons of scarlatina or diphtheria. The epithelium
which lines Bowman’s capsule, on the other hand, par-

EXCRETION | 273

takes more of the nature of ordinary endothelium, such
as lines a lymph space, and, when irritated, responds like
the latter by the production of connective tissue.

The volume of urine produced by the kidney depends
upon the amount of blood passing through it in a given
time, and the blood-pressure in the renal capillaries.
Care must be taken to distinguish between a high general
blood-pressure and a high renal pressure, for the latter
may occur independently of the former. If, for example,
the cutaneous vessels become contracted from exposure
to cold, the vessels of the abdominal organs, including
those of the kidney, become overfilled, and the renal
pressure rises, with the result that more water is excreted
in the urine; and yet this may happen without there
being any rise of general blood-pressure. All that has
taken place has been a redistribution of blood in the
body (see p. 167). It is in this way that exposure to cold
increases the volume of the urine, whilst warmth, hot-air
baths, and a mild climate—all of which tend to ‘ de-
termine’ blood to the surface—lessen the pressure in
the kidney, and are therefore useful in nephritis and
renal congestion. If, again, the control exercised by
the vasomotor nerves over the renal bloodvessels is
relaxed, more blood goes to the kidney, the pressure in
the glomeruli rises, and more water is excreted. This is
the explanation of the polyuria of nervousness and
_ hysteria. On the other hand, constriction of the renal

vessels, with consequent diminution of the urine, occurs
in asphyxia and in the convulsions of epilepsy and
strychnine-poisoning.

Tn all these cases we are dealing simply with an altera-

18

274 APPLIED PHYSIOLOGY

tion in the distribution of the blood, which results in the
kidney getting more or less than its usual share.

On the other hand, the amount of urine is also influ-
enced by alterations in the general blood-pressure, pro-
vided the kidney participates in them. If the general
pressure falls, the amount of water excreted by the
kidney is lessened, and if the fall in the renal capillaries
be great enough (down to 40 millimetres), excretion stops
altogether. In conditions of shock the urine may become
very scanty from the fall of blood-pressure, which results
from ‘pooling’ of the blood in the abdominal veins.
The polyuria of chronic nephritis, on the other hand, is
probably due, in part at least, to a marked rise of general
blood-pressure. One must distinguish between the
polyuria which results from alterations in the blood-
supply of the kidney, and which consists mainly in an in-
creased excretion of water, and a true diuresis, in which
the specific organic constituents of the urine are also
voided more freely. The latter can only be brought
about by an increased activity of the epithelial cells, but
of the factors which determine such an increased activity
we know little, except that one of them may be the pres-
ence in the blood of an unusual amount of waste material
to be eliminated. Some diuretic drugs, however, such
as caffeine, appear to possess the power of stimulating
the renal cells, and it is in such a property that their
chief virtue as medicines resides. |

Important effects upon the renal circulation in certain
circumstances are brought about by the fact that the
capsule of the kidney is comparatively inelastic. When,
therefore, the epithelium of the organ swells, as it does,

EXCRETION 275

for example, in acute inflammation, the capillaries
become compressed, the organ is rendered comparatively
anemic, and the volume of urine falls. This effect is
exactly comparable to the cerebral anemia, and con-
sequent paralysis of brain functions, which results from
cerebral compression and increased intracranial pressure
(see p. 175), and attempts have been made in some cases
of acute nephritis to relieve the pressure by incision
of the capsule, and so restore again the blood-flow
through the organ, just as one relieves intracranial
tension by trephining.

In view of this ‘renal anemia,’ if must be obvious
that any attempt to ‘wash out the renal tubules,’ by
causing the patient to drink large quantities of water,
is not likely to be successful, even were the existence of
such blocking probable in itself.

Physiologists have not succeeded in proving the
existence of any secretory nerves for the kidney, and
experimental variations in the volume of the urine can
only be brought about through the vasomotor nerves
(splanchnics) of the organ. ‘The occurrence of what is
known as ‘reflex suppression,’ however, is at least
suggestive of the existence of secretory fibres. Whether
or not the kidney produces an internal secretion is
also still under dispute. Experimentally it is found
that, if a sufficiently large amount of renal substance be
excised, the volume of the urine is—for unknown reasons
—permanently increased, and at the same time a wide-
spread disturbance of metabolism, manifested by a great
rise in urea production, sets in. It has been suggested
that this is due to the withdrawal of an internal secretion.

18—2

276 APPLIED PHYSIOLOGY

These experiments have a very direct bearing on some
of the clinical phenomena of contracted kidney.

The Normal Constituents of the Urine.

Water.—The amount of water excreted in the urine
varies greatly, for reasons already considered, and
depends also upon the amount of water drunk. In
health, however, the quantity in the urine is always
greater than that taken in by the mouth. Even although
the amount of solids and liquids in the diet be the same,
the amount of water excreted varies greatly in the same
individual in different circumstances and in different
individuals in the same circumstances. This is due to
the reciprocal action of the skin and kidneys; for the
greater the amount of the insensible perspiration, the
less the amount of water excreted by the kidney, and
vice versd. In other words, some individuals have active
skins, and others active kidneys. The former excrete
a more concentrated urine, and are more prone to suffer
from gravel and stone; the latter, one which is more
dilute, and are probably more subject to renal ones
and inflammation.

