incorporated into his often fantastic philosophy the ill-worked-out
conclusions of Copernicus (p. 88). Nominally adopting the Copernican
theory, he modified it fundamentally. Copernicus, having placed the Sun
at the center of the World, and made the Earth and other planets circle
round it, had still left the stars at a fixed and definite distance, as
had the ancient astronomers. The limitation of the sphere of the fixed
stars was obnoxious to Giordano, and he removed the boundaries of the
Universe to an infinite distance, in accordance with the principles
of his philosophy. The change may seem unimportant save for astronomy,
but, in fact, it came to influence every department of scientific
thought, for the endlessness of Nature is implicit in the modern
scientific attitude.
Giordano was burned at the stake at Rome, after seven years’
imprisonment, in 1600. In the same year the experimental era was
ushered in with the work of William Gilbert (1544-1603), _On the
Magnet_, in which he not only demonstrates experimentally the
properties of magnets but also shows that the Earth itself is a magnet.
In the same year, too, Tycho Brahe (1546-1601) handed over the torch to
Johannes Kepler. Tycho was the last of the older astronomers who worked
on the Aristotelian view of circular and uniform movements of heavenly
bodies. Kepler was the real founder of the modern astronomical system.
The period from 1600 onward lies with new men, Galileo (1564-1642) and
Kepler (1571-1630) among astronomers and physicists, Harvey (1578-1657)
among biologists, Descartes (1596-1650) among philosophers.
The seventeenth century opened with an extraordinary wealth of
scientific discovery. As we glance at the mass of fundamental work
produced during that period, we perceive the major departments of
Science, as we know them to-day, becoming clearly differentiated.
The acceptance of Observation and Experiment as the only method of
eliciting the Laws of Nature reaches an ever-widening circle. Even
to enumerate the names of the seventeenth-century pioneers would be
a formidable task. The sciences penetrated to the Universities and
influenced the curricula. The number of scientific men became so large
and so influential that separate organizations were formed by them in
the interests of their studies. It is the age of the foundation of the
‘Academies’, of which the English Royal Society is a type.
From the multitude of workers on these subjects we can but select a few
names. In the first half of the century Galileo and Kepler are the main
exponents of natural law. Descartes takes his place here as the first
since antiquity who sought to explain the phenomenal universe on a
unitary basis. In the second half of the period comes the mighty figure
of Newton, whose researches ushered in that phase in our story in which
we live to-day.
The early training of Galileo Galilei had been scholastic and
Aristotelian. By 1590, however, he had begun to doubt, and was making
experiments on the rate of acceleration of falling bodies. His
conclusions were demonstrated in 1591 from the leaning tower of Pisa.
By that famous experiment he showed, in the most public manner, the
error of the Aristotelian view that the rate of fall was a function not
of the weight of the object but of the period of fall. Revolutionary
also was Galileo’s work of 1604. In that year a new star appeared in
the constellation _Serpentarius_. He demonstrated that this star was
situated beyond the planets and among the remote heavenly bodies.
Now this remote region was regarded in the Aristotelian scheme
as absolutely changeless. Although new stars had been previously
noticed, they had been considered to belong to the lower and less
perfect regions nearer to earth. To the same lower region, according
to the then current theory, belonged such temporary and rapidly
changing bodies as meteors and comets. But Galileo had attacked the
incorruptible and unchangeable heavens.
In 1609 Galileo made accessible two instruments that were to have a
deep influence on the subsequent development of Science, the Telescope
and Microscope. It is with the former instrument that his name is most
frequently associated. His first discoveries made by means of the
Telescope were issued in 1610. That year was crowded with important
observations especially on the inner planets and notably on Venus. It
had been rightly claimed in criticizing the Copernican hypothesis that,
if the planets resemble the Earth in revolving round the Sun, only such
parts of them should be luminous as are exposed to the Sun’s rays. In
other words, they should exhibit phases like the Moon. Such phases in
Venus were now actually observed by Galileo. In the following year he
described sunspots and traced them round the Sun’s disk.
