in much the same
degree of heat as destroys insects; all which evince that they are
living animals.

And it is probable, that other or similar animalcules may be produced
in the air, or near the surface of the earth, but it is not so easy to
view them as in water; which as it is transparent, the creatures
produced in it can easily be observed by applying a drop to a
microscope. I hope that microscopic researches may again excite the
attention of philosophers, as unforeseen advantages may probably be
derived from them, like the discovery of a new world.

ADDITIONAL NOTES. II.

THE FACULTIES OF THE SENSORIUM.

Next the long nerves unite their silver train,
And young Sensation permeates the brain.
CANT. I. l. 250.

I. The fibres, which constitute the muscles and organs of sense,
possess a power of contraction. The circumstances attending the
exertion of this power of contraction constitute the laws of animal
motion, as the circumstances attending the exertion of the power of
attraction constitute the laws of motion of inanimate matter.

II. The spirit of animation is the immediate cause of the contraction
of animal fibres, it resides in the brain and nerves, and is liable to
general or partial diminution or accumulation.

III. The stimulus of bodies external to the moving organ is the remote
cause of the original contractions of animal fibres.

IV. A certain quantity of stimulus produces irritation, which is an
exertion of the spirit of animation exciting the fibres into
contraction.

V. A certain quantity of contraction of animal fibres, if it be
perceived at all, produces pleasure; a greater or less quantity of
contraction, if it be perceived at all, produces pain; these
constitute sensation.

VI. A certain quantity of sensation produces desire or aversion; these
constitute volition.

VII. All animal motions which have occurred at the same time, or in
immediate succession, become so connected, that when one of them is
reproduced, the other has a tendency to accompany or succeed it. When
fibrous contractions succeed or accompany other fibrous contractions,
the connexion is termed association; when fibrous contractions succeed
sensorial motions, the connexion is termed causation; when fibrous and
sensorial motions reciprocally introduce each other, it is termed
catenation of animal motions.

VIII. These four faculties of the sensorium during their inactiv