The rate at which water is excreted by the | Gane
probably varies in different persons, but as a rule, if a
litre of it be swallowed, it has usually all reappeared in
the urine before the lapse of three hours.

In health the volume of urine excreted by day is
much greater than that produced during the night;
but in cases of renal disease the quantity of day and
night urine is more nearly equal. The reason for this

EXCRETION QT7

is not understood, but it may be due in part to the
kidney acting more slowly when diseased.

Solid substances excreted by the kidney tend to carry
a certain amount of water with them. The polyuria of
diabetes mellitus is a good example of the excretion of
sugar causing such a flow of water. Some diuretics
probably owe their power of increasing the volume of
the urine to the same mechanism.

Acidity.—The acid reaction of the urine is due to the
presence of acid phosphates and organic acids. Much
discussion took place at one time as to how it is that the
kidney can separate an acid urine from an alkaline fluid
such as the blood. It must be remembered, however,
that, although the blood is alkaline to litmus, its chief
salts, acid phosphates, and bicarbonates, are technically
acid. ‘The former acid is eliminated by the kidney, the
latter (CO,) by the lung; hence the preponderance of
acid in the renal excretion. The mineral constituents
of an animal diet yield an acid, and those of a vegetable
diet an alkaline ash, which is the reason why the urine
of carnivora is highly acid, whilst that of herbivora is
alkaline.

Advantage may be taken of this effect of diet in
modifying the reaction of the urine in cases of disease.

The total amount of acid eliminated by the kidney is
much greater during the day than during the night, but
owing to the concentration of the night urine its per-
centage acidity is greater than that of the day. It is
for this reason that uric acid is more apt to separate out
in the urine secreted by night, a fact which must be
borne in mind when one is treating cases of gravel.

278 | APPLIED PHYSIOLOGY

The percentage acidity of the day urine is also reduced
by the ‘alkaline tide’ which follows meals, and which
is due to the alkaline carbonates set free in the blood as
the result of the elaboration of the gastric juice.

By estimating the total acidity of the urine and that
part of it which is due to phosphoric acid separately,
one can arrive at a measure of the amount of the
acidity which is due to the presence of unoxidized
organic acids, and which are often an index of some
disorder of metabolism. A method of doing this has
been devised by M. Joulie, and has been largely
employed in clinical work in France.

Nitrogenous Constituents.

Of the total amount of nitrogen (about 16 grammes)
excreted in the urine on an ordinary diet—

84 to 87 per cent. is in the form of urea ;
2 to 5 per cent. is in the form of ammonia
compounds ;
1 to 8 per cent. is in the form of uric acid;

whilst the balance is contained in such substances as
purin bases, hippuric acid, creatinin, and some undeter-
mined compounds.

Urea.—The amount of urea present in the urine
depends almost entirely upon the amount of protein in
the food. It is therefore useless to estimate it for
clinical purposes unless the composition of the diet is
taken into consideration. Seeing that it is mainly
formed in the liver from ammonia compounds, it is

EXCRETION 279

diminished in severe disease of that organ, such as
acute yellow atrophy, its place being taken by salts of
ammonia and amino-bodies. As it is merely picked out
of the blood by the kidneys, it accumulates in the
circulation in cases of severe impairment of renal
function, and, being very soluble, may be found in any
of the secretions—e.g., the sweat.

Urie Acid.—The origin of the uric acid in the urine
has been considered in a previous chapter (p. 45), but
it must again be emphasized here that its amount is
very largely dependent upon the amount of purin bodies
in the food, and that it bears no constant ratio to urea.
The influence of diet is shown by the following figures
(von Noorden) :

Daily excretion of uric acid on a ‘ purin-

free’ diet aa dai Gs ... 0°25 to 0°6 gramme.
Daily excretion of uric acid ‘on a mixed
diet sa He has ... 0° tol gramme.

Daily excretion of uric acid on a largely
meat diet ed ven oe ... 1 to 1} or 2 grammes.

Ammonia.—The amount of ammonia excreted in the
urine may be taken as an index of the amount of acid
entering the circulation, for it is by the neutralization
of acid by carbonate of ammonia that the body protects
itself against ‘acidification.’ The amount is therefore
greater on an animal than on a vegetable diet, whilst
in some pathological states, such as in the later stages
of diabetes, and in some of the toxeemias of pregnancy,
when organic acids are entering the blood in large
quantities, the excretion of ammonia may rise enormously.

Of the remaining nitrogenous constituents, creatinin

280 APPLIED PHYSIOLOGY

is derived partly from meat in the food and partly from
the muscles of the body. On a diet free from meat the
amount of it excreted is very constant for any given
individual under the same conditions. Creatinin is of
little clinical importance, but it is interesting to note
that, as might be expected, the amount of it excreted is
greatly diminished in cases in which there is extensive
muscular atrophy.