We need not follow the further astronomical observations of Galileo,
nor need we discuss the contest with the older school on which he
embarked. It is sufficient to remind ourselves that the appearance
of a new star, the behavior of the rings of Saturn, the observations
of the phases of Venus and of the Sun’s spots, struck a blow at the
Aristotelian astronomy comparable to that delivered against the
Aristotelian physics by the falling weights from the leaning tower of
Pisa. Aristotelian astronomy demanded heavens eternally changeless.
Here were changes and new appearances in the heavens, clearly visible
to all who would see.
During these years too, Galileo was laying firm the foundations of the
science of Mechanics. Out of his mechanical researches came a new way
of looking at the objects of Nature which has profoundly influenced
the entire subsequent course of science. That way is best expressed
in Galileo’s own words, which place him among the philosophers whose
thought influences all those who deal with scientific themes.
‘As soon as I form a conception of a material or corporeal
substance, I simultaneously feel the necessity of conceiving
that it has boundaries and is of some shape or other; that
relatively to others it is great or small; that it is in this
or that place, in this or that time; that it is in motion or
at rest; that it touches, or does not touch, another body;
that it is unique, rare, or common; nor can I, by any act of
imagination, disjoin it from these qualities. But I do not find
myself absolutely compelled to apprehend it as necessarily
accompanied by such conditions as that it must be white or
red, bitter or sweet, sonorous or silent, smelling sweetly
or disagreeably; and if the senses had not pointed out these
qualities language and imagination alone could never have
arrived at them. Therefore I think that these tastes, smells,
colors, &c., with regard to the object in which they appear to
reside, are nothing more than mere names. They exist only in
the sensitive body, for when the living creature is removed
all these qualities are carried off and annihilated, although
we have imposed particular names upon them, and would fain
persuade ourselves that they truly and in fact exist. I do
not believe that there exists anything in external bodies for
exciting tastes, smells and sounds, &c., except size, shape,
quantity, and motion. If ears, tongues, and noses were removed,
I am of opinion that shape, quantity, and motion would remain,
but there would be an end of smells, tastes, and sounds, which
abstractedly from the living creature I take to be mere words.’
This passage is a veritable Charter of Science. From Galileo’s day to
ours, men of science have occupied
themselves in measuring size, shape, quantity, and motion, the
‘primary qualities’, and expressing their knowledge in that measured
form. They have relegated colors, smells, tastes, sounds, and other
sense-impressions to the position of ‘secondary qualities’, and have
tried to express them, when they express them at all, in terms of the
primary qualities. We need not enter on the philosophical discussion
as to how far the primary qualities are in truth more real than the
secondary, but it is a fact that, since the time of Galileo, Science
has come to be regarded more and more widely as an exact process.
_Science is Measurement._ It is a conception that has affected the
medical no less than the other sciences, and it is a conception that
Medicine, for good or ill, owes to Galileo.
[Illustration:
FIG. 37. SANCTORIUS IN HIS BALANCE. Sanctorius was able to eat and
even to sleep in his balance, counterpoised by a weight working on
the principle of the steelyard. He was thus able to test his weight
under various conditions, and notably to estimate the amount of
the ‘insensible’ perspiration. His were the first experiments on
‘Metabolism’ (see p. 108).
]
§ 5. _The Revival of Physiology._
The first to apply Galilean principles of measurement to biological
matters was Sanctorius (1561-1636), a professor at Padua. He described
a thermometer for use in taking the temperature of the human body
(Figs. 39 and 40), and an apparatus for comparing the rate of pulse
beats (Fig. 41). Both these he modified from devices suggested by
Galileo (Fig. 38). It is an indication of the transitional character
of the Science of the time that he describes these instruments in a
commentary on a medieval translation of the _Canon_ of Avicenna (p.
67). He also sought to compare the weight of the body at different
times and in different circumstances. In the process of doing this, he
demonstrated that the body loses weight by mere exposure, a process
which he ascribed to ‘insensible perspiration’ (Fig. 37). By these
experiments he laid the foundation of the modern study of ‘Metabolism’
(p. 220).
[Illustration:
FIG. 38. The principle of Galileo’s thermometer. A tube ending in a
bulb A is inverted over a mercury bath B. If the temperature fall the
air in A will contract and mercury be drawn up into the tube. If the
temperature rise the air in A will expand and mercury be driven out
of the tube. The height of the mercury can be read on the scale SS.
