Erasmus Darwin.

Zoonomia, Vol. I Or, the Laws of Organic Life online

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Principiò coelum, ac terras, camposque liquentes,
Lucentemque globum lunæ, titaniaque astra,
Spiritus intùs alit, totamque infusa per artus
Mens agitat molem, et magno se corpore miscet. - VIRG. Æn. vi.

Earth, on whose lap a thousand nations tread,
And Ocean, brooding his prolific bed,
Night's changeful orb, blue pole, and silvery zones,
Where other worlds encircle other suns,
One Mind inhabits, one diffusive Soul
Wields the large limbs, and mingles with the whole.

* * * * *


* * * * *


Entered at Stationers' Hall.

* * * * *


To the candid and ingenious Members of the College of Physicians, of the
Royal Philosophical Society, of the Two Universities, and to all those, who
study the Operations of the Mind as a Science, or who practice Medicine as
a Profession, the subsequent Work is, with great respect, inscribed by the

DERBY, May 1, 1794.


SECT. I. _Of Motion._
II. _Explanations and Definitions._
III. _The Motions of the Retina demonstrated by Experiments._
IV. _Laws of Animal Causation._
V. _Of the four Faculties or Motions of the Sensorium._
VI. _Of the four Classes of Fibrous Motions._
VII. _Of Irritative Motions._
VIII. _Of Sensitive Motions._
IX. _Of Voluntary Motions._
X. _Of Associate Motions._
XI. _Additional Observations on the Sensorial Powers._
XII. _Of Stimulus, Sensorial Exertion, and Fibrous Contraction._
XIII. _Of Vegetable Animation._
XIV. _Of the Production of Ideas._
XV. _Of the Classes of Ideas._
XVI. _Of Instinct._
XVII. _The Catenation of Animal Motions._
XVIII. _Of Sleep._
XIX. _Of Reverie._
XX. _Of Vertigo._
XXI. _Of Drunkenness._
XXII. _Of Propensity to Motion. Repetition. Imitation._
XXIII. _Of the Circulatory System._
XXIV. _Of the Secretion of Saliva, and of Tears. And of the
Lacrymal Sack._
XXV. _Of the Stomach and Intestines._
XXVI. _Of the Capillary Glands, and of the Membranes._
XXVII. _Of Hemorrhages._
XXVIII. _The Paralysis of the Lacteals._
XXIX. _The Retrograde Motions of the Absorbent Vessels._
XXX. _The Paralysis of the Liver._
XXXI. _Of Temperaments._
XXXII. _Diseases of Irritation._
XXXIII. - - _of Sensation._
XXXIV. - - _of Volition._
XXXV. - - _of Relation._
XXXVI. _The Periods of Diseases._
XXXVII. _Of Digestion, Secretion, Nutrition._
XXXVIII. _Of the Oxygenation of the Blood in the Lungs and Placenta._
XXXIX. _Of Generation._
XL. _Of Ocular Spectra._

