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Full text of "Applied physiology"

APPLIED PHYSIOLOGY 






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 



^ 



si, ^^ 



LONDON 



<^»r 



/iU 



EDWARD ARNOLD /\V 
1908 ^ ^ 

[All rights reserved] 



PREFACE 

With 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 



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 facts 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. Eainey for kindly 
revising the proofs. 

K. H. 

1908. 



CONTENTS 



CHAPTER PAGE 

I. THE APPLIED PHYSIOLOGY OF METABOLISM - 1 

II. THE APPLIED PHYSIOLOGY OF BODY HEAT - 49 

III. THE APPLIED PHYSIOLOGY OF THE BLOOD AND 

HEMOPOIETIC ORGANS - - - 71 

IV. THE APPLIED PHYSIOLOGY OF THE HEART - 105 
V. THE APPLIED PHYSIOLOGY OF THE CIRCULATION - 141 

VI. THE APPLIED PHYSIOLOGY OF RESPIRATION - 177 

VII. THE APPLIED PHYSIOLOGY OF DIGESTION- - 225 

VIII. THE APPLIED PHYSIOLOGY OF EXCRETION ' • 270 

INDEX - - - - - - 291 



IX 



LIST OF DIAGRAMS 
IN COLOUR 

•LATE FACING PAGE 

I. THE INNERVATION OF THE HEART (AFTER POWELL) 122 

II. DIAGRAM OF A LOBULE OF THE LUNG (AFTER STOHR) 183 

III. THE RESPIRATORY CENTRE AND ITS CONNECTIONS 204 



Iia. PAGE 

1. ABSOLUTE NUMBER OF LEUCOCYTES PER CUBIC 

MILLIMETRE AT DIFFERENT AGES - - 88 

2. DIFFERENTIAL PERCENTAGE COUNTS THROUGHOUT 

LIFE (AFTER CARSTANJEN) - - - 89 

3. SERIES OF VENTRICULAR SYSTOLES (AFTER WENCKE- 

BACH) - - - - - - 118 

4. HEART SOUNDS - - - - - 138 

5. PULSE TRACING, SHOWING VENTRICULAR INTER- 

MISSION (after cushny) - - - 138 

6. pulse tracing, showing auricular intermission 

(after cushny) - - - - - 139 

7. change in shape of an artery during passage 

of the pulse wave - - - - 145 

8. SPHYGMOGRAM of radial PULSE (MACKENZIE) - 148 

9. INFUNDIBULUM AT THE END OF COMPLETE INSPIRA- 

TION AND EXPIRATION (HARRY CAMPBELL) - 184 

xi 



xii LIST OF DIAGRAMS 

FIG. PAGE 

10. 'pull' exerted by the lungs by means of their 

contractibility - - - - - 190 

11. cross section of the right lung, showing 

DIRECTIONS OF EXPANSION (kEITH) - - 196 

12. RIGHT LUNG FROM THE SIDE, SHOWING DIRECTIONS 

OF EXPANSION (KEITH) - - - - 197 

13. VERTICAL SECTION OF THE RIGHT LUNG TO SHOW 

EXPANSION (KEITH ) - - - - 198 

14. VITAL CAPACITY (AFTER HUTCHINSON) - - 200 

15. POSITION OF SHADOW DURING THE SWALLOWING 

OF A MOUTHFUL OF MILK CONTAINING BISMUTH 
CARBONATE (HERTZ) - - - - 230 

16. FUNCTIONAL DIVISIONS OF THE STOMACH - - 243 

17. SEGMENTATION IN HUMAN SMALL INTESTINES 

OCCURRING SIMULTANEOUSLY WITH PERISTALSIS 
(hertz) ...--- 259 

18. average time at which various points of the 

colon are reached after a bismuth break- 
FAST (hertz) - - - - 261 



APPLIED PHYSIOLOGY 

CHAPTER I 
THE APPLIED PHYSIOLOGY OF METABOLISM 

The 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 Metabolism.* 
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 3 

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 

1—2 



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 kilogrammes) 
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 semjyer et uhique et ah 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. 

Storage of Surplus Building- Material. — In any dis- 
cussion of the conservation of matt er in the body, two 
influences must be considered : (1) the effect of growth, 



METABOLISM 7 

and (2) the influence of muscular labour. As regards 
gro\Tth, 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 mammae. 

As regards the influence of muscular labour, experi- 
ment has clearly shown that the waste of tissue which 
it 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 an- 
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. 

2. The Conservation of Bodily Energry. 

1. Expenditure of Energ"y. — 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 ; (iii.) 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 impo^ij^e. The work 
of the heart alone amounts to abo^HEO,000 kgm. 
(133 Calories),* or about 64 foot-tonJUbr 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. ^^^Mfent 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.e., 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. 

(iii.) 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 i^ 
which the skeletal as opposed to the visceral muscles 
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 — i.e., lOd. 
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, whicV 
is better than that of any human invention.* 

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

* Thurston, ' The Animal as a Prime Mover ' (Smithsonian 
Eeport for 1896). 

f 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 ... ... ... 4*1 Calories. 

Carbohydrate ... ... 4*1 „ 

Fat 9-3 

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. Eickets, 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 Ag-e 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.y 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 
great 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. 

3. 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 m 
the case of a man of about 10 stone weight (Magnus- 
Levy) : 

Calories. 

At rest in bed 2,000 

Besting indoors 2,230 

With light industrial work 2,600 

With moderate muscular labour ... 3,100 
With severe muscular labour 3,500 

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. E.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 
313 Calories of energy, or li ounces of fat (Zuntz). If a man of 
70 kilogrammes weight takes to Uving up a stair 15 metres high, 
and goes up four times a day, he does 4,200 kilogrammes of work 
daily ; but, as only 30 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 
3 "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 ; i.e., 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 4|- ounces of fat). 

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

2—2 



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.' 

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 I'Organisme,' Montpellier, 1907 (rev. in Brit. Med, 
Journ., 1907, ii. 539). 



METABOLISM ^1 

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 metaboHsm, 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 
L, 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. 

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,' Arcliiv. of Fliil. Psychol, 
and Scientific Methods, No. 7, July, 1906; New York, Science 
Press (abst. in Brit. Med. Journ., 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 Tvay 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.f 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. 



