influence the secretions? Give an illustration.

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434. _The secretory organs require the stimulus of pure blood._ If
this fluid is vitiated, the action of the secretory organs will be
more or less modified. Either the quantity will be affected or the
quality will be altered.

_Observation._ The impurity of the blood arising from the inhalation
of the vitiated air of sleeping rooms, diminishes and changes the
character of the secretions of the mouth and stomach. This accounts
for the thirst, coated tongue, and disagreeable taste of the mouth
when impure air is breathed during sleep. The disease it induces, is
indigestion or dyspepsia.

435. _The amount of action modifies the condition of the secretory
organs._ When a secretory organ is excessively stimulated, its vigor
and energy are reduced. The subsequent debility may be so great as to
suppress or destroy its functional power.

_Illustrations._ 1st. In those sections of the country where flax is
spun on a "foot-wheel," it is not unfrequent that the spinners moisten
the thread with the secretions of the mouth. This seems to operate
economically for a time, but debility of the salivary organs soon
follows, which incapacitates them from supplying saliva sufficient to
moisten the food, producing in a short time disease of the digestive
organs.

2d. The habit of continual spitting, which attends the chewing of
tobacco and gums, and other substances, between meals, induces
debility, not only of the salivary glands, but of the system
generally.

436. _One secretory organ may do the office of another._ This
increased action of a secretory organ may be sustained for a limited
time without permanent injury, but, if long continued, a diseased
action of the organ will follow. Of morbid secretions we have examples
in the ossification of the valves of the heart, cancerous and other
tumors.

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434. What is the effect of impure blood on the secretory organs? 435.
What results from stimulating excessively a secretory organ? How is
this illustrated? 436. What is the effect when one secretory organ
performs the office of another?

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_Observation._ In the evenings of the warm season, a chill upon the
impressible skin, that suppresses the perspiration, is frequently
followed by a diarrhoea, dysentery, or cholera morbus. These can be
prevented by avoiding the chill. An efficient means of relief, i