Of the inorganic constituents of the urine, the
sulphates are derived chiefly from the decomposition
of proteins in the body, and the quantity of them
eliminated therefore runs closely parallel to the elimina-
tion of nitrogen. Sulphur is met with in the urine in
three forms—(1) as inorganic sulphates; (2) as organic
or ethereal sulphates; (8) as neutral or unoxidized
sulphur. The inorganic sulphates are derived almost
entirely from the ‘exogenous’ metabolism of food-
protein, and their amount is therefore dependent upon
the nature of the diet. The organic sulphates are
produced partly metabolically and partly as the result
of the union of aromatic substances produced by in-
testinal putrefaction (phenol, indoxyl, skatoxyl) with
sulphuric acid. They are therefore only to some degree
an index of the extent of such putrefaction, and not an
absolute gauge of it, as has sometimes been assumed
clinically. The neutral sulphur is derived entirely from
the endogenous metabolism of body-protein, and is a
measure of its intensity.

Of the other inorganic constituents, common salt is
derived entirely from the food, and provided its amount
in the latter be constant, the excretion of it is also con-

EXCRETION 281

stant. It is retained in the body whenever water is
being retained (e.g., in dropsy), and also, although for
unknown reasons, in some febrile conditions. The
phosphates of the urine are derived mainly from the
food, but also to some extent from the decomposition
of phosphorus compounds—e.g., nuclein, in metabolism.
The condition termed ‘ phosphaturia’ is really in most
cases not an indication of an excessive excretion of
phosphorus, but of a diminished acidity of the urine,
which causes the earthy phosphates to be thrown out.
In some instances it appears to be the result of an
excessive excretion of calcium by the urine, so that the
normal mono-di-calcium phosphates are replaced by the
much less soluble tri-calcium salt. It would appear, too,
that the amount of phosphates in the urine is determined
to some extent by the amount of calcium in the food.
When this is high, as in herbivora, phosphorus is excreted
by the bowel as calcium phosphate.

Oxalie acid is present in the urine to a small nisin
chiefly combined with calcium. It is derived partly
from vegetable foods, of which some, such as rhubarb
and spinach, are specially rich in it, and is partly pro-
duced in the body in some unknown way as the result
of metabolic processes. It cannot, therefore, be made
to disappear entirely from the urine even if the diet be
free from it. The presence of magnesium salts in the
urine helps to keep it in solution, and poverty of these
is one cause of ‘oxaluria.’ Of the origin of normal
urine pigment (urochrome) we know nothing, although
it is probably derived somehow from hemoglobin, and it
is therefore of little clinical interest. Urobilin is present

282 APPLIED PHYSIOLOGY

in traces in normal urine, and is often greatly increased
in disease. It is identical with the so-called stercobilin
of the faces, and is derived by absorption from the
intestine. It is therefore apt to appear in the urine in
augmented quantity whenever blood destruction, and
therefore bile-pigment formation, is excessive—e.g., in
extensive extravasations and in pernicious anemia.
Conversely, it disappears from the urine when bile-
pigment formation is defective, as in cirrhosis of the
liver, or when bile is unable to enter the intestine, as
in occlusion of the common duct.

Exeretion by the Liver.

The liver differs from the kidney as an excretory
organ in that it actually forms the waste matters which
it excretes, instead of merely picking them out of the
blood. This has led to some dispute as to whether
bile is to be regarded as an excretion or a secretion, and
in the domain of pathology as to whether jaundice may
be hematogenous as well as hepatogenous in origin.
Since it has been established by physiologists, however,
that the constituents of bile are formed by the liver and
do not pre-exist in the blood, it has come to be recognized
that all forms of jaundice are in the last resort hepato-
genous, or, in other words, that without the liver jaundice
would be impossible.

The chief waste matter which the liver excretes is
the pigment derived from the destruction of red blood
corpuscles in the portal system. Under the action of
the liver cells hemoglobin is converted into hematin,

EXCRETION 283

then into hemochromogen, and finally into bilirubin,
which is the cause of the golden-yellow colour of normal
fresh bile. If the destruction of blood corpuscles be
excessive, so much bile pigment may be formed that the
bile capillaries get choked, and some of the bile is re-
absorbed—hence the so-called ‘hematogenous’ jaundice;
whilst, if the destruction be greater still, some hemo-
globin may escape into the bile unconverted, or even
into the general circulation, and reach the urine.

In the intestine bilirubin is reduced under the action
of micro-organisms to urobilin ; but if diarrhoea be present
there is no time for this to take place, and the stools
may then contain bile pigment. Owing to the absence
of micro-organisms from the intestine of the newly-born
child, the meconium contains no urobilin.

Bile pigment seems to act like a weak acid, and forms
salts with alkalies or earth: a combination of bilirubin
with calcium, for instance, is a common ingredient of
gall-stones.