* * * * *






* * * * *

HAIL TO THE BARD! who sung, from Chaos hurl'd
How suns and planets form'd the whirling world;
How sphere on sphere Earth's hidden strata bend,
And caves of rock her central fires defend;
Where gems new-born their twinkling eyes unfold, 5
And young ores shoot in arborescent gold.
How the fair Flower, by Zephyr woo'd, unfurls
Its panting leaves, and waves its azure curls;
Or spreads in gay undress its lucid form
To meet the sun, and shuts it to the storm; 10
While in green veins impassion'd eddies move,
And Beauty kindles into life and love.
How the first embryon-fibre, sphere, or cube,
Lives in new forms, - a line, - a ring, - a tube;
Closed in the womb with limbs unfinish'd laves, 15
Sips with rude mouth the salutary waves;
Seeks round its cell the sanguine streams, that pass,
And drinks with crimson gills the vital gas;
Weaves with soft threads the blue meandering vein,
The heart's red concave, and the silver brain; 20
Leads the long nerve, expands the impatient sense,
And clothes in silken skin the nascent Ens.
Erewhile, emerging from its liquid bed,
It lifts in gelid air its nodding head;
The lights first dawn with trembling eyelid hails, 25
With lungs untaught arrests the balmy gales;
Tries its new tongue in tones unknown, and hears
The strange vibrations with unpractised ears;
Seeks with spread hands the bosom's velvet orbs.
With closing lips the milky fount absorbs; 30
And, as compress'd the dulcet streams distil,
Drinks warmth and fragrance from the living rill; -
Eyes with mute rapture every waving line,
Prints with adoring kiss the Paphian shrine,
And learns erelong, the perfect form confess'd, 35
Ideal Beauty from its mother's breast.
Now in strong lines, with bolder tints design'd,
You sketch ideas, and portray the mind;
Teach how fine atoms of impinging light
To ceaseless change the visual sense excite; 40
While the bright lens collects the rays, that swerve,
And bends their focus on the moving nerve.
How thoughts to thoughts are link'd with viewless chains,
Tribes leading tribes, and trains pursuing trains;
With shadowy trident how Volition guides, 45
Surge after surge, his intellectual tides;
Or, Queen of Sleep, Imagination roves
With frantic Sorrows, or delirious Loves.
Go on, O FRIEND! explore with eagle-eye;
Where wrapp'd in night retiring Causes lie: 50
Trace their slight bands, their secret haunts betray,
And give new wonders to the beam of day;
Till, link by link with step aspiring trod,
You climb from NATURE to the throne of GOD.
- So saw the Patriarch with admiring eyes 55
From earth to heaven a golden ladder rise;
Involv'd in clouds the mystic scale ascends,
And brutes and angels crowd the distant ends.

TRIN. COL. CAMBRIDGE, _Jan._ 1, 1794.

* * * * *


_Botanic Garden._ Part I.

Line 1. Canto I. l. 105.
- - 3. - - IV. l. 402.
- - 4. - - I. l. 140.
- - 5. - - III. l. 401.
- - 8. - - IV. l. 452.
- - 9. - - I. l. 14.


- - 12. Sect. XIII.
- - 13. - - XXXIX. 4. 1.
- - 18. - - XVI. 2. and XXXVIII.
- - 26. - - XVI. 4.
- - 30. - - XVI. 4.
- - 36. - - XVI. 6.
- - 38. - - III. and VII.
- - 43. - - X.
- - 44. - - XVIII. 17.
- - 45. - - XVII. 3. 7.
- - 47. - - XVIII. 8.
- - 50. - - XXXIX. 4. 8.
- - 51. - - XXXIX the Motto.
- - 54. - - XXXIX. 8.

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* * * * *

The purport of the following pages is an endeavour to reduce the facts
belonging to ANIMAL LIFE into classes, orders, genera, and species; and, by
comparing them with each other, to unravel the theory of diseases. It
happened, perhaps unfortunately for the inquirers into the knowledge of
diseases, that other sciences had received improvement previous to their
own; whence, instead of comparing the properties belonging to animated
nature with each other, they, idly ingenious, busied themselves in
attempting to explain the laws of life by those of mechanism and chemistry;
they considered the body as an hydraulic machine, and the fluids as passing
through a series of chemical changes, forgetting that animation was its
essential characteristic.

The great CREATOR of all things has infinitely diversified the works of his
hands, but has at the same time stamped a certain similitude on the
features of nature, that demonstrates to us, that _the whole is one family
of one parent_. On this similitude is founded all rational analogy; which,
so long as it is concerned in comparing the essential properties of bodies,
leads us to many and important discoveries; but when with licentious
activity it links together objects, otherwise discordant, by some fanciful
similitude; it may indeed collect ornaments for wit and poetry, but
philosophy and truth recoil from its combinations.

The want of a theory, deduced from such strict analogy, to conduct the
practice of medicine is lamented by its professors; for, as a great number
of unconnected facts are difficult to be acquired, and to be reasoned from,
the art of medicine is in many instances less efficacious under the
direction of its wisest practitioners; and by that busy crowd, who either
boldly wade in darkness, or are led into endless error by the glare of
false theory, it is daily practised to the destruction of thousands; add to
this the unceasing injury which accrues to the public by the perpetual
advertisements of pretended nostrums; the minds of the indolent become
superstitiously fearful of diseases, which they do not labour under; and
thus become the daily prey of some crafty empyric.

