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^IH

ZOONOMI A;

O R,

THE LAWS

O F

ORGANIC LIFE.

V b L. I.

By ERJSMUS DARJFIN, M.D.F.R.S.

AUTHOR OF THE BOTANIC GARDEN.

Principio ccelum, ac terras, campofque liquentes,
Lucentemque globum lunae, titaniaque aftra,
Spiritus intus alit, totamqne infufa per artus
Mens agitat molem, et magno fe corpore raifcet.

ViRG. ^n, vi.

Earth, on whofe lap a thoufand nations tread.

And Ocean, brooding his proliiic bed.

Night's changeful orb, blue pole, and filvery zones.

Where other worlds encircle other funs.

One Mind inhabits, one diffufive Soul

Wields the large limbs, and mingles \vith the whole.

LONDON:
PRINTED FOR J. JOHNSON, IN ST. PAUl's CHURCH-YARD.

1794.

€mmti at ^tutitxnm' f all*

DEDICATION,

JL o the candid and ingenious Members of the College of
Phyficians, of the Royal Philofophical Society, of the
Two Universities, and to all thofe, who ftudy the Ope-
rations of the Mind as a Science, or who praclife Medi-
^ cine as a ProfefTion, the fubfequent Work is^ with great
refpetSj infcribed by the Author^

Derby, May i, 1794,

A 2

1 "^r?-J.f~;0

J- 4

CONTENTS.

Preface.

Sect. I. Of Motion,

II. Explanations and Defnitlons.

III. 'The Motions of the Retina demonf rated by Experiments.

IV. Laws of Animal Caufation.

V. Of the four Faculties or Motions of the Senforium.

VI. Of the four Claffes of Fibrous Motions.

VII. Of Irritative Motions.

VIII. Of Senftive Motions.

IX. Of Voluntary Motions.

X. Of Affociate Motions.

XI. Additional Obfervations on the Senforial Powers.

XII. Of Stimulus^ Senforial Exertion., and Fibrous Contraction.

XIII. Of Vegetable Animation.

XIV. Of the ProduElion of Ideas.
XV. O/'z/j^ C/fl^j o/'Mflj.

XVI. Oflnjiina.

XVII. The Catenation (f Animal Motions^

XVIII. Of Sleep.

XIX. Of Reverie,

XX. Of Vertigo,

XXI. Of Drunkennefs,

XXII. Of Propenfty to Motion. Repetition. Imitation,

Sect.

CONTENTS.

Sect. XXIII.
XXIV.

XXV.

XXVI.

XXVII.

XXVIII.

XXIX,

XXX.

XXXI.

XXXII.

XXXIII.

XXXIV.

XXXV.

XXXVI.

XXXVII.

XXXVIII.

XXIX.

Of the Circulatory Syjlem.

Of the Secretion of Saliva, and of Tears, And of the
Lacryinal Sack.

Of the Stomach and Inteflines.

Of the Capillary Glands^ and of the Metnbranes.

Of Hcemorrhages .

The Paralyfis of the La^eah.

The Retrograde Motiofis of the Abforbent Vejfels,

The Paralyfis of the Liver.

Of Temperaments.

Difeafes of Irritation.

of Senfation.

— of Volition.

— • of Affociation.

The Periods of Difeafes.

Of Digejiion, -Secretion, Nut ration.

Of the Oxygenation of the Blood in the Lungs a7id Placenta.

Of Generation.

OJ Ocular SpcRra^

ERASMUS DARWIN,

ON HIS WORK INTITLED

ZOONOMIA.

By DE^HURSr BILSBORROM-^.

Hail to the Bard ! wlio fung, from Chaos hurl'd

How funs and planets form'd the whirling world;

How fphere on fphere Earth's hidden ftrata bend,

And caves of rock her central fires defend ;

Where gems new-born their twinkling eyes unfold, t

And young ores flioot in arborefcent gold.

How the fair Flower, by Zephyr woo'd, unfurls
Its panting leaves, and waves its azure curls ;
Or fpreads in gay undrefs its lucid form

To meet the fun, and fliuts it to the ftorm , lo

While in green veins impaffion'd eddies move,
And Beauty kindles into life and love.

How the firfl: embryon-fibre, fphere, or cube.
Lives in new forms, — a line, — a ring,^ — a tube ;

Clofed in the womb with limbs unfinifli'd laves, i^

Sips with rude mouth the falutary waves ;
Seeks round its cell the fanguine flxeams, that pafs.
And drinks with crimfon gills the vital gas ;
Weaves with foft threads the blue meandering vein,
The heart's red concave, and the fllver brain ; 20

Leads the long nerve, expands the impatient fenfe.
And clothes in filken fkin the nafcent Ens.

Erewhile, emerging from its liquid bed.
It lifts in gelid air its nodding head ;

The light's firft dawn with trembling eyelid hails, 25

With lungs untaught arrefls the balmy gales ;
Tries its new tongue in tones unknown, and hears
The ftrange vibrations with unpradifed ears ;

Seeks

viu

TO ERASMUS DARWIN.

Trim

Seeks with fpread hands the bofom's velvet orbs,
With clofirig hps tlie milky fount abforbs ;
And, as comprefs'd the dulcet ftreams diftil.
Drinks warmth and fragrance from the living rill ; —
Eyes with mute rapture every waving line,-
Prints with adoring kifs the Paphian ferine.
And learns erelong, the perfeft form confefs'd.
Ideal Beauty "from its mother's breaft.

. Now in ftrong lines, with bolder tints defign'd,
You fketch ideas, and portray the mind ;
Teach how fine atoms of impinging light
To ceafelefs change the vifual fenfe excite ;
While the bright lens colleas the rays, that fwerve,
And bends their focus on the moving nerve.
How thoughts to thoughts are link'd with viewlefs chains,
Tribes leading tribes, and trains purfuing trains ;
With Ihadowy trident how Volition guides,
Surge after furge, his intelleftual 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 Caufes lie :
Trace their flight Jjands, their fecret haunts betray.
And give new wonders to the beam of day ;
Till, link by link with Itep afpiring trod,
You climb from Nature to the throne of God,
— — So faw the Patriarch with admiring eyes
From earth to heaven a golden ladder rife ;
Involved in clouds the myfl;ic feale afcends.
And brutes and angels crowd the diftant ends.
, Col. Cambridge, Jan. r, 1794.

4S:

REFERENCES TO THE WORK.

Line i.

Bofitnic Garden, Part I.
Caiitu I. 1. 105.

IV. 1. 402.

I. 1. 140.

III. I, 401.

IV. 1.452.

1. 1. 14-

Zaonom'ia,

.12. -ieft. XIII.

• 13: XXXIX. 4.1.

Line 18.

Sea. XVI. 2. and XXXVIII.

26.

XVL4.

30.

XVI. 4.

— 36.

. . XVI. 6.

. 38.

IH and VII.

43.

44-

XVIII. 17.

~45-

XVII. 3. 7.

——47.

——XVIII. 8.

.— 50.

XXXIX, 4. 8.

— SI-

XXXIX. the Motro.

54'

— - XXXIX. 8,

PREFACE.

A H E purport of the following pages is an endeavour to reduce the
fa<9:s belonging to Animal Life into clafles, orders, genera, and
fpecies ; and, by comparing them with each other, to unravel th»
theory of difeafes. It happened, perhaps unfortunately for the in-
quirers into the knowledge of difeafes, that other fciences had re-
ceived improvement previous to their own ; whence, inftead of com-
paring the properties belonging to animated nature with each other,
they, idly ingenious, bufied themfelves in attempting to explain the
laws of life by thofe of mechanifm and chemiftry ; they confidered
the body as an hydraulic machine, and the fluids as paffing through
a feries of chemical changes, forgetting that animation was its effen-
tial charaderiftic.

The great Creator of all things has infinitely divcrfified the
works of his hands, but has at the fame time ftamped a certain
iimilitude on the features of nature, that demonflrates to us, that the
'whole is cne family of one partnt. On this Similitude is founded all
rational analogy; which, fo long as it is concerned in comparing the
efiential properties of bodies, leads us to many and important difco-
veries; but when with licentious adlivity it links together objefts,
otherwifc difcordant, by feme fanciful fimilitude; it may indeed
collect ornaments for wit and poetry, but philofophy and truth recoil
from its combinations.

The want of a theory, deduced from fuch flrift analogy, to con-
duct the pratlice of medicine is lamented by its profeflbrs ; for, as a
^reat number of unconnected fa£ls are difficult to be acquired, and to
be reafoned from, the art of medicine is in many inflances lefs cffica-

B cious

a T R E F A C E.

clous under the dire£t'ion of its wlfeft praftitioners ; and by that bnfy
crowd, who either boldly wade in darknefs, or are led into endlefs
error by the glare of falfe theory, it is daily pradlifed to the deftruc-
tion of thoufands ; add to this the unceafing injury which accrues to
the public by the perpetual advertifements of pretended noftrums;
the minds of the indolent become fuperftitioufly fearful of difeaiis^-
which they do not Jabour under ; and thus become the daily prey of
fome crafty empyric.

A theory founded upon nature, that fhould bind together the fcat-
tered fads of medical knowledge, and c(^nverge into one point of view
the laws of organic life, would thus on many accounts contribute to the
interefl of fociety. It would capacitate men of moderate abilities to
pradife the art of healing with real advantage to the public; it would
enable every one of literary acquirements to diftinguifti the genuine
difciples of medicine from thofe of boaftful effrontery, or of wily ad-
drefs ; and would teach mankind in fome important fituations the
knowledge of themf elves.

There are fome modern pra£litioners, who declaim againft medical
theory in general, not confidering that to think is to theorize ; and
that no one can dire£l a method of cure to a perfon labouring under
difeafe without thinking, that is, without theorizing ; and happy
therefore is the patient, whofe phyfician pofleffes the beft theory.

The words idea, perception, fenfation, recoUedion, fuggeftion,
and affociation, are each of them ufed in this treatife in a more li-
mited fenfe than in the writers of metaphyfic. The author was in
doubt, whether he ftiould rather have fubftltuted new words inftead
of them ; but was at length of opinion, that new definitions of words,
already in ufe would be lefs burthenfome ta the memory of the
reader.

A great part of this work has lain by the writer above twenty
years, as fome of his friends can teflify : he had hoped by frequent
revifion to have made it more worthy the acceptance of the public ;

this

PREFACE. J

this however his other perpetual occupations have in part prevented,
and may continue to prevent, as long as he may be capable of revif-
iiig it; he therefore begs of the candid reader to accept of it in its
prefent ftate, and to excufe any inaccuracies of exprefiion, or of coii-
clufion, into which the intricacy of his fubje<5l, the general imper-
feftion of language, or the frailty he has in common with other
men, may have betrayed him ; and from which he has not the va-
nity to believe this treatife to be exempt.

B 2 ZOONOMIA.

Z O O N O M I A.

SECT. I.

OF MOTION.

J. HE WHOLE OF NATURE may be fuppofed to coniifl of two ef-
fenccs or fubftances ; one of which may be termed fplrit, and the
Other matter. The former of thefe poffeffes the power to commence
or produce motion, and the latter to receive and communicate it. So
that motion, confidered as a caufe, immediately precedes every ef-
fed; and, confidered as an effed, it immediately fucceeds every
caufe.

The MOTIONS OF MATTER may be divided into two kinds, pri-
mary and fecondary. The fecondary motions are thofe, which are
given to or received from other matter in motion. Their laws have
been fuccefsfully inveftigated by philofophers in their treatifes on me-
chanic powers. Thefe motions are diflinguifhed by this circum-
ftance, that the velocity multiplied into the quantity of matter of the
body afted upon is equal to the velocity multiplied into the quantity
of matter of the a£ling body.

The primary motions of matter may be divided into three claffes,,
thofe belonging to gravitation, to chemiftry, and to life; and eacbs.
clafs has its peculiar laws. Though thefe three claffes include the
motions of folid, hquid, and aerial bodies ; there is neverthelefs a
fourth divifion of motions ; I mean thofe of the fuppofed ethereal
fluids of magnetifm, eledlricity, heat, and light ; whofe properties
are not fo well inveftigated as to be claffed with fuiEcient accuracy.

6 OF MOTION. Sect. I.

ly?. The gravitating motions include the annual and diurnal rota-
tion of the earth and planets, the flux and reflux of the ocean, the-
defcent of heavy bodies, and other phaenomena of gravitation The
unparalleled fagacity of the great Newton has deduced the laws of
this clafs of motions from the fimple principle of the general attrac-
tion of matter. Thefe motions are diftinguifhed by their tendency
to or from the centers of the fun or planets.

zd. The chemical clafs of motions includes all the various appear-
ances of chemiftry. Many of the fa£ts, which belong to thefe branches
of fcience, are nicely afcertained, and elegantly clafled ; but their laws
have not yet been developed from fuch fimple principles as thofe
above-mentioned; though it is probable, that they depend on the fpe-
cific attractions belonging to the particles of bodies, or to the differ-
ence of the quantity of attraftion belonging to the fides and angles of
thofe particles. The chemical motions are diftinguifhed by their be-
ing generally attended with an evident decompofition or new combi-
nation of the adlive materials.

3J. The third clafs includes all the motions of the animal and ve-
getable world ; as well thofe of the veffels, which circulate their
juices, and of the mufcles, which perform their locomotion, as thofe
of the organs of fenfe, which conftitute their ideas.

This laft clafs of motion is the fubjeft of the following pages ;
which, though confcious of their many imperfections, I hope may
givefome pleafure to the patient reader, and contribute fomething to
ihe knowledge and to the cure of difeafes,.

SECT.

Sect. II. DEFINITIONS.

SECT. II. I.

EXPLANATIONS AND DEFINITIONS.