The ultimate source of the bile acids is unknown, but
they may fairly be regarded as excretory products, for
from 30 to 40 per cent. of them appears in the feces,
and traces also in the urine. The remaining 50 to
60 per cent., however, is reabsorbed from the intestine,
and returned to the liver, to be again excreted. This
circulation of the larger part of the bile acids between
the intestine and liver is rather peculiar, and it is diffi-
cult to see the reason for it. It is true that the bile
salts incidentally aid in keeping the cholesterin of the
bile in solution, and by this circulatory arrangement
a small amount of bile salts is enabled to go a long way,

| 284 APPLIED PHYSIOLOGY

but this is hardly likely to be the sole reason for its
occurrence. If the bile escapes by a fistula the reabsorp-
tion of bile salts is, of course, arrested; hence fistula
bile is always poorer in that ingredient than natural
bile, and the results of analysis of the former cannot
be taken as representing the true composition of the
natural secretion.

The bile salts have a distinctly toxic action in the
body, causing destruction of red blood corpuscles, a
slowing of the heart by direct action upon its muscle
and the cardiac ganglia, and a paralyzing action on the
higher cerebral centres, which results in coma and death.
To these effects some of the clinical sen se of jaundice
have been attributed.

The cholesterin of the bile is now generally admitted
to be derived from the cells lining the biliary passages
and gall-bladder. In catarrh of these the amount of
cholesterin produced may be increased beyond the power
of the bile salts to keep it in solution, and the formation
of cholesterin gall-stones is favoured. Attempts have
been made, but without much success, to dissolve such
stones by administering bile salts by the mouth. wb

It used to be believed that the cholesterin of bile was

a waste product derived from the nervous system, and ~

one theory of cholemia was based upon the assumption
that the symptoms of that condition were due to an
insufficient removal of waste products from the brain
and nervous system. Since the true source of choles-
terin has been discovered, however, this theory has been
abandoned.

The chief mineral constituent of the bile is calcium,

EXCRETION 285

which, as has already been mentioned, is often found in
gall-stones in combination with bile pigment ; whether
or not an increased consumption of calcium salts in the
food is followed by an augmented excretion of them in
the bile is still disputed. The question is one of interest
in relation to the dietetic treatment of cholelithiasis.

The total volume of bile produced daily seems to
‘vary between 500 and 1,100 c¢.c. Its amount probably
depends upon the activity of the general metabolism,
but it is almost impossible to increase it by artificial
means. Diet has no appreciable influence upon it, nor
has the amount of water drunk. The effect of drugs is
very uncertain, and, as far as most experiments go,
negative; but any agent which causes an increased
destruction of red corpuscles will, of course, increase
the excretion of bile pigments. Administration of bile
acids or dried bile by the mouth has been said to
stimulate the liver to form more bile, but this statement
is apparently based upon a misinterpretation of the
results of experiments upon animals or patients with
biliary fistule. The greater richness of the bile observed
in such cases when dried bile is given by the mouth is
not due to the liver forming more natural bile, but
merely to its excreting that portion of the artificially
administered bile which has been absorbed from the
intestine. We are still, therefore, without a true chola-
_ gogue or hepatic stimulant.

Bile is produced at a very low pressure—not more
than 16 to 24 millimetres of mercury. One consequence
of this is that a comparatively slight obstruction in the
bile passages is sufficient to retard its escape, and may

286 APPLIED PHYSIOLOGY

cause jaundice. By squeezing the liver between the
diaphragm and the abdominal muscles the pressure is
raised, and the escape of bile favoured. This is believed
to explain the beneficial effect of horseback exercise in
some cases. During the act of vomiting the liver is
forcibly squeezed in this way, and the older school of
physicians used often to induce an artificial vomit at the
outset of an acute fever, in the belief that by this means
poisonous materials could be voided from the liver.

The discharge of bile into the intestine reaches its
maximum about three hours after a meal, and is ap-
parently brought about by contraction of the muscular
coat of the gall-bladder, the motor nerve for which is the
vagus, whilst the sympathetic supplies it with relaxing
fibres. If the gall-bladder contains biliary calculi its
contraction causes pain, and the occurrence of this at
a definite period after the taking of food is apt to suggest
that the pain is of gastric origin, and to lead to errors of
diagnosis.

In addition to the well-recognized biliary constituents,
it is probable that the liver excretes or destroys other
toxic materials, some of which may be derived from the
bowel, and inefficiency in performing this function has
been advanced as an explanation of biliousness. The
liver, in fact, may be regarded as a filter placed between
the portal system and the general circulation, the
purpose of which is to prevent the escape of poisonous ~
materials from the former into the latter. Seeing, too,
that the liver is concerned in the final stages of the
formation of urea, and in the destruction of uric acid,
it must be regarded as in every respect one of the most

EXCRETION 287

important organs for dealing with the waste products of
the body, and it is not surprising that extensive disease
of it is often associated with pronounced toxic symptoms.
Its reserve power, however, is so great that probably only
about one-fifth of its actual substance is essential for life,
which explains how it is that the organ may be the seat of

the most extensive cirrhosis without health being greatly
affected.

Excretion by the Intestine.

The intestine excretes (1) the residue of the intestinal
juices; (2) the unabsorbed remains of the food; (8) certain
mineral salts, such as calcium and iron.

On an ordinary mixed diet the amount of feces
excreted is from 120 to 150 grammes, containing 80 to
37 grammes of solid matter. Their composition is very
uniform. They are to be regarded as chiefly made up of
the residue of the digestive juices; they also contain,
however, some starch granules, vegetable débris, and
a few muscle fibres derived from the food. In reaction
the normal feces are neutral or slightly alkaline. The
alkalinity is the result of putrefaction, and is therefore
more pronounced if there is much protein in the diet.

