Science has developed prodigiously along the lines into which Newton
led her. In reliance on the universality of Natural Law, the stars in
their courses have been paced, weighed, measured, analysed. The same
process, directed to our own planet, has traced its history, determined
its composition, demonstrated its relation to other bodies. Physicist
and chemist have suggested a structure in terrestrial matter similar
to that of the stars and suns. The world has been reduced to a unitary
system. Wherever men have sought Law, they have found Law. With search
skilful enough and patient enough, Law has ever emerged. It has been
_the Age of the Reign of Law_.
It is true that in our own time philosophers in general have come to
see that these Laws of Nature are within us as much as without; that
they are, in part at least, the result of the structure of our minds.
This is a point of view, however, which has not affected, and perhaps
will not affect, the working man of science. His constant occupation,
since the days of Newton, has been the pursuit of Law, and he has
always been satisfied that Law has only to be sought in order to be
found. This conception has affected the medical and biological sciences
very deeply. Thus the influence of the Newtonian philosophy is as
traceable in them as it is in the astronomical and physical sciences.
Galileo showed men of science that weighing and measuring are worth
while. Newton convinced a large proportion of them that weighing and
measuring are the _only_ investigations that are worth while. The
question as to whether this view is ultimately true or philosophically
justifiable does not need discussion at the moment. The point, for our
immediate purpose, is that the view has been and is very widely held.
§ 2. _The Rise of Clinical Teaching._
The eighteenth century dawned with the refreshing breeze of Newtonian
philosophy blowing through it. During the previous two hundred years
there had been an immense amount of new and fruitful research along
diverse lines. Chemistry and Mechanics, Botany and Comparative
Anatomy, Descriptive Anatomy and Experimental Physiology, Epidemiology
and Microscopic Analysis, all had yielded startling results. The
new generation was bewildered with the very mass and novelty of the
material. The Biologists of the time must have been well nigh hopeless
of reducing their vast accumulations to order, when they contemplated
the beauty and symmetry of the mathematical relations that Newton
and his followers had introduced into Cosmic conceptions. Thus the
eighteenth century is a period for Biology of pause and consolidation
during which attempts were made to introduce unitary conceptions
into the mass of accumulated material. It was, moreover, a period of
consolidation not only of ideas but also of teaching. These tasks
at first turned men’s minds away from the immediate accumulation of
further knowledge. So it is that the first half of the eighteenth
century exhibits something of a gap in the progress of Research. The
medical field is largely filled by two great figures, Boerhaave and
Haller.
Until the seventeenth century there was no systematic clinical
teaching. The Universities gave medical degrees on the basis of a
spoken disputation. No contact with the patient was demanded. The
first effective attempt to change this was at Leyden, where about 1636
clinical teaching was instituted. Owing to this, and to the fact that,
as at Padua, students of every religious denomination were accepted,
Leyden became much frequented by foreign and especially by Protestant
students. The attractions of the place were increased by Sylvius (pp.
131-2) who, in the second half of the seventeenth century, added
laboratory instruction to his clinical teaching. Leyden had several
eminent anatomists, while its botanic garden and museums added to the
practical character of the medical instruction that it offered.
Hermann Boerhaave (1668-1738) was first appointed as a teacher at
Leyden in 1701. At once the medical school attained a front rank
reputation which rapidly came to surpass even that of Padua. Boerhaave
had very few beds at his disposal, but never did man make better
use of his opportunities. Besides clinical, chemical, botanical
and anatomical instruction he followed such of his patients as died
into the post-mortem room and there demonstrated to his students the
relation of lesions to symptoms. He is thus the introducer of the
method of medical instruction still in vogue in our modern medical
schools.
Boerhaave was a man of wide culture. He rescued and published the
plates of the priceless _Bible of Nature_ of Swammerdam (p. 121). He
brought to Leyden the best anatomist of his age, Bernard Siegfried
Albinus (1697-1770). With him Boerhaave edited in superb form the
collected works of Vesalius (1725, p. 85 ff.). The edition exhibits
remarkable prevision of the scientific needs of the scholarship of
our own time. To Albinus, and indirectly to Boerhaave, we owe the
most beautiful of all works on muscular anatomy (1747), a book still
in current use (Fig. 66). Apart from his clinical ability and acumen
Boerhaave was a skilled chemist, botanist, and anatomist.