I. Outline of the animal economy. — II. i. Of the Jenjorium. i. Of the brain and
nervous medulla. 3. A nerve. 4. A mufcular fibre. 5. ne immediate organs
offenfe. 6. The external organs of fenfe. ^ . An idea or fenfual motion. Z. Per^
ception. 9. Senfation. 10. RecolleSiion and fuggeftion. ii. Habit, caujation,
qfociationy catenation. 12. Reflex ideas. 13. Stimulus defined.

As fome explanations and definitions will be neceffary in the profecution 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,
tin an apt opportunity occurs to evince their truth ; to which I fhaU prc-
mife a very Ihort outline of the animal economy.

I. — I. THE nervous fyftetn has its origin from the brain, and is
diftributed to every part of the body. Thofe nerves, which ferve the
fenfes, prmcipally arife from that part of the brain, which is lodged in
the head; and thofe, which ferve the purpofes of mufcular motion,
principally arife from that part of the brain, which is lodged in the
neck and back, and which is erroneoufly called the fpinal marrow.
The ultimate fibrils of thefe nerves terminate in the immediate or-
gans of fenfe and mufcular fibres, and if a ligature be put on any part
of their paffage from the head or fpine, all motion and perception
ceafe in the parts beneath the ligature.

a. The longitudinal mufcular fibres compofe the locomotive mus-
cles, whofe contra£lions move the bones of the limbs and trunk, to
which their extremities are attached. The annular oj- fpiral mufcu-
lar

8 DEFINITIONS. Sect. II. i.

lar fibres compole the vafcular mufcles, which Gonftitute the iutef-
tinal canal, the arteries, veins, glands, and abforbent veffels.

3. The immediate organs of Cen-fe^ as the retina of the eye, pro-
bably confift of moving fibrils, with a power of contradtion fimilar to
that of the larger mufcles above defcribed.

4. The cellular membrane confifls of cells, which refemble thofe
of a fponge, communicating with each other, and connecting toge-
ther all the other parts of the body.

5. The arterial {y&:em confifts of the aortal and the pulmonary ar-
tery, which are attended through their whole courfe with their cor-
refpondent veins. The pulmonary artery receives the blood from
the right chamber of the heart, and carries it to the minute extenfive
ramifications of the lungs, where it is expofed to the adtion of the air
on a furface equal to that of the whole external fkin, through the
thin moift coats of thofe veflels, which are fpread on the air-cells,
which conftitute the minute terminal ramifications of the wind-pipe.
Here the blood changes its colour from a dark red to a bright fcarlet.
It is then colle£led by the branches of the pulmonary vein, and cou-
ireyed 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 afcending and defcending branches to
every other part of the fyflemj the extremities of this artery terrni-
:nate either in glands, as the falivary glands, lacrymal glands, &c. or
in capillary veifels, which are probably lefs involuted glands; in
thefe fome fluid, as faliva, tears, perfpiration, are feparated from the
blood ; and the remainder of the blood is abforbed or drank up by
branches of veins correfpondent to the branches of the artery ; which
are furnifhed 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 fyftem ; for the veins which drink up the re-

7 fluent

Sect.II. I. DEFINITIONS. 9

fluent blood from thofe arteries, which are fpread on the bowels and
mefentery, unite into a trunk in the liver, and form a kind of ar-
tery, which is branched into the whole fubftance of the liver, and is
called the vena portarum ; and from which the bile is feparated by the
numerous hepatic glands, which conftitute that vifcus.

7. The glands may be divided into three fyftems, the convoluted
glands, fuch as thofe above defcribed, which feparate bile, tears, fa-
liva, &c. Secondly, the glands without convolution, as the ca-
pillary veffels, which unite the terminations of the arteries and
veins ; and feparate both the mucus, which lubricates the cellular

'membrane, and the perfpirable matter, which preferves the Ikin
moift and flexible. And thirdly, the whole abforbent fyftem,
confiding of the lafteals, which open their mouths into the fto-
mach and inteftines, and of the lymphatics, which ooen their-
mouths on the external furface of the body, and on the internal lin-
ings of all the cells- of the cellular membrane, and other cavities of
the body.

Thefe la£teal and lymphatic veflels are furnifhed with numerous
valves to prevent the return of the fluids, which they abforb, and
terminate in glands, called lymphatic glands, and may hence be con-
lidered as long necks or mouths belonging to thefe glands. To thefe
they convey the chyle and mucus, with a part of the perfpirable mat-
ter, and atmofpheric moifture ; all which, after having paffed through
thefe glands, and having fufFered fome change in them, are carried
forward into the blood, and fupply perpetual nourifliment to the {yf-
tem, or replace its hourly wafte.

8. The ftomach and inteflinal canal have a conftant Vermicular
"motion, which carries forwards their contents, after the ladeals

have drank up the chyle from them ; and which is excited into ac-
tion by the ftimulus of the aliment we fvvallow, but which becomes
occafionally inverted or retrograde, as in vomiting, and in the iliac
paffion.

C II. I.

xo DEFINITIONS. Sect. 11. 2.

II. I. The vj or di fenforlurnm th.Q following pages is defigned to
exprefs not only the medullary part of the brain, fpinal marrow,
nerves, organs of fenfe, and of the mufcles j but alio at the fame
time that living principle, or fpiiit of animation, which refides
throughout the body, without being cognizable to our fenfes,
except by its effeds. The changes which occafionally take place ia
the fenforium, as during the exertions of vohtion, or the fenfations
of pleafure or pain, are t.erxx\eAfenforial7notwns.

2. The fimilarity of the texture of the brain to that of the pan-
creas, and fome other glands of the body, has induced the inquirers
into this fubje£l to believe, that a fluid, perhaps much more fubtile
than the eleftric aura, is feparated from the blood by that organ for
the purpofes of motion and fenfation. When we recolledt, that the
eledric fluid itfelf is adually accumulated and given out voluntarily
by the torpedo and the gymnotus ele6tricus, that an eleftric (hock
will frequently fl;imulate into motion a paralytic limb, and laftly
that it needs no perceptible tubes to convey it, this opinion feems not
without probability ; and the Angular figure of the brain and nervous
lyftem feems well adapted to diflribute it over every part of the body.
For the medullary fubAance of the brain not only occupies the ca-
vities of the head and fpine, but pafles along the innumerable ramifi-
cations of the nerves to the various mufcles and organs of fenfe. In
thefe it lays afide its coverings, and is intermixed with the flender
fibres, which conftitute thofe mufcles and organs of fenfe. Thus all
thefe diflant ramifications of the fenforium are united at one of their
extremities, that is, in the head and fpine; and thus thefe central
parts of the fenforium confiitute a communication between all the or-
gans of fenfe and mufcles.

3. A nerve is a continuation of the medullary fubftance of the
brain from the head or fpine towards the other parts of the body,
wrapped in its proper membrane.

4. The mufcular fibres are moving organs intermixed with that

medullary

Sect. II. 2. DEFINITIONS. n

medullary fubflance which is continued along the nerves, as meji-
tioned above. They are indued with the pov/er of coutra6lion, and
are again elongated either by antagonift mufcles, by circulating
fluids, or by elaftic ligannents. So the mufcles on one fide of the fore-
arm bend the fingers by means of their tendons, and thofe on the
other fide of the fore-arm extend them again. The arteries are dif-
tended by the circulating blood ; and in the necks of quadrupeds
there is a flrong elaftic ligament, which affifts the mufcles, which
elevate the head, to keep it in its horizontal pofition, and to raife it
after it has been depreffed.

5. The immediate organs of fenfe confift in like manner of moving
fibres enveloped in the medullary fubftance above mentioned ; and
are erroneoufly fuppofed to be fimply an expanfion of the nervous me-
dulla, as the retina of the eye, and the rete mucofum of the Ikin,
which are the immediate organs of vifion, and of touch. Hence
when we fpeak of the contractions of the fibrous parts of the body,
we lliall mean both the contradiions of the mufcles, and thofe of the
immediate organs of fenfe. Thefe fibrous motions are thus diftin-
guiflied from the. fenforial motions above mentioned.

6. The external organs of fenfe are the coverings of the immediate
organs of fenfe, and are mechanically adapted for the reception or
tranfmifiion 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 tonsiue.

7. The word idea has various meanings in the writers of metaphy-
fic : it is here ufed fimply for thofe notions of external things,
which our organs of fenfe bring us acquainted with originally; and is
defined a contradlion, or motion, or configuration, of the fibres,
v/hich conftitute the immediate organ of fenfe ; which will be ex-
plained at large in another part of the work. Synonymous with the
word idea, we fhall fometimes ufe the v/ords fenfual motion in con-
iradiftinction to miifcular motion.

C 2 8. The

12 DEFINITIONS. Sect. II. 2.

8. The word perception includes both the a£tIoii of the organ of
fenfe in confequence of the impa£l of external obje(£ls, and our atten-
tion to that a£i;ion ; that is, it expreffes both the motion of the organ
of fenfe, or idea, and the pain or pleafure that fucceeds or accompa-
nies it.

9. The pleafure or pain which neceflarily accompanies all thofe

perceptions or ideas which we attend to, either gradually fubfides, or

is fucceeded by other fibrous motions. In the latter cafe it is termed

Jenfation, as explained in Seft. V. 2, and VI. 2. — The reader is iu-

treated to keep this in his mind, that through all this treatife the
word fenfation is lafed to exprefs pleafure or pain only in its adlive
ftate, by whatever means it is introduced into the fyftem, without
any reference to the ftimulation of external objects.
, 10. The vulgar ufe of the word memory is too unlimited for our
purpofe : thofe ideas which we voluntarily recall are here termed
ideas of rec&Ue£iion, as when we will to repeat the alphabet back-
wards. And thofe ideas which are fuggefted to us by preceding ideas
are here termed ideas oi fuggejllon, as whilft we repeat the alphabet
in the ufual order ; when by habits previoufly acquired B is fuggefted
by A, and C by B, without any effort of deliberation.

1 1 . The word affociat'ion properly fignifies a fociety or conventloa
of things In fome refpe£ls firailar to each other. We never fay ia
common language, that the efFetTt is aflbciated with the caufe, though
they neceffarily accompany or fucceed each other. Thus the con-
traftions of ourmufcles and organs of fenfe may be faid to be afTociated
together, but cannot with propriety be faid to be afTociated with irri-
tations, or with volition, or with fenfation; becaufe they are caufed by
them, as mentioned in Se6l. IV". When fibrous contraftions fucceed
other fibrous contra6tions, the connexion is termed aJJ'oclation ; when
fibrous contradlions fucceed fenforial motions, the connedlion is
termed caufation ; when fibrous and fenforial motions reciprocally in-
troduce each other in progreflive trains or tribes, it is termed catena-^

tlm-

Sect. II. 2. DEFINITIONS. 13

iion of animal motions. All thefe connections are faid to be produced
by habit ; that is, by frequent repetition.

12. It may be proper to obferve, that by the unavoidable idiom of
our language the ideas of perception, of recoUedlion, or of imagina-
tion, in the plural number fignify the ideas belonging to perception,
to recolle6lion, or to imagination ; vvhilft the idea of perception, of
recolledlion, or of imagination, in the lingular number is ufed for
what is termed " a reflex idea of aay of thofe operations of the fen-
forium."

13. By the \NOX^ Jlimulus is not only meant the application of ex-
ternal bodies to our organs of fenfe and mufcular fibres, which ex-
cites into ailion the fenforial power termed irritation ; but alfo plea-
fure or pain, when they excite into action the fenforial power termed
fenfation ; and defire or averfion, when they excite into adlion the.
power of volition ; and lafHy, the fibrous contraftlons which. precede:
aflbciation ; as is further explained in Sedt. XII. 2. i»

SECT.

14 MOTIONS OF THE RETINA. Sect. III. r.

SECT. III.

THE MOTIONS OF THE RETINA DEMONSTRATED BY
EXPERIMENTS.

I. Of animal motions and of ideas. II. The fibrous flruElure of the retina. 111. Thf
activity of the retina in vifion. i. Rays of light have no momentum. i. Ob'

je5is long viewed become fainter. 3. SpeElra of black objects become luminous.
4. Varying fpeBra from gyration. 5. From long infpeSiion of various colours.
IV. Motions of the organs of fenfe conjiitute ideas, i. Light fromi prejjing the
eye-ball, and found from the pulfation of the caroted artery. 1. Ideas in fleep
miftaken for perceptions. 3. Ideas of imagination produce pain and ftcknefs like

fenfations. 4. When the organ of fenfe is dejlroyed, the ideas belonging to that

fenfe perifh. V. Analogy between mufcular motions and fenfual motions., or ideas.
I. 'ihey are both originally excited by irritations. 2. And affociated together in
the fame manner. 3. Both a£f in nearly the fame times. 4. Are alike flrength-
ened or fatigued by exercife. 5. Are alike painful from inflammation. 6. Are
alike benumbed by compreffion. 7. Are alike liable to par alyfis. 8. 21? convul-

fton. 9. T'o the influence of old age. — VI. ObjeStions anfwered. 1. Why we
cannot invent new ideas. 2. If ideas refemble external objeSis. 3. Of the ima-
gined fenfation in an amputated limb. 4. Abftra5f ideas. — VII. What are idtas,
if they are not animal motions ?

BEFORE the great variety of animal motions can be duly ar-
ranged into natural claffes and orders, it is neceffary to fmooth the
way to this yet unconquered field of fcience, by removing fome ob-
flacles which thwart our paffage. I. To demonftrate that the retina
and other immediate organs of fenfe polTefs a power of motion, and
that thefe motions conftitute our ideas, according to the fifth and
feventh of the preceding affertions, claims our firft attention.

Animal motions are diftinguifhed from the communicated motions,

mentioned

Sect. III. i. MOTIONS OF THE RETINA. ^15

mentioned in the firft fedion, as they have no mechanical proportion
to their caufe ; for the goad of a fpur on the ikin of a horfe (hall induce
him to move a load of hay. They differ from the gravitating mo-
tions there mentioned as they are exerted with equal facility in all di-
redions, and they d tFer from the chemical clafs of motions, becaufe
no apparent decompofitions or new combinations are produced in the
movins; materials.

