h
sensation is excited in the lungs; which is another argument in favour of
the existence of a peculiar set of nerves for the purpose of perceiving the
universal fluid matter of heat, in which all things are immersed. See Sect.
XIV. 6. Yet are the lungs nevertheless very sensible to the deficiency of
oxygen in the atmosphere, as all people experience, when they go into a
room crowded with company and candles, and complain, that it is so close,
they can scarcely breathe; and the same in some hot days in summer.

There are two diseases, which bear the name of asthma. The first is the
torpor or inability of the minute vessels of the lungs, consisting of the
terminations of the pulmonary and bronchial arteries and veins, and their
attendant lymphatics; in this circumstance it resembles the difficulty of
breathing, which attends cold bathing. If this continues long, a congestion
of fluid in the air-cells succeeds, as the absorbent actions cease
completely before the secerning ones; as explained in Class I. 1. 2. 3. And
the coldness, which attends the inaction of these vessels, prevents the
usual quantity of exhalation. Some fits cease before this congestion takes
place, and in them no violent sweating nor any expuition of phlegm occurs.
This is the humoral asthma, described at Class II. 1. 1. 7.

The second kind of asthma consists in the convulsive actions in consequence
of the disagreeable sensations thus induced; which in some fits of asthma
are very great, as appears in the violent efforts to raise the ribs, and to
depress the diaphragm, by lifting the shoulders. These, so long as they
contribute to remove the cause of the disease, are not properly
convulsions, but exertions immediately caused by sensation; but in this
kind of asthma they are only efforts to relieve pain, and are frequently
preceded by other epileptic convulsions.

These two kinds of asthmas have so many resembling features, and are so
frequently intermixed, that it often requires great attention to
distinguish them; but as one of them is allied to anasarca, and the other
to epilepsy, we shall acquire a clearer idea of them by comparing them with
those disorders. A criterion of the humoral or hydropic asthma is, that it
is relieved by copious sweats about the head and breast, which are to be
ascribed to the sensitive exertions of the pulmonary vessels to relieve the
pain occasioned by the anasarcous congestion in the air-cells; and which is
effected by t