MEDICAL AND PHYSIOLOGICAL METEOROLOGY
The starting point in any study of the physiological effects of weather
and climate upon humanity is the remarkable fact that, on the hottest
days of summer and the coldest of winter, in tropical deserts and amid
polar snows, the temperature within the body of a healthy man remains
constant to a fraction of a degree. There are slight temperature
differences between different parts of the body; there is a periodic
daily variation of about half a degree; and there are other slight
changes, due to eating and exercise; but an internal temperature
of about 98.6 degrees F. is maintained with little or no regard to
fluctuations in the temperature of the air.
The body has often been compared to a building in which the temperature
is regulated by a thermostat, but the comparison is not exact. The
thermostat controls the temperature merely by regulating the combustion
of fuel; and with the advent of mild weather we let the fires go out
altogether. In the body the fires are always burning, the briskness
with which they burn--or, to drop the metaphor, the rate at which
bodily heat is generated--depending, above all, upon muscular activity,
but also upon other causes. It is true that we possess a nervous
mechanism, analogous to the thermostat, which tends to adjust the
production of animal heat in such a manner as to offset the cooling
effect of our environment; but this mechanism appears to be less
important in maintaining our constant temperature than another, which
regulates the loss of heat from the body. According to M. J. Rosenau:
“Heat is lost from the body chiefly in two ways; (1) by _heat
transfer_, or loss by radiation, conduction, and convection; (2) by
_evaporation_, chiefly by the evaporation of the water of perspiration.
Pettenkofer and Voit estimated the loss of water by the lungs at
286 grams, and from the skin at from 500 to 1,700 grams daily. This
will give some idea of the effects here concerned. The loss by heat
transfer diminishes as the temperature of the surrounding air rises.
The temperature of the body would rise when the atmospheric temperature
goes above 70 degrees F. were not perspiration then secreted. So long
as the perspiration can evaporate freely the heat production and heat
loss are balanced. With a high humidity evaporation is lessened and the
balance is maintained by rushing blood to the skin, which causes an
elevation of the temperature of the surface, and thus the loss of heat
by radiation, conduction, and convection is facilitated.”
Human sensations of temperature are paradoxical. We talk of being “hot”
and “cold,” as if we belonged to the class of cold-blooded animals--the
fishes and the reptiles--that actually undergo great variations of
temperature, with variations in the temperature of their environment.
We hear people say, for example, that they are most comfortable at a
temperature of 65; yet we know that their temperature is always 98½,
except just at the surface of the body.
The human body is, in fact, a poor thermometer. Our sensations do not
register the temperature of the air, but they do, in a way, register
the cooling power of the air, which depends upon temperature, humidity,
and air movement, and they register, especially, changes in this
cooling power, for within certain limits the body soon adapts itself
to a constant rate of cooling, so as to lose any impression of heat or
cold. When a steady outflow of heat from the body has been set up and
the external cooling power is suddenly increased, we become conscious
of a difference between the temperature at the surface of the body
and the “blood temperature” beneath. The action of the nerves at the
surface and the nerves underneath, under these circumstances, has been
compared to that of a thermo-junction, in which an electric current is
produced by differences of temperature. The rate of evaporation from
the skin, also, has a marked effect upon our sensations of comfort and
discomfort.
The common thermometer was long ago discredited as a means of measuring
atmospheric comfort. Then, for a time, the wet-bulb thermometer had its
day, and its indications were once published on a large scale in this
country as representing the “sensible temperature,” or temperature that
we actually feel. The wet-bulb thermometer is cooled by evaporation
below the air temperature, except when the air is saturated with
moisture, and may therefore give a rough indication of the temperature
acquired by the skin when moistened with perspiration. The temperature
of the skin is not, however, an accurate indication of our feelings
of heat or cold, nor is it a satisfactory guide to the physiological
effects of atmospheric conditions.
Several instruments have been devised for the purpose of measuring the
cooling power of the air, to which the bodily mechanism must respond
in order to maintain a uniform temperature within. One of these was
invented nearly half a century ago by J. W. Osborne. A porous cylinder
was filled with warm water, and an agitator, driven by clockwork, kept
the water in the cylinder at uniform temperature at any given moment.