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 g,t 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 machind to 
explain pathological phenomena which would be other- 
wise difiicult 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 metabolism are turned into the blood-stream, and, 
being diffused throughout the body, may conceivably 
influence chemical processes in remote parts. It would 



U 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 excirtion, 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 strict 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. Myxcedema, 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 myxcedema, 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 thj^roid 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 an^ 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 27 

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 c(^sumption 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 
myxoedema 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 suhjudice. 

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 the 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 



S2 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. ^ 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 
well. 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. 

3—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 ^-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 formulae : 

CHg - CH2 - CH2 - CO2 H = Butyric acid. 

CaHsCCHa-CHg-CHg- 002)3 = Glyceryl tributyrate, a 

typical fat. 
H(0H3 - OH - OH - CH2 - CO2) =^-oxybutyric 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. 

3. 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 outlin.es 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 ejrperimentum cnicis 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 ordinary 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, which 
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. 

* It should be remembered that in health the whole volume 
of the blood contams less than ^ 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. 

It 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. 

„ laevulose ... 140 to 160 „ „ 

„ cane-sugar 150 to 200 „ „ 

„ milk-sugar 80 to 120 ,, „ 

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 leevulose, and such * alimentary laevulosuria ' 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 41 

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 tjre 
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 result 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 genera} 
protein metabolism, and pursues special lines of its ow6. 
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 

* goutiness ' 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 : 

N = CH 

I I 

HO C-NH\ 

il II >H 

N-O-N ^ 
Uric acid is trioxypurin : 

HN-CO . H-N-CO 

II ' ' , 
OC\C-NH. QC C-ATH. 



^-. 



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 {e.g., 
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 hy the breaking down of 
body tissues tvhich contain amino-purins (e.g., adenin and 
guanin) and oxypurins {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 leukaemia. 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, etc. 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 at 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. Still, a small percentage may be 
derived from lactic, tartronic, and /i?-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 haemoglobin); 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. / 



CHAPTEK II 

THE APPLIED PHYSIOLOGY OF BODY HEAT 

Heat 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 it 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 3,000 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 anaesthetics are amongst 
such agents, and it is a well-known fact that oold is 

49 4 



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 v^^hat 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 
18|° 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. So 
stereotyped, however, has the normal type of meta- 
bolism become through long habit that such inversions 
of it are but rarely met with. 



BODY HEAT 63 

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 Regrulation, 

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

(a) The Natural Channels of Heat Loss are — 





Percentage of 
Total Heat Loss. 


(i.) The skin ... 


87-5 


(ii.) The lungs ... 


10-7 


(iii.) The excreta 


1-8 



* Gibson, 'The Effects of Transposition of the Daily Eoutine 
on the Ehythm of Temperature Variation' (^Amer. Journ. Med, 
Sci., 1905, cxxix., 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. 

3. 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. 
Kadiation 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). 

3. Convection only comes into play when the body 
is exposed to the influence of air in motion. Draughts, 
for instance, produce their local chilling effects by this 
means, and wind^ 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 {ibid., 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. 

(h) 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 f 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. 

* Eubner, 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. 

t ' 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 Eumford 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 35° F. noted. 
The results were as follows : 



When surrounded with— 


Seconds. 


Twisted silk ... 


917 


Fine lint 


... 1,032 


Cotton-wool ... 


... 1,046 


Sheep's wool ... 


... 1,118 


Eider-down ... 


... 1,305 


Hare's fur 


... 1,312 



* Phil. Trans., Key. 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 difiBcult 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 cHmate. ... 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 quickene d. 
a^d_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 state 
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 
a semi-involuntary 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. 



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 myxoedema. 



Temperature 
of Bath. 



59° F. 

77° F. 
95° F. 



Increased Heat 

Production 

Caused. 



407 Calories 
167 „ 

7 „ 



Increased 

Destruction 

of Fat. 



43 grammes 
18 „ 
0-7 „ 



After-ECfect 
on Fat. 



9 grammes 
4 „ 




Combined 

Effects, before 

and after. 



52 grammes 
22 „ 
0-7 „ 



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. 

The Nerve Mechanism of Temperature Eegulation. 

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 anaesthetic 

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 — i.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). Everyone 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 fact, 
a tonic effect very like that of strychnine. 

Whether or not there is a special centre in the brain 
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° F. 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 anassthesia 
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 anaesthetized 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-Eegulating 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 p?«d^ction alone be the cause of 



BODY HEAT 69 

fever, for in that case the rise of temperature of the body 
would 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 t-hat (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 ; Le., 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. There 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 
H.EMOPOIETIC ORGANS 

General Functions of the Blood. 

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 



n 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 * hsematology ' has assumed such a large 
place in latter-day medicine. 

We have spoken of the blood as a fluid medium 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 HEMOPOIETIC 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 consequences 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 Blood. 

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 haemoglobin 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 



74 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). Each corpuscle 
is stuffed full of haemoglobin, 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 condition 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 3^ 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 HEMOPOIETIC ORGANS 75 

allow the passage outwards of haemoglobin, and this is 
probably how blood pigment gets into the plasma in 
cases of Eaynaud's disease. Haemolysins also affect in 
some way the permeability of the envelope without 
necessarily dissolving the corpuscle. 

Th e red cells are also fairly rich in s alts of potash , a 
recognition of which fact, indeed, has led some people to 
recommend the treatment of pernicious anaemia by the 
administration of potassium compounds.* 

Practically, then, one may regard a red corpuscle as 
an elastic bag designed for the transportation of haemo- 
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 haemoglobin 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 330 feet ascended causing an increase 
of about 100,000 per cubic millimetre. The cause of 
* Bumpf, B&rlm. Klrni, 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 
greater 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 ^f 
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 polycythaemia 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 Hochgebirge,' St. Petersburg 
Med. Woch., 1901, xxvi. 643. 



BLOOD AND HiEMOPOIETIC ORGANS 77 

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 sometimes 
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 anaemia, 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 

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

Hsemoglobin 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 (hsematin) 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 haemoglobin 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 at an 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 haemoglobin 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 haemoglobin is only 
built up rather slowly, and that it takes some time, after 



BLOOD AND H.^MOPOIETIC ORGANS 79 

a haemorrhage, for the new corpuscles to be loaded up 
with it, so that one finds that the percentage of haemo- 
globin in the blood remains low for a considerable time 
after the red cells have reached their normal number. 
Long before haemoglobin was known to contain iron, the 
power of the latter metal as a remedy in some forms of 
anaemia was well known to physicians ; but the natural 
inference that such forms of anaemia 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. 

