power of volition
is incapable of exertion, and in a great degree the external senses become
incapable of perceiving their adapted stimuli, because the whole sensorial
power is employed or expended on the ideas excited by pleasurable
sensation.

This kind of delirium is distinguished from that which attends the fevers
above mentioned from its not being accompanied with general debility, but
simply with excess of pleasurable sensation; and is therefore in some
measure allied to madness or to reverie; it differs from the delirium of
dreams, as in this the power of volition is not totally suspended, nor are
the senses precluded from external stimulation; there is therefore a degree
of consistency, in this kind of delirium, and a degree of attention to
external objects, neither of which exist in the delirium of fevers or in
dreams.

5. It would appear, that the vascular system of other animals are less
liable to be put into action by their general sum of pleasurable or painful
sensation; and that the trains of their ideas, and the muscular motions
usually associated with them, are less powerfully connected than in the
human system. For other animals neither weep, nor smile, nor laugh; and are
hence seldom subject to delirium, as treated of in Sect. XVI. on Instinct.
Now as our epidemic and contagious diseases are probably produced by
disagreeable sensation, and not simply by irritation; there appears a
reason, why brute animals are less liable to epidemic or contagious
diseases; and secondly, why none of our contagions, as the small-pox or
measles, can be communicated to them, though one of theirs, viz. the
hydrophobia, as well as many of their poisons, as those of snakes and of in
insects, communicate their deleterious or painful effects to mankind.

Where the quantity of general painful sensation is too great in the system,
inordinate voluntary exertions are produced either of our ideas, as in
melancholy and madness, or of our muscles, as in convulsion. From these
maladies also brute animals are much more exempt than mankind, owing to
their greater inaptitude to voluntary exertion, as mentioned in Sect. XVI.
on Instinct.

II. 1. When any moving organ is excited into such violent motions, that a
quantity of pleasurable or painful sensation is produced, it frequently
happens (but not always) that new motions of the affected organ are
generated in consequence of the pain or pleasure, which are termed
inflammation.

The