The reading will not be accurate because the instrument is, in fact,
also a barometer, since the mercury in B is exposed to the atmospheric
pressure, which will therefore affect the rise in the tube.
FIG. 39. The application of the same system by Sanctorius who used a
curved tube.
FIG. 40 is not, as might be thought, a man trying to swallow a
centipede, but the adaptation of the instrument of Sanctorius as a
clinical thermometer.
FIG. 41. Galileo’s simple and effective ‘pulsimeter’. It consists only
of a weight suspended on a thread. This thread is held in the hand and
the weight made to oscillate as a pendulum. As the thread is shortened
the oscillations increase in frequency. The process is continued until
the pendulum oscillates to time with the pulse. The length of the free
thread is then read off on the accompanying scale. It was used by
Sanctorius.
]
While Sanctorius was engaged in this pioneer work at Padua, the
movement that Vesalius had inaugurated there was making further
conquests in the purely biological line. Vesalius had been succeeded
at Padua by a series of anatomists of great eminence. Perhaps the
most prominent among these was Jerome Fabricius (1537-1619), usually
called ‘of Aquapendente’, after the small Tuscan village where he
was born. This Fabricius of Aquapendente taught at Padua for over
fifty years, from 1565 till his death at eighty-two in 1619. He made
many contributions to the advancement of anatomy, most of which had
physiological bearings. Thus, he was the effective founder of modern
embryology and the author of the first illustrated work on that
subject, in which he describes the formation of the chick in the egg.
He was the first to give accurate figures of the structure of the
eye. He developed the mechanics of muscular motion. He added to his
qualities as an observer the power of attracting younger men.
In spite of all his powers, however, Fabricius never shook himself free
from ancient views, and especially he was steeped in the theories of
Aristotle and Galen. This backward-looking habit prevented his work
from being as important as it might otherwise have been. In connection
with the circulation, for instance, he made a striking discovery, but
wholly failed to draw out its most important lesson.
[Illustration:
FIG. 42. DISSECTION OF A VEIN in the thigh and leg from a work _On the
Valves of the Veins_, published by Fabricius in 1603 at Padua. These
valves prevent the passage of the blood in any direction except toward
the heart. They may be seen at the points P, Q, R, S, and T.
]
In 1600 he published his book, _On the Valves of the Veins_. In it he
says that these structures are so placed that their mouths are always
directed _toward_ the heart (Fig. 42), yet he never gets an inkling
that the effect of these valves must be to prevent blood flowing
into the veins except toward the heart. He is too set on the old
Galenic physiology to permit such a revolutionary thought. The real
importance of Fabricius is, therefore, not so much as an investigator
but rather as a teacher, a capacity in which he shone above all other
physiologists for generations to come. He would deserve our remembrance
if only as the master of the discoverer of the circulation of the
blood, William Harvey.
The Englishman, William Harvey (1578-1657), after education at
Cambridge, went to Padua in 1599, when Fabricius was at the height
of his powers. Returning to England in 1602, he set up in practice
in London. During the years which followed, he was dissecting and
experimenting very industriously, and by 1615 had reached a clear
conception of the circulation of the blood (Fig. 43), though he did not
publish his discovery till some thirteen years later.
To discuss the actual steps by which Harvey made his discovery
would be beyond our scope. He had, however, been well trained in
experimenting on living animals by Fabricius, and had read widely in
anatomical literature. He was of a contemplative turn of mind and
his quiet and cautious temper, united with his enthusiasm and skill
as an experimenter, provided a superb mental equipment for a life of
scientific investigation.
Harvey, early in his work, reached two fundamental conceptions
concerning the vascular system. He perceived that the valves in the
veins would permit the blood to pass only towards the heart (Fig.