With all these accomplishments Boerhaave was better able than any man
of his time to achieve something like a medical synthesis, to bring
all the sciences to the service of the patient. Taking one thing
with another, considering his influence as a teacher, his clinical
acumen, his power of inspiring younger workers, his wide learning,
his balanced vision, his eagerness for new knowledge, his sanity, his
humanity, his generosity, and his prophetic power, Boerhaave must
be regarded as the greatest physician of modern times. To him the
debt of British Medicine, and through it of British well-being, is
quite incalculable. Through his pupils he is the real founder of the
Edinburgh Medical School, and through it of the best medical teaching
in the English-speaking countries of the world. The success of the
Edinburgh school, founded while the great Leyden professor was still in
his prime, can be ascribed to two causes which are perhaps reducible to
one--the inspiration of Boerhaave. These two causes are, firstly, the
enthusiasm of its early teachers, and, secondly, the concentration of
all the medical teaching, both clinical and subsidiary, in one great
university school.
[Illustration: FIG. 66. TWO PLATES FROM BERNARD SIEGFRIED ALBINUS.
_Anatomical Plates of the Muscles of Man_, Leyden, 1747. These are the
most beautiful and among the most accurate anatomical figures ever
published.]
§ 3. _Physiology passes to the Modern Stage._
The only figure in the eighteenth century whose influence is comparable
to that of Boerhaave is his pupil, the Swiss Albrecht von Haller
(1708-77), one of the most accomplished men of all time. In actual
scientific achievement Haller stands, indeed, far above his master.
He achieved distinction as poet, botanist, anatomist, and novelist,
carried on a prodigious correspondence, was an exceedingly learned
bibliographer, and perhaps the most voluminous of all scientific
authors. His special distinction, however, is as a physiologist.
Haller’s great work, _Elements of the Physiology of the Human Body_
(1759-66), marks the modernization of the subject of which it treats.
Of the highest importance were his researches on the Mechanics of
Respiration, on the formation of bone, and on the development of the
embryo. He did good work on the action of the digestive juices. His
most important contributions, however, are his conceptions of the
nature of living substance and of the action of the nervous system.
These conceptions formed the main background of biological thinking
for a hundred years, and are still integral parts of physiological
doctrine.
All departments of Medicine must be influenced by the views we may hold
on the nature and action of the nervous system, just as all parts of
the body are influenced and indeed are linked together by that system.
Thus the growth in knowledge of the physiology of the nervous system is
extremely important to us if we would gain a true idea of the progress
of Rational Medicine.
When we look into the history of nervous Physiology before Haller, we
shall be struck by the smallness of the observational foundation of a
vast speculative structure. That we may be the more charitable in our
judgment of such fanciful developments, we may recall that the Mind is
so constructed that it can take little interest in the accumulation of
instances unless it can adduce general laws therefrom. Theory is thus
as necessary to practice as practice to theory. The earlier doctrines
of the nature of nervous action are, however, so unlike those we
now hold that we can afford to pass over them lightly. They consist
of speculations on the topic of the seat of the soul, together with
explanations which suppose the passage either of a fluid or of some
chemical change down the nerves. Haller was the first to construct a
theory of the nervous system that has an appearance of modernity.
During the seventeenth century the favorite doctrine of nervous action
supposed the existence of a nervous fluid. This, it was held, passed
down the nerves to inflate or extend the muscle fibers. Inflation was
supposed to shorten the fibers and so the muscle came to contract. An
exquisite experiment by Swammerdam with his nerve-muscle preparation
had disproved this (p. 123). But Swammerdam’s work was unknown till
published by Boerhaave in 1736, and so the matter stood till Haller’s
time.
Haller concentrated the problem on an investigation of the fibers.
A muscle fiber, he pointed out, had in itself a tendency to shorten
with any stimulus, and afterward to expand again to its normal length.