Hence, when we fay animal motion is excited by irritation, we do
not mean that the motion bears any proportion to the mechanical im-
pulfe of the ftimulus ; nor that it is afFc;6led by the general gravitatioa
of the two bodies ; nor by their chemical properties, but folely that
certain animal fibres are excited into a6tion by fomething external to
the moving organ.

In this fenle the ftimulus of the blood produces the contradtions of
the heart ; and the fubftances we take into our ftomach and bowels
ir.itate them to perform their neceflary fundions. The rays of light
excite the retina into animal motion by their ftimulus ; at the fame
time that thofe rays of light themfelves are phyfically converged to a
focus by the inactive humours of the eye. The vibrations of the air
irritate the auditory nerve into animal action ; while it is probable
that the tympanum of the ear at the fame time undergoes a mecha-
nical vibration.

To render this circumftance more eafy to be comprehended, mO'
tion may be defined to be a variation of figure ; for the whole univerfe
may be conlidered as one thing poffefling a certain figure ; the mo-
tions of any of its parts are a variation of this figure of the whole :
this definition of motion will be further explained in Section XIV.
2. 2. on the produdlion of ideas.

Now the motions of an organ of fenfe are a fucceffion of configur-
ations of that organ ; thefe configurations fucceed each other quicker
or flower; and whatever configuration of this organ of fenfe, that is,
whatever portion of the motion of it is, or has ufually been, attended
5 to.

j6 motions of the RETINA. Sect. III. i.

to, conftitutes an idea. Hence the configuration is not to be confi-
dered as an efFe£t of the motion of the organ, but rather as a part or
temporary termination of it; and that, whether a paufe fucceeds it,
or a new configuration immediately takes place. Thus when a fuc-'
ceffion of moving objedls are prefented to our view, the ideas of
<irumpets, horns, lords and ladies, trains and canopies, are confi-
gurations, that is, parts or links of the fucceflive motions of the or-
gan of vifion.

Thefe motions or configurations of the organs of fenfe differ from
the fenfbrial motions to be defcribed hereafter, as they appear to be
fimply contradtions of the fibrous extremities of thofe organs, and in
that relpe6t exactly refemble the motions or contraftions of the larger
mufcles, as appears from the following experiment. Place a circular
piece of red filk about an inch in diameter on a fheet of white paper
in a ftrong light, as in Plate I. — look for a minute on this area, or
till the eye becomes fomewhat fatigued, and then, gently clofing
your eyes, and Ihading them with your hand, a circular green area
of the fame apparent diameter becomes vifible in the clofed eye. This
green area is the colour reverfe to the red area, which had been pre-
vioufly infpecled, as explained in the experiments on ocular fpe£lra
at the end of the work, and in Botanical Garden, P. I. additional
note. No. I. Hence it appears, that a part of the retina, which had
been fatigued by contra £lion in one diredtion, reheves itfelf by exert-
ing the antagonifl fibres, and producing a contradion in an oppofite
dire£lion, as is common in the exertions of our mufcles. Thus when
we are tired with long aftion of our arms in one diredion, as in hold-
ing a bridle on a journey, we occafionally throw them into an oppo-
fite pofition to relieve the fatigued mufcles.

Mr. Locke has defined an idea to be " whatever is prefent to the
mind;" but this would include the exertions of volition, and the fen-
fations of pleafure and pain, as well as thofe operations of our fyf-
tem, which acquaint us with external objeds ; and is therefore too

unlimited

Sect.III. 2. MOTIONS OF THE RETINA. i

unlimited for our purpofe. Mr. Lock feems to have fallea into a
further error, by conceiving, that the min4 could form a general or
ab/bradt idea by its own operation, which was the copy of no parti-
cular perception J as of a triangle in general, that was neither acute,
obtufe, nor right angled. The ingenious Dr. Berkley and Mr.
Hume have demonftrated, that fuch general ideas have no exiftence
in nature, not even in the mind of their celebrated inventor. We
fhall therefore take for granted at prefent, that our recoUedlion or
imagination of external obje£ls confifts of a partial repetition of the
perceptions, which were excited by thofe external objects, at the
time we became acquainted with them ; and that our reflex ideas of
the operations of our minds are partial repetitions of thofe opera-
tions.

IT. The following article evinces that the organ of vifion confifts
of a fibrous part as well as of the nervous medulla, like other white
mufcles ; and hence, as it refembles the mufcular parts of the body
in its ftrufture^ we may conclude, that it mufl refemble them in
poffeffing a power of being excited into animal motion. — The fub-
fequent experiments on the optic nerve, and on the colours remaining
in the eye, are copied from a paper on ocular fpedlra publifhed in the
feventy-fixth volume of the Philof. Tranf. by Dr. R. Darwin of
Shrevvfbury ; which, as I fhall have frequent occafion to refer to, is
reprinted in this work, Sedl. XL. The retina of an ox's eye was
fufpended in a glafs of warm water, and forcibly torn in a few places ;
the edges of thefe parts appeared jagged and hairy, and did not con-
tract and become fmooth like fimple mucus, when it is diftended till
it breaks ; which evinced that it confided of fibres. This fibrous
conftruflion became flill more diflin<ft to the fight by adding fome
caufi:ic alcali to the- water-; as the adhering mucus was firft eroded,
and the hair;7rike fibres remained floating in the veffel. Nor does the
degree of tranfparency of the retina invalidate this evidence of its fi-

D brous

i8 MOTIONS OF THE RETINA. Sect. IH. j.

brous flnifture, lince Leeuwenhoek has {hewn, that the cryftallinc
humour itlelfconfifts of fibres. Arc. Nat. V. I. 70.

Hence it appears, that as the mufcles confift of larger fibres inter-
mixed with a^fmaller quantity of nervous medulla, the organ of vi-
lion confifls of a greater quantity of nervous medulla intermixed with-
fmaller fibres. It is probable that the locomotive mufcles of micro-
fcopic animals may have greater tenuity than thefe of the retina; and
there is reafon to conclude from analogy, that the other immediatft
organs of fenfe, as the portio mollis of the auditory nerve, and the
rete mucofum of the Ikin, poffefs a fimilarity of flru6ture with the.
retina, and a fimilar power of being excited into animal motion.

III. The fubfequent articles fhew, that neither mechanical im-
preffions, nor chemical combinations of light, but that the animal
aftivity of the retina conftitutes vifion.

I . Much has been conjedtured by philofophers about the momen-
tum of the rays of light ; to fubje£t this to experiment a very light
horizontal balance was conflruded by Mr. Michel, with about aix
inch fquare of thin leaf- copper fufpended at each end of it, as de-
fcribcd in Dr. Prieftley's Hiftory of Light and Colours. The focus,
of a very large convex mirror was thrown by Dr. Powel, in his lec-
tures on experimental philofophy, in my prefence, on one wing of
this delicate balance, and it receded from the light ; thrown on. the
other wing, it approached towards the light, and this repeatedly j
fo that no fenfible impulfe could be obferved, but what might well
be afcribed to the afcent of heated air.

Whence it is reafonable to conclude, that the light of the day muft
be much too weak in its dilute ftate to make any mechanical impref-
fion on fo tenacious a fubftance as the retina of the eye. — Add to
this, that as the retina is nearly tranfparent, it could therefore make
lefs refiftance to the mechanical impulfe of light ^ which, according
to the obfervations related by Mr. Melvil in the Edinburgh Literary

Effays,

Sect. III. 3- MOTIONS OF THE RETINA. 19

Eflays, only communicates heat, and fliould therefore only commu-
nicate momentum, where it is obftrucled, refledled, or refracted. —
From whence alfo mav be collected the final caufe of this deo;ree of
tranfparency of the retina, viz. leaft by the focus of flronger lights,
heat and pain fhould have been produced in the retina, inftead of that
ftimulus which excites it into animal motion.

2. On lookincr long; on an area of fcarlet filk of about an inch in
diameter laid on white paper, as in Plate I. the fcarlet colour be-
comes fainter, till at length it entirely vanifhes, though the eye is
kept uniformly and fleadily upon it. Now if the change or motion
of the retina was a mechanical impreffion, or a chemical tinge of
coloured light, the perception would every minute become flronger
and flronger, — whereas in this experiment it becomes every inflant
weaker and weaker. The fame circumflance obtains in the conti-
nued application of found, oroffapid bodies, or of odorous ones, or
of tangible ones, to their adapted organs of fenfe.

Thus when a circular coin, as a fliilling, is preffed on the palm of
the hand, the fenfe of touch is mechanically compreffed ; but it is
the flimulus of this preffure that excites the organ of touch into ani-
mal adlion, which conflitutes the perception of hardnefs and of figure :
for in fome minutes the perception ceafes, though the mechanical
preffure of the obje£l remains.

3. Make with ink on white paper a very black fpot about half an
inch in diameter, with a tail about an inch in length, fo as to refera-
ble a tadpole, as in Plate II. ; look fteadfaftly for a minute on the
center of this fpot, and, on moving the eye a little, the figure of the
tadpole will be feen on the white part of the paper ; which figure of
the tadpole will appear more luminous than the other part of the white
paper ; which can only be explained by fuppofing that a part of the
retina, on which the tadpole was delineated, to have become more
fenfible to light than the other parts of it, which were expofed to the

D 2 white

20 MOTIONS OF THE RETINA. Sect. III. 3,

white paper ; and not from any idea of mechanical impreffion or che-
mical combination of light with the retina.

4. When any one turns round rapidly, till he becomes dizzy,
and falls upon the ground, the fpedlra of the ambient objefts continue
to prefent themfelves in rotation, and he feems to behold the ob]e£ts
flill in motion. Now if thefe fpeftra were impreffions on a paflive
organ, they either muft continue as they were received laft, or not
continue at all.

5. Place a piece of red filk about an inch in diameter on a (heet of
white paper in a ftrong light, as in Plate I. ; look fleadily upon it
from the diftance of about half a yard for a minute ; then clofing
your eye-lids, cover them with your hands and handkerchief, and a
green fpeclrum will be feen in your eyes refembling in form the
piece of red filk. After fome feconds of time the fpe6lrum will dlf-
appear, and in a few more feconds u'ill reappear; and thus alter-
nately three or four times, if the experiment be well made, till at
length it vanifhes entirely.

6. Place a circular piece of white paper, about four inches in di-
ameter, in the funfliine, cover the center of this with a circular
piece of black filk, about three inches in diameter; and the center
of the black filk with a circle of pink filk, about two inches in dia-
meter; and the center -of the puik filk with a circle of yellow filk,
about one inch in diameter ; and the center of this with a circle of
blue filk, about half an inch in diameter ; make a fmall fpot with ink
in the center of the blue filk, as in Plate III. look fteadily for a mi-
nute on this central fpot, and then clofing your eyes, and applying
your hand at about an inch diftance before them, fo as to prevent too
much or too little light from pafiing through the eye-lids, and you
-will fee the mofi: beautiful circles of colours that imagination can con-
ceive ; which are moft refembled by the colours occafioned by pour-
ing a drop or two of oil on a ftill lake in a bright day. But thefe

circular

Sect. III. 4. MOTIONS OF THE RETINA. 21

circular irifes of colours are not only different from the colours of the
filks above mentioned, but are at the fame time perpetually chang-
ing as long as they exift.

From all thefe experiments it appears, that thefe fpe6lra in the eye
are not owing to the mechanical impulfe of light impreffed on the re-
tina; nor to its chemical combination with that organ; nor to the
abforption and emiflion of light, as is fuppofed, perhaps erroneoufly,
to take place in calcined fliells and other phofphorefcent bodies, after
having been expofed to the light : for in all thefe cafes the fpeclra in
the eye fhould either remain of the fame colour, or gradually decay,
when the object is withdrawn ; and neither their evanefcence during
the prefence of their obje£t, as in the fecond experiment, nor their
change from dark to luminous, as in the third experiment, nor their
rotation, as in the fourth experiment, nor the alternate prefence and
evanefcence of them, as in the fifth experiment, nor the perpetual
change of colours of them, as in the laft experiment, could exift,

IV. The fubfequent articles fhew, that thefe animal motions or
configurations of our organs of fenfe conftitute our ideas.

1. If any one in the dark preffes the ball of his eye, by applying
his finger to the external corner of it, a luminous appearance is ob-
served ^ and by a fmart ftroke on the eye great flafhes of fire are per-
ceived. (Newton's Optics.) So that when the arteries, that are near
the auditory nerve, make ftronger pulfations than ufual, as in fome
fevers, an undulating found is excited in the ears. Hence it is not
the prefence of the light and found, but the motions of the organ,
that are immediately neceflary to conftitute the perception or idea of
light and found.

2. During the time of fleep, or in delirium, the ideas of imagina-
tion are miftaken for the perceptions of external objedls ; whence it
appears, that thefe ideas of imagination are no other than a reiteration
of thofe motions of the organs of fenfe, which were originally ex-
cited by the ftimulus of external objeds : and in cur waking hours

5 the

2,2 MOTIONS OF THE RETINA. Sect, HI. 4:

tke fimple ideas, that we call up bj recoUedion or by imagination, as
the colour of red, or the fmell of a rofe, are exaft refemblances of
the fame fimple ideas from perception ; and in confequence mufl be
a repetition of thofe very motions.

3. The difagreeable fenfation called the tooth-edge is originally
excited by the painful jarring of the teeth in biting the edge of ttje
glafs, or porcelain cup, in which our food was given us in our in-
fancy, as is further explained in the Se(Slion XVI. 10, on Inftin6t. —
This difagreeable fenfation is afterwards excitable not only by a repe-
tition of the found, that was then produced, but by imagination alone,
as I have myfelf frequently experienced ; in this cafe the idea of bit-
ing a china cup, when I imagine it very diftindlly, or when I fee an-
other perfon bite a cup or glafs, excites an a£lual pain in the nerves
of my teeth. So that this idea and pain feem to be nothing more
than the reiterated motions of thofe nerves, that were formerly fo
difagreeably afFe£led.