The normal colour of the stools is due in part to
stercobilin, but it is greatly influenced by the nature of
the food. Thus, if there be much meat in the diet, the
feeces are very dark, and if more fat be taken than can
be completely absorbed, they assume a clay colour.
Normal bile pigment (bilirubin) is never present in the
stools in ordinary circumstances except in early infancy,
but it may appear if diarrhea be present. If the stools

288 APPLIED PHYSIOLOGY

be acid, the bilirubin may be converted into biliverdin,
and they then become green. The usual amount of
water in the feces is about 75 per cent., but if there
be any delay in the large intestine, the stools may
become much drier, as is often seen in constipation.
The bulkiness of the stools on a vegetable diet is largely
due to the presence of an excess of moisture.

As will be seen from what has been said, the influence
of the food upon the physical and chemical character
of the stools is so great that it is necessary, when one
wishes to investigate the digestive processes in the intes-
tine clinically, to put the patient upon a standard or
‘test diet,’ the character of the feces that result from
which in health is known.

The intestine is also responsible for the excretion of the
greater part of the calcium which is absorbed from the
food, and crystals of calcium phosphate are often found
even in normal feces, and make up a large part of the
‘intestinal sand’ sometimes excreted in cases of disease.

In some pathological conditions the intestine seems to
be unable to excrete calcium, which then appears in the
urine in abnormal quantity, producing one wane of
so-called ‘ phosphaturia ’ (see p. 281). Mo

Iron is also mainly excreted by the intestine, and so
probably is copper. The recovery of these metals from
the stools is therefore no proof, that they have not been
absorbed and passed through the body, although the
artificial colouring of vegetables with sulphate of copper
has sometimes been excused on the ground that most
of the metal can be recovered from the stools, and has
therefore not been absorbed.

EXCRETION 289

It will be observed from a study of the excretory
functions of the intestine that they are so entirely
different from those of the kidney that it is unlikely
that the bowel can be made to replace the kidney to
any extent as a channel of excretion in cases of renal
disease.

The excretory functions of the lung's have been con-
sidered in another chapter (Chap. VI.), and, as regards
the skin, it need only be said that the sweat is essentially
a secretion which is of use in regulating the body
temperature, and is not properly an excretion ai all.
Incidentally it may contain any soluble substance which
is present in excess in the blood—such, for example, as
urea; but, like the intestine, it can never be made to
take the place of the kidney to any appreciable degree,
and the value of maintaining a free action of the skin in
cases of renal disease is probably to be ascribed to effects
other than the promotion of excretion. |

19

INDEX

ABDOMINAL respiration, 195

Absorption, gastric, 251
intestinal, 262

Accelerator nerves to heart, 122

Achylia, 247

Addison’s disease, 26

Adenin, 46

Adenoid tissue, 83

Adipose tissue, 16

Adrenalin, 26

Air, complemental, 199
residual, 198
supplemental, 199
tidal, 199

Air passages, 177

Alanin as source of sugar, 41

Albumose, Bence Jones’s, 272

Alimentary glycosuria, 39
leevulosuria, 40

Alkaline tide, 278

Alveoli, pulmonary, 182

Amido-acids, 30, 34

Amino-purins, 46

Ammonia of urine, 279

Anemia, cerebral, 175
renal, 275.

Antiperistalsis, 267

Apex-beat, 109

Apnea, 253

Appetite, 238

Arterial circulation, 142
pulse, 144

Arteries, 142

Asphyxia, 213

Auerbach’s plexus, 259

Augmentor nerves to heart, 122

Bacteria, intestinal, 264
Balfour on the heart, 128

291

Banting treatment, 17, 36
Barr on the pleura, 185, 191
‘Basophile valle 85, 87
Beard on the thymus, 102
Beat, cardiac, 105, 132
Bence Jones’s albumose, 272
Beri-beri and protein diet, 6
Bier’s treatment of dropsy, 155
Bile, 80, 282
acids, 283
antiseptic properties of, 256
in digestion, 256
discharge, 286
excretion or secretion, 282
pigment, 79, 282
pressure, 285
a secretion, 256
volume of, 285
Bilirubin, 283, 287
Biliverdin, 288
Blood, 71-104
cellular constituents, 73
corpuscles, red, 73
white, 81
distribution in body, 167
plasma, 91
platelets, 90
Buckmaster on, 90
-pressure, 159
arterial, 159
capillary, 155
diastolic and
160
intracranial, 174
regulation of, 166
variations in, 163
reaction, 92
sugar in, 94
Bodily energy, 2 ef seq.