The rate at which heat was lost from the wet surface of the cylinder
was determined by a thermometer, having its bulb immersed in the water,
and a stop watch. A different plan was adopted by A. Piche, in an
instrument which he called the _deperditometer_, and which was supposed
to imitate more closely the behavior of the body. A porous vessel is
filled with water, the temperature of which is kept constantly at
“blood heat” (98.6 degrees F.) by a gas jet provided with an automatic
regulator. The amount of gas burned in a given time is then supposed to
measure the cooling power of the atmosphere as it affects humanity. J.
R. Milne’s _psuchrainometer_ is constructed on the same principle, but
heat is supplied and measured electrically.
Among many other instruments of this class, one that now enjoys special
favor is the _katathermometer_, devised by Prof. Leonard Hill, in
England. This consists of a pair of large-bulbed spirit thermometers,
one of which has its bulb covered with fine cotton mesh. To use the
instrument, the bulbs are immersed in water at about 150 degrees
F. until the spirit rises to the top of the thermometer tubes. The
excess of water is then jerked off the wet bulb, and the other bulb
is dried. The instruments are finally suspended in the air, and the
rate of cooling from 110 to 100 degrees, or from 100 to 90 degrees,
is taken with a stop watch. The dry-bulb measurements are supposed to
show how fast the human body loses heat at its surface by radiation
and convection, while the wet-bulb measurements also take account of
evaporation.
In order to connect the readings of this device with human sensations,
Hill and his collaborators have used the instrument under a great
variety of atmospheric conditions, both indoors and out, and compared
the readings with independent estimates of comfort and discomfort. On
an ideal summer day the “wet kata” fell from 110 to 100 in 25 seconds,
and the “dry kata” in 85 seconds. Indoors at the seaside in summer,
under comfortable conditions, the readings were 50 seconds and 140
seconds, respectively. A large number of other readings, taken under
different conditions in various parts of the word, have been published.
The katathermometer is now used in both Great Britain and the United
States in the study of ventilation problems, and has acquired a rather
extensive literature. According to its inventor, “the heating and
ventilation of rooms should be arranged so that the wet-bulb falls from
100 to 90 degrees in about one minute, and the dry-bulb in about three
minutes.”
[Illustration: A WEATHER BUREAU KIOSK, IN UNION SQUARE, SAN FRANCISCO.
(_Photograph, U. S. Weather Bureau._)]
[Illustration: THE UNITED STATES WEATHER BUREAU STATION, OBSERVATORY
TYPE, AT PEORIA, ILLINOIS. (_Photograph, U. S. Weather Bureau._)]
Regardless of the merits of these particular instruments, it is
certain that the cooling power of the air--which is quite a different
thing from the temperature of the air--is a very important factor in
determining our comfort and our health. Within certain limits the body
can easily adjust itself to changes in the cooling power of the air;
within wider limits the adjustment is effected with difficulty, and we
experience discomfort and possibly suffer in health; and finally
there are extreme conditions, in either direction, to which adjustment
is not possible; the internal temperature is then either lowered or
raised, as the case may be, and a comparatively small change of this
sort is fatal; i. e., death results by chilling or by heat stroke.
[Illustration:
Photo U. S. Weather Bureau
THE CENTRAL OFFICE OF THE UNITED STATES WEATHER BUREAU IN WASHINGTON]
One interesting result of recent inquiries on this subject is the
discovery that the bad effects of crowded, “stuffy” rooms are not
generally due to impurities in the air, but to heat, humidity, and
especially lack of air movement. It seems to be now demonstrated
that there is no such thing as “crowd-poisoning,” and that the
bad smells of confined places are no indication that the air is
deleterious. Professor Hill, who has done more than anybody else to
upset traditional ideas with regard to ventilation, tells us that
“the deaths in the Black Hole of Calcutta, the depression, headache,
etc., experienced in close rooms are alike due to heat stagnation; the
victims of the Black Hole died of heat stroke.” Most recent writers
on physiology also discredit the time-honored methods of testing the
purity of the air by measuring the percentage of carbon dioxide it
contains. The amount of this gas normally present in the free air is
about three-hundredths of one per cent, but experiments have shown
that thirty times this amount--a percentage higher than is found in
the worst ventilated rooms--may be breathed for hours together without
detrimental effects. A further departure from old-fashioned views
is seen in the assertion of recent authorities that a deficiency
of oxygen, unless far more pronounced than ever actually occurs in
buildings, mines, etc., where the supply of this gas has been the
subject of so much solicitude, has no physiological significance
whatever. In support of this assertion it is pointed out that at
mountain health resorts the concentration of oxygen out-of-doors is
much less than that found in the worst ventilated rooms at sea-level.