Other ideas that are excited by imagination or recolle£lion in many
inftances produce fimilar effedls on the conftitution, as our percep-
tions had formerly produced, and are therefore undoubtedly a repe-
tition of the fame motions. A ftory which the celebrated Baron Van
Swieton relates of himfelf is to this purpofe. He was prefent when
the putrid carcafe of a dead dog exploded with prodigious flench j
and fome years afterwards, accidentally riding along the fame road,
he was thrown into the fame ficknefs and vomiting by the idea of
the flench, as he had before experienced from the perception of it.

4. Where the organ of fenfe is totally deflroyed, the ideas which
were received by that organ feem to perifh along with it, as well as
the power of perception. Of this a fatisfa£tory inflance has fallen
under my obfervation. A gentleman about fixty years of age had
been totally deaf for near thirty years : he appeared to be a man of
•good underflanding, and amufed himfelf with reading, and by con-
verfing eithep by the ufe of the pen, or by figns made with his fin-
gers,

Sect. III. 5- MOTIONS OF THE RETINA. 2^

gers, to reprefeiit letters. I obferved that he had fo far forgot ther
pronunciation of the language, that when he attempted to fpeak,
none of his words had diftindl articulation, thouoh his relations could
fometimes underftand his meaning. But,^ which is much to the
point, he affured me, that in his dreams he always imagined that
people converfed with him by figns or writing, and never that he
heard any cue fpeak to him. From hence it appears, that with the
perceptions of founds he has alfo loft the ideas of them ; though the:
organs of fpeech ftill retain fomewhat of their ufual habits of articu-
lation.

This obfervation may throw fome light on the medical treatment
of deaf people ; as it may be learnt from their dreams whether the
auditory nerve be paralytic, or their deafnefs be owing to feme de-
feat of the external organ.

It rarely happens that the immediate organ of vifion is perfeftly
deftroyed. The moft frequent caufes of blindnefs are occafioned by
defedls of the external organ, as in caterafts and obfufcations of the
cornea. But I have had the opportunity of converfing with two-
men, who had been fome years blind ; one of them had a complete
gutta ferena, and the other had loft the whole fubftance of his eyes..
They both told me that they did not remember to have ever dreamt
of vifible obje£ls, fince the total lofs of their fight.

V. Another method of difcovering that our ideas are animal mo^
tions of the organs of fenfe, is from confidering the great analogy
they bear to the motions of the larger mufcles of the body. In the-
foUowing articles it will appear that they are originally excited intO'
aftion by the irritation of external objects like our mufcles; are aflb»>
ciated together like our mufcular motions ; a<5t in fimilar time with
them ; are fatigued by continued exertion like them ; and that the
organs of fenfe are fubjeft to inflammation, numbnefs, palfy, con-
vulfion, and the defeds of old age, in the fame manner as the mu^
cular fibres.

4 J. All

24 MOTIONS OF THE RETINA. Sect. III. 5.

1. All our perceptions or ideas of external objects are univerfally
allowed to have been originally excited by the flimulus of thofe ex-
ternal objefts ; and it will be fliewn in a fucceeding fedlion, that it is
probable that all our mufcular motions, as well thofe that are become
voluntary as thofe of the heart and glandular fyffem, were originally
in like manner excited by the ftimulus of fomething external to the
organ of motion.

2. Our ideas are alfo aflbciated together after their produdtion pre-
cifely in the fame manlier as our mufcular motions; which will
likewife be fully explained in the fucceeding fedlion.

3. The time taken up in performing an idea is likewife much the
fame as that taken up in performing a mufcular motion. A mufi-
cian can prefs the keys of an harpfichord with his fingers in the or-
der of a tune he has been accuflomed to play, in as little time as he
can run over thofe notes in his mind. So we many times in an hour
cover our eye-balls with our eye-lids without perceiving that we are
in the dark ; hence the perception or idea of light is not changed for
that of dar^nefs in fo fmall a time as the twinkling of an eye j fo that
in this cafe the mufcular motion of the eye-lid is performed quicker
than the perception of light can be changed for that of darknefs. — So
if a fire- flick be whirled round in the dark, a luminous circle appears
to the obferver ; if it be whirled fomewhat flower, this circle be-
comes interrupted in one part ; and then the time taken up in fuch a
revolution of the flick is the fame that the obferver ufes in changing
his ideas: thus the SoXiKognoTov e^Kpj of Homer, the long fhadow of
the flying javelin, is elegantly defigned to give us an idea of its velo-
city, and not of its length.

4. The fatigue that follows a continued attention of the mind to
one obje£l is relieved by changing the fubjedl of our thoughts ; as
the continued movement of one limb is relieved by moving another
in its flead. Whereas a due exercife of the faculties of the mind
flrengthens and improves thofe faculties, whether of imagination or

recoUedion

Sect. in. 5- MOTIONS OF THE RETINA. 2$

recolkdion ; as the exerclfe of our limbs m dancing or fencing ia-
creafes the flrength and agility of the mufcles thus employed.
. 5. If the mufcles of any limb are inflamed, they do not move
without pain ; lb when the retina is inflamed, its motions alio are
painful. Hence light is as intolerable in this kind of ophthalmia, as
preiTure is to the finger in the paronychia. In this difeafe the patients
frequently dream of having their eyes painfully dazzled ; hence the idea
of flrong light is painful as well as the reality. The firll of thefe (a.&s
evinces that our perceptions are motions of the organs of feufe ; and
the latter j that our imaginations are alfo motions of the fame organs.

6. The organs of fenfe, like the moving mufcles, are liable to be-
come benumbed, or lefs fenfible, from compreffion. Thus, if any
perfon on a light day looks on a white wall, he may perceive the ra-
mifications of the optic artery, at every pulfation of it, reprefented by
darker branches on the white wall ; which is evidently owing to its
compreffing the retina during the diaftole of the artery. Savage
Nofolog.

7. The organs of fenfe and the moving mufcles are alike liable to
be afFefted with palfy, as in the gutta ferena, and in fome cafes of
deafnefs ; and one fide of the face has fometimes loft its power of fen-
fation, but retained its power of motion ; other parts of the body have
loft their motions but retained their fenfation, as in the common he-
miplagia ; and in other inftances both thele powers have perifhed
together.

8. In fome convulfive difeafes a delirium or inlanity fupervenes,
and the convulfions ceafe ; and converfely the convulfions ftiall fuper-
vene, and the delirium ceafe. Of this I have been a witnefs many
times in a day in the paroxyfms of violent epilepfies ; which evinces
that one kind of delirium is a convulfion of the organs of fenfe, and
that our ideas are the motions of thefe organs : the fubfequent cafes
will illuftrate this obfervation.

E. Mifs

26 MOTIONS OF THE RETINA. Sect. III. 5.

Mlfs G , a fair young lady, with light eyes and hair, was feized

with moft violent convalfions of her limbs, with ovitrageous hic-
cough, and moft vehement efforts to vomit : after near an hour was
elapfed this tragedy ceafed, and a calm talkative delirium fupervened
for about another hour ; and thefe relieved each other at intervals
during the greateft part of three or four days. After having carefully
confidered this difeafe, I thought the convulfions of her ideas lefs dan-
gerous than thofe of her mufcles ; and having in vain attempted to
make any opiate continue in her ftomach, an ounce of laudanum was
rubbed along the fpine of her back, and a drain of it was ufed as an
enema ; by-this medicine a kind of drunken delirium was continued
many hours ; and when it ceafed the convulfions did not return ; and
the lady continued well many years, except fome {lighter relapfes,
which were relieved in the fame manner.

Mifs H— — -, an accompliflied young lady, with light eyes and
hair, was feized with convulfions of her limbs, with hiccough, and
efforts to vomk, more violent than words can exprefs ; thefe conti-
nued near an hour, and were fucceeded with a cataleptic fpafin
of one arm, with the hand applied to her head ; and after about
twenty minutes thefe fpafms ceafed, and a talkative reverie fupervened
for near another hour, from which no violence, which it was proper
to ufe, could awaken her. Theie periods of convulfions, firft of the
mufcles, and then of the ideas, returned twice a day for feveral weeks ;
and were at length removed by great doles of opium, after a great va-
riety of other medicines and applications had been in vain experienced.
This lady was fubjea: to frequent relapfes, once or twice a year for
many years, and was as frequently relieved by the fame method.

]Vlifs W , an elegant young lady, with black eyes and hair,

had fometimes a violent pain of her fide, at other times a moft painful

ftrano-ury, which were every day fucceeded by delirium ; which gave

a temporary relief to the painful fpafms. After the vain exhibition

« of

Sect. III. 6. MOTIONS OF THE RETINA. 27

of variety of medicines ana applications by different phyticians, for
more than a twelvemonth, fne was direcled to take fome dofes of
opium, which were gradually increafed, by which a drunken deliri-
um was kept up for a day or two, and the pains prevented from re-
turning. A flefh diet, with a little wine or beer, in (lead of the low
regimen flie had previoufly uied, in a few weeks completely efta-
blillied her health ; which, except a few relapfes, has continued for
many years.

9. JLaftly, as we advance in life all the parts of the body become
more rigid, and are rendered leis iufceptible of new habits of motion,
though they retain thofe that were before ellablifhed. This is fen-
llbly obferved by thofe who apply themfelves late in life to mufic,
fencing, or any of the mechanic arts. In the fame manner many
elderly people retain the ideas they had learned early in life, but find
great difficulty in acquiring new trains of mem.ory ; infomuch that in
extreme old age we frequently fee a forgetfulnefs of the bufinefs of
yeflerday, and at the fame time a circumftantial remembrance of
the amufements of their j'outh ; till at length the ideas of recollec-
tion and adivity of the body gradually ceafe together,— -fuch is the
condition of humanity ! — and nothing remains but the vital motions
and fenfations.

VI. I. In oppofition to this dodrine of the produ£lion of our ideas,
it may be afked, if fome of our ideas, like other animal motions, are
voluntary, Vv'hy can we not invent new ones, that have not been re-
ceived by perception ? The anfwer will be better underftood after
having perufed the fucceeding fetlion, where it will be explained, that
the mufcular motions like wife are originally excited by the ftimulus
of bodies external to the moving organ ; and that the will has only the!
power of repeating the motions thus excited.

2. Another objedor may alk. Can the motion of an organ of fenfe
refemble an odour or a colour ? To which I can only anfwer, that it
has not been deraonftrated that any of our ideas refemble the.objeds'

E z that

28 MOTIONS OF THE RETINA. Sect. III. 6.

that excite them ; it has generally been believed that they do not ;
but this fliall be difcuffed at large in Se<fl. XIV.

3. There is another objeftion that at firft view would feem lefs-
eafy to furmount. After the amputation of a foot or a finger,, it has
frequently happened, that an injury being offered to the ftump of the
amputated limb, whether from cold air, too great preflure, or other
accidents, the patient has complained of a fenfation of pain in the foot
or fino-er. that was cut off. Does not this evince that all our ideas
are excited in the brain, and not in the organs of fenfe ? This objec-
tion is anfwered, by obferving that our ideas of the fhape, place, and
folidity of our limbs, are acquired by our organs of touch and of fight,
which are fituated in our fingers and eyes, ai>d not by any fenfationa
in the limb itfelf.

In this cafe the pain or lenfation, which formerly has arifen in the
foot or toes, and been propagated along the nerves to the central part
of the fenforium, was at the fame time accompanied with a vifible
idea of the fhape and place, and with a tangible idea of the folidity of
the affefted limb : now when thefe nerves are afterwards afFefted by any
injury done to the remaining ftump with a fimilar degree or kind of
pain, the ideas of the fhape, place, or folidity of the loft limb, return
by affociation ; as thefe ideas belong to the organs of fight and touch,,
^n which they were firft excited.

4. If you wonder what organs of fenfe can be excited into motion,,
when you call up the ideas of wifdom or benevolence, which Mr^
Locke has termed abftradled ideas ; I alk you by what organs of fenfe
you firft became acquainted with thefe ideas ? And the anfwer will
be reciprocal ; for it is certain that all our ideas were originally ac-
quired by our organs of fenfe ; for whatever excites our perception
muft be external to the organ that perceives it,, and we have no other
inlets to knowledge but by our perceptions : as will be further
explained in Setflion XIV. and XV. on the Produdions and ClalTes

"^ '''''■ vn.if

Sect. III. 7. MOTIONS OF THE RETINA. 29

VII. If our recolIe£lion or imagination be not a repetition of animal
movements, I aik, in my turn, What is it .'' You tell me it confifts
of images or pictures of things. Where is this extenfive canvas hung
up ? or where are the numerous receptacles in which thofe are depo-
fited } or to what elfe in the animal fyflem have they any fimili-
tude ?

That pleafing pifture of objects, reprefented in miniature on the
retina of the eye, feems to have given rife to this illufive oratory ! It
was forgot that this reprefentation belongs rather to the laws of light,
than to thofe of life ; and may with equal elegance be feen in the
camera obfcura as in the eye ; and that the pi<^ure vanilhes for ever^
when the obje£t is withdrawfli.

SECT.

■ANIMAL CAUSATION. Sect. IV. j.

S E C T. IV.

LAWS OF ANIMAL CAUSATION.

I. THE fibres, which conftitute the mufcles and organs of fenfe,
poffefs a power of coiitra£lion. The cu-cun'^itances atteaduig the ex-
ertion of this power of contraction coriftitute the laws of animal
motion, as the circumftances attending the exertion of the power of
ATTRACTION conftitute the laws of motion of inanimate matter.

II. The fpirit of animation is the immediate caufe of the contrac-
tion of animal fibres, it refides in the brain and nerves, and is liable to
general or partial diminution or accumulation.

III. The flimulus of bodies external to the moving organ is the
remote caufe of the original contradHons of animal fibres.