Haemoglobin 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 haematoidin, which is 
met with at the site of old haemorrhages, such as apo- 
plectic cysts. 

Haematoporphyrin is another iron-free derivative of 
haemoglobin, 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. 

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

Methsemog'lobin is met with in the urine in small 
* See Stockman, Brit. Med. Journ., 1893, i. 881. 



80 APPLIED PHYSIOLOGY 

amounts in the rare and interesting disease methsemo- 
globinuria. It probably owes its production to the 
action of the acids of the urine on hsemoglobin. It is 
also produced from haemoglobin 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 debris 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. 
(3 ounces) of blood, but not more ; and should the de- 
struction of blood in the portal area be greatly increased, 

* See Hunter, ' Pernicious Anaemia,' and Heinz, Beitr, z. Path. 
Anat. u. Allgem. Path., 1901, xxix, 299. 



BLOOD AND H^^MOPOIETIC 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 hsematogenous jaundice result (see p. 283). 

The destruction of haemoglobin 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 anssmic 
subjects. 

White Cells. — Ever since the publication of Yirchow'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), 23 per cent. 
Q)) Large mononuclears, 2 per cent. 

2. Granular: ^^. 

(a) Polymorphonuclear, with abundant neutrophil 
granulations, 70 per cent. 

(h) 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 HiEMOPOIETIC ORGANS 83 

varieties 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 bone s, t he 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 leukaemia 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 leukaemia. 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 leukaemia 
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) BasophU. 



(&) Neutrophil. 



Polynuclear leucocytes — 

(a) With basophil granulation. / 

(jS) With neutrophil granulation. / 

In process of development, according to ihis 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 H.EMOPOIETIC 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 leukaemia. 

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.^., 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.y 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 HEMOPOIETIC 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) haemoglobin 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 ... ... ... 2,000 

Large mononuclears ... ... 350 

Eosinophils ... ... ... 150 

* See Howard and Perkins, Johns HopMns Hospital BeportSt 
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. 



20.000 




Fig. 1. — Absolute Number of Leucocytes per Cubic Millimetre 
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 HEMOPOIETIC 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 dupation 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 





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Fig. 2. — Differential Percentage Counts throughout Life. 

(After Carstanjen.) 

days. Hence any theory of immunity which is based 
upon the * education ' of individual leucocytes in deahng 
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 
debris 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 amoeboid movement, and that they certainly are not 
degeneration products, but are probably independent 
elements of the blood. 

On the other hand, Buckmasterf 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 role in pathology, and they cannot be considered 
of much interest to the clinician. 

* Deetjen, Virchow's Arcliiv, 1901, clxiv. 239. 
t 'The Morphology of Normal and Pathological Blood' (John 
Murray 1906), p. 132. 



BLOOD AND H^EMOPOIETIC ORGANS 91 

The Blood 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 4J to 3, 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.g., in 
diabetic coma, and also in anaemia. 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 HEMOPOIETIC ORGANS 93 

the lymph spaces of the tissues.* Free acids or acid 
salts are neutralized partly by the alkaline sodium 
phosphate (NasHPOJ of the blood, which they convert 
into sodium acid phosphate (NaHsPOJ, and which is 
voided in the urine, and partly by the sodium carbonate 
of the plasma with the liberation of CO2, 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 krdney. 
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, 
t Vi/rchow's Archive 1891, cxxv. 566. 



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 diarrhoea. 

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 oesophageal 



BLOOD AND HEMOPOIETIC ORGANS 95 

obstruction, in which no food can reach the stomach,* 
and in diabetic coma it may be present in such qu?(fitity 
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. Haemorrhage, 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 f 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 (Schmaltz j). 

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 3J litres 
(about 6 pints). In health this amount is probably as 

* Boninger, Zeit. f. Klin. Med., 1901, xlii. 65. 
t Askanazy, Deut. Arch. f. Klin. Med., 1897, lix. 385; 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 anaemia 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, Trcms. of the Path. Soc. of London, 1900, 
li. part 311. 



BLOOD AND HEMOPOIETIC 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, (3) 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, Zoc. ci^., 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 haemorrhage in scurvy. 
Albumoses appear to have a power of inhibiting coagula- 
tion. In a 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 haemorrhage 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 HiEMOPOIETIC 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 pathology 

* See the collected works of William Hewson, F.K.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. Eichly 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 
d6bris or corpuscles which have been broken down 
elsewhere. It is uncertain, in other words, whether the 
spleen is an active agent in haemolysis 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 anaemia, 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. 



BLOOD AND HEMOPOIETIC ORGANS 101 

complicated by the fact that splenic anaemia 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 anaemia. 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 haemolysis, 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 cle 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 
trabeculae. 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 trabeculae 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 transformation of the 
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. 



BLOOD AND H.EMOPOIETIC 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 leuksemia, 
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 Hopitaux, 1899, Ixxii. 1321. 
t 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 ArcTiiv^ 1899, civ. 335. 



CHAPTEK IV 
THE APPLIED PHYSIOLOGY OF THE HEART 

The Beat of the Heart. 

The 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.! 

* 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. 

f 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 ivhole 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 
conductivity 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 co-^Whiated shortening of all 
their fibres — not by a peril^^c wave — by which the 
ventricular systole is produceo^p These fibres are partly 
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 destrojpd by disease, the propagation of the wave 
of contraction is pre^mited, and a condition of 'heart-block' 
results. In such a case the ventricles take on an independent 
action, and contract <iitythmically at a rate 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 it 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, f 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 Journal of Anatomy and Physiology, 1907, 
vol. xlii. 

■j* See Martins : ' 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. f 

After their contraction, the walls of the ventricles 
rebound in diastole. Whether this is due merely to an 
elastic recoil of the compressed columnae carnese 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 heart, but it 
seems to play a 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 (Schafer's ' Physiology,' ii. 20). 

f Graham Steell. 



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 4|- 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 wall 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. Journ., 1900, ii. 895. 