19—2

systolic,

292

Body heat, 49-70

chemical regulation of,
60

Clifford Allbutt on, 61
Davy on, 61
Hobday on, 61
internal regulation, 68
Jurgensen on, 61
nervous mechanism of, 64
physical seo aa of, 53
Rubner on, 61
sources of, 64

sibel ee 258

Bouchard on metabolism, 28

Bowman, vital theory of urine pro-

duction, 271

Bradycardia, 134

Broadbent on the pulse, 152

Brodie on circulation, 169

on pulmonary bloodvessels,
183

Bronchi, 180

Buckmaster on blood platelets, 90
on coagulation, 97

Bunge on proteins, 91

Caisson disease, 218
Calcium salts in bile, 283-4
and coagulation, 97
Calorimetric experiments, 8
Campbell, H., on pulmonary cir-
cu ation, 184
Cannon on digestion, 245, 248
Capillary circulation, 153
pressure, 155
Carbohydrate assimilation, 40
conversion to fat, 40
diet as source of energy, 13
metabolism, 37
and pancreas, 42
Cardiac beat, 105
irregularity, 132 et seq.
conductivity, 106, 119
contractility, 118
excitability, 131
innervation, 121
physiological properties of,
118

rhythmicity, 131
tonicity, 119
muscle, 105
rhythm, 106, 180 e¢ seq.

APPLIED PHYSIOLOGY

Castration, effects of, 26
Cerebral circulation, 174
metabolism, 20
pressure, 174
Chemistry of respiration, 209
Cheyne on diet, 46
Cheyne-Stokes respiration, 205,
223
Chittenden’s standard dietary, 4
14

Chlorosis, 96
Cholesterin of bile, 284

Chyle, 264
Circulation, 141-176
arterial, 142

cerebral, 175
and respiration, 173
venous, 157
Claude Bernard on glycosuria, 43

Clifford Allbutt on body heat,

61
Clothes and body heat, 56
Coagulation, 96 ef seq.
Cohnheim on metabolism, 28
Cold, clinical effects of, 65
Colon, bacteriology of, 265
functions of, 262
movements of, 268
Compressed-air baths, 219
Conduction, in the body, 54
Count Rumford on, 57
Conductivity of cardiac muscle, 106,
119
Conservation of bodily energy, 8
of tissue substance, 2
Contractility of cardiac muscle,
118
Convection, 55
Convoluted tubules of kidney, func-
tions, 271
Costal respiration, 195

Coughing, 203, 221
Count Rumford on conduction,
57

Creatinin of urine, 31, 279
Crile on peripheral resistance, 161-2

Davy on body heat, 61
Defecation, 268 ;
Deglutition, 229
Denitrification, 31 et seq.
Depressor nerves, 126

INDEX 293

Diabetes, 14, 28, 36, 38, 42
and heat production, 62
phloridzin, 43

Diabetic coma, 215
Pembrey on, 215

Diaphragm, action of, 193

Diastasic ferment of pancreatic

juice, 255

Diet, standard, 3 et seq.
and growth, 6

Digestion, 225-269
duodenal, 254
intestinal, 257
rate of gastric, 248

Dropsy, causes of, 157

Duodenal digestion, 254

Dyspnea, 207

Elasticity, arterial, 142
Emphysema, 185, 194, 199, 219
Energy, conservation ‘of bodily, 8

expenditure of bodily, 8 et seq.

in exertion, 19
income of, 12
physiological expenditure, 8,
19

protein, 31

repair of bodily, 31

sources of, 12, 20

surplus storage of, 15
Enterokinase, 255, 257
Eosinophil cells, 86
Epithelium, physiological functions

of living, 211

Lorrain Smith on, 211

Erasmus Wilson on evaporation,
55

Erepsin, 257
Erythromelalgia, 170
Evans on gases of stomach, 251
Evaporation, 55

Erasmus Wilson on, 55
Excitability, cardiac, 131
Excretion, 270-289

cutaneous, 289

hepatic, 282

intestinal, 287

pulmonary, 209

renal, 271

versus secretion, 24

Feces, 268, 287

Fats, assimilation of, 34
in the body, 16
in diet, 13
derived from protein, 36
as source of energy, 13, 35
storage in tissues, 15
Fatty tissues, 16
Ferments, enterokinase, 255, 257
erepsin, 257
fibrin, 86, 97
gastric, 235
leucocytic, 86
lipase, 255
pancreatic, 42, 255, 257
pepsin, 241
plasmase, 97
ptyalin, 226
salivary, 226
thrombin, 96
trypsinogen, 255
Fever, 68
and protein diet, 32
temperatures, 220
Fibrin ferment, 97
Food, heating power of, 64
Freudberg on reaction of blood,
93

Gases of intestine, 266
of stomach, 251
Gaskell “4 conductivity of heart,
13
on vagus control, 122
Gastric absorption, 250
digestion, 231
flatulence, 252
innervation, 246
juice, 232 et seq.
movements, 243
pressure, 241
regulation of food temperature,
233
secretion, 235
tension, 241
tonicity, 241
Gastric juice, antiseptic action,

composition, 239
secretion, 235
Gelatin and coagulation, 98
as a

food, 13
Glénard’s disease, 193-4

294. APPLIED PHYSIOLOGY

Globin, 78

Glomeruli, functions of, 271

Glycosuria, alimentary, 39
puncture, 43

Gossage on the heart, 131

Graves’ disease, 26

Gravity, influence on circulation,

Growth and diet, 6 ef seq.
Guanin, 46

Hematin, 78, 282 ;

