contractile energy of the diaphragm and muscles that elevate the
ribs, is much diminished, and the lungs are not so fully inflated, as
when the mind is influenced by joy or other exhilarating emotions. The
depressing passions likewise lessen the frequency of respiration. By
the influence of these causes, the blood is but partially purified,
and the whole system becomes enfeebled. Here we may see the admirable
harmony between the different parts of the body, and the adaptation of
all the functions to each other.

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Give another test. How can the amount of pressure necessary to prevent
the enlargement of the chest be demonstrated? 530. Show the effect of
position on the movements of the ribs and diaphragm. 531. Show the
effect of habit on the respiratory movements. 532. State the influence
of the mind upon respiration.

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533. As the quantity of air inhaled at each unimpeded inspiration in
lungs of ample size, is about forty cubic inches, it follows, if the
movement of the ribs and diaphragm is restricted by an enfeebled
action of the respiratory muscles, or by any other means, the blood
will not be perfectly purified. In the experiment, (Sec. 522, 523,)
suppose forty cubic inches of air must pass over the membrane twenty
times every minute, and that this is the amount required to remove the
vapor which arises from the membrane; if only half of this amount of
air be supplied each minute, only one half as much water will be
removed from the alcohol through the membrane in twenty-four hours;
consequently, the alcohol would be impure from the water not being
entirely removed.

534. Restrain the elevation of the ribs and depression of the
diaphragm, so that the quantity of air conveyed into the lungs will be
reduced to twenty cubic inches, when forty are needed, and the results
will be as follows: Only one half of the carbonic acid will be
eliminated from the system, and the blood will receive but one half as
much oxygen as it requires. This fluid will then be imperfectly
oxydated, and partially freed of its impurities. The impure blood will
be returned to the left side of the heart, and the whole system will
suffer from an infringement of organic laws.

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533. Illustrate the effect upon the blood when the respiratory muscles
are enfeebled in their action. 534. Show how the blood is imperfectly
purified by restricting the movements of the