110 APPLIED PHYSIOLOGY 

an hypertrophied heart always displays a strong apex- 
beat. 

The exact way in which the 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 hefore 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 hefore 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 lihe 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- 



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,' La^zce^, 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. 

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 instnfment 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. Journ., 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 diamet er of the 
h^ftfig^pf th^^he art undergoes such a marked "diminution 
during systole in consequence o f the contraction of the 
circular muscle of the ventricular wall. In other words, 
the 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. 
KecQpt investigations by Keith* tend to show that the 
backflow of blood into the venae cavse 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. 
with vol. xxxvii. of Journ. of Anat. and Physiol.). 

8 



114 APPLIED PHYSIOLOGY 

substance of the ventricles, (2) that which results from 
the stretching of the auriculo-ventricular valves. One 
says 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. Either 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. 



1% Second. Ventricular Systole. 



1^(5 Second. Ventricular Diastole. 



Compression 

Time, 

jij Second. 



All valves 
closed; 
a p e X - 
beat pro- 
duced 



Expression Time, 
A Second. 



Auriculo - ven- 
tricular valves 
closed, blood 
being expelled ; 
recession of 
apex 



First Opening 
sound of 

semilunar 
valves 



Second 
sound 



Auricular 

Systole, 

■^ Second. 



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,' Zeitf. KUn. 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 If 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 30 per cent, of the normal time.t 
Hence the blood must be expelled more rapidly — i.e., 
more work must be done. 

It has been calculated that if a lesion is so bad as to flT^ ) 
require 7*7 times as much energy as usual to com- viljy 
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. 
Even in health, however, the law may be temporarily 

* See Hill in Schiifer'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 systoHc 
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 



Fig 3. — Series of Ventricular Systoles (after Wenckebach.) 

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

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

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^^H 
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 excitabihty are diminished, and when tone is 
diminished these are increased.! Now, diminution of 

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



THE HEART 121 

tonicity is one of the commonest events in cardiac 
disease, and, probably in consequence of this, increased 
excitabiUty 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 dimmish 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, t 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. 

t Gaskell, however, believes that the vagus does lower tonicity 
(Sehafer's 'Physiology,' ii. 215). 



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 
greatly 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. 37 (Stuttgart, 1896). 



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 Keid Hunt, Amer. Joum. of Physiol., 1899, ii. 395. 



I 



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 d ue to ^a ^ tempo rary ) 
drminutrbiTof vagus toneTanJ 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. 

t See Ferrier's Harveian Oration on 'The Heart and Nervous 
System,' Brit. Med. Journ., 1902, ii. 1336. 



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 
a 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 
... I 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 he 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.* / 

' 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 Lacedaemon, 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. 



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., I^ng 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 fareweU, 
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. 

3. 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, f 



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 Eeid Hunt, Amer, Journ. of Physiol.^ 1899, ii. 395. 



THE HEART 131 

condition of the muscle waH ; (2) the influence of the 
nervous mechanism. ^•.. 

Rhythnjicity 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 Khythm of the Heart ' 
{Brit. Med. Journ., 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. 

3. 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. 



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 dyspncea 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 sadden 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, t 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 a dose 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. 

Martins, ' Tachycardie ' (Stuttgart, 1895). 

t Dehio, 'Ueber die Bradycardie der Reconvalescenten,' Deut. 
Arch./. Klin. Med., 1894, lii. 74. 



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 : 

—2 1 2 1 2 Normal. 



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

2 1 2 1 Prolongation of diastole (brady- 
cardia). 

— 2 — 1 — 2 — 1 — 2 — 1 — 2 — 1 — 2 — Shortening of systole and dia- 
stole (tic-tac rhythm). 

2 1 2 1 2 1 Shortening of diastole (tachy- 
cardia). 

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

* Determann, ' Ueber Herz-und Gefassneurosen/ Volkmann's 
Samml. Klin. Vort., 1894, Inn. Med., Nr. 30, 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. 

3. 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 



1 



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.' (3) 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, f 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 (Schafer's 'Physiology,' 
ii. 195). 

t Wenckebach, ' Zur Analyse des Unregelmassigen 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. 



c — 



a — Normal heart sounds 



Fig. 4. 

h 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 




I T, I 



I .a I 



I T"? I 7C • 



73 ' 76 ' 7* ' 76 ' 132 ' 77 ' 76 ' 72 ' 73 ' 

Fig. 5. — Pulse Tracing, showing Ventricular Injbrmission. 
(After Cushny.) (The Figures represent Onb-hundrbdths 
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.* 



\J 




84- ' 88 ' 158 ' 88 94< 85 94. 97 



Fig. 6.— Pulse Tracing, showing Auricular Intermission. 

(After Cushny.) 

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,' Journ. of 
Exper. Med., 1899, vol. iv., p. 327, and Brit. Med. Journ., 
1900, ii. 892. 

t 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 synclironism 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.t 

^ Engelmann, Arch. f. d. Ges. Physiol., 1896, Ixii. 543. 
t Porter, ' The Co-ordination of the Ventricles,' Amer. Journ. of 
Fhysiol., 1899, ii. 127. 



CHAPTER V 
APPLIED PHYSIOLOGY OF THE CIECULATION 

It 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 it 
follows ; at the same time the flow of blood approximates 



1 



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, Journ. of Physiol, 1902, vol. xxviii. 220. 



144 APPLIED PHYSIOLOGY 

arrest of haemorrhage. 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 clinicaii 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. -^^ 

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 tliis is the pulse, is erroneous, though it may 
be admitted that such a misconception need not make 
a 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, 



o O 



Fig. 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 



146 



APPLIED PHYSIOLOGY 



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



Foetus 


130-140. 


0-1 year .. 


130. 


1-2 years .. 


115-120 


3-4 „ .. 


105-110. 


5-9 ,, .. 


95-100 


9-10 „ .. 


90. 


16-17 „ .. 


80. 


Adults 


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 have no 
influence, but warm meals result in quickening. 

Every sensation of burning, pressure or nausea 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 haemorrhage. 

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

The Sphygrmogram.— If 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 




Fig. 8.— Sphygmogeam of Eadial Pulse. (Mackenzie.) 

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

BO 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.' 