A theory founded upon nature, that should bind together the scattered facts
of medical knowledge, and converge into one point of view the laws of
organic life, would thus on many accounts contribute to the interest of
society. It would capacitate men of moderate abilities to practise the art
of healing with real advantage to the public; it would enable every one of
literary acquirements to distinguish the genuine disciples of medicine from
those of boastful effrontery, or of wily address; and would teach mankind
in some important situations the _knowledge of themselves_.

There are some modern practitioners, who declaim against medical theory in
general, not considering that to think is to theorize; and that no one can
direct a method of cure to a person labouring under disease without
thinking, that is, without theorizing; and happy therefore is the patient,
whose physician possesses the best theory.

The words idea, perception, sensation, recollection, suggestion, and
association, are each of them used in this treatise in a more limited sense
than in the writers of metaphysic. The author was in doubt, whether he
should rather have substituted new words instead of them; but was at length
of opinion, that new definitions of words already in use would be less
burthensome to the memory of the reader.

A great part of this work has lain by the writer above twenty years, as
some of his friends can testify: he had hoped by frequent revision to have
made it more worthy the acceptance of the public; this however his other
perpetual occupations have in part prevented, and may continue to prevent,
as long as he may be capable of revising it; he therefore begs of the
candid reader to accept of it in its present state, and to excuse any
inaccuracies of expression, or of conclusion, into which the intricacy of
his subject, the general imperfection of language, or the frailty he has in
common with other men, may have betrayed him; and from which he has not the
vanity to believe this treatise to be exempt.

* * * * *


* * * * *



The whole of nature may be supposed to consist of two essences or
substances; one of which may be termed spirit, and the other matter. The
former of these possesses the power to commence or produce motion, and the
latter to receive and communicate it. So that motion, considered as a
cause, immediately precedes every effect; and, considered as an effect, it
immediately succeeds every cause.

The MOTIONS OF MATTER may be divided into two kinds, primary and secondary.
The secondary motions are those, which are given to or received from other
matter in motion. Their laws have been successfully investigated by
philosophers in their treatises on mechanic powers. These motions are
distinguished by this circumstance, that the velocity multiplied into the
quantity of matter of the body acted upon is equal to the velocity
multiplied into the quantity of matter of the acting body.

The primary motions of matter may be divided into three classes, those
belonging to gravitation, to chemistry, and to life; and each class has its
peculiar laws. Though these three classes include the motions of solid,
liquid, and aerial bodies; there is nevertheless a fourth division of
motions; I mean those of the supposed ethereal fluids of magnetism,
electricity, heat, and light; whose properties are not so well investigated
as to be classed with sufficient accuracy.

_1st._ The gravitating motions include the annual and diurnal rotation of
the earth and planets, the flux and reflux of the ocean, the descent of
heavy bodies, and other phænomena of gravitation. The unparalleled sagacity
of the great NEWTON has deduced the laws of this class of motions from the
simple principle of the general attraction of matter. These motions are
distinguished by their tendency to or from the centers of the sun or

_2d._ The chemical class of motions includes all the various appearances of
chemistry. Many of the facts, which belong to these branches of science,
are nicely ascertained, and elegantly classed; but their laws have not yet
been developed from such simple principles as those above-mentioned; though
it is probable, that they depend on the specific attractions belonging to
the particles of bodies, or to the difference of the quantity of attraction
belonging to the sides and angles of those particles. The chemical motions
are distinguished by their being generally attended with an evident
decomposition or new combination of the active materials.

_3d._ The third class includes all the motions of the animal and vegetable
world; as well those of the vessels, which circulate their juices, and of
the muscles, which perform their locomotion, as those of the organs of
sense, which constitute their ideas.

This last class of motion is the subject of the following pages; which,
though conscious of their many imperfections, I hope may give some pleasure
to the patient reader, and contribute something to the knowledge and to the
cure of diseases.