This capacity for contraction Haller, following a predecessor, called
_irritability_. He recognized the existence of ‘irritability’ as an
element in the movement of the viscera, and notably of the heart, and
of the intestines. The feature of ‘irritability’ is that a very slight
stimulus produces a movement altogether out of proportion to itself,
and that it would continue to do this repeatedly so long as the fiber
remained alive.
But besides the force inherent in a muscle fiber Haller showed that
there was another force which comes to it from without, is carried
from the central nervous system by the nerves, and is the power by
which muscles are normally called into action. This force, like that
of irritability, is independent of the will, and like it can be called
into action after the death of the animal. Haller thus distinguished
the _inherent muscular force_ from the _nerve force_. Both these forces
he further distinguished from the natural tendency to contraction and
expansion, under changing conditions of humidity, pressure and so on,
of all tissues, living or dead.
Haller, having dealt with the question of movement, turned to that
of feeling. He was able to show that the tissues are not themselves
capable of sensation, but that the nerves are the sole channels or
instruments of this process. He showed how all the nerves are gathered
together into the brain, and he believed that they tended to its
central part. These views he supported by experiments and observations
involving injuries or stimulation to the nerves and different parts
of the brain. He ascribed special importance to the cortex, but the
central parts of the brain he regarded as the essential seat of the
living principle, the Soul.
Throughout his discussion Haller never falters in his display of the
rational spirit. He develops no mystical or obscure themes, and,
although his view of the nature of Soul may lack clarity, he separates
such conceptions sharply from those which he is able to deduce from
actual experience. He is essentially a modern physiological thinker,
and certain of his themes were developed by workers who come on the
frontiers of what we have called the ‘period of consolidation’.
Among these workers we would select the Scottish surgeon Sir Charles
Bell (1774-1842), who in 1811 showed that of the two roots from the
spinal cord by which all the nerves of the body arise one root conveys
only sensory elements while the other conveys only motor elements (Fig.
98, p. 208). By this discovery Bell not only completed the views of
Haller on the central nervous system, but also brought them within the
range of practical Medicine.
§ 4. _Some Physiological Advances._
Haller provided a philosophical basis to physiological conceptions.
There were, however, other workers of the time who added to the
knowledge of actual workings of the animal body. First among these,
both in time and eminence, stands the English country clergyman
Stephen Hales.
The Rev. Stephen Hales (1677-1761) was by temper a biologist, but he
had received a training in Mathematics and Physics. With this ideal
equipment, he proceeded to investigate the Dynamics of the Circulation.
His method consisted in applying the principle of the pressure gauge
or manometer to living things. By tying tubes into the arteries and
veins of animals, he was able to record and measure the blood-pressure.
He thus laid the foundation of an important mode of studying the
diagnosing disease. He extended his exact investigations into most of
the mechanical aspects of the circulation. He computed the circulation
rate and he estimated the actual velocity of the blood in veins,
arteries, and capillary vessels. He made a very important contribution
by showing that the capillary vessels are liable to constriction and
dilatation, a knowledge that has since become not only important for
physiological theory but of primary significance to the practising
physician (p. 309). He began to explore the wonderful mechanism of
the heart by which that organ adjusts itself to its needs of output.
He exhibited his versatility by important contributions to many other
departments, as, for instance, his discoveries on Respiration, his
improvements in Ventilation (Fig. 67), and his campaign for Temperance.
All his work is characterized by simplicity and directness, the supreme
marks of his genius.
[Illustration:
FIG. 67. WINDMILL VENTILATOR designed by the Rev. Stephen Hales, and
erected by order of the Aldermen of the City of London, in 1752, on the
roof of Dick Whittington’s Gate at Newgate Prison. From a print in the
British Museum.
]
In the meantime considerable progress was made in the knowledge of the
digestive processes. The French naturalist, René Antoine de Réaumur
(1683-1757), best remembered for his thermometer (1731) and for his
superb work on insects (1734-42), made a series of experiments on
gastric digestion in birds (1752). By an ingenious contrivance he
succeeded in obtaining gastric juice in a pure state. He was able to
demonstrate its power to dissolve food substances in a test-tube kept
at body temperature. This was important, since many believed that
the process of solution was the result of a churning process induced
mechanically by the muscles of the stomach-wall. Réaumur thus gave the
death-blow to the Iatrophysical conception of digestion (p. 130).