The most probable explanation of the dicrotic wave is 
given by Mackenzie as follows : f * 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 {Journ. of Anat. and Physiol., 1906-7, xli. 137), 
concludes that, in the great majority of cases, the primary and 
predicrotic waves are both genuine, and are of central origin. 

t ' The Pulse,' p. 20. 



1 



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 aortic 
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 30 feet per second. Owing to the elasticity of the 
great 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 



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 : 

'It 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 Cipculation. 

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 J 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 circula- 
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 at the 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- 
cythsemia, 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. 




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 haemorrhage 



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 as a 
secretion of the capillaries, just as milk is a secretion of 
the mammae 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 ot 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 



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 ' essential ' 
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 



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 sima total of the * peripheral resistance ' 
there can be no doubt. The influence 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. 

3. 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 
haemorrhage — 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 — e.g., 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-J 
metres of Hg. He makes use of the pneumatic suit in order 
produce an artificial peripheral resistance in cases of shock, 
which the general vasomotor centre is completely paralyzed (se( 
* Blood-pressure in Surgery '). 



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 — i.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- 
horuiTii et morbus dominorum. 

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 haemorrhage 
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. 



Regrulation 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. 



THE CIRCULATION 167 

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 anaemia of the 
medulla stimulates the general vasomotor centre, and 
in this way a fall of blood-pressure from haemorrhage 
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 



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. 



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. 
V V That the veins of a part as well as its arteries are ^ 
z-' 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 nervous 
system. 

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 hcemostatic pressure, as opposed to the licemodynamic 
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 a man 
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 haamodynamic pressure, the more pro- 
nounced is the effect of the haemostatic 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.e., 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 



THE CIRCULATION 175 

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.' Seeing 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 hyperaemia 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 anaemic. If the anaemia 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 



O^ 



V 



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 anaemia 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. 



CHAPTEE VI 
THE APPLIED PHYSIOLOGY OF RESPIEATION 

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 so 
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 vibrissas, 
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 aesthetic. 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 so 
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 to the 
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, Journ. of Physiol., 1903, xxix. 97, 
and Trans, of the Path. Soc. of London 1903, liv. 17. 

f See Mackenzie, Amer. Journ. of Med. Sciences, 1883, Ixxxvi., 
106; also Eiegel and Edinger, Zeit.f Klin. Med., 1882, v. 413. 



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 ; (3) 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, Pfiilger'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, 



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. 
t 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 by a 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). 



^ 



Mvary Artery. 



Brorvchlolea. 




Plate II. — Diagram of a Lobule of the Lung 

(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 Lymphatics 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 
left 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 





Fig. 9. 

These diagi-ams represent an infundibulum, A, at the end of a complete 
inspiration, and B, at the end of a complete expiration, b = alveolar 
wall ; a = bloodvessels of the same. It will be seen that tlie 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 complete 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 haemorrhage 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 venae cavse, as occurs 
when the lungs themselves are the seat of the obstruc- 
tion — e.g.y 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 j^ 
susceptible to the action of adrenalin. Advantage has 
been taken of this fact by Barr in the treatment of 
£leuTaJ_effu8ion. 

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 a helps to determine the greater 
liabilit^Loit he apices j o_bec ome the^ ^jt^qf 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. Kim. 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 stomach. 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.'t 

* See Salter, Lecture on Dyspnoea, Lancet, 1865, ii. 111. 
t Samuel West, Med. Chir. Soc. Trans., 1898, Ixxxi. 273. 



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- 




FiG. 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 (hydrothora^ when 

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



Normal inspiration 

Normal expiration ... 

Deep inspiration 

Deep expiration 

Deep inspiration with air passages closed 

Deep expiration with air passages closed 



Milligrammes 
Hg. 

- 10 

- 7 
~ 40 

- 

- 100 
+ 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.y 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.' 

Eespiration 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 
it 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 



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 vertebrae 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 Glenard's Disease,' London Hosjp, 
Qaz., 1902, ix. 56. 

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 Gl^nard'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 
]Si 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. Kim. Med., 1896, xxx. 37. 



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 mammae 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. 

13—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 oedema of 
the lungs is produced in laryngeal or tracheal obstruc- 
tion. If the chest wall is very soft, it may be unable to 



Anjt^;; ^u^^ 




Fig. 11. — Cross Section of the Right Lung, 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 



d 



RESPIRATION 



197 



expand either up\^ards, 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 



Apeoo 




V^ 



Fig. 12. — Eight Lung from the Side, showing Directions 
OF Expansion. (Keith.) 



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 13). 
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 300 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 




Fig. 13. — Vertical Section of the Right Lung to show 
Expansion. (Keith.) ^^ 



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 dyspnoea 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 
Tidal 
Reserve 
Besidual 




Fig. 14. — Diagram of Vital Capacity. (After Hutchinson.) 

/ 

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 pleurae 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. 
255 ,, ,, ,, sitting erect. 

230 „ „ „ lying supine. 

220 „ „ „ „ prone. 

— Hutchinson. 

This shows how it is that patients with dyspnoea 
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. ^^ 

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 



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 w^ay 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- 
ments. 

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. KUn. Med., No. 26, and Stirling, ibid., 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 breathhig 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. 

If, again, the phrenic nerve be in any way 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 



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 dyspnoea. 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. 



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 per cent. 16*03 per cent. 

Nitrogen ... 79 per cent. 79 per cent. 

CO2 ... 0*04 per cent. 4*4 per cent.* 

In addition, the expired air is saturated with water 

* Variations in ' respiratory exchange ' — i.e., the total consump- 
tion of oxygen and excretion of COg — usually discussed under 
* Kespiration,' 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 COg and less 
oxygen than ordinary expired air, the oxygen amounting 
to only 13 or 14 per cent., and the CO2 to 5 or 6 per 
cent. Further, this method of analysis has shown that 
the partial pressure of COg 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 CO2 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, it 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 CO2, just as ursemia 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- 

* Jomn. of Physiol, 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. Kespiration 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 20 parts. 

Nitrogen 1-2 „ 

Carbonic acid 40 „ 

Of the oxygen less than one volume is in solution in 
the plasma. The rest is combined with haemoglobin 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 haemoglobin in the blood can be 

* ' The Physiology of Common Life,' 1869, 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 haemoglobin in the 
blood is greatly reduced, as, for example, in an£emia, 
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 18^ per cent, 
combined Og by vol., and 0*6 per cent, dissolved O2 by vol. 