* * * * *



I. _Outline of the animal economy._ - II. 1. _Of the sensorium._ 2. _Of
the brain and nervous medulla._ 3. _A nerve._ 4. _A muscular fibre._ 5.
_The immediate organs of sense._ 6. _The external organs of sense._ 7.
_An idea or sensual motion._ 8. _Perception._ 9. _Sensation._ 10.
_Recollection and suggestion._ 11. _Habit, causation, association,
catenation._ 12. _Reflex ideas._ 13. _Stimulus defined._

* * * * *

As some explanations and definitions will be necessary in the
prosecution of the work, the reader is troubled with them in this
place, and is intreated to keep them in his mind as he proceeds, and to
take them for granted, till an apt opportunity occurs to evince their
truth; to which I shall premise a very short outline of the animal

* * * * *

I. - 1. The nervous system has its origin from the brain, and is distributed
to every part of the body. Those nerves, which serve the senses,
principally arise from that part of the brain, which is lodged in the head;
and those, which serve the purposes of muscular motion, principally arise
from that part of the brain, which is lodged in the neck and back, and
which is erroneously called the spinal marrow. The ultimate fibrils of
these nerves terminate in the immediate organs of sense and muscular
fibres, and if a ligature be put on any part of their passage from the head
or spine, all motion and perception cease in the parts beneath the

2. The longitudinal muscular fibres compose the locomotive muscles, whose
contractions move the bones of the limbs and trunk, to which their
extremities are attached. The annular or spiral muscular fibres compose the
vascular muscles, which constitute the intestinal canal, the arteries,
veins, glands, and absorbent vessels.

3. The immediate organs of sense, as the retina of the eye, probably
consist of moving fibrils, with a power of contraction similar to that of
the larger muscles above described.

4. The cellular membrane consists of cells, which resemble those of a
sponge, communicating with each other, and connecting together all the
other parts of the body.

5. The arterial system consists of the aortal and the pulmonary artery,
which are attended through their whole course with their correspondent
veins. The pulmonary artery receives the blood from the right chamber of
the heart, and carries it to the minute extensive ramifications of the
lungs, where it is exposed to the action of the air on a surface equal to
that of the whole external skin, through the thin moist coats of those
vessels, which are spread on the air-cells, which constitute the minute
terminal ramifications of the wind-pipe. Here the blood changes its colour
from a dark red to a bright scarlet. It is then collected by the branches
of the pulmonary vein, and conveyed to the left chamber of the heart.

6. The aorta is another large artery, which receives the blood from the
left chamber of the heart, after it has been thus aerated in the lungs, and
conveys it by ascending and descending branches to every other part of the
system; the extremities of this artery terminate either in glands, as the
salivary glands, lacrymal glands, &c. or in capillary vessels, which are
probably less involuted glands; in these some fluid, as saliva, tears,
perspiration, are separated from the blood; and the remainder of the blood
is absorbed or drank up by branches of veins correspondent to the branches
of the artery; which are furnished with valves to prevent its return; and
is thus carried back, after having again changed its colour to a dark red,
to the right chamber of the heart. The circulation of the blood in the
liver differs from this general system; for the veins which drink up the
refluent blood from those arteries, which are spread on the bowels and
mesentery, unite into a trunk in the liver, and form a kind of artery,
which is branched into the whole substance of the liver, and is called the
vena portarum; and from which the bile is separated by the numerous hepatic
glands, which constitute that viscus.

7. The glands may be divided into three systems, the convoluted glands,
such as those above described, which separate bile, tears, saliva, &c.
Secondly, the glands without convolution, as the capillary vessels, which
unite the terminations of the arteries and veins; and separate both the
mucus, which lubricates the cellular membrane, and the perspirable matter,
which preserves the skin moist and flexible. And thirdly, the whole
absorbent system, consisting of the lacteals, which open their mouths into
the stomach and intestines, and of the lymphatics, which open their mouths
on the external surface of the body, and on the internal linings of all the
cells of the cellular membrane, and other cavities of the body.