The investigation of gastric digestion was further pursued by a
versatile Italian, the Abbé Lazaro Spallanzani (1729-99), who showed
that the churning action is an aid, but not an essential, to the
process of digestion (1782). He proved that digestion was not of the
nature of putrefaction and differed essentially from the fermentation
of wine. Spallanzani thus improved on the view of Sylvius (p. 132),
and took a step towards that solution of the natures of putrefaction,
fermentation, and digestion which was finally provided by Pasteur (p.
225). He showed that the gastric juice was secreted by the stomach
itself, and not introduced into it from other organs. A suspicion
that the gastric juice contained a free acid crossed his mind. He
observed that it curdled milk and so began our knowledge of a separate
ferment, that of ‘rennet’. Spallanzani’s results may be summarized
by saying that he showed that gastric juice had a solvent power _sui
generis_, and that this power or faculty was of a different order from
putrefaction or vinous fermentation.
The phase of digestive physiology represented by Réaumur and
Spallanzani was brought to a close by the English physician William
Prout (1785-1850), who demonstrated in 1823 the existence of free
Hydrochloric Acid in the stomach. He showed that the presence of this
acid was necessary for gastric digestion, but that the actual process
of solution of food was the work of another agent. The matter was at
last brought into the range of medical practice by an American Army
Surgeon, William Beaumont (1785-1853), who, in the ten years ending
1833, had the opportunity to investigate gastric juice in a man who,
having been shot in the stomach, had a permanent fistula. Through this
the juice could be obtained and the lining membrane of the stomach
examined at will.
[Illustration:
Experiments illustrating the effects of metallic contacts on the nerves
and muscles of frogs’ legs. From A. Galvani, _On Electric Forces_, 1792.
FIG. 68. Contact is established between water in two dishes. In one
lies the end of the nerve with the spinal cord and vertebral column
attached. In the other are the feet of the frog.
FIG. 69 shows contact by a metal bar with two damp mats on one of which
lies the spinal cord and on the other are the feet.
FIG. 70 shows a broken contact which can be completed by bringing the
metal rods together.
]
An important department of Physiology was opened by the extension
of the knowledge of electric phenomena to the living body. Static
electricity had been studied since the beginning of the seventeenth
century. Luigi Galvani (1737-98) of Bologna, while investigating the
susceptibility of nerves to irritation, showed that nervous action
could be induced by electrical phenomena (1791). He was, as a matter of
fact, producing an electrical current. Many thought at the time that a
new kind of ‘animal electricity’ had been produced and they dubbed it
‘galvanism’.
Alessandro Volta (1745-1827) of Pavia, deviser of the ‘Voltaic pile’
(Figs. 71-3), had long been working at electricity. He was able to
demonstrate (1800) that galvanism is without any essential animal
relationship, and showed that a muscle can be thrown into continuous
contraction by repeating electric stimulations.
Humbug and misunderstanding in connection with the electrical relations
of living tissues were rife, and it was not till after the period we
are now considering that electricity came to take a place in rational
Medicine. The change came with E. Du Bois-Reymond (1818-96), who took
the matter up scientifically about the middle of the nineteenth century
(1843 onwards). He showed that a nervous impulse is accompanied by the
passage along the nerve of a change of electrical potential. It should
be added that, despite all the work since done upon the nervous system,
this is still the only physical accompaniment of a nerve impulse that
has been detected.
[Illustration: FIGS. 71, 72, and 73. From an article by Volta, _On the
Electricity excited by the mere Contact of Substances of different
kinds_, published in 1800.
FIG. 71 is the famous ‘Couronne de tasses’. It consists of a series of
vessels containing salt water, in which are steeped plates of alternate
silver A and zinc Z. The plates are connected by strips of metal _a_
_a_ _a_. If the first and the last cup be connected by a conductor, a
current flows from one to the other.