When pure oxygen is breathed, arterial blood contains 18*7 per cent, 
combined O2 by vol., and 3 percent, dissolved O2 by vol.— Haldane. 



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.' t 

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 CO2, 
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,' Zeit f. didt. 
u. phys. Therapie, 1900, iv. 122. 

t Schafer'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 haemoglobin. 
It is the alkalinity of the blood which gives it its chief 
power as a CO2 carrier, for sodium carbonate (NagCOg) is 
able to take up one molecule of the gas, forming sodium 
bicarbonate (NaHCOs). There seems to be a constant 
struggle going on between the proteins of the blood and 
CO2 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 CO2 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 
CO2 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 
4-526 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 CO2, that of Arnside, near the Lake District, con- 
tained only 3*237. 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 
CO2 than the external air, even when it is well ventilated. The 
writer concludes that a certain amount of COg is in some way 
retained by the walls, and is constantly passing back into the room. 

The amount of CO2 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 COg in the air of the room below 10 parts 
per 10,000. 

A room heated by a gas fire contains more CO2 than one heated 
by a coal fire. 



RESPIRATION 217 

indeed, is that either an excess of CO2 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 7iot due 
either to want of oxygen or to the presence of an excess 
of CO2, 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 subject 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 
CO2 in an inhabited room should not exceed 12 parts per 10,000 
during daylight, and 20 parts per 10,000 when gashght is used. 



218 APPLIED PHYSIOLOGY 

oxygen.* This may possibly be the reason why the 
East-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, Joum. of Physiol.^ 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 CO2 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. It is 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. 

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. 399. 



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 anaemia. 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 uraemic 
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 apnoea 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 



2^4 APPLIED PHYSIOLOGY 

able to abolish the apnoeic period by causing a patient 
exhibiting Cheyne- Stokes respiration to inhale carbonic 
acid. 

Ehythmical 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. 



CHAPTEK VII 
THE APPLIED PHYSIOLOGY OF DIGESTION 

Digestion in the Mouth. 

The 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 
(Na2HP04), 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 CO2 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,t 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 Eichards, Amer. Journ. of Physiol., 1898, 
i. 461. 

t See Nicolas and Dubief, Journ. de Phys. et Pathol. Gen. 
1899, i. 979. 



DIGESTION 227 

it. Hence the taking of acid fluids — e.g.y 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,' Aitohison Kobertson, Journ. 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 it is 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 jof 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 

Deglutition. 

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 
oesophagus 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 



oesophagus 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 oesophagus very slowly, and may, 




/4«w- 



^^•^^K-3^ 








Fig. 15. — To show Position of Shadow at Intervals oi* One 
Second during the Swallowing of a Mouthful of Milk 

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 oesophagus caused by the presence of 
solid lumps of food, which only pass very slowly down- 
wards. 



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 oesophagus 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 
oesophagus, 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 oesophagus 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 oesophagus is possible seems to be proved 
by the occurrence of rumination in some subjects. 



Dig-estion 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) Tq 



APPLIED PHYSIOLOGY 

act as a reservoir, from which the intestine may be 
gradually supplied ; (2) to sterilize the food to some 
extent ; (3) 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 — i.e., it 
renders meals possible. The practical convenience of 
this does not need to be pointed out. The capacity of 
the stomach varied considerably in different individuals 
and in the same individual at different periods of life. 
Koughly 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. -^ 

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. 

3. 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 
60° 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. 



5!34 APPLIED PITi'SIOLOGY 

same point.* Hence cold fluids are more apt to escape 
over into the intestine imperfectly warmed, and may thus 
excite diarrhoea. 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, {b) 
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 sensitive in 
the ordinary sense, or, at all events, any sensations winch 
proceed from it fail to reach the seat of consciousness. 
It would appear, however, that the degree of anaesthesia 
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. /. Didt und Phys. Therapie, 1905, Bd. viiL, 
Heft 11. 
t Nenmann, Arcliiv f. Verdauungskrankh^l^On ^'saL &L. 



DIGESTION 235 

not to the stomach itself, but to the skin of the epi- 
gastrium, just as pain is in cases of gastric hypersesthesia 
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 
Einorexia 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 oesophagus 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 aesthetic qualities 
and flavour of their food, as well as by the administration 
of exciters of appetite such as bitters.f 

* SJcandinav. Archiv 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 Kussian 
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 
oesophageal 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). 

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 



I 



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 (Ewald's) varies from 0*11 to 0*26 
per cent, in different individuals, and the proportion of 
free HCl from 0*07 to 0"2 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. Verdcmv/ngsTirajikh.^ 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) ; (3) 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 lo 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. 
more 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. t 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, Deuts. Archiv f. Klin. Med., 1894, liii. 209, 
and Schlile, Zeit. f. KUn. Med., 1895, xxviii. 461, and 1896, 
xxix. 49. 

t See Dobrovici, ArcJiiv f. Verdauungskranlch., 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 mucosae, 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 330 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.* 




Wcb^res of 
conatrictioTh 

Fig. 16.— Functional Divisions of the Stomach. 

2. Active Movements. — From 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 Ageron, Arcliiv. f. VerdauungsJcrankh., 1905, 
xi. 460. 

16—2 



244 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 -et 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. 



M6 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 Moritzf 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. y 

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. Journ.^ 1902, ii. 779. 
t ZeiUf. Biologie, 1895, xxxii. 313. 



DIGESTION 247 

take place quite efiSciently 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 fistulas 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 idj-^ 
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. 



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. 663. 



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 
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 oesophagus, 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 oesophagus, 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 oesophagus and 
spread out over the stomach. A horse is unable to vomit 
because the longitudinal fibres of its oesophagus wind 
round spirally in the neighbourhood of the cardia 
instead of running straight on to the stomach, as in 
most mammals. 



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. VerdauungskranTch., 1904, 
X. 93. 



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 nitrog en and COg , 
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 2 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. Journ., 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 thorax is lowered. The cardiac orifice then opens, 
and the oesophagus 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). Occa- 
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 



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 anaemia 
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 anaemia o r ^j ^^ergim ia, in intoxica- 
tions — e.g., uraemia — 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 Digrestion. 