In mines an ample supply of oxygen may be positively dangerous, as
favoring the occurrence of explosions. These were rare before the
enactment of laws requiring a high percentage of oxygen in mine air.
[Illustration: HILL’S KATATHERMOMETER]
Excessive dryness of the skin, which is a common cause of discomfort,
is not very closely related to the humidity of the air. “In winter,”
says Hill, “if there be a wind the rate of evaporation is so
accelerated that the skin feels dry, because in order to check the
loss of body heat the sweat glands are inactive and the blood vessels
of the chilled skin are constricted.” There has been a great deal of
discussion about the dry air of American buildings in winter, and
startling figures have been adduced to show that the air of such
buildings is dryer than that of deserts. So far as measurements of
relative humidity go, this is perfectly true; but, as Dr. G. T.
Palmer, of the New York State Commission on Ventilation, has pointed
out, there is an important difference between dryness and “dryingness.”
The latter depends upon the movement of the air, as well as the
relative humidity. The circulation of the air in a desert is generally
much more active than that of the air in a building with the windows
shut, and therefore much more conducive to rapid evaporation. There are
systems of ventilation in which the air is kept in steady and rapid
motion, and it is probably only in such cases that the air of our
heated houses can be compared to that of a desert. From the European
point of view American buildings are notoriously overheated, but this
is probably due to the fact that our hot summers--much hotter than
those of Europe--have adapted us to a tropical climate.
It is natural to inquire whether the atmospheric conditions that
affect the comfort of man do not also exercise a marked influence
upon his muscular efficiency and his mental powers. This question has
been answered in the affirmative by a number of ingenious writers,
who have sought to establish definite quantitative relations between
certain states of the atmosphere and the output of work in factories,
the grades attained by school children, etc. Thus, Dr. Ellsworth
Huntington, a well-known worker in this field, declares that the most
favorable daily mean temperature for mental activity (the temperature
being measured out-of-doors) is about 40 degrees F., and for physical
activity about 60 degrees F. Contrary to the common opinion, he holds
that our general efficiency is at low ebb in midwinter and fairly high
in summer. Variability in temperature, within certain limits, he finds
to be stimulating; equable temperature the reverse. He has drawn
charts showing the distribution of what he calls “climatic energy”--i.
e., the combination of certain weather factors supposed to control
human efficiency--throughout the world, and other charts showing a
more or less similar distribution of “civilization.” He has also made
an ambitious attempt to interpret the history of mankind in terms of
weather and climate.
Another fruitful worker along similar lines is Dr. Griffith Taylor,
of Australia, who has made interesting studies of the control of
settlement in his own country and elsewhere by temperature and
humidity, and has introduced some novel graphic methods (“climographs”)
for comparing climates with respect to their effects on humanity.
There has, in short, arisen a new school of climatologists whose aim
is to develop exact mathematical formulæ whereby we shall be able
to adjust the economic arrangements of mankind on an intelligent
basis as regards climate. The success of their efforts is a question
for the future to decide, but there is no doubt that their work is
profoundly suggestive. These undertakings, it may be noted, bear a
striking analogy to those of the present generation of agricultural
meteorologists, who are applying climatic statistics to the problem of
selecting crops and to the improvement of agricultural methods.
A certain number of specialists are engaged in studying the
physiological effects of sunlight and other special kinds of solar
radiation, the distribution of which varies greatly from place to
place and from time to time, especially on account of differences in
the selective absorption of such rays by the atmosphere. The chemical
action of sunshine that causes sunburn--even at very low temperatures,
as, for example, on high mountains--may have far-reaching effects on
the human organism (as it certainly has on plants), and there is great
need of collecting more data of “photochemical climate” than we now
possess, in order that this subject may be thoroughly investigated. One
of the few institutions in the world at which a large amount of work
has been done in this line is the private observatory of Dr. C. Dorno,
at Davos, the well-known health resort in the Alps. Dorno’s studies
throw a good deal of light upon the therapeutic effects of sunshine in
a mountain climate.