IV. A certain quantity of ftimulus produces irritation, which is
an exertion of the fpirit of animation exciting the fibres into con-
tra£lion.

V. A certain quantity of contraftion of animal fibres, if it be per-
ceived at all, produces pleafure ; a greater or lefs quantity of con-
traflion, if it be perceived at all, produces pain ; thefe conftitute
fenfation.

VI. A certain quantity of fenfation produces defire or averfion ;
thefe conftitute volition.

VII. All animal motions which have occurred at the fame time,
or in immediate fuccefiion, become fo connected, that when one of
them is reproduced, the other has a tendency to accompany or fuc-
ceed it. When fibrous contra£tions fucceed or accompany other
fibrous contradions, the conneition is termed alTociationj when

fibrous

Sect.IV. 7. ANIMAL CAUSATION. 31,

fibrous contraftiotis fucceed fenforial motions, the connexion is term-
ed caufation ; when fibrous and fenforial motions reciprocally intro-
duce each other, it is termed catenation of animal motions. All
thefe connexions are faid to be produced by habit, that is, by fre-
quent repetition. Thefe laws of animal caufation will be evinced by
numerous fads, which occur in our daily exertions ; and will after-
wards be employed to explain the more recondite phenomena of the
produftion, growth, difeafes, and decay of the animal fyftcm.

S E C T.

j2 SENSORIAL FACULTIES. S^ct.V,

S E C T. V.

OF THE FOUR FACULTIES OR MOTIONS OF THE SENSORIUM.

"I. Four fenforial powers. i. Irritation, fetifation, volition, affociation defined.
3, Senjorial motions diftinguijhed from fibrous motions^

1. THE fpirit of animation has four different modes of a£lion, or
in other words the animal fenforium poffefles four different faculties,
which are occafionally exerted, and caufe all the contradlions of the
fibrous parts of the body. Thefe are the faculty of caufing fibrous
contradlions in confequence of the irritations excited by external
bodies, in confequence of the fenfations of pleafure or pain, in confe-
quence of volition, and in confequence of the affociations of fibrous
contradioins with other fibrous contraftions, which precede or accom-
pany them.

Thefe four faculties of the fenforium during their ina£tive ftate are
termed irritability, fenfibility, voluntarity, and affociability ; in their
aSive flate they are termed as above, irritation, fenfation, volition,
affociation.

2. Irritation is an exertion or change of fome extreme part of
the fenforium refiding in the mufcles or organs of fenfe, in confe-
quence of the appulfes of external bodies.

Sensation is an exertion or change of the central parts of the fen-
forium, or of the whole of it, heginning at fome of thofe extreme
parts of it, which refide in the mufcles or organs of fenfe.

Volition is an exertion or change of the central parts of the fen-
forium, or of the whole of it, terminating in fome of thofe extreme
parts of it, which refide in the mufcles or organs of fenfe.

Association

Sect.V. sensorial FACULTIES.

Association is an exertion or change of fome extreme part of
the fenforium refiding in the mufcles or organs of fenfe, ia confe-
quence of fome antecedent or attendant fibrous contradlions.

3. Thefe four faculties of the animal fenforium may at the time of
their exertions be termed motions without impropriety of language;
for we cannot pafs from a ftate of infenfibility or inaftion to a flate of
fenfibility or of exertion without fome change of the fenforium, and
every change includes motion. We (hall therefore fometimes term
the above def^znhed faculties Jen/oria/ moiiofis to diftinguifh them from
fibrous motions ; which latter expreffion includes the motions of the
mufcles and organs of fenfe.

The adive motions of the fibres, whether thofe of the mufcles or
organs of fenfe, are probably fimple contraftions; the fibres being
again elongated by antagonifl mufcles, by circulating fluids, or fome-
times by elaftic ligaments, as in the necks of quadrupeds. The fea-
forial motions, which conftitute the fenfations of pleafure or pain, and
which conftitute volition, and which caufe the fibrous contraflions
in confequence of irritation or of affociation, are not here fuppofed to
be flu6luations or refludtuations of the fpirit of animation ; nor are they
fuppofed to be vibrations or revibrations, nor condenfations or equili-
brations of it ; but to be changes or motions of it peculiar to life.

SECT.

34 FIBROUS CONTRACTIONS. Sect. VI. j.

SECT. VI.

OF THE FOUR CLASSES OF FIBROUS MOTIONS.

I. Origin of fibrous contraSlions. II. Biftribution ef them into four daJfeSf
irritative- motionsy fenjitive motionsy voluntary motions^ and ajfociati motions,
defined,

I. ALL the fibrous contractions of animal bodies originate from
the fenforium, and refolve themfelves into four claffes, correfpondent
with the four powers or motions of the fenforium above dcfcribed,.
and from which thej have their caufation.

1. Thefe fibrous contractions were originally caufed by the irrita-
tions excited by objects, which are external to the moving organ. As
the pulfations of the heart are owing to the irritations excited by the
ftimulus of the blbod ; and the ideas of perception are owing to the
irritations excited by external bodies.

2. But as painful or pleafurable fenfations frequently accompanied
thofe irritations, by habit thefe fibrous contractions became caufeable
by the fenfations, and the irritations ceafed to be uecefiary to their
produ£lion. As the fecretion of tears in grief is caufed by the fenfa-
tion of pain; and the ideas of imagination, as in dreams or delirium,
are excited by the pleafure or pain, with which they were formerljr
accompanied..

3. But as the efforts of the will frequently accompanied thefe pain-
ful or pleafureable fenfations, by habit the fibrous contraftions became
caufable by vohtion ; and both the irritations and fenfations ceafed to-
be neceflary to their produdion. As the deliberate locomotions of

2 . the-

Sect. VI. 2. FIBROUS CONTRACTIONS. 3s

the body, and the ideas of recolleclion, as when we will to repeat the
alphabet backwards.

4. But as many of thefe fibrous contraclions frequently accom-
panied other fibrous contradions, by habit they became caufable
by their aflbciations with them ; and the irritations, fenfations, and ,
volition, ceafed to be neceffary to .their produ<Sion. As the aftionsj
of the mufcles of the lower limbs in fencing are affociated withj
thofe of the arms ; and the ideas of fuggeftion are affociated with
other ideas, which precede or accompany them ; as in repeating care-
lefsly the alphabet in its ufual order after having began it.

II. We fhall give the following names to thefe four claffes of fibrous
motions, and fubjoin their definitions.

1. Irritative motions. That exertion or change of the {en-
forium, which is caufed by the appulfes of external bodies, either
fimply fubfides, or is fucceeded by fenfation, or it produces
fibrous motions ; it is termed irritation, and irritative motions are
thofe CGntra£lions of the mufcular fibres, or of the organs of {enfe^
that are immediately confequent to this exertion or change of the
fenforium.

2. Senfitive motions. That exertion or change of the fenforium,
which conflitutes pleafure or pain, either fimply fubfides, or is
fucceeded by volition, or it produces fibrous motions ; it is term.ed
fenfation, and the fenfitive motions are thofe contraftions of the muf-
cular fibres,' or of the organs of fenfe, that are immediately confe-
quent to this exertion or change of the fenforium,

3. Voluntary motions. That exertion or change of the fen-
forium, which conftitutes defire or averfion, either fimply fubfides,
or is fucceeded by fibrous motions ; it is then termed volition, and
voluntary motions are thofe contraftions of the mufcular fibres, or of
the organs of fenfe, that are immediately confequent to this exertion
or change of the fenforium.

F Z 4. Affociate

36 FIBROUS CONTRACTIONS. Sect.YI. a.::

4. Affociate motions. That exertion or change of the fenfo-:
rium, which accompanies fibrous motions, either fimply fubfides,
or is fucceeded by fenfation or vohtion, or it produces other fibrous
motions; it is then termed affociation, and the affociate motions
are thofe contradtions of the mufcular fibres, or of the organs of
fenfe, that are immediately confequent to this exertion or change of
the fenfoiium.

SECT.

Sect. VII. I. IRRITATIVE MOTIONS. ^,

SECT. VII.

OF IRRITATIVE MOTIONS,

I. I. Some mufcular motions are excited hy perpetual irritations. i. Others more
frequently hy Jenjatlons. 3. Others by volition. Cafe of involuntary ftr etchings
in paralytic limbs. 4. Some fenfual motions are excited by perpetual irritaticms,
5. Others more frequently byfenfation or volition,

II. I. Mufcular motions excited by perpetual irritations occafionally become obedient
tofenfation and to volition, a. And the fenfual motions.

III. I. Other mufcular motions are affociated with the irritative ones. 2. And
other ideas with irritative ones. Of letters, language, hieroglyphics. Irrita-r
five ideas exifi without our attention to them.

I. I. MANY of our mufcular motions are excited by perpetual ir-
ritations, as thofe of the heart and arterial fyftem by the circumfluent
blood. Many other of them are excited by intermitted irritations, as
thofe of the flomach and bowels by the aliment we fwallow ; of the
bile-du£ts by the bile ; of the kidneys, pancreas, and many other
glands, by the peculiar fluids they feparate from the blood ; and thofe
of the ladleal and other abforbent veflels by the chyle, lymph, and
moifture of the atmofphere. Thefe motions are accelerated or re-
tarded, as their correfpondent irritations are increased or diminifhed,
without our attention or confcioufnefs, in the fame manner as' the
various fecretions of fruit, gum, refin, wax, and honey, are pro-
duced in the vegetable world, and as the juices of the earth and
the molfture of the atmofphere are abforbed by their roots and

foliage.

2. Other

38 IRRITATIVE MOTIONS. Sect. VII. i.

2. Other mufcular motions, that are moft frequently conne£ted
with our fenfations, as thofe of the fphiiifters of the bladder and anus,
and the mufculi ereftores penis, were originally excited into motion hy
irritation, for young children make water, and have other evacua-
tions without attention to thefe circumftances ; " et primis etiam ab
incunabulis tenduntur faspius puerorum penes, amore nondum ex-
pergefafto." So the nipples of young women are liable to become
turgid by irritation, long before they are in a fituation to be excited by
the pleafure of giving milk to the lips of a child.

3. The contractions of the larger mufcles of our bodies, that are
moft frequently coiinedled with volition, were originally excited into
a^ion by internal irritations : as appears from the ftretching or yawn^
ing of all animals after long fleep. In the beginning of fome fevers
this irritation of the mufcles produces. perpetual ftretching and yawn-
ing; in other periods of fever an univerfal reftleflhefs arifes from the
fame caufe, the patient changing the attitude of his body every mi-
nute. The repeated ftruggles of the foetus in the uterus muft be
owing to this internal irritation : for the foetus can have no other in-
ducement to move its limbs but the toedium or irkfomenefs of a con-
tinued pofture.

The following cafe evinces, that the motions of ftretching the
limbs after a continued attitude are not always owing to the power of
the will. Mr. Dean, a mafon, of Auftry in Leicefterfhire had the
fpine of the third vertebra of the back enlarged ; in fome weeks his
lower extremities became feeble, and at length quite paralytic : nei-
ther the pain of blifters, the heat of fomentations, nor the utmoft ef-
forts of the will could produce the leaft motion in thefe limbs ; yet
twice or thrice a day for many months his feet, legs, and thighs,
were affeded for many minutes with forceable ftretchings, attended
with the fenfation of fatigue ; and he at length recovered the ufe of
his limbs, though the Ipine continued protuberant. The fame cir-
cumftance is frequently feen in a lefs degree in the common hemipla-

gia;

Sect. VII. 2. IRRITATIVE MOTIONS. 39

gia ; and when this happens, I have believed repeated and flrong
fhocks of eledlricity to have been of great advantage.

4. In like manner the various organs of fenfe are originally excited
into motion by various external flimuli adapted to this purpofe, which
motions are termed perceptions or ideas ; and many of thefe motions
during our waking hours are excited by perpetual irritation, as thofe
of the organs of hearing and of touch. The former by the couftant
low indiflinft noifes that murmur around us, and the latter by the
weight of our bodies on the parts which fupport themj and by the
■unceafing variations of the heat, moifture, and preflure of the atmof-
phere; and thefe fenfual motions, precifely as the mufcular ones
above mentioned, obey their correfpondent irritations without our at-
tention or confcioufnefs.

5. Other clafTes of our ideas are more frequently excited by our
fenfations of pleafure or pain, and others by volition : but that thele
have all been originally excited by ftimuli from external objedls, and
only vary in their combinations or feparations, has been fully evinced
by Mr. Locke ; and are by him termed the ideas of perception in con-
tradiftindlion to thofe, which he calls the ideas of refledlion.

11. I. Thefe mufcular motions, that are excited by perpetual irri-
tation, are neverthelefs occafionally excitable by the fenfations of
pleafure or pain, or by volition , as appears by the palpitation of the
heart from fear, the increafed fecretion of faliva at the fidit of a^ree-
able food, and the glow on the fkin of thofe who are afhamed. There
is an inftance told in the Philofophical Tranfadions of a man, who
could for a time flop the motion of his heart when he pleafed ; and
Mr. D. has often told me, he could fo far increafe the periftaltic mo-
tion of his bowels by voluntary efforts, as to produce an evacuation by
flool at any time in half an hour.

2. In like manner the fenfual motions, or ideas, that are excited
by perpetual irritation, are neverthelefs occafionally excitable by fen'-
lation or volition ; as in the night, when we liften under the influ-
ence

40 IRRITATIVE MOTIONS. Sect. VII. 3.

fence of fear, or from, voluntary attention, the motions excited in the
organ of hearing by the whifpering of the air in our room, the pul-
fation of our own arteries, or the faint beating of a diftaut watch,
become objects of perception.