FIG. 72 is a simple voltaic pile, consisting of alternate disks of
silver and zinc, sandwiched between wet strips of leather. The pile
is held by glass rods _m_ _m_ _m_. From the lowermost disk a strip of
metal passes to a vessel containing salt water. A current will pass
from the uppermost disk to the vessel if the two are connected by a
conductor.
FIG. 73 is a similar apparatus with two piles connected by a metal
plate _c c_, and two vessels _b_ _b_. A current will pass between the
two vessels _b_ _b_ if they are joined by a conductor.
]
§ 5. _Discovery of the Nature of the Air._
The seventeenth century saw advances in the knowledge of the air.
Boyle (1654, p. 124) had shown by means of his air-pump that air was
a material substance and could be weighed. By exhausting the air from
a vessel in which an animal had been placed, he showed that it was
this material substance and no ether, spirit, or other mysterious
entity which supported respiration. Mayow (1668, p. 126) proved that
a part only of the air was necessary for life, and later that this
same part was removed equally by respiration and combustion (Figs.
74-5). His work was forgotten for a hundred years. The great theorists,
Stahl, Boerhaave and Haller, knew him not, and Stahl’s doctrine of
_phlogiston_ set back the hands of the clock. No advance was made till
the work of Joseph Black (1728-99) which appeared soon after the middle
of the eighteenth century.
[Illustration: FIGS. 74 and 75, illustrating the chemistry of burning
and breathing, from a work issued by Mayow in 1674. The experiments
show the essential similarity of the two processes in their effect upon
the air.
FIG. 74. A candle is burning and a piece of inflammable material is
being ignited in a glass vial by a burning-glass, the mouth of which is
under the surface of the water. The air can, if desired, be changed or
sampled through the attached tube.
FIG. 75. A mouse confined under a glass cover. The air under this cover
communicates with that in the vessel below, and can be cut off more or
less completely by means of a more or less porous diaphragm.
]
Black was a cautious investigator and his success was due to the
accuracy of his measurements. He was aware of the fact that chalk, when
heated, is transformed into quicklime (equation 1, p. 152), thereby
losing its power of effervescing with acids, but gaining the power of
absorbing water (equation 2). In modern nomenclature, the changes are:
(1) CaCO_{3} = CaO + CO
(2) CaO + HO = Ca(OH)_{2}
The first achievement of Black was to show that in the process of
heating the chalk lost weight (equation 1). This was a blow at the
phlogiston theory, for it had been supposed that quicklime consisted
of chalk _plus_ phlogiston, and that the phlogiston was conveyed to it
during the heating. Black now showed that if slaked lime be treated
with a mild alkali, such as the carbonate of sodium, it is changed back
to the state in which it was before heating, in fact into chalk, while
the mild alkali is converted into a caustic alkali. As we now express
it:
(3) Ca(OH)_{2} + Na_{2}CO_{3} = CaCO_{3} + 2NaOH
Black’s triumph consisted essentially in showing that reactions (1) and
(3) were indefinitely reversible and that the same amount of CaCO_{3}
could always be extracted from (3) as was put into (1). Moreover, he
showed that a definite amount of chalk, whether heated into quicklime
or not, neutralized an equal weight of acid, the only difference being
that the neutralization took place with effervescence and loss of
weight if the chalk were unheated, and without effervescence or loss of
weight if the chalk were first heated into quicklime. Thus:
(4) _Unheated_ CaCO_{3} + 2HCl = CaCl_{2} + H_{2}O + CO_{2}
(5) _Heated_ CaO + 2HCl = CaCl_{2} + H_{2}O
The substance given off by the chalk in (1), absorbed by it in (3),
and produced by the reaction (4), he named _fixed air_. We now call it
_Carbon dioxide_. The conversion of caustic lime into ordinary chalk
by exposure, CaO + CO_{2} = CaCO_{3}, proves that Carbon dioxide is a
normal constituent of the atmosphere. Black learned something of its
properties, and his work is also of very great importance as the first
detailed quantitative study of a chemical reaction and its reversal.
The properties of Carbon dioxide were further investigated (1766) by
Henry Cavendish (1731-1810).