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Page 5
Up to the present it has been assumed that the environment of the
amoeba is that to which it has become adapted and which is favorable
to its existence. Under these conditions its structure conforms to the
type of the species, as do also the phenomena which it exhibits, and
it can assimilate food, grow and multiply. If, during the observation,
a small crystal of salt be placed in the fluid, changes almost
instantly take place. Motion ceases, the amoeb� appear to shrink into
smaller compass, and they become more granular and opaque. If they
remain a sufficiently long time in this fluid, they do not regain
their usual condition when placed again in fresh water. None of the
phenomena which characterized the living amoeb� appear: we say they
are dead. After a time they begin to disintegrate, and the bacteria
contained in the water and on which the amoeb� fed now invade their
tissue and assist in the disintegration. By varying the duration of
the exposure to the salt water or the amount of salt added, a point
can be reached where some, but not all, of the amoeb� are destroyed.
Whether few or many survive depends upon the degree of injury
produced. Much the same phenomena can be produced by gradually heating
the water in which the amoeb� are contained. It is even possible
gradually to accustom such small organisms to an environment which
would destroy them if suddenly subjected to it, but in the process of
adaptation many individuals will have perished.
It is evident from such an experiment that when a living organism is
subject to an environment to which it has not become adapted and which
is unfavorable, such alterations in its structure may be produced that
it is incapable of living even when it is again returned to the
conditions natural to it. Such alterations of structure or injuries
are called the _lesions_ of disease. We have seen that in certain
individuals the injury was sufficient to inhibit for a time only the
usual manifestations of life; these returned when the organism was
removed from the unfavorable conditions, and with this or preceding it
the organisms, if visibly altered, regained the usual form and
structure. We may regard this as disease and recovery. In the disease
there is both the injury or lesion and the derangement of vital
activity dependent upon this. The cause of the disease acted on the
organism from without, it was external to it. Whether the injurious
external conditions act as in this case by a change in the surrounding
osmotic pressure, or by the destruction of ferments within the cell,
or by the introduction into the cell of substances which form stable
chemical union with certain of its constituents, and thus prevent
chemical processes taking place which are necessary for life, the
result is the same.
The experiments with the amoeb� show also two of the most striking
characteristics of living matter. 1. It is _adaptable_. Under the
influence of unusual conditions, alterations in structure and possibly
in substance, may take place, in consequence of which the organisms
under such external conditions may still exhibit the usual phenomena.
The organism cannot adapt itself to such changes without undergoing
change in structure, although there may be no evidence of such changes
visible. This alteration of structure does not constitute a disease,
provided the harmonious relation of the organism with the environment
be not impaired. An individual without a liver should not be regarded
as diseased, provided there can be such an internal adjustment that
all of the vital phenomena could go on in the usual manner without the
aid of this useful and frequently maligned organ. 2. It is
_individual_. In the varying degrees of exposure to unfavorable
conditions of a more serious nature some, but not all, of the
organisms are destroyed; in the slight exposure, few; in the longer,
many. Unfavorable conditions which will destroy all individuals of a
species exposed to them must be extremely rare.[1] There is no such
individuality in non-living things. In a mass of sugar grains each
grain shows just the same characteristics and reacts in exactly the
same way as all the other grains of the mass. Individuality, however
expressed, is due to structural variation. It is almost impossible to
conceive in the enormous complexity of living things that any two
individuals, whether they be single cells or whether they be formed of
cell masses, can be exactly the same. It is not necessary to assume in
such individual differences that there be any variation in the amount
and character of the component elements, but the individuality may be
due to differences in the atomic or molecular arrangements. There are
two forms of tartaric-acid crystals of precisely the same chemical
formula, one of which reflects polarized light to the left, and the
other to the right. All the left-sided crystals and all the
right-sided are, however, precisely the same. The number of possible
variations in the chemical structure of a substance so complex as is
protoplasm is inconceivable.
In no way is the individuality of living matter more strongly
expressed than in the resistance to disease. The variation in the
degree of resistance to an unfavorable environment is seen in every
tale of shipwreck and exposure. In the most extensive epidemics
certain individuals are spared; but here care must be exercised in
interpreting the immunity, for there must be differences in the degree
of exposure to the cause of the epidemic. It would not do to interpret
the immunity to bullets in battle as due to any individual
peculiarity, save possibly a tendency in certain individuals to remove
the body from the vicinity of the bullets; in battle and in epidemics
the factors of chance and of prudence enter. No other living organism
is so resistant to changes in environment as is man, and to this
resistance he owes his supremacy. By means of his intelligence he can
change the environment. He is able to resist the action of cold by
means of houses, fire and clothing; without such power of intelligent
creation of the immediate environment the climatic area in which man
could live would be very narrow. Just as disease can be acquired by an
unfavorable environment, man can so adjust his environment to an
injury that harmony will result in spite of the injury. The
environment which is necessary to compensate for an injury may become
very narrow. For an individual with a badly working heart more and
more restriction of the free life is necessary, until finally the only
environment in which life is even tolerably harmonious is between
blankets and within the walls of a room.
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