III. Innumerable trains or tribes of other motions are affociatcd
with thefe mufcular motions which are excited by irritation ; as by
the ftimulus of the blood in the right chamber of the heart, the lungs
are induced to expand themfelves ; and the peroral and intercoftal muf-
cles, and the diaphragm, a£l at the fame time by their allbciations
with them. And when the pharinx is irritated by agreeable food,
the mufcles of deglutition are brought into aftion by aflbciation. Thus
when a greater light falls on the eye, the iris is brought into a£tion
without our attention ; and the ciliary procefs, when the focus is
formed before or behind the retina, by their affociations with the in-
creafed irritative motions of the organ of vifion. Many common ac-
tions of life are produced in a fimilar manner. If a fly fettle on my
forehead, whilft I am intent on my prefent occupation, I diflodge it
with my finger, without exciting my attention or breaking the train
of my ideas.

2. In like manner the irritative ideas fuggeft to us many other
trains or tribes of ideas that are aflbciated with them. On this kind
of connexion, language, letters, hieroglyphics, and ever kind ©f fym-
Ibol, depend. The fymbols themfelves produce irritative ideas, or
fenfual motions, which we do not attend to ; and other ideas, that
are fucceeded by fenfation, are excited by their aflbciation with them.
And as thefe irritative ideas make up a part of the chain of our wak-
ing thoughts, introducing other ideas that engage oui* attention,
though themfelves are unattended to, we find it very difficult to in-
veftigate by what fteps many of our hourly trains of ideas gain their
admittance.

It may appear paradoxical, that ideas can exift, and not be attended

to ; but all our perceptions are ideas excited by irritation, and fuc-

j eeeded

Sect. VII. 3. IRRITATIVE MOTIONS. 41

ceeded by fenfation. Now when tbefe ideas excited by irritation give
us neither pleafure nor pain, we ceafe to attend to them. Thus
whilft I am walking through that grove before my window, I do
not run againft the trees or the benches, though my thoughts are
ftrenuoufly exerted on fome other object. This leads us to a diftinft
knowledge of irritative ideas, for the idea of the tree or bench, which
I avoid, exifts on my retina, and induces by aflbciation the adtion of
certain locomotive mufcles ; though neither itfelf nor the a£lions of
thofe mufcles engage my attention.

Thus whilft we are converfing on this fubjeft, the tone, note,
and articulation of every individual word forms its correfpondent irri-
tative idea on the organ of hearing ; but we only attend to the aflbci-
ated ideas, that are attached by habit to thefe irritative ones, and are
fucceeded by fenfation ; thus when we read the words " printing-
press" we do not attend to the fhape, fize, or exiflience of the let-
ters which compofe thefe words, though each of them excites a cor-
refpondent irritative motion of our organ of vifion, but they intro-
duce by aflbciation our idea of the moft ufeful of modern inventions ;
the capacious refervoir of human knowledge, whofe branching ftreams
diiFufe fciences, arts, and morality, through all nations and all ages.

G SECT.

42 SENSITIVE MOTIONS. Sect.VIII. u

SECT. VIII.

OF SENSITIVE MOTIONS.

I. I. Senftttve mujcular motions were originally excited into aSion hy irritation,
2. And Jenfitive Jenjual motions, ideas of iinagination, dreams. II. \. Senfttive
mujcular motions are occafionally obedient to volition. i. And fenfttive fenfudl
motions. III. i. Other mujcular motions are ajfociated with the Jenjitive ones.
1. And other Jenjual motions. '•

I. I. MANY of the motions of our mufcles, that are excited into
aftiou by irritation, are at the fame time accompanied with painful or
pleafurable fenfations ; and at length become by habit caufable by the
fenfations. Thus the motions of the fpinfters of the bladder and anus
were originally excited into a6tion by irritation ; for young children
■give no attention to thefe evacuations ; but as foon as they become
fenfible of the inconvenience of obeying thefe irritations, they fufFer
the water or excrement to accumulate, till it difagreeably afFe£ts
them J and the aftlon of thofe fpinders is then in confequence of this
difagreeable fenfation. So the fecretion of faliva, which in young
children is copioufly produced by irritation, and drops from their
mouths, is frequently attended with the agreeable fenfation produced
by the'maftication of tafteful food; till at length the fight of fuch
food to a hungry perfon excites into adlion thefe falival glands ; as is
feen in the Havering of hungry dogs.

The motions of thofe mufcles, which are affetted by lafcivious
ideas, and thofe which are exerted in fmiling, weeping, ftarting from
fear, and winking at the approach of danger to the eye, and at times
the aftions of every large mufcle of the body become caufable by our

fenfations.

Sect.VIII. 2. SENSITIVE MOTIONS. 43

fenfations. And all thefe motions are performed with ftrength and
velocity in proportion to the energy of the fenfation that excites
thetp, and the quantity of fenforial power,

2. Many of the motions of our organs of fetife, or ideas, that were
Qriginally excited into adion by irritation, become in like manner
more frequently caufable by our fenfations of pleafure or pain. Thefe
motions are then termed the ideas of imagination, and make up all
the fcenery and tranfadions of our dreams. Thus when any painful
Qf pleafurable fenfations poflefs us, as of love, anger, fear; whether
in our fleep or waking hours, the ideas, that have been formerly ex-
cited by the objedls of thefe fenfations, now vividly recur before us by
their connexion with thefe fenfations themfelves. So the fair fmil-
ing virgin, that excited your love by her prefence, whenever that
fenfation recurs, rifes before you in imagination; and that with all
the pleafmg cii-cumflances, that had before engaged your attention.
And in fleep, when you dream under the influence of fear, all the
nobbers, fireSj arid precipices, that you formerly have feen or heard
of, arife before you with terrible vivacity. All thefe fenfual motions,
like the mufcular ones above mentioned, are performed with flrength
and velocity in proportion to the energy of the fenfation of pleafure or
pain, which excites them, and the quantity of fenforial power.

II. I. Many of thefe mufcular motions above defcribed, that are
moft frequently excited by our fenfations, are neverthelefs occafion-
ally caufable by volition ; for we can fmile or frown fpontaneoufly,
can make water before the quantity or acrimony of the urine pro-
duces a difagreeable fenfation, and can voluntarily maflicate a naufeous
drug, or fvvallow a bitter draught, though our fenfation would
flrongly difTuade us.

2. In like manner the fenfual motions, or ideas, that are moft fre-
quently excited by our fenfations, are neverthelefs occafionally caufe-
able by volition, as we can fpontaneoufly call tip our lafl night's
dream before us, tracing it induflrioufly flep by ftep through all its

G 2 variety

44 SENSITIVE MOTIONS. Sect.VIIL 5.

variety of fcenery and tranfaftion ; or can voluntarily examine or re-
peat the ideas, that have been excited by our difguft or admiration.

III. I. Innumei-able trains or tribes of motions are aflbciated with
thefe fenfitive mufcular motions above mentioned ; as when a drop
of water falling into the wind-pipe difagreeably afFedts the air-veffels
of the lungs, they are excited into violent adlion ; and with thefe
fenfitive motions are aflbciated the aftions of the pe£toral and inter-
coftal mufcles, and the diaphragm; till by their united and repeated
fuecuffions the drop is returned through the larinx. The fame occurs
when any thing difagreeably affedls the noflrils, or the ftomach, or
the uterus ; variety of mufcles are excited by aflbciation into forcible
adion, not to be fupprefled by the utm'oft efforts of the will ; as in
fneezing, vomiting, and parturition.

2. In like manner with thefe fenfitive fenfual motions, or ideas of
imagination, are aflbciated many other trains or tribes of ideas, which
by fome writers of metaphyfics have been clafled under the terms of
refemblance, caufation, and contiguity ; and will be more fully^
treated of hereafter.

SECT.

Sect. IX. i. VOLUNTARY MOTIONS. 45

SECT. IX.

OF VOLUNTARY MOTIONS.

I. I. Volmtary mujcular motions are originally excited by irritations. 2. ^nd vo-
luntary ideas. Of rea/on. II. i . Voluntary mujcular motions are occaftonally
caujable by Jeitjations. 1. And voluntary ideas. III. i. Voluntary mujcular
motions are occajionally obedient to irritations. 1. And voluntary ideas.
IV. I. Voluntary mijcular motions are ajfociated with other mujcular mo-
tions. 2. And voluntary ideas.

WHEN pleafure or pain affedl the animal fyftem, many of its
motions both mufcular and fenfual are brought into aftlon ; as was
Ihewn in the preceding fe£lion, and were called fenfitive motions.
The general tendency of thefe motions is to arreft and to poffefs the
pleafure, or to diflodge or avoid the pain : bat if this cannot imme-
diately be accomplifhed, defire or averfion are produced, and the
motions in confequence of this new faculty of the fenforium are called
voluntary.

I. I. Thofe mufcles of the body that are attached to bones, have
in general their principal connexions with volition, as I move my
pen or raife my body. Thefe motions were originally excited by ir.^
ritation, as was explained in the feftion on that fubjeft, afterwards
the fenfations of pleafure or pain, that accompanied the motions thus
excited, induced a repetition of them ; and at length many of them

were

44 VOLUNTARY MOTIONS. Sect. IX,. r,

-were voluntarily praftifed in fucceffion or in combination for the
common purpofes of life, as in learning to walk, or to fpeak ;
and are performed with ftrength and velocity in proportion to the
energy of the volition, that excites them, and the quantity of fen-
forial power.

2. Another great clafs of voluntary motions confifls of the ideas of
recolledlion. We will to repeat a certain train of ideas, as of the
alphabet backwards ; and if any ideas, that do not belong to this
intended train, intrude themfelves by other connedions, we will to
rejedl them, and voluntarily perfift in the determined train. So at
my approach to a houfe which I have but once vifited, and that at
the diftance of many months, I will to recoiled the names of the
numerous family I expe6l to fee there, and I do recoiled them.
. On this voluntary recolledion of ideas our faculty of reafon de-
pends, as it enables us to acquire an idea of the diffimilitude of
any two ideas. Thus if you voluntarily produce the idea of a
right-angled triangle, and then of a fquare ; and after having ex-
cited thefe ideas repeatedly, you excite the idea of their difference,
which is that of another right-angled triangle inverted over the
former ; you are faid to reafon upon this fubjed, or to compare
your ideas.

• Thefe' ideas of recolledion, like the raufcular motions above
mentioned, were originally excited by the irritation of external
bodies, and were termed ideas of perception : afterwards the plea-
fure or pain, that accompanied thefe motions, induced a repetition,
of them in the abfence of the external body, by which they were
lirft excited ; and then they were termed ideas of imagination,.
At length they become voluntarily pradifed in fucceffion or in com-
bination for the common purpofes of life ; as when we make our-
felves mafters of the hiftory of mankind, or of the fciences they.
liave:invefligated ; and are then called ideas of recolledion ; and
4 - are

Sect. IX. 4- VOLUNTARY MOTIONS. 47

are performed with ftrength aod velocity in proportion to the
energy of the volition that excites them, and the quantityof fenfq-
rial power.

II. I.- The mufcular motions above defcribed, that are moil fre-
quently obedient to the will, are neverthelefs occafionally caufable by
painful or pleafurable fenfation, as in the flarting from fear, and the
contradlion of the calf of the leg in the cramp.

2. In like manner the fenfual motions, or ideas, that are moft
frequently connefted with volition, are neverthelefs occafionally
caufable by painful or pleafurable fenfation. As the hiftories of men,
or the defcrlption of places, which we have voluntarily taken pains to
remember, fometimes occur to us in our dreams.

III. I. The mufcular motions that are generally fubfervient to
volition, are alfo occafionally caufable by irritation, as in ftretching
the limbs after fleep, and yawning. In this manner a contraction
of the arm is produced by pafling the eleftric fluid from the Leyden
phial along its mufcles ; and that even though the limb is para-
lytic. The fudden motion of the arm produces a difagreeable fenfa-
tion in the joint, but the mufcles feem to be brought into adlion
fimply by irritation.

2. The ideas, that are generally fubfervient to the will, are
in like manner occafionally excited by irritation ; as when we
view again an object, we have before well fludied, and often re-
eoUedted.

IV. I. Innumerable trains or tribes of motions are affociated with
thefe voluntary mufcular motions above mentioned ; as \vhen I will
to extend my arm to a diftant objeft, fome other mufcles are brought
into a£lion, and preferve the balance of my body. And when I wifh
to perform any fteady exertion, as in threading a needle, or chop-
ping with an ax, the pe(Sloral mufcles are at the fame time brought

into-

48 VOLUNTARY MOTIONS. Sect. DC. 4^

into aftion to preferve the trunk of the body motionlefs, and we
ceafe to refpire for a time.

2. In like manner the voluntary fenfual motions, or ideas of
recolleflion, are aflbciated with many other trains or tribes of ideas.
As when I voluntarily recollect a gothic window, that I faw fome
time ago, the whole front of the cathedral occurs to me at the
fame time.

SECT.

Sect. X.I. ASSOCIATE MOTIONS. 49

SECT. X.

OF ASSOCIATE MOTIONS.

I. I. Many mujcular motions excited by irritations in trains or tribes become ajfoci-
ated. 2. And many ideas. II. i. Many Jenjitive mujcular motions become
ajfociated. 2. And many Jenjitive ideas. III. 1. Many voluntary mujcular
motions become ajfociated. 2. And then become obedient tojenjation or irritation.
3. And many voluntary ideas becomt ajfociated,

ALL the fibrous motions, whether mufcular or fenfual, which
are frequently brought into aftion together, either in combined
tribes, or in fucceflive trains, become fo conne£led by habit, that
when one of them is reproduced the others have a tendency to fuc-
ceed or accompany it.

I. I. Many of our mufcular motions were originally excited iii
fucceflive trains, as the contractions of the auricles and of the ven-
tricles of the heart ; and others in combined tribes, as the various
divifions of the mufcles which compofe the calf of the leg, which
were originally irritated into iynchronous action by the tedium or
irkfomenefs of a continued poflure. By frequent repetitions thefe
motions acquire aflbciations, which continue during our lives, and
even after the deftruftion of the greatefl part of the fenforium ; for
the heart of a viper or frog will continue to pulfate long after it is
taken from the body ; and when it has entirely ceafed to move, if
any part of it is goaded with a pin, the whole heart will again re-
new its pulfations. This kind of connection we fhall term irri-

H tative

so ASSOCIATE MOTIONS, StcT. X.. 2.

tatlve affociation, to diftinguifli it from fenfitive and voluntary
aflbciations.

