Zoonomia, Vol. I | Page 6

organ of sense, or
idea, and the pain or pleasure that succeeds or accompanies it.
9. The pleasure or pain which necessarily accompanies all those
perceptions or ideas which we attend to, either gradually subsides, or is
succeeded by other fibrous motions. In the latter case it is termed
sensation, as explained in Sect. V. 2, and VI. 2.--The reader is intreated
to keep this in his mind, that through all this treatise the word sensation
is used to express pleasure or pain only in its active state, by whatever
means it is introduced into the system, without any reference to the
stimulation of external objects.
10. The vulgar use of the word memory is too unlimited for our purpose:
those ideas which we voluntarily recall are here termed ideas of
recollection, as when we will to repeat the alphabet backwards. And
those ideas which are suggested to us by preceding ideas are here
termed ideas of suggestion, as whilst we repeat the alphabet in the
usual order; when by habits previously acquired B is suggested by A,
and C by B, without any effort of deliberation.
11. The word association properly signifies a society or convention of
things in some respects similar to each other. We never say in common
language, that the effect is associated with the cause, though they
necessarily accompany or succeed each other. Thus the contractions of
our muscles and organs of sense may be said to be associated together,
but cannot with propriety be said to be associated with irritations, or
with volition, or with sensation; because they are caused by them, as
mentioned in Sect. IV. When fibrous contractions succeed other fibrous

contractions, the connection is termed _association_; when fibrous
contractions succeed sensorial motions, the connection is termed
_causation_; when fibrous and sensorial motions reciprocally introduce
each other in progressive trains or tribes, it is termed catenation of
animal motions. All these connections are said to be produced by
_habit_; that is, by frequent repetition.
12. It may be proper to observe, that by the unavoidable idiom of our
language the ideas of perception, of recollection, or of imagination, in
the plural number signify the ideas belonging to perception, to
recollection, or to imagination; whilst the idea of perception, of
recollection, or of imagination, in the singular number is used for what
is termed "a reflex idea of any of those operations of the sensorium."
13. By the word stimulus is not only meant the application of external
bodies to our organs of sense and muscular fibres, which excites into
action the sensorial power termed irritation; but also pleasure or pain,
when they excite into action the sensorial power termed sensation; and
desire or aversion, when they excite into action the power of volition;
and lastly, the fibrous contractions which precede association; as is
further explained in Sect. XII. 2. 1.
* * * * *
SECT. III.
THE MOTIONS OF THE RETINA DEMONSTRATED BY
EXPERIMENTS.
I. _Of animal motions and of ideas._ II. _The fibrous structure of the
retina._ III. _The activity of the retina in vision._ 1. _Rays of light have
no momentum._ 2. _Objects long viewed become fainter._ 3. _Spectra
of black objects become luminous._ 4. _Varying spectra from
gyration._ 5. _From long inspection of various colours._ IV. _Motions
of the organs of sense constitute ideas._ 1. _Light from pressing the
eye-ball, and sound from the pulsation of the carotid artery._ 2. _Ideas
in sleep mistaken for perceptions._ 3. _Ideas of imagination produce
pain and sickness like sensations._ 4. _When the organ of sense is

destroyed, the ideas belonging to that sense perish._ V. _Analogy
between muscular motions and sensual motions, or ideas._ 1. _They are
both originally excited by irritations._ 2. _And associated together in
the same manner._ 3. _Both act in nearly the same times._ 4. _Are
alike strengthened or fatigued by exercise._ 5. _Are alike painful from
inflammation._ 6. _Are alike benumbed by compression._ 7. _Are alike
liable to paralysis._ 8. _To convulsion._ 9. _To the influence of old
age._--VI. _Objections answered._ 1. _Why we cannot invent new
ideas._ 2. _If ideas resemble external objects._ 3. _Of the imagined
sensation in an amputated limb._ 4. _Abstract ideas._--VII. _What are
ideas, if they are not animal motions?_
Before the great variety of animal motions can be duly arranged into
natural classes and orders, it is necessary to smooth the way to this yet
unconquered field of science, by removing some obstacles which
thwart our passage. I. To demonstrate that the retina and other
immediate organs of sense possess a power of motion, and that these
motions constitute our ideas, according to the fifth and seventh of the
preceding assertions, claims our first attention.
Animal motions are distinguished from the communicated motions,
mentioned in the first section, as they have no