Hematogenous jaundice, 81, 283

Hematoidin, 79

Hematology, 72

Hematoporphyrin, 79

Hemin, 79

Heemochromogen, 283

Hemodynamic pressure, 170

Hemoglobin, 78, 282

Hemolysins, 75

Hemopoietic organs, 71-104

Hemostatic pressure, 170

Haig on diet, 46

Haldane on respiration, 213, 217

Harris tweed, 59

HCl hs gastric juice, 232, 239-40,
24

Heart, 105-140
beat, 105, 132
conductivity, 119
contractility, 118
innervation, 121
nervous control of, 121
rhythm, 130
sounds, 113, 135
tonicity, 119
valvular mechanism, 112
work done by, 8, 115
Heat production, 9, 51
| action of alcohol, 67
centre for, 66
chemical regulation of,
60
internal regulation, 68
and myxcedema, 62
nerve mechanism of, 64
physical regulation, 53
Heating power of food, 64
Heidenhain’s vital theory of secre-
tory cells, 156
Hepatic excretion, 282

Hepatogenous jaundice, 282
Hertz on indigestion, 230
on peristalsis, 260, 267
Hibernation, 51
Hiccough, 222 .
High altitudes, effect of, 75
Hill on capillary pressure, 155
on cerebral pressure, 176
on splanchnic system, 169
Hobday on body heat, 61
Hueppe on work, 11
Hutchinson on vital capacity, 201
Hydrothorax, 185, 190
Hyperpyrexia, 69

Ileum, bacteriology of, 265
reaction, 265
Internal secretion, 23
of kidney, 275
Intestinal absorption, 262
bacteriology, 264
digestion, 257
excretion, 287
movements, 258
Intragastric tension, 242
Intrathoracic pressure, 190
Iodothyrin, 24
Islands of Langerhans, 42

Janeway on arterial pressure, 160
Jaundice, 282
hematogenous, 81, 283
hepatogenous, 282
Jones on ventilation, 216
Joulie’s method of estimating
acidity, 278 }
Jurgensen on heat production,

Keith on the heart, 113
on the lung, 189, 192

Kidney, excretion by, 271
innervation, 275
internal secretion, 275

Levulosuria, 40
Laughing and crying, 223
Leucocytes, 81 e¢ seq.
functions, 85
number, 87
vitality, 89
Leukemia, 83-4

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INDEX

Lewes on body heat, 62

Lipase, 255

Liver, excretion by, 282
functions of, 286

Locke on clothing, 59

Lorrain Smith on epithelium,
211
Ludwig, mechanical theory of

capillary interchanges, 156
mechanical theory of urine
production, 271
Luxus consumption, 4
Lymphatic gland, functions, 103
Lymphatics, pulmonary, 185
Lymphocytes, 83
functions, 86
Lymphoid cells, 84

MacAlister on the heart, 112
Machine, the human, 2, 11

Mackenzie on the pulse, 133-4,

148

Massage and metabolism, 20
Mast cells, 85
Mechanics of respiration, 188
Menopause, the, 26
Menstruation, 26
Mental work and metabolism, 20
Metabolic balance-sheet, 15-17
Metabolism, 1-48

re age and sex, 17

anabolic, 2

and body temperature, 52

carbohydrate, 37, 42

cerebral, 20

fat, 34

katabolic, 2

and massage, 20

and mental work, 20

and muscular tone, 22

and nervous system, 21

protein, 29

qualitative, 29

quantitative, 2

and reproductive glands, 26

and stature, 17

and suprarenals, 26
Metchnikoff on phagocytosis, 85
Methemoglobin, 79
Milk as standard diet, 4
Muir on white blood corpuscles,

88

295

Miller on expenditure of energy,

Muscular tone, 22
work, 8, 10 e¢ seq.
and tissue waste, 7
Muskens on vagus control, 122
Myogenic versus neurogenic theory
of cardiac action, 105, 131
Myxcedema, 25
and heat production, 62

Negative pressure of pleural cavity,
190

of thorax, 173
Nervous control of heart, 121
diarrhea, 259
mechanism of respiration, 201
of temperature regulation,
4

system and metabolism, 21
Nitrogenous constituents of urine,
278
equilibrium, 3

Obesity, metabolism of, 28
treatment of, 36
Oliver on blood-pressure, 165
va extract in ovariotomy,
2
Oxalic acid of urine, 281
Oxygen inhalation, 213