2. la like manner many of our ideas are originally excited in
tribes; as all the objedts of fight, after we become fo well ac-
quainted with the laws of vifion, as to diftinguifli figure and dif-
tance as well as colour; or in trains, as while we pafs along the
objects that furround us. The tribes thus received by irritation be-
come affociated by habit, and have been termed complex ideas by
the writers of raetaphyfics, as this book, or that orange. The
trains have received no particular name, but thefe are alike aflbci-
ations of ideas, and frequently continue during our lives. So the
tafte of a pine-apple, though we eat it blindfold, recalls the colour
and fliape of it ; and we can fcarcely think on folidity without
figure.

II. I. By the various efforts of our fenfations to acquire or avoid
their objefts, many mufcles are daily brought into fucceffive or
fynchrcnous a£lions ; thefe become aflbciated by habit, and are then,
excited together with great facility, and in many inftances gain in-
diflbluble connexions. So the play of puppies and kittens is a re-
prefentation of their mode of fighting or of taking their prey; and
the motions of the mufcles neceflary for thofe purpofes become
aflbciated by habit, and gain a great adroitnefs of adlion by thefe
early repetitions : fo the motions of the abdominal mufcles, which
were originally brought into concurrent adtion with the protrufive
motion of the redlum or bladder by fenfation, become fo conjoined
with them by habit, that they not only eafily obey thefe fenfa-
tions occafioned by the flimulus of the excrement and urine, but
are brought into violent and unreftrainable adtion in the flrangury
and tenefmus. This kind of connedlion we fhall term fenfitive af-
fociation.

2. So many of our ideas, that have been excited together or in
fuccefiion by our fenfations, gain fynchrcnous or fucceflive aflbci-
ations.

Sect. X. 3- ASSOCIATE MOTIONS. 51

ations, that are fometimes indiffoluble but with life. Hence the
idea of an inhuman or diihonourable action perpetually calls up
before us the idea of the wretch that was guilty of it. And hence
thofe unconquerable antipathies are formed, which fome people have
to the fight of peculiar kinds of food, of which in their infancy they
have eaten to excefs or by conftraiut.

III. I. In learning any mechanic art, as mufic, dancing, or the
ufe of the fword, we teach many of our mufcles to a6l together or
' in fucceffion by repeated voluntary efforts ; which by habit become
formed into tribes or trains of affociation, and ferve all our pur-
pofes with great facility, and in fome inftances acquire an indif-
Ibluble union. Thefe motions are gradually formed into a habit
of ailing together by a multitude of repetitions, whilft they are
yet feparately caufable by the will, as is evident from the long
time that is taken up by children in learning to walk and to
fpeak ; and is experienced by every one, when he firil: attempts to
Ikate upon the ice or to fwim : thefe we fhall term voluntary
affociations.

2. All theie mufcular movements, when they are thus aflbciated
into tribes or trains, become afterwards not only obedient to volition,
but to the lenfations and irritations ; and the fame movement com-
pofes a part of many different tribes or trains of motion. Thus
a fingle mufcle, when it a6ts in confort with its neighbours on
one fide, affifts to move the limb in one direftion ; and in an-
other, when it .a£ls with thofe in its neighbourhood on the
other fide ; and in other diredions, when it acts feparately or joint-
ly with thofe that lie immediately under or above it ; and all
thefe with equal facility after their affociations have been well
eftablifhed.

The facility, witii which each mufcle changes from one aflbciated
tribe to another, and that either backwards or forwards, is well
obfervable in the mufcles of the arm in moving the \\indlafs of an

H 2 air-

52 ASSOCIATE MOTIONS. Sect. X. 3.

air-pump ; and the flownefs of thofe mufcular movements, that
have not been afibciated by habit, may be experienced by any one,
who (hall attempt to faw the air quick perpendicularly with one hand,
and horizontally with the other at the fame time.

3. In learning every kind of faience we voluntarily affociate many
tribes and trains of ideas, which afterwards are ready for all the
purpofes either of volition, fenfation, or irritation ; and in fome in-
ftances acquire indiflbluble habits of a£ling together, fo as to afFe£t
our reafoning, and influence our actions. Hence the neceffity of a
good education.

Thefe affociate ideas are gradually formed into habits of a£ling
together by frequent repetition, while they are yet feparately obe-
dient to the will ; as is evident from the difficulty we experience
in gaining fo exadl an idea of the front of St. Paul's church, as to
be able to delineate it with accuracy, or in recollefting a poem of a
few pages.

And thefe ideas, thus affociated into tribes, not only make up
the parts of the trains of volition, fenfation, and irritation ; but the
fame idea compofes a part of many different tribes and trains of
, ideas. So the limple idea of whitenefs compofes a part of the com-
plex idea of fnow, milk, ivory ; and the complex idea of the letter A
compofes a part of the feveral affociated trains of ideas that make up
the variety of words, in which this letter enters.

The numerous trains of thefe affociated ideas are divided by Mr.
Hume into three claffes, which he has termed contiguity, cau&-
tion, and refemblance. Nor fhould we wonder to find them thus
connected together, fince it is the bufinefs of our lives to difpofe
them into thefe three claffes ; and we become valuable to ourfelves
and our friends, as we fucceed in it. Thofe who have combined
an extenfive clafs of ideas by the contiguity of time or place, are
men learned in the hiftory of mankind, and of the fciences they
have cultivated, Thofe who have connefted a great clafs of ideas

Sect. X. 3- ASSOCIATE MOTIONS. 53

of refemblancefs, poffefs the fource of the ornaments of poetry and
oratory, and of all rational analogy. While thofe who have
connefted great clafles of ideas of caufation, are furniflied with the
powers of producing efFefts. Thefe are the men of aftive wifdom,
who lead armies to viftory, and kingdoms to profperity ; or difcover
and improve the fciences, which meliorate and adorn the condition
of humanity.

SECT^

54 SENSORIAL ACTIONS, Sect. XL i.

SECT. xr.

ADDITIONAL OBSERVATIONS ON THE SENSORIAL POWERS.

I. Stimulation is of various kinds adapted to the organs of fenje, to the mufcles, to
hollow membranes, and glands. Some ohjeSs irritate our fenjes by repeated im-
pulfes. II. I. Senfation and volition frequently affeSl the whole feiiforium.
2. Emotions, pajjions, appetites. 3. Origin of defire and averfion. Criterion
of voluntary aSiions, difference of brutes and men, 4. Senfibility and volunta-
rily. III. Affociations formed before nativity, irritative motions mifiaken for
ajfociated ones.

Irr'tiatipn.

I. THE various organs of fenfe require various kinds of ftimula-
tion to excite them into adlion ; the particles of light penetrate the
cornea and humours of the eye, and then irritate the naked retina ;
fapid particles, diflblved or difFufed in M'ater or faliva, and odorous
ones, mixed or combined with the air, irritate the extremities of the
nerves of tafte and fmell ; which either penetrate, or are expanded
on the membranes of the tongue and noftrils ; . the auditory nerves
are ftimulated by the vibrations of the atmofphere communicated by
means of the tympanum and of the fluid, whether of air or of water,
behind it ; and the nerves of touch by the hardnefs of furrounding
bodies, though the cuticle is interpofed between thefe bodies and the
medulla of the nerve.

As the nerves of the fenfes have each their appropriated objefls,
which ftimulate them into aftivity; fo the mufcular fibres, which
are the terminations of other fets of nerves, have their peculiar ob-

jefts,

Sect. XI. r. SENSORIAL ACTIONS. 55

je£ls, which excite them into a6lion ; the longitudinal mufcles are
ftimulated into contraftioa by extenfion, whence the ftretching or
pandiculation after a long continued pofture, during which they have
been kept in a Hate of extenfion ; and the hollow mufcles are excited
into a<5i:ion by diftention, as thofe of the re£lum and bladder are In-
duced to protrude their contents from their fenfe of the dlflention
rather than of the acrimony of thofe contents.

There are other objedls adapted to ftimulate the nerves, which
terminate in variety of membranes, and thofe efpecially which form
the terminations of canals ; thus the preparations of mercury particu-
larly afFe£l the falivary glands, ipecacuhana afFefts the fphindler of
the anus, cantharides that of the bladder, and laftly every gland of
the body appears to be indued with a kind of tafte, by which it fe-
lefts or forms each its peculiar fluid from the blood ; and by which
it is irritated into aftivity.

Many of thefe external properties of bodies, which Simulate our
organs of fenfe, do not feem to efFedl this by a fingle impulfe, but
by repeated impulfes ; as the nerve of the ear is probably not excit-
able by a fingle vibration of air, nor the optic nerve by a fingle par-
ticle of light ; which circumftance produces fome analogy between
thofe two fenfes, at the fame time the folidity of bodies is perceived
by a fingle application of a folid body to the nerves of touch, and
that even through the cuticle ; and we are probably pofleiled of a pe-
culiar fenfe to diftinguifh the nice degrees of heat and cold.

The fenfes of touch and of hearing acquaint us with the mechani-
cal impaft and vibration of bodies, thofe of fmell and tafte feem to
acquaint us with fome of their chemical properties, while the fenfe
of vifion and of heat acquaint us with the exiftence of their peculiar
fluids.

Senfatiim

56 SENSORIAL ACTIONS. Sect.XI. 2,

Senfation and Folition.

II. Many motions are produced by pleafure or 'pain, and that even
in contradiftion to the power of volition, as in laughing, or in the
ftrangury; but as no name has been given to pleafure or pain, at the
time it is exerted fo as to caufe fibrous motions, vs^e have ufed the
term fenfation for this purpofe ; and mean it to bear the fame analogy
to pleafure and pain, that the word volition does to defire and
averfion.

I. It was mentioned in the fifth Sedion, that what we have
termed fenfation is a motion of the central parts, or of the whole
fenforium, beginning at fome of the extremities of it. This appears '
firft, becaufe our pains and pleafures are always caufed by our ideas
or mufcular motions, which are the motions of the extremities of the
fenforium. And, fecondly, becaufe the fenfation of pleafure or pain
frequently continues fome time after the ideas or mufcular motions
which excited it have ceafed : for we often feel a glow of pleafure
from an agreeable reverie, for many minutes after the ideas, that were
the fubjed of it, have efcaped our memory ; and frequently experi-
ence a dejedion of fpirits without being able to affign the caufe of it
but by much recolle£lion.

When the fenforial faculty of defire or averfion is exerted fo as to
caufe fibrous motions, it is termed volition ; which is faid in Sedl. V»
to be a motion of the central parts, or of the whole fenforium,
terminating in fome of the extremities of it. This appears, firfl,
becaufe our defires and averfions always terminate in recolleding and
comparing our ideas, or in exerting our mufcles ; which are the mo-
tions of tl)e extremities of the fenforium. And, fecondly, becaufe
defire or averfion begins, and frequently continues for a time in the
central parts of the fenforium, before it is peculiarly exerted at the

• - ' • extremities

'[ '♦

Sect. XI. 2. SENSORIAL ACTIONS. ^f

extremities of it : for we fometimes feel defire or averfiou without
immediately knowing their obje£ls, and in confequence without im-
mediately exerting any of our mufcular or fenfual motions to attain
them : as in the beginning of the pailion of love, and perhaps of hun-
ger, or in the ennui of indolent people.

Though fenfation and volition begin or terminate at the extremities
or central parts of the fenforium, yet the whole of it is frequently in-
fluenced by the exertion of thefe faculties, as appears from their ef-
feds on the external habit : for the whole Ikin is reddened by fhame,
and an univerfal trembling is produced by fear : and every mufcle of
the body is agitated in angry people by the defire of revenge.

There is another very curious circumftance, which fhews that fen-
fation and volition are movements of the fenforium in contrary di-
redlions ; that is, that volition begins at the central parts of it, and
proceeds to the extremities ; and that fenfation begins at the extre-
mities, and proceeds to the central parts : I mean that thefe two fen-
forial faculties cannot be ftrongly exerted at the fame time ; for when
we exert our volition ftrongly, we do not attend to pleafure or pain ;
and converfely, when we are ftrongly affe£led with the fenfation of
pleafure or pain, we ufe no volition. As will be further explained in
Section XVIII. on fleep, and Sedion XXXIV. on volition.

jz. All our emotions and paffions feem to arife out of the exertions
of thefe two faculties of the animal fenforium. Pride, hope, joy, are
the names of particular pleafures : fhame, defpair, forrow, are the
names of peculiar pains : and love, ambition, avarice, of particular
defires : hatred, difgufl, fear, anxiety, of particular averfions.
Whilfl: the paffion of anger includes the pain from a recent injury,
and the averfion to the adverfary that occafioned it. And compaflion
is the pain we experience at the fight of mifery, and the defire of re-
lieving it.

There is another tribe of defires, which are commonly termed ap-
petites, and are the immediate confequences of the abfence of fonae

I irritative

jS SENSORIAL ACTIONS. Sect.XI. 2-

irritative motions. Thofe, whicli arife from defeft of internal irrita-
tions, have proper names conferred upon them, as hunger, thirft,
luft, and the defire of air, when our refpiration is impaired by noxi-
ous vapours; and of warmth, when we are expofed to too great a
degree of cold. But thofe, whofe ftimuli are external to the body,
are named from the ob]e(5ls, which are by nature conftituted to ex-
cite them ; thefe defires originate from our pafl: experience of the
pleafurable fenfations they occafion, as the fmellof an hyacinth, 'or the
tafte of a pine-apple.

