The self-preservation of man and kindred animals is effected
through mechanisms which transform latent energy into kinetic energy
to accomplish adaptive ends. Man appropriates from environment
the energy he requires in the form of crude food which is refined
by the digestive system; oxygen is taken to the blood and carbon
dioxid is taken from the blood by the respiratory system;
to and from the myriads of working cells of the body, food and oxygen
and waste are carried by the circulatory system; the body is cleared
of waste by the urinary system; procreation is accomplished through
the genital system; but none of these systems was evolved primarily
for the purpose of transforming potential energy into kinetic energy
for specific ends. Each system transforms such amounts of potential
into kinetic energy as are required to perform its specific work;
but no one of them transforms latent into kinetic energy for the purposes
of escaping, fighting, pursuing, nor for combating infection.
The stomach, the kidneys, the lungs, the heart strike no physical
blow-their role is to do certain work to the end that the blow may
be struck by another system evolved for that purpose. I propose
to offer evidence that there is in the body a system evolved primarily
for the transformation of latent energy into motion and into heat.
This system I propose to designate "The Kinetic System."
The kinetic system does not directly circulate the blood,
nor does it exchange oxygen and carbon dioxid; nor does it perform
the functions of digestion, urinary elimination, and procreation;
but though the kinetic system does not directly perform these functions,
it does play indirectly an important role in each, just as the kinetic
system itself is aided indirectly by the other systems.
The principal organs which comprise the kinetic system are
the brain, the thyroid, the adrenals, the liver, and the muscles.
The brain is the great central battery which drives the body;
the thyroid governs the conditions favoring tissue oxidation;
the adrenals govern immediate oxidation processes; the liver fabricates
and stores glycogen; and the muscles are the great converters
of latent energy into heat and motion.
Adrenalin alone, thyroid extract alone, brain activity alone,
and muscular activity alone are capable of causing the body temperature
to rise above the normal. The functional activity of no other gland
of the body alone, and the secretion of no other gland alone, can cause
a comparable rise in body temperature--that is, neither increased
functional activity nor any active principle derived from the kidney,
the liver, the stomach, the pancreas, the hypophysis, the parathyroids,
the spleen, the intestines, the thymus, the lymphatic glands,
or the bones can, _per se_, cause a rise in the general body
temperature comparable to the rise that may be caused by the activity
of the brain or the muscles, or by the injection of adrenalin
or thyroid extract. Then, too, when the brain, the thyroid,
the adrenals, the liver, or the muscles are eliminated, the power
of the body to convert latent into kinetic energy is impaired or lost.
I shall offer evidence tending to show that an excess of either
internal or external environmental stimuli may modify one or more
organs of the kinetic system, and that this modification may cause
certain diseases. For example, alterations in the efficiency
of the cerebral link may yield neurasthenia, mania, dementia;
of the thyroid link, Graves' disease, myxedema; of the adrenal link,
Addison's disease, cardiovascular disease.
This introduction may serve to give the line of our argument.
We shall now consider briefly certain salient facts which relate to
the conversion of latent into kinetic energy as an adaptive reaction.
The experimental data are so many that they will later be published
in a monograph.
The amount of latent energy which may be converted into kinetic
energy for adaptive ends varies in different species, in individuals
of the same species, in the same individual in different seasons;
in the life cycle of growth, reproduction and decay;
in the waking and sleeping hours; in disease and in activity.
We shall here consider briefly the reasons for some of those variations
and the mechanisms which make them possible.
Biologic Consideration of the Adaptive Variation in Amounts
of Energy Stored in Various Animals
Energy is appropriated from the physical forces of nature
that constitute the environment. This energy is stored in
the body in quantities in excess of the needs of the moment.
In some animals this excess storage is greater than in other animals.
Those animals whose self-preservation is dependent on purely
mechanical or chemical means of defense--such animals as crustaceans,
porcupines, skunks or cobras--have a relatively small amount
of convertible (adaptive) energy stored in their bodies.
On the contrary, the more an animal is dependent on its muscular
activity for self-preservation, the more surplus available
(adaptive) energy there is stored in its body. It may be true that all
animals have approximately an equal amount per kilo of chemical energy--
but certainly they have not an equal amount stored in a form
which is available for immediate conversion for adaptive ends.
Adaptive Variation in the Rate of Energy Discharge
What chance for survival would a skunk have without odor; a cobra
without venom; a turtle without carapace; or a porcupine shorn
of its barbs, in an environment of powerful and hostile carnivora?