These lacteal and lymphatic vessels are furnished with numerous valves to
prevent the return of the fluids, which they absorb, and terminate in
glands, called lymphatic glands, and may hence be considered as long necks
or mouths belonging to these glands. To these they convey the chyle and
mucus, with a part of the perspirable matter, and atmospheric moisture; all
which, after having passed through these glands, and having suffered some
change in them, are carried forward into the blood, and supply perpetual
nourishment to the system, or replace its hourly waste.

8. The stomach and intestinal canal have a constant vermicular motion,
which carries forwards their contents, after the lacteals have drank up the
chyle from them; and which is excited into action by the stimulus of the
aliment we swallow, but which becomes occasionally inverted or retrograde,
as in vomiting, and in the iliac passion.

II. 1. The word _sensorium_ in the following pages is designed to express
not only the medullary part of the brain, spinal marrow, nerves, organs of
sense, and of the muscles; but also at the same time that living principle,
or spirit of animation, which resides throughout the body, without being
cognizable to our senses, except by its effects. The changes which
occasionally take place in the sensorium, as during the exertions of
volition, or the sensations of pleasure or pain, are termed _sensorial

2. The similarity of the texture of the brain to that of the pancreas, and
some other glands of the body, has induced the inquirers into this subject
to believe, that a fluid, perhaps much more subtile than the electric aura,
is separated from the blood by that organ for the purposes of motion and
sensation. When we recollect, that the electric fluid itself is actually
accumulated and given out voluntarily by the torpedo and the gymnotus
electricus, that an electric shock will frequently stimulate into motion a
paralytic limb, and lastly that it needs no perceptible tubes to convey it,
this opinion seems not without probability; and the singular figure of the
brain and nervous system seems well adapted to distribute it over every
part of the body.

For the medullary substance of the brain not only occupies the cavities of
the head and spine, but passes along the innumerable ramifications of the
nerves to the various muscles and organs of sense. In these it lays aside
its coverings, and is intermixed with the slender fibres, which constitute
those muscles and organs of sense. Thus all these distant ramifications of
the sensorium are united at one of their extremities, that is, in the head
and spine; and thus these central parts of the sensorium constitute a
communication between all the organs of sense and muscles.

3. A _nerve_ is a continuation of the medullary substance of the brain from
the head or spine towards the other parts of the body, wrapped in its
proper membrane.

4. The _muscular fibres_ are moving organs intermixed with that medullary
substance, which is continued along the nerves, as mentioned above. They
are indued with the power of contraction, and are again elongated either by
antagonist muscles, by circulating fluids, or by elastic ligaments. So the
muscles on one side of the forearm bend the fingers by means of their
tendons, and those on the other side of the fore-arm extend them again. The
arteries are distended by the circulating blood; and in the necks of
quadrupeds there is a strong elastic ligament, which assists the muscles,
which elevate the head, to keep it in its horizontal position, and to raise
it after it has been depressed.

5. The _immediate organs of sense_ consist in like manner of moving fibres
enveloped in the medullary substance above mentioned; and are erroneously
supposed to be simply an expansion of the nervous medulla, as the retina of
the eye, and the rete mucosum of the skin, which are the immediate organs
of vision, and of touch. Hence when we speak of the contractions of the
fibrous parts of the body, we shall mean both the contractions of the
muscles, and those of the immediate organs of sense. These _fibrous
motions_ are thus distinguished from the _sensorial motions_ above

6. The _external organs_ of sense are the coverings of the immediate organs
of sense, and are mechanically adapted for the reception or transmission of
peculiar bodies, or of their qualities, as the cornea and humours of the
eye, the tympanum of the ear, the cuticle of the finders and tongue.

7. The word _idea_ has various meanings in the writers of metaphysic: it is
here used simply for those notions of external things, which our organs of
sense bring us acquainted with originally; and is defined a contraction, or
motion, or configuration, of the fibres, which constitute the immediate
organ of sense; which will be explained at large in another part of the
work. Synonymous with the word idea, we shall sometimes use the words
_sensual motion_ in contradistinction to _muscular motion_.

8. The word _perception_ includes both the action of the organ of sense in
consequence of the impact of external objects, and our attention to that