Many forms of dust in the atmosphere are capable of producing
pronounced physiological and pathological effects. There is a long
list of “dusty trades” in which the production of excessive dust has
notoriously evil effects upon the health of workmen, leading especially
to pulmonary diseases; sometimes to various kinds of poisoning. These
harmful dusts are by no means confined to factories, mines, quarries,
and the like. The air of the average city street abounds in them. Dr.
J. G. Ogden states that 61 per cent of the dust found in the air of the
New York subways consists of jagged splinters of steel, resulting from
the wearing away of brake shoes, wheels, and rails.
The amount of danger to human health incurred through the presence
of disease germs in the atmosphere has been the subject of much
controversy. The present tendency is to regard this danger as very
slight, under ordinary conditions. Thus, Dr. F. S. Lee writes:
“Evidence that disease germs pass through the air from room to room
of a house or from a hospital to its immediate surroundings always
breaks down when examined critically. It is indeed not rare now to
treat cases of different infectious diseases in the same hospital
ward. The one place of possible danger is in the immediate vicinity
of a person suffering from a disease affecting the air passages, the
mouth, throat, or lungs, such as a ‘cold’ or tuberculosis. Such a
person may give out the characteristic microbe for a distance of a few
feet from his body, not in quiet expiration, for simple expired air is
sterile, but attached to droplets that may be expelled in coughing,
sneezing, or forcible speaking. In this manner infection may, and
probably does, occur, the evidence being perhaps strongest in the case
of tuberculosis. But apart from this source there appears to be little
danger of contracting an infectious disease from germs that float in
the air.”
In regard to sewer gas, which still inspires so much dread in the
popular mind, Dr. Lee says:
“Workmen in sewers are notoriously strong, vigorous, healthy men,
with a low death rate among them. The specter of an invisible monster
entering our homes surreptitiously from our plumbing pipes and sapping
our lives and the lives of our children must be laid aside; we need no
longer leave saucers of so-called ‘chlorides’ standing about our floors
to neutralize in an impossible manner mysterious effluvia that do not
exist; and when we return to our town houses in the autumn we may enter
them with no fears that we are risking our lives by coming into a
toxic, germ-infected, sewer gas-laden, deadly atmosphere.”
Present-day knowledge on the subject of infectious diseases discredits
many ideas that once prevailed with regard to the effects of tropical
climates on health. The remarkable results accomplished by vigorous
sanitary measures in such places as Havana, the Isthmus of Panama and
Guayaquil have aroused hopes--perhaps too sanguine--that eventually
all parts of the tropics will be made healthful for the white race. In
the Canal Zone the death rate of the large population of American men,
women, and children is not higher than prevails in many cities of the
United States; whereas, a generation ago, when the French were at work
on the canal, the “climate” of this region was regarded as one of the
most unhealthful in the world. Some authorities go so far as to assert
that the deterioration in the general health and efficiency of white
people in the tropics, so far as it actually occurs, is due entirely
to preventable diseases. It would seem more rational, however, to
assume that there are climates both in and out of the tropics which,
on account of their heat, humidity, and other purely physical factors,
are not so suitable for habitation for any race of humanity as others.
How far acclimatization can go toward offsetting the effects of these
atmospheric conditions is problematical.
The changes in the barometer that occur from day to day in regions
where these changes are most pronounced are, on an average,
not greater than those encountered in going from the bottom to
the top of a good-sized hill, and are probably not directly of
physiological importance. Certain European investigators, however,
ascribe pathological effects to the minute and rapid barometric
fluctuations--too small to be detected with an ordinary barometer--that
occur, for example, when the foehn wind is blowing. Whether this is
the cause, or a contributory cause, of “foehn-sickness,” of which one
hears in Switzerland, is still uncertain.