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. As a 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, Zeit f. Klin. Med., 1890, xvii. 155. 

t Glaessner, Zeit. f. Physiol. Chemie, 1903-4, xl. 465. 



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,t '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 faeces 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, Journ. of Pathology, 1896, iii. 245 ; see 
also Krehl's ' Clinical Pathology,' English translation, p. 280. 

t ' Kecent Advances in the Physiology of Digestion ' (Constable), 
1906, p. 117. 

I Mueller, Zeit f. KUn. 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. 30). 

17 



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 laevulose, 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 substances, as well as some 
purgatives, excite diarrhoea. 

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 (Auer bach's plexus), but they are also, 
apparently, under the influence of the central nervous 
system, especially through the medium of the splanchnics, 






I 



k. 



Fig. 17. — Diagram of Segmentation in Human Small Intestines 

OCCURRING simultaneously WITH PERISTALSIS. (HeRTZ.) 

which appear to exert a slight tonic inhibition of them. 
Thus paralysis of the solar plexus induces an exaggerated 
peristalsis with diarrhoea, and * nervous diarrhoea ' is 
probably brought about in 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. VerdauungskranJch., 
1903, 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 found t 
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. Hertz,! 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). / 

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. Physiol, 1898, Ixxi. 492. 
•j- Neucki, MacFadyen, and Sieber, Archiv f. Exper. Path, und 
Pharmak., 1891, xxviii. 311. 

I Gwy'8 Hospital Beports, 1907, Ixi. 389. 



DIGESTION 261 

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 




Fig. 18.— Average Time at which Various Points of the 
Colon are reached after a Bismuth Breakfast taken 
AT 8 A.M. (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'a Archiv^ 1858, xiv. 140. 



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 anaemia, 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 diarrhoea due entirely to disease of 
the colon a patient's nutrition does not appreciably 
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 caecum they contain only from 5 to 10 per cent, of 
solid matter, and as they amount to something like 
J to 1 pint in the twenty-four hours, the activity with 
which water is absorbed in order to convert them into 
solid faeces 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, it may be taken that the nutritive 
constituents of an ordinary mixed diet are absorbed to 
the following extent : 

Proteins ... ... 92 per cent. 

Fats ... ... ... 94^- „ 

Carbohydrates ... ... 98 J ,, 

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. Joum., 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 

* earlier, Brit. Med. Journ., 1902, ii. 175 ; and Veau, Gaz. dea 
Hop., October 30, 1906 (?), p. 1205. 

t Bruini, Archiv f. Verdmmngslcra/nTchf 1905, xL 162. 



DIGESTION 265 

the faeces of many animals in Arctic regions are free 
from them. Nor is the number or character of the 
bacteria in the faeces 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 faecal 
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 upt — 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 Archiv f. Verdauungs'krankli, 1904, x. 530. 
I Neucki, etc., loc. cit. 

% Lorrain Smith and Tennant, Brit Med. Journ., 1902, ii. 1941. 
§ Backman, Zeit./. Klin. Med., 1902, xliv. 458. 



266 APPLIED PHYSIOLOGY 

hand, and the contents of the bowel acquire a faecal 
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 
ofifensive. 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 ; HgS from proteins ; and 
marsh gas and hydrogen from cellulose, and chiefly by 
bacteria present in the colon. COg 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 
7 chemical stimulant also. Sulphur apparently owes its 

laxative properties to the production from it of H2S, 
whilst the constipating action of bismuth may be due in 
part to its power of fixing that gas. COg 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 caecum 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 csecal 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 
t ransverse colon are usually nearly as solid as thos e 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-caeca l 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.| 

Fig. 18 shows the average rate at which the colon is 
traversed by a bismuth meal according to the observation 
of Hertz. § 

* Grutzner, Pfluger's Archiv, 1898, Ixxi. 492. 

•j- See Neucki, etc., loc. cit. 

X See Mohroof, Indian Med. Gaz. 1902, xxxvii. 394. 

§ Loc. cit. 



268 APPLIED PHYSIOLOGY 



Defsecation. 



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 defaecation, 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 faeces 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. 

The functions of the colon as an organ of^xcretion 
will be considered in another chapter (p. 287). 

Eeviewing 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 diarrhoea 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 EXCEETION 

Much 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 discharge, may be 
arranged as follows : ^^ 

Organ. Excrdion. 

Kidney Waste products of nitrogenous metabolism, 

soluble mineral matters, and water. 

Liver Waste products of the red blood corpuscles. 

Lung ... ... ... Waste products of 'carbonaceous' meta- 
bolism and water. 

Intestine ... ... 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 haemoglobin by the 
kidney in paroxysmal haemoglobinuria, 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 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. 
In 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 diuresiSf 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. 



d 



EXCRETION 275 

for example, in acute inflammation, the capillaries 
become compressed, the organ is rendered comparatively 
anaemic, and the volume of urine falls. This effect is 
exactly comparable to the cerebral anaemia, 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 anaemia,' it 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 versa. 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 congestion 
and inflammation. 

The rate at which water is excreted by the kidney 
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 277 

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 (COg) 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 3 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^ndeter- 
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. 

Uric 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 0"25 to 0*6 gramme. 

Daily excretion of uric acid on a mixed 

diet 0"5 to 1 gramme. 

Daily excretion of uric acid on a largely 

meat diet 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 toxaemias 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. 

Oxalic acid is present in the urine to a small extent, 
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 pigrment (urochrome) we know nothing, although 
it is probably derived somehow from haemoglobin, and it 
is therefore of little clinical interest. Urobilin is present 



APPLIED PHYSIOLOGY 

in traces in normal urine, and is often greatly increased 
in disease. It is identical with the so-called stercobilin 
of the faeces, 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 ansemia. 
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. 



Excretion 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 haematogenous 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 haemoglobin is converted into haematin, 



EXCRETION 283 

then into haemochromogen, 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 'haematogenous' jaundice; 
whilst, if the destruction be greater still, some haemo- 
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 faeces, 
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 symptoms 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. 

It used to be believed that the cholesterin of bile was 
a waste product derived from the nervous system, and 
one theory of cholaemia 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 fistulae. 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; (3) certain 
mineral salts, such as calcium and iron. 

