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Page 53
The power of the heart in meeting these conditions, however various
they are and however variously they act, seems little short of
marvellous, and it goes on throwing three and one-third ounces of
blood seventy or eighty times a minute into a tube against nine feet
of water pressure, working often perfectly under conditions which
would be fatal to a machine. As long as this goes on the injury is
said to be compensated for; the increased work which the heart is able
to accomplish by the exercise of its reserve force and by becoming
larger and stronger enables it to cope with the adverse conditions.
With increased demand for work there is a gradual diminution of the
reserve force. An individual may be able to carry easily forty pounds
up a hill and by exerting all his force may carry eighty pounds, but
if he habitually carries the eighty pounds, even though the muscles
become stronger by exercise the load cannot be again doubled. The
dilatation of the heart which is so important in compensation is
fraught with danger, because any weakening of the muscle increases the
dilatation, until a point is reached when, owing to the dilatation of
the orifices between auricles and ventricles, the valves become
incompetent to close them.
When the heart is not able to accomplish its work, the effect of the
condition becomes apparent by the accumulation of blood within the
veins and a less active circulation. This affects the nutrition and
the capacity for work of all the organs of the body, and the imperfect
function of the organs may in a variety of ways make still greater
demands upon an already overloaded heart. Other conditions supervene.
The increased pressure within the veins and capillaries due to the
impossibility of the blood in the usual amount passing through or from
the heart increases the amount of fluid in the tissues. There is
always an interchange between the blood within the vessels and the
fluid outside of them; the passage of fluid from the vessels is
facilitated by the increased pressure within them, just as pressure
upon a filtering fluid increases the rapidity of filtration, and the
increase of pressure within veins and capillaries impedes passage of
tissue fluid into them. The fluid accumulates within the tissues
leading to dropsy, or the accumulation may take place in some of the
cavities of the body. The diminished flow of blood through the lungs
prevents its proper oxygenation; this may also be interfered with by
the accumulation of fluid within the air spaces of the lungs.
Every additional burden thrown upon the heart increases the evil. In
women the additional burden of pregnancy may suffice to overcome a
compensation which has been perfect, and the same may result from an
acute attack of disease. Age, diminishing as it does the capacity for
work in all organs, diminishes the compensation capacity of the heart,
and a heart which at the age of forty acts perfectly may break down at
the age of fifty. Compensation may be gained in other ways, as by
reducing the demand made upon the heart by changing the mode of life,
by leading an inactive rather than an active life, by avoiding
excitement or any condition which entails work of the heart. Social
conditions are of great importance; it makes a great difference
whether the unfortunate possessor of such a heart be a stevedore whose
capital lies in the strength of his muscles, or a more fortunately
placed member of society for whom the stevedore works and whose
occupation or lack of occupation does not interfere with the
adjustment of his external relations to the condition of his heart.
Disease of the nervous system does not differ from disease elsewhere.
The system is complex in structure and in function. It consists in
nerves which are composed of very fine fibrils distributed in all
parts of the body and serve the purpose of conduction, and a central
body composed of the brain and spinal cord which is largely cellular
in character; it receives impressions by means of the nerves and sends
out impulses which produce or affect action in all parts. By means of
the organs of special sense, the brain receives impressions from the
outer world which it transforms into the concepts of consciousness.
Many of the impressions which the central nervous system receives from
nerves other than those of special sense and even many of the
impressions from these and the impulses which it sends out do not
affect consciousness. The memory faculty is seated in the brain and
all parts of the brain are closely connected by means of small nerve
fibres. The nervous system plays an important part in the internal
regulation and coordination of all parts of the body, and it is by
means of this that the general adjustment of man with his environment
is effected.
Malformations of the brain, except very gross conditions which are
incompatible with extra-uterine existence, are not very common. At
birth those parts of the brain which are the seat of memory and what
are understood as the higher faculties are very imperfectly developed.
Variations in structure are extremely common, there are differences in
different individuals in the nerves and in the number, size, form and
arrangement of the nerve cells, and so complex is the structure that
considerable variation can exist without detection. The tissue of the
central nervous system has a considerable degree of resistance to the
action of bacteria, but is, however, very susceptible to injury by
means of poisons. Serious injury or destruction of tissue of the brain
and spinal cord is never regenerated or repaired, but adjustment to
such conditions may be effected by reciprocity of function, other
cells taking up the functions of those which were destroyed.
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