43), while those in the great arteries arising from the heart would
permit the blood to pass only away from the heart. In connection with
the movement of the blood, Harvey’s crucial point is that it must be
_continuous_, and _always in one direction_. This really clinches
the matter, for consider the capacity of the heart. Let us suppose
that either ventricle holds but 2 ounces of blood. The pulse beats 72
times a minute and 72 × 60 times an hour. In the course of one hour,
therefore, the left ventricle will throw into the aorta, or the right
ventricle into the pulmonary artery, no less than 72 × 60 × 2 = 8,640
ounces = 38 stones 8 lb. In other words, in one hour the ventricle will
throw into the great artery more than three times the body weight of
a heavy man. Where can all this blood come from? Whither can it all
go? It cannot come from the ingested food and drink, for no one could
consume so much in one hour! It cannot reach and remain in the tissues,
for they would soon all burst and ooze with blood! The solution of the
puzzle, Harvey came to see, is that it is the same blood that is always
being pumped into the arteries, and the same blood that is always
coming back through the veins. In other words the blood _circulates_, a
fact which Harvey proceeded to demonstrate with convincing thoroughness
(Fig. 43).
[Illustration:
FIG. 43. DIAGRAM TO ILLUSTRATE THE NATURE OF THE CIRCULATION OF THE
BLOOD. Leaving the _left ventricle_, when the walls of that cavity
contract, the blood is forced through the valves into the great artery
known as the _aorta_. From the aorta it passes into smaller and ever
smaller arteries, finally reaching the _systemic capillaries_ or the
_portal capillaries_. After travelling through one or other capillary
network it enters a vein. Thence it passes into larger and ever larger
veins, until it ultimately enters the great vein known as the _vena
cava_ that opens into the _right auricle_. It has now completed the
Greater Circulation. As the right auricle contracts the blood passes
through the valves between the right auricle and right ventricle into
the _right ventricle_. From there it enters the Lesser Circulation,
passing into the great _pulmonary artery_, which conducts it to the
lung. In the lung the pulmonary artery breaks up into branches and
finally into capillaries. Through these the blood travels until it
reaches a tributary of the _pulmonary vein_ and finally the pulmonary
vein itself. The pulmonary vein empties its blood into the _left
auricle_. From the left auricle the blood passes at last into the left
ventricle from which it started, having traversed both the Greater and
the Lesser Circulations.
To understand the change which Harvey wrought in the conception of the
workings of the body, this description and diagram should be compared
with the description and diagram on pages 56-59.
]
We may note that, though Harvey demonstrated the existence of the
circulation, he was never able to follow it throughout, for he did not
see the capillary vessels by which the blood is conveyed from the
terminal branches of the arteries to the smallest tributaries of the
veins. These were first demonstrated by Malpighi (p. 116).
The knowledge of the circulation of the blood has been the basis of
the whole of modern Physiology and with it of the whole of modern
rational Medicine. The attitude of Galen and Aristotle towards the
heart and the great vessels passed into the shadow. The blood, it was
seen, is a carrier always going round and round on the same beat. What
it carries, and why, how and where it takes up its loads, and how,
where, and why it parts with them, these are questions the answering
of which has been the main task of Physiology in the centuries that
have followed. As each of the questions has obtained a more and more
rational answer, so clinical Medicine has always made a step forward,
and has come to approach more nearly to a true science. Thus it is that
the work of Harvey lies at the back of almost every important medical
advance.
[Illustration:
FIG. 44. THE VALVES in the superficial veins as seen in the bandaged
arms of living men, from William Harvey’s great work on the
_Circulation of the Blood_, printed in 1628. The bandage is seen on the
upper arm in each case, and the valves are indicated, as in life, by
nodes or swellings in the veins. If a finger is pressed along the vein
from one valve to another as from node O to node H in a direction away
from the heart, the vein from O to H will be emptied of blood. It will
remain empty, since the valve at O does not permit the passage of blood
away from the heart, but only towards it. This observation was Harvey’s
starting point for his great discovery.
]
§ 6. _Microscopic Analysis of the Animal Body._
The compound microscope was first made into an effective instrument by
Galileo. It was, as it were, a _by-product_ of his invention of the
telescope. With that instrument he had seen enough to convince himself
that the movement of the Sun round the Earth was but an appearance.
At the very time that Harvey was giving his first course of lectures
securely in London, Galileo’s teaching was attracting the unwelcome
attention of the Inquisition in Rome.
Galileo’s microscopes, however, were far less satisfactory than his
telescopes. For optical reasons which we need not discuss, these early
compound microscopes failed to give a clear picture. With any high
degree of magnification, the image was always blurred and distorted.