On an ordinary mixed diet the amount of faeces 
excreted is from 120 to 150 grammes, containing 30 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 d6bris, and 
a few muscle fibres derived from the food. In reaction 
the normal faeces 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 
faeces 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 diarrhoea 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 faeces 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 faeces 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 faeces, 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 variety of 
so-called * phosphaturia ' (see p. 281). 

Iron is also mainly excreted by the intestrtle, 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 lungfs 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 at 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 

Ipevulosuria, 40 
Alkaline tide, 278 
Alveoli, pulmonary, 182 
Amido-acids, 30, 34 
Amino-purins, 46 
Ammonia of urine, 279 
Anaemia, cerebral, 175 

renal, 275 
Antiperistalsis, 267 
Apex-beat, 109 
Apncea, 253 
Appetite, 238 
Arterial ciiculation, 142 

pulse, 144 
Arteries, 142 
Asphyxia, 213 
Auerbach's plexus, 259 
Augmentor nerves to heart, 122 

Bacteria, intestinal, 264 
Balfour on the heart, 128 



Banting treatment, 17, 36 
Barr on the pleura, 185, 191 
•Basophile cells, 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 
pla-sma, 91 
platelets, 90 

Buckmaster on, 90 
-pressure, 159 
arterial, 159 
capillary, 155 
diastolic and systolic, 

160 
intracranial, 174 
regulation of, 166 
variations in, 163 
reaction, 92 
sugar in, 94 
Bodily energy, 2 et seq. 

291 19—3 



292 



APPLIED PHYSIOLOGY 



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 regulation of, 53 

Rubner on, 61 

sources of, 64 
Borborygmi, 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- 
culation, 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, 130 et seq. 



Castration, effects of, 26 
Cerebral circulation, 174 

metabolism, 20 

pressure, 174 
Chemistry of respiration, 209 
Cheyne on diet, 46 
Cheyne- Stokes respiration, 206, 

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 e^ 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 oflJadney, func- 
tions, 271 
Costal respiration, 195 
Coughing, 203, 221 
Count Rumford on conduction, 

67 
Creatinin of urine, 31, 279 
Crile on peripheral resistance, 161-2 



Davy on body heat, 61 
Defsecation, 268 
Deglutition, 229 
Denitrification, 31 et seq. 
Depressor nerves, 126 



I 



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 
Dyspnoea, 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 

cutaneoas, 289 

hepatic, 282 

intestinal, 287 

pulmonaiy, 209 

renal, 271 

versus secretion, 24 

Faeces, 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 
FeiTnents, 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 fennent, 97 
Food, heating power of, 64 
Freudberg on reaction of blood, 
93 

Gases of intestine, 266 

of stomach, 251 
Gaskell on conductivity of heart, 
137 
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, 
232 
composition, 239 
secretion, 235 
Gelatin and coagulation, 98 

as a food, 13 
Glenard's disease, 193-4 



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, 

170 
Growth and diet, 6 ct seq. 
Guanin, 46 

Haematin, 78, 282 

Hematogenous jaundice, 81, 283 

Hpematoidin, 79 

Hsematology, 72 

Hffimatoporphyrin, 79 

Haemin, 79 

Htemochromogen, 283 

Hpemodynamic pressure, 170 

Heemoglobin, 78, 282 

Hsemolysins, 75 

Hemopoietic organs, 71-104 

Hemostatic pressure, 170 

Haig on diet, 46 

Haldane on respiration, 213, 217 

Harris tweed, 59 

HCl in gastric juice, 232, 239-40, 

247 
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, Q^ 
and myxoedema, 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 pressiire, 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 
lodothyrin, 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, 61 

Keith on the heart, \\2> 
on the lung, 189, 192 

Kidney, excretion by, 271 
innervation, 275 
internal secretion, 275 

Levulosuria, 40 
Laughing and crying, 223 
Leucocytes, %\ et seq. 

functions, 85 

number, 87 

vitality, 89 
Leukemia. 83-4 



INDEX 



^5 



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, fimctions, 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 
Metchnikofi" on phagocytosis, 85 
Methtemoglobin, 79 
Milk as standard diet, 4 
Muir on white blood corpuscles, 
88 



Miiller 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 
Myxoedema, 25 

and heat production, 62 

Negative pressure of pleural cavity, 
190 
of thorax, 173 
Nervous control of heart, 121 
diarrhcea, 259 

mechanism of respiration, 201 
of temperature regulation, 
64 
system and metabolism, 21 
Nitrogenous constituents of urine, 
278 
equilibrium, 3 

Obesity, metabolism of, 28 

treatment of, 36 
Oliver on blood-pressure, 165 
Ovarian extract in ovariotomy, 

27 
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 digestion, 

240 
Pericardium, 111 
Peristaltic movements, 259 
anti-, 267 



296 



APPLIED PHYSIOLOGY 



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 
Polycythaemia, 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 et 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 



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 anaemia, 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, 24 

internal, 23 ^^^ 

Secretory nerves, 227 

to kidney, 275 
Seidelin on gastric digestion, 240 
Sensibility of heart, 1 26 

of intestine, 261 

of stomach, 234 
Serum, 98 

proteins, 30 
Sibson on the lungs, 199 
Sighing, 222 
Skodaic resonance, 189 
Sneezing, 203, 221 



INDEX 



297 



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 
Succiis eniericus, 254 257 
Sugar, assimilation of, 40 

conversion into fat, 40 
into glycogen, 37 

fermentable, 39 

protein source of, 41 
Sulphates of urine, 280 
Supplemental air, 199 
Suprarenals in metabolism, 26 
Sweat, 289 

Sympathetic nerves to heart, 
123-4 

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 

gastric, 241 
Trachea, 180 



Traube on respiration, 203 
Trophic nerves, 22 
Trypsiuogen, 255, 257 

Uraemia, 211 

Urea, 278 

Uric acid, 44, 279 

endogenous, 46 
exogenous, 45 
metabolism, 44 
synthesis of, 47 
Urinary pigments, 281 
Urine, constituents of, 276 et 
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 



S98 



APPLIED PHYSIOLOGY 



White corpuscles, 81 

classification, 82 
enumeration, 87 
Work, digestive, 8, 9 
internal, 8 
muscular, 8, 10 et seq. 



Xanthin, 46 

Yawning, 222 

Zuntz on expenditure of energy, 
19 



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