Chapter V: Part I: Experiments in Physiology (3)

Let any man, who has but touched the study of physiology, consider what is involved in even the most superficial observation of the simplest facts of the nervous system: for instance, the ordinary nerve-muscle preparation that is taught to every medical student, or the microscopic structure of the spinal cord, or the Wallerian method. Or let him consider how the physiology of the nervous system has been founded on the lower forms of life: the work of Romanes and others on the Medusa and the Echinodermata, and Huxley's work in biology, and the endless chain of forces that are alike in man and in jelly-fishes. Then let him try to estimate the output of hard thinking, for the advance from lower to higher structures, and up to man; the vigilant criticism of all theories and foregone conclusions, the incessant self-judgment and wearisome doubts and disputes all the way, elusiveness of facts, and vagueness of words. And the results thus wrung out of science had still to be stated in terms of practice, and tested by the facts of medicine, surgery, and pathology, and used in every hospital in the civilised world, not only for the saving of life, but also for the diagnosis and medical or surgical treatment of innumerable varieties of disease or injury of the brain, the cord, or the nerves. Sir Michael Foster, in a short summary of the problems of physiology, puts clearly these consummate difficulties of the physiology of the nervous system:--

"In the first place there are what may be called general
problems, such as, How the food, after its preparation and
elaboration into blood, is built up into the living substance of
the several tissues? How the living substance breaks down into
the dead waste? How the building up and breaking down differ in
the different tissues in such a way that energy is set free in
different modes, the muscular tissue contracting, the nervous
tissue thrilling with a nervous impulse, the secreting tissue
doing chemical work, and the like? To these general questions
the answers which we can at present give can hardly be called
answers at all.

"In the second place there are what may be called special
problems, such as, What are the various steps by which the blood
is kept replenished with food and oxygen, and kept free from an
accumulation of water; and how is the activity of the digestive,
respiratory, and excretory organs, which effect this, regulated
and adapted to the stress of circumstances? What are the details
of the vascular mechanism by which each and every tissue is for
ever bathed with fresh blood, and how is that working delicately
adapted to all the varied changes of the body? And, _compared
with which all other problems are insignificant and preparatory
only_, how do nervous impulses so flit to and fro within the
nervous system as to issue in the movements which make up what
we sometimes call the life of man?"

The physiology of the nervous system is wrought to finer issues now than in the time of Bell and Magendie; and this generation of students may live to see the present facts and methods of cerebral localisation as the mere rudiments or elements of science. Happily for mankind, science has already so far elucidated them that they have done good service for the diagnosis and treatment of disease, and for the saving of lives.

* * * * *

Some examples have been given, in the foregoing chapters, of the value of physiological experiments on animals. It would be easy to lengthen the list, for there is no general subject in all physiology that does not owe something to this method: as Mr. Darwin said, in his evidence before the Royal Commission of 1875, "I am fully convinced that physiology can progress only by the aid of experiments on living animals. I cannot think of any one step which has been made in physiology without that aid." Many examples have been left out altogether--the work of Boyle, Hunter, Lavoisier, Haldane, Despretz, and Regnault, on animal heat and on respiration; of Petit, Dupuy, Breschet, and Reid, on the sympathetic system; of Galvani, Volta, Haller, du Bois-Reymond, and Pflüger, on muscular contractility: nothing has been said of the work lately done on the suprarenal glands and "adrenalin," and on the blood-pressure in its relation to secretion. For the most part, only those examples have been taken that occur far back in the history of physiology: more has been said about the past than about the present. First, because it was necessary to put an end to the false statements that are made, by those who are opposed to all experiments on animals, about the work done in the past. Next, because the abstruse details of physiology, in the present, are not intelligible for general reading. Next, because it is impossible now to isolate physiology, or to say what belongs to physiology alone, to have back the simpler problems of the past, to discover the circulation of the blood twice. But the experimental method, alike in the past and in the present, has been the chief way of advance. And if a forecast may be made without offence, it is certain that the work of physiology, as in the past and the present, so in the near future, will exercise a profound influence for good on medical and surgical treatment. Among the subjects that especially occupy physiologists now are, the more exact localisation and interpretation of the special sense-centres, and the better knowledge of the internal secretions and chemical influences of the glands and tissues of the body. It would be hard to find two fields of work more sure to favour the growth of the _arbor vitæ_ side by side with the _arbor scientiæ_.