Pancreas and carbohydrate meta-
bolism, 42
ferments of, 42
Pancreatic juice, 254, 257
ferments of, 255, 257
Parry on body heat, 67
Pavy on sugar production, 37
Pawlow on digestion, 225, 236-7,
241, 255
Pembrey on diabetic coma, 215
on Cheyne-Stokes respiration,
224
on heat regulation, 67
Pentosuria, 39
Penzoldt on _ gastric
240
Pericardium, 111

digestion,

Peristaltic movements, 259

anti-, 267

296

Phagocytosis, 85
Metchnikoff on, 85
Phloridzin diabetes, 43
Phosphates of urine, 281
Phosphaturia, 281
Phosphoric acid as brain food,
20
elimination of, 20
Physiological personality, 27
Pigments, bile, 282 et seq.
blood, 78
urinary, 281
Plasma, 91
Plasmase, 97
Pleural effusion, 185
pressure, 190
Pneumothorax, 190-1
Traube on, 203
Poikilocytosis, 74
Polycythemia, 76
Polyuria, 273
Precipitin, 99
Pressure, in bile-ducts, 285
capillary, 155
cerebral, 174
gastric, 241
intrathoracic, 190
pleural, 190
Priestley on respiration, 219
Protein, denitrification of, 31
diet, 2, 29
and beri-beri, 6
and tuberculosis, 6
energy, 31
equation, 3 et seq.
metabolism, 2 e¢ seq., 29
repair, 31
serum, 30
source of energy, 4 et seq.
fat, 36
sugar, 41
-Sparers, 32
tissue, 30
in tissue waste, 2
Ptyalin, 226
Pulmonary circulation, 183
innervation, 183, 201
respiration, 209
Pulse, arterial, 144
Pulsus paradoxus, 174
Puncture, glycosuric, 43
Claude Bernard on, 43

APPLIED PHYSIOLOGY

Purin bodies, 45

Qualitative metabolism, 29
Quantitative metabolism, 2

Radiation, 54
Raynaud’s disease, 75, 170
Red blood corpuscles, 73
Red marrow, 73, 77, 83
Reflex inhibition of heart, 129
Renal anemia, 275
Repair protein, 31
Reproductive glands and meta-
bolism, 26
Residual air, 198
Respiration, 170-224
abdominal, 195
at high altitudes, 218
centre for, 201
chemistry of, 209
and circulation, 173
costal, 195
nervous mechanism of, 201
pulmonary, 209
Respiratory centre, 201
exchanges, 209
Rhythmicity of heart, 131
Rickets, 14
Rubner on body heat, 61

Saliva, constituents of, 226
ferments, 226
Salivary glands, excretory functions
of, 228
secretion, 225
Salt in urine, 280
Schmaltz on volume of plasma,
95
Secretion and excretion,
internal, 23 eee
Secretory nerves, 227
to kidney, 275
Seidelin on gastric digestion, 240
Sensibility of heart, 126
of intestine, 261
of stomach, 234
Serum, 98
proteins, 30
Sibson on the lungs, 199
Sighing, 222 .
Skodaic resonance, 189
Sneezing, 203, 221

INDEX

Sobbing, 222
Sounds of heart, 113, 135
Specific heat of body, 69
Sphygmogram, 147
Splanchnic system, 168
Hill on the, 169
Spleen, 99
Standard dietaries, 3 et seq.
Starling on bile, 256
Starling’s law of the intestines,
259

Stercobilin, 282, 287
Stolnikow on liver, 169
Stenosis, aortic, 117

mitral, 116
Stomach, 231 et seq.

functional divisions of, 243

innervation, 246

pressure in, 241, 245

uses of, 231
Succus entericus, 254 257
Sugar, assimilation of, 40

conversion into fat, 40

into glycogen, 37
fermentable, 39
rotein source of, 41
Sulphates of urine, 280
Supplemental air, 199
Suprarenals in metabolism, 26
Sweat, 289
Sympathetic
123-4

nerves to_ heart,

Tachycardia, 123, 134
Temperament, 27-29
Temperature, body, 49
chemical regulation of, 65
nervous mechanism of, 64
physical, 53
Thrombin, 96
Thymus, 102
Thyroid secretion, 24
Tidal air, 199
Tissue proteins, 30
repair, 2
respiration, 219
substance, conservation, 2
tension, 161
waste, 2 et seq.
Tonicity, cardiac, 119
tric, 241
Trachea, 180

297

Traube on respiration, 203
Trophic nerves, 22
Trypsinogen, 255, 257

Uremia, 211
Urea, 278
Uric acid, 44, 279
endogenous, 46
exogenous, 45
metabolism, 44
synthesis of, 47
Urinary pigments, 281
Urine, constituents of, 276 e
seq.
ammonia, 279
creatinin, 31, 279
oxalic acid, 281
phosphates, 281
salts, 280
sulphates, 280
urea, 278
uric acid, 279
water, 276
reaction of, 277
production, vital and me-
chanical theories re, 271
volume of, 273, 276
Urobilin, 281, 283

Vagus control of heart, 122
in respiration, 202
Valves of heart, 112
Vegetarian diet, 3
Venous circulation, 157
Ventilation, 215
Virchow on the blood, 81
Vital capacity, 200
Voit’s standard dietary, 3
Vomiting, 252
centre for, 253
Von Noorden, balance-sheet of
energy, 14
on glycogen, 38
on uric acid, 279
on work, 19

Warm-blooded animals, 50

Weather and metabolism, 21

Wenckebach on cardiac contractility,
118

298 APPLIED PHYSIOLOGY _
White corpuscles, 81 Xanthin, 46 1
classification, 82

enumeration, 87 Yawning, 222 <n r
Work, digestive, 8, 9
inter:

‘ Zuntz on expenditure of energy =
muscular, 8, 10 ef seq. 19 a

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