More than three centuries were to pass before a better compound system
was introduced. But about 1650 a way was found of constructing and
mounting simple lenses of very high power. Many of the most important
microscopical discoveries of the second half of the seventeenth
century were, therefore, made with a simple lens. This was notably
the case with much of the work of the great investigators Malpighi and
Leeuwenhoek (Fig. 49 A).
[Illustration:
FIG. 45. LUNGS OF FROG, showing the capillary vessels from a figure
by Malpighi in the rare first edition of his work _On the Lungs_,
published at Bologna in 1661. A is the part of the larynx, B is the
opening of the larynx into the trachea or air-tube leading to the lung.
The letters EEE represent the outer surface of the lung and exhibit
the network of capillary vessels. On the other side the sack-like lung
has been laid open, and is viewed from the inside. The letters HHH are
placed upon veins on the inner surface of the lung. These arise from
capillaries which are indicated between the veins.
]
Marcello Malpighi (1628-94) was born in the year in which Harvey’s work
was published. He became a professor at Bologna, having early developed
great skill in minute investigation. His first work, which appeared in
1661, supplied the element missing in the investigations of Harvey,
for he describes the actual passage of blood from the arteries to the
veins through the ‘capillary’ blood-vessels (Fig. 45). Harvey, who
did not use a microscope, knew nothing of the capillaries. The object
which yielded up the secret was the lung of the frog. This organ in the
frog happens to be almost transparent, is very simple in structure,
and is furnished on its surface with particularly conspicuous capillary
vessels. Malpighi could hardly have selected an object better suited
for this particular research. This important discovery of his drew the
attention of scientific men in England. The Royal Society soon entered
into correspondence with him, and during the remainder of his life
undertook the publication of his researches.
[Illustration: In 1673 Malpighi published in London his work _On the
Formation of the Chick in the Egg_. Thirteen years later, in 1686, he
published extensions and corrections of this work. Our figures are
taken from the later work.
FIG. 46 is the whole embryonic area, at about the end of the second day
of incubation. The embryo itself is seen with its large head containing
the three ‘cerebral vesicles’ (which are the rudiments of the brain),
the large eye, the protuberant coiled heart (NM), from which vessels
pass to the ‘vascular area’. The segmented vertebral column is well
seen, as well as the vessels forming a network as they meander over the
vascular area.
FIG. 47 exhibits the embryo more enlarged and in greater detail.
FIG. 48 is an enlarged figure of the heart; the part D will ultimately
form the ventricle, B the auricle, and A the vena cava. At F the
aorta sends forth three branches which unite again. The nature of
these branches was not understood in Malpighi’s time. They have
been explained in modern times by embryologists working under the
inspiration of evolutionary theory as having once furnished the
blood-supply to the gills of a fish-like ancestor.
FIG. 49 is a part of the segmented vertebral column still more enlarged.
]
[Illustration:
FIG. 49A. ONE OF LEEUWENHOEK’S MICROSCOPES. To understand the figure
turn the book at right angles to the line of print. The object to be
examined--here the tail of a small eel--is placed in water in the
test-tube B. This test-tube is held firmly by two springs in the frame
A. The microscope itself is simply a flat metal plate D, into which is
let a very minute lens, the setting of which is shown above the letter
D (when the head of the eel is downwards). The lens is focused by means
of a fine screw which moves the whole plate.
]
The contributions of Malpighi to biological knowledge were very
numerous and important. The study of early development, embryology as
it is now called, was greatly extended by him. The later stages of
embryological development had been investigated by Fabricius (p. 110)
and some additions to the subject had been made by Harvey. Malpighi,
applying his microscope to the earlier germ of the animal body,
described in detail the development of the organs, notably of the
heart and the nervous system (Figs. 46-49). He also demonstrated the
minute structure of the skin, spleen and liver, in all of which there
are anatomical structures that still bear his name. He investigated
microscopically the structure and physiology of insects and plants, and
his figures of the cell-walls of the latter are good and clear.
[Illustration: FIGS. 50-53 illustrate the blood corpuscles and
circulation after Leeuwenhoek.
FIG. 50. Oval blood corpuscles of salmon showing nuclei.
FIG. 51. Human red blood corpuscles.