The physiological effects of a rarefied atmosphere, as experienced
in mountain climbing, ballooning, and aviation, are not yet well
understood, despite the large amount of study that has been devoted to
this subject. Recent views are thus summarized by Rosenau:
“The symptoms produced by a marked diminution in atmospheric pressure
vary with circumstances. The effects are increased by cold, active
muscular exertion, or improper clothing. The noticeable symptoms are
increased rapidity of respiration and acceleration of the circulation,
noises in the head and dizziness, impairment of the senses of sight,
hearing, and touch, dullness of the intellectual faculties, and a
strong desire to sleep. Sudden changes to a rarefied atmosphere cause
syncope, weakness, dyspnœa, dizziness, and nausea. These threatening
symptoms go by the name of ‘mountain sickness,’ Bert and Journet
believe this condition is due to lack of oxygen, and the symptoms may,
in fact, be relieved by adding oxygen to the air inspired. Kronecker
concludes that mountain sickness is caused by a congestion of the
lungs, impeding the flow of blood through them. Mosso and his followers
attribute the physical disturbances of a reduced atmospheric pressure
to the fact that the blood loses carbon dioxide more quickly than it
loses oxygen, and they ascribe mountain sickness to this decrease of
carbon dioxide in the blood. Cohnheim believes there is a concentration
of the blood at high altitudes; in fact, insignificant increases have
been found by competent observers.”
Divers and workers in caissons are subjected to high barometric
pressure, amounting, at the maximum, to about 4½ atmospheres.
According to Rosenau:
“The physiological effects of an increased atmospheric pressure
are mainly due to an increase in the amount of atmospheric gases
(especially nitrogen) which are taken up by the blood, and also to an
increase in the chemical absorption of oxygen by the blood. The serious
consequences usually result from too rapid decompression. As the
pressure is released gas bubbles form. Gradual decompression gives a
chance for the gas to escape from the lungs and be expelled without the
production of bubbles.”
The health and comfort of many people seem to be affected, in a
rather striking way, by the passage of the barometric depressions and
areas of high pressure that alternate at intervals of a few days in
the temperate zones. These effects should not be ascribed to changes
of pressure, but rather to the accompanying changes in the other
meteorological conditions. The late Dr. Weir Mitchell, who was a
pioneer student of such phenomena, wrote of “a neuralgic belt, within
which, as it sweeps along in advance of the storm, prevail in the hurt
and maimed limbs of men, in the tender nerves and rheumatic joints,
renewed torments called into existence by the stir and perturbation of
the elements.” Victims of neuralgia and rheumatism are probably quite
justified in regarding themselves as human barometers, capable of
predicting with considerable accuracy the advent of stormy and rainy
weather.
The fluctuations of temperature, humidity, and wind that attend
the passage of barometric highs and lows would seem, in virtue
of their effects on the heat-regulating mechanism of the body and
consequent reactions upon the nervous system in general, to supply
an ample explanation of the unpleasant symptoms above noted in the
case of sensitive people; conditions to which the collective name of
“cyclonopathy” has been given by European investigators, and which are
extensively discussed in the works of Hellpach, Frankenhäuser, and
Berliner. Some authorities have, however, invoked in this connection
the possible effects of atmospheric electricity, and pointed to the
extreme sensitiveness of many persons to the approach of thunderstorms;
a condition which Dr. G. M. Beard named “astraphobia.” It is stated
that the passage of a low-pressure area favors the emission of
radioactive emanations from the ground, that the ionization of the
atmosphere, and hence its electrical conductivity, is thus increased,
and that the electric charge of the body is carried away more rapidly
than usual. Here we enter upon a debatable subject, but one that
thoroughly merits investigation. The human organism is the seat of
various electrical phenomena, and these certainly cannot be independent
of changes in the electrical state of the atmosphere.
Apart from possible direct effects of atmospheric electricity upon
the human system, it has been suggested that electrical changes in
the atmosphere affect the rate of reproduction of bacteria, and may
therefore have some influence on the spread of infectious diseases.
The weather has many subtle influences upon the human mind, producing
moods of cheerfulness and depression, and manifesting themselves in
the records of the behavior of school children, in statistics of
crime, insanity, suicide, drunkenness, etc. An interesting account of
these manifestations is given by Dr. E. G. Dexter in his book “Weather
Influences” (New York, 1904).
Finally, the aspect of meteorology that has thus far acquired the most
definite shape in medical circles and given rise to the most coherent
body of literature is Medical Climatology, which is designed to be
applied in the climatic treatment of disease (climatotherapy). Thus
many compilations have been made of the climatic statistics of health
resorts, and these resorts have been classified with respect to their
supposed climatic effects upon various diseases. From the point of view
of the physical climatologist, the statistics found in such books seem,
in general, both meager and ill adapted to bring out important features
of the climates discussed; to say nothing of the fact that the whole
subject of climatotherapy is fraught with controversy--whereof the
history of the treatment of tuberculosis furnishes a shining example!