And yet in such an hostile environment many unprotected animals
survive by their muscular power of flight alone. It is evident that
the provision for the storage of "adaptive" energy is not the only
evolved characteristic which relates to the energy of the body.
The more the self-preservation of the animal depends on motor activity,
the greater is the range of variation in the rate of discharge of energy.
The rate of energy discharge is especially high in animals evolved
along the line of hunter and hunted, such as the carnivora and
the herbivora of the great plains.
Influences That Cause Variation in the Rate of Output of Energy
in the Individual
Not only is there a variation in the rate of output of energy among
various species of animals, but one finds also variations in the rate
of output of energy among individuals of the same species.
If our thesis that men and animals are mechanisms responding to
environmental stimuli be correct, and further, if the speed of energy
output be due to changes in the activating organs as a result of
adaptive stimulation, then we should expect to find physical changes
in the activating glands during the cycles of increased activation.
What are the facts? We know that most animals have breeding
seasons evolved as adaptations to the food supply and weather.
Hence there is in most animals a mating season in advance of
the season of maximum food supply so that the young may appear at
the period when food is most abundant. In the springtime most birds
and mammals mate, and in the springtime at least one of the great
activating glands is enlarged--the thyroid in man and in animals shows
seasonal enlargement. The effect of the increased activity is seen
in the song, the courting, the fighting, in the quickened pulse,
and in a slightly raised temperature. Even more activation
than that connected with the season is seen in the physical state
of mating, when the thyroid is known to enlarge materially,
though this increased activity, as we shall show later, is probably
no greater than the increased activity of other activating glands.
In the mating season the kinetic activity is speeded up; in short,
there exists a state--a fleeting state--of mild Graves' disease.
In the early stages of Graves' disease, before the destructive phenomena
are felt, the kinetic speed is high, and life is on a sensuous edge.
Not only is there a seasonal rhythm to the rate of flow of energy,
but there is a diurnal variation--the ebb is at night,
and the full tide in the daytime. This observation is verified
by the experiments which show that certain organs in the kinetic
chain are histologically exhausted, the depleted cells being
for the most part restored by sleep.
We have seen that there are variations in speed in different species,
and that in the same species speed varies with the season of the year
and with the time of day. In addition there are variations also in
the rate of discharge of energy in the various cycles of the life
of the individual. The young are evolved at high speed for growth,
so that as soon as possible they may attain to their own power
of self-defense; they must adapt themselves to innumerable bacteria,
to food, and to all the elements in their external environment.
Against their gross enemies the young are measurably protected
by their parents; but the parents--except to a limited extent in
the case of man--are unable to assist in the protection of the young
against infectious disease.
The cycle of greatest kinetic energy for physiologic ends is the period
of reproduction. In the female especially there is a cycle of increased
activity just prior to her development into the procreative state.
During this time secondary sexual characters are developed--
the pelvis expands, the ovaries and the uterus grow rapidly,
the mammary glands develop. Again in this period of increasing
speed in the expenditure of energy we find the thyroid,
the adrenals, and the hypophysis also in rapid growth.
Without the normal development of the ovary, the thyroid,
and the hypophysis, neither the male nor the female can develop
the secondary sexual characters, nor do they develop sexual desire
nor show seasonal cycles of activity, nor can they procreate.
The secondary sexual characters--sexual desire, fertility--may be
developed at will, for example, by feeding thyroid products from
alien species to the individual deprived of the thyroid.
At the close of the child-bearing period there is a permanent
diminution of the speed of energy discharge, for energy is no
longer needed as it was for the self-preservation of the offspring
before adolescence, and for the propagation of the species
during the procreative period. Unless other factors intervene,
this reduction in speed is progressive until senescent death.
The diminished size of the thyroid of the aged bears testimony
to the part the activating organs bear in the general decline.
We have now referred to variations in the rate of discharge of
energy in different species; in individuals of the same species;
in cycles in the same individual--such as the seasons of food supply,
the periods of wakefulness and of sleep, the procreative period,
and we have spoken of those variations caused artificially
by thyroid feeding, thus far having confined our discussion
to the conversion for adaptive purposes of latent into kinetic
energy in muscular and in procreative action. We shall now consider
the conversion of latent into kinetic energy in the production of
heat,[*] and endeavor to answer the questions which arise at once:
Is there one mechanism for the conversion of latent energy into heat
and another mechanism for its conversion into muscular action?
What is the adaptive advantage of fever in infection?
[*] We use the terms "heat" and "muscular action" in the popular sense,
though physicists use them to designate one and the same kind of energy.