But the last word here must be said by a physiologist of the very highest authority, Professor Starling. He has kindly given me, for this edition, the following note:--

"Among the researches of the last thirty years, those bearing on
the _Circulation of the Blood_ must take an important place,
both for their physiological interest and for the weighty
influence they have exerted on our knowledge and treatment of
disorders of the vascular system, such as heart disease. We have
learned to measure accurately the work done by the great
heart-pump; and by studying the manner in which this work is
affected by different conditions, we are enabled to increase or
diminish it, according to the needs of the organ. Experiments in
what is often regarded as the most transcendental department of
physiology--_i.e._ that which treats of muscle and nerve--have
thrown light on the wonderful process of 'compensation,' by
which a diseased heart is able to keep up a normal circulation.

"_Vaso-motor System._--Largely by the labours of British
physiologists, the exquisite control exercised by the nervous
system over every blood-vessel in the body has been brought to
light, the paths tracked out, and the mechanisms elucidated, by
means of which the circulation through each part of the body is
subordinated to the needs of the whole. Since the chief
vaso-motor nerves take their course through the sympathetic
system, the researches on their distribution have led to the
mapping out of the whole of this system, and to an accurate
knowledge of its functions. We are now acquainted with the
course, to all parts of the body, of the nerves which not only
determine the changes in the calibre of the blood-vessels, but
affect also the secretion of sweat and the erection of the
hairs. Incidentally, the mapping out of these nerves, in the
hands of Mackenzie, Head, and others, has led to more power of
localising the seat of visceral disease.

"_Digestion._--Our knowledge of the processes of digestion has
of late years received a great accession by the work of
Professor Pawlow, of St. Petersburg. His success is largely due
to his recognition of the importance of keeping his experimental
animals under the most normal conditions possible, and of
studying the different parts of the alimentary tract in animals
which were not anæsthetised, but which were free from any pain
or even discomfort, either of which conditions materially
interferes with the activity of the digestive glands. He
therefore established in dogs fistulæ in chosen portions of the
alimentary canal, analogous to the fistula which accident
rendered so valuable in the case of Alexis St. Martin. Not only
has the knowledge thus gained enabled the physician to
understand the sequel of events in disordered digestion, but the
success of the operative measures undertaken by physiologists
for the elucidation of their science has emboldened surgeons to
attack disease in the most various parts of the alimentary
canal.

"Renewed study of the secretion of pancreatic juice evoked by
the passage of the acid digestive products from the stomach into
the small intestine, which had been described by Pawlow, has
resulted in the discovery of a new class of chemical agents,
which act as special messengers from one part of the body to
another, and exercise an important function in determining the
action of all parts to one common end.

"_Respiration._--The investigation of the chemical properties of
the colouring matter of blood, and of its compound with carbon
monoxide, has resulted, in the hands of Dr. Haldane, in the
laying down of measures for the prevention of accidents from
choke-damp or after-damp in mines. The same investigation has
resulted in the discovery of a method of determining the total
amount of blood circulating in the body of a living man. The
application of this method has already added largely to our
knowledge of the pathology of different forms of anæmia, as well
as of the conditions obtaining in heart disease. Experiments by
Hill and others on the physiological effects of compressed air
have shown the precautions which should be observed in all
diving operations. A proper appreciation of these results by
diving-engineers would not only entirely obviate the cases of
'caisson disease,' but would enable diving to be carried on
safely to a greater depth than has hitherto been attempted.

"It is impossible, however, to enumerate all the physiological
gains of the last twenty or thirty years, or to point out their
manifold applications in the cure and prevention of disease. The
full control of the processes of disease, which is the goal of
the physician and the surgeon, can only be attained through an
accurate knowledge of the conditions governing the functions of
the healthy body. The foundation of medicine and surgery is
physiology: and it is only on living animals that the processes
of life can be investigated."