Whence it appears, that our pleafures and pains are at leaft as vari-
ous and as numerous as our irritations; and that our defires and aver-
fions muft be as numerous as our pleafures and pains. And that as
fenfation is here ufed as a general term for our numerous pleafures and
pains, when they produce the contradions of our fibres ; fo voUtioa
is the general name for our defires and averfions, when they produce-
fibrous contractions. Thus when a motion of the central parts, or of
. the whole fenforium, terminates in the exertion of our mufcles, it is
generally called voluntary adlion ; when it terminates in the exertion
of our ideas, it is termed recolledion, reafoning, determining.

3. As the fenfations of pleafure and pain are originally introduced by
the irritations of external objects : fo our defires and averfions are ori-
. ginally introduced by thofe fenfations; for when the objeCls of our
pleafures or pains are at a diftance, and we cannot inftantaneoufly
poffefs the one, or avoid the other, then defire or averfion is pro-
duced, and a voluntary exertion of our ideas or mufcles fucceeds.

The pain of hunger excites you to lookout for food, the tree, that
Ihades you, prefents its odoriferous fruit before your eyes,, you ap;-
proach, pluck, and eat.

The various movements of walking to the tree, gathering the
fruit, and mafticating it, are aflbciated motions introduced by their
connexion with fenfation ; but if from the uncommon height of the
trce> the fruit be inacceffible, and you ai'e^ prevented from quickly

poffeffing

Sect.XI. 2. SENSORIAL ACTIONS. 59

poffeffing the intended pleafure, defire is produced. The confequence
of this defire is, firft, a deliberation about the means to gain the ob-
je(5t of pleafure in procefs of time, as it cannot be procured immedi-
ately ; and, fecondlj, the mufcular aftion neceflary for this purpofe.

You voluntarily call up all your ideas of caufation,^that are related
to the effect you defire, and voluntarily examine and compare them,
and at length determine vi'hether to afcend the tree, or to gather
flones from the neighbouring brook, is eafier to pradife, or more
promifing of fuccefs ; and, finally, you gather the llones, and re-
peatedly fling them to diflodge the fruit.

Hence then we gain a criterion to diftinguifli voluntary afts or
thoughts from thofe caufed by fenfation. As the former are always
employed about the means to acquire pleafurable objects, or the means
to avoid painful ones ;' while the latter are employed in the polTeffion
of thofe, which are already in our power.

Hence the activity of this power of volition produces the great dif-
ference between the human and the brute creation. The ideas and
the actions of brutes are almoft perpetually employed about their pre-
fent pleafures, or their prefent pains j and, except in the few inflances
which arc mentioned in Section XVI. on inftinft, they feldom bufy
themfelves about the means of procuring future blifs, or of avoiding
future mifery ; fo that the acquiring of languages, the. making of
tools, and labouring for money, which are all only the means to pro-
cure pleafures ; and the praying to the Deity, as another means to
procure happinefs, are chara£teriftic of human nature.

4. As there are many difeafes produced by the quantity of the fen-
fation of pain or pleafure being too great or too little ; (o are there
difeafes produced by the fufceptibility of the conftitution to motions
caufable by thefe fenfations being too dull or too vivid. This fufcepti-
bilityof the fyftem to fenfitive motions is termed fenfibllity, todif-.
tinguifli it from fenfation, which is the a<5tual exiftence or exertion of

pain or pleafure.

I 2 Other

^o SENSORIAL ACTIONS. Sect. XI. 3.

Other clafles of difeafes are owing to the exceffive promptitude, or
fluggifhnefs of the conftitution to voluntary exertions, as well as to
the quantity of defire or of aversion. This fufceptibility of the
fyftem to voluntary motions is termed voluntarity, to diftinguiih it
from volition, which is the exertion of defire or averfion : thefe difeafes
will be treated of at length in the progrefs of the work.

j^JJ'ociation.

III. I. It is not eafy to affign a caufe, why thofe animal move-
ments; that have once occurred in fucceffion, or in combination,
fhould afterwards have a tendency to fucceed or accompany each other.
It is a property of animation, and diftinguiflies this order of being
from the other produftions of nature.

When a child firft wrote the word man, it was diftingiuiflied in his
mind into three letters, and thofe letters into many parts of letters j
but by repeated ufe the word man becomes to his hand in writing it,
as to his organs of fpeech in pronouncing it, but one movement
without any deliberation, or fenfation, or irritation, interpofed be-
tween the parts of it. And as many feparate motions of our mufcles
thus become united, and form, as it were, one motion ; fo each fe-
parate motion before fuch union may be conceived to confift of many
parts or fpaces moved through ; and perhaps even the individual fibres
of our mufcles have thus gradually been brought to adt in concert,
which habits began to be acquired as early as the very formation of
the moving organs, long before the nativity of the animal ; as ex-
plained in the Section XVI. 2. on inftinft.

2. There are many motions of the body, belonging to the irritative
cfafs, which might by a hafty obferver be miftaken for affociate^
ones ; as the periftaltic motion of the ftomach and inteftines, and the
contractions of the heart and 'arteries', might be fuppofcd to be afloci-

ated

&ECT.XI. 3- SENSORIAL ACTIONS. 6t

ated with the irritative motions of their nerves of fenfe, rather than
to be excited by the irritation of their mufcular fibres by the dlften-
tion, acrimony, or momentum of the blood. So the diftention or
elongation of mufcles by obje£ls external to them irritates them into
contradtion, though the cuticle or other parts may intervene betvi^eea
the Simulating body and the contradling mufcle. Thus a horfe voids
his excrement when its weight or bulk Irritates the recftum or fphinfter
ani. The motion of thefe mufcles a£l from the irritation of diften-
tion, when he excludes his excrement, but the mufcles of the abdo-
men and diaphragm are brought into motion by aflbciation with thofe
of the fphinder and redum.

SECT.

2(6. OF. STIMULUS AND EXERTION. Sect. XIL

SECT. XII.

OF STIMULUS, SENSORIAL EXERTION, AND FIBROUS
CONTRACTION.

I, Of fibrous contraftion. i. two particles of a fibre cannot approach without
the intervention of Jomething, as in ma^etijm, ekilricity, elaflicity. Spirit of
life is not eleStric ether. Galvani's experiments. 2. ContraSlion of a fibre.
3. Relaxation fucceeds. 4. SucceJJive contraSiions, with intervals, ^mk
pulfe from debility y from paucity of blood. Weak contr anions performed in lefs
time, and with porter intervals. 5. haft: fituation of the fibres continues
after contraction. 6. ContraSlion greater than ufual induces pleafure or pain.
7. Mobility of the fibres uniform. ^antity of fenforial power fluctuates.
Conftitutes excitability. II. Of fenforial exertion, i. Animal motion includes
fiimulus, fenforial power, and contraSiile fibres. "The fenforial faculties ail
Jeparately or conjointly. Stimulus of four kinds. Strength and weaknefs defined.
Senforial power perpetually exhaufted and renewed. Weaknefs from defeSl of
fiimulus. From defeSl of fenforial power, the direSl and indireSl debility of
'Dr. Brown. Why we become warm in Buxton bath after a time, and fee
well after a time in a darkifh room. Fibres may aEl violently, or with their
whole force, and yet feebly. Great exertion in inflammation explained. Great
mufcular force of fome injane people. 2. Otcafional accumulation of fenforial
power in mufcles fubjeSi to conftant fiimulus. In animals fieeping in winter-.
In eggs, feeds, f chirr ous tumours, tendons, hones. 3. Great exertion intro-
duces pleafure or pain. Inflammation. Libration of the fyftem between torpor
and activity. Fever fits. 4. Defire and averfion introduced. Excefs of vo-
lition cures fevers. III. Of repeated llimulus. i. yi fiimulus repeated too
frequejitly lofes effeCl. As opium, wine, grief Hence old age. Opium and
aloes in fmall dofes, 2. A fiimulus not repeated too frequently dies not loje

* . . \ tffeSt,

SscT.Xri. OF STIMULUS AND EXERTION. 63

effe5t. Perpetual movement of the vital organs. 3. A ftimulus repeated at
uniform tirries produces greater effsil. Irritation combined with ajfociation.
4. A ftimulus repeated frequently and uniformly may be withdrawn^ and the'
aSfion of the organ will continue. Hence the bark cures agues, and ftrengthens
weak conftitutions. 5. DefeSl of ftimidus repeated at certain intervals catfes
fever-fits. 6. Stimulus long applied ceafes to aSt a fecond time. '], If a fti-
mulus excites fenfation in an organ not ufually excited into fenfation, inflam-
mation is produced. IV. Of ftimulus greater than natural, i. A ftimulus
greater than natural dinnnifhes the quantity- of fenforial power in general. 2. In
particular organs. 3. Induces the organ into fpafmodic aSlions- 4, Induces
the antagonift fihres into. aEiion, 5, Induces the organ into convulfive' or fixed
fpqfms. 6. Produces paralyfis of the organ. V. Of ftimulus left than^ na--
turaL I. Stimulus lefs than natural oecafions accumulation of fenforial power'
in general. 2. In particular organs, fluflnng of the face in a frofty morning^.
In fibres fubjeSl to perpetual ftimulus only, ^antity of fenforial power in-
verfely as the ftimulus. 3. Induces pain. As of cold, hunger, head-ach.
4. Induces more feeble and frequent contraSlion. As in low fevers. Which
are frequently owing to deficiency of fenforial power rather than to deficiency
of ftimulus. 5. Inverts fucceffive trains of motion. Inverts ideas. 6. In-
duces paralyfis and d!eath. VI. Cure of increafed exertion. 1. Natural cure
of exhauftion of fenforial power, 1. Decreafe the irritations. VenefeSlion^
Cold. Abftinence. 3. Prevent the previous cold fit. Opium. Bark..
Warmth. Anger. Surprife.. 4. Excite fame- other part of the fyftem..
Opium and warm bath relieve pains both from defeSl and from excefs of fti-
mulus. 5.. Firft increafe the ftimulus above, and then decreafe it beneath
the natural quantity.. VII. Cure of decreafed exertion, i. Natural cure,
by accumulation of fenforial power. Ague-fits. Syncope.. 2.. Increafe the
ftitnulation, by wine, opium, given fo as not to ifjtoxicaie. Cheerful ideas.
3. Change the kinds of ftimuliis. 4. Stimulate the affociated organs, Blifters
of ufe in heart-burn,, and cold extremities, 5. Decreafe the ftimulation for
a time, cold bath. 6. Decreafe the ftimulation below natural, and then in-
creafe it above natural. Bark after emetics. Opium after veneJeSfion,
Pra£fi(e of Sydenham, in cMorofis. 7. Prevent iinneceffary ■ expenditure of

fenJoriaU

€4 OF STIMULUS AND E;XERTI0N. Sect. XII. r.

Jenforial foiva: Becumhent fojiure, Jilemet darknejs. Fulfe quickened hy
rifing out cf led. 8. 'To the great eft degree of quiejcence apply the leaft
Jiimulus. Otherwije faralyfis or inflammation cf the organ enfues. Gin,
wine, hlifterSy deftroy by too great ftimulation in fevers with debility. In-
toxication in the flighteft degree fucceeded by debility. Golden rule for de-
termining the beft degree of ftinmlus in low fevers. Another golden rule for
determining the quantity of ffirit which thofe, who are debilitated by drinking it,
ptayfafely omit.

I. Of fibrous contraB'ton.

I. IF two particles of Iron lie near each other without motion,
and afterwards approach each other ; it is reafonable to conclude that
fomething befides the iron particles is the caufe of tHeir approxima-
tion ; this invifible fomething is termed magnetifm. In the fame
manner, if the particles, which compofe an animal mufcle, do not
touch each other in the relaxed ftate of the mufcle, and are brought
into contact during the contraction of the mufcle ; it is reafonable to
conclude, that fome other agent is the caufe of this new approxima-
tion. For nothing can ad:, where it does not exift ; for to aft in-
cludes to exift ; and therefore the particles of the mufeular fibre
(which in its ftate of relaxation are fuppofed not to touch) cannot af-
fe£l each other without the influence of fome intermediate agent;
this agent is here termed the fpirit of animation, or fenforial power,
but may with equal propriety be termed the power, which caufes
contradtion j or may be called by any other name, which the reader
may choofe to affix to it.

The contradion of a mufeular fibre may be compared to the follow-
ing electric experiment, which is here mentioned not as a philofophi-
cal analogy, but as an illuftration or fimile to facilitate the conception
of a difficult fubjed. Let twenty very fmall Leyden phials properly

4. coated-

SEOT.Xrr. I. OF STIMULUS AND EXERTION. 65

coated be hung in a row by fine filk. threads at a fmali diftance from
each other ; let the internal charge of one phial be pofitive, and of the
other negative alternately, if a communication be made from the in-
•ternal furface of the firft to the external furface of the laft in the row,
they will all of them imuintly approach each other, and thus fhorteii
a line that might connect them like a mufcular fibre. See Botanic
Garden, p. i. Canto I. 1. 202, note on Gymnotus.

The attradions of eledlricity or of magnetifm do not apply philo-
rophically to the illuftration of the contraftion of animal fibres, fince
the force of thofe attra£tions increafes in fome proportion inversely as
the diftance, but in mulcular motion there appears no difference in
velocity or ftrength during the beginning or end of the contraftion,
but what may be clearly afcribed to the varying mechanic advancao^e
in the approximation of one bone to another. Nor can mufcular mo-
tion be aflimilated with greater plaufibility to the attra'«3;ion of cohefion
or elafticity; for in bending a fteel fpring, as a fmall fword, a lefs
force is reqpired to bend it the firft inch than the fecond ; and the
fecond than the third ; the particles of fteel on the convex fide of the
bent fpring endeavouring to reftore themfelves more powerfully tlic
further they are drawn from each other. See Botanic Garden, P. r.
addit. Note XVIII.

I am aware that this may be explained another way, by fuppofino-
the elafticity of the fpring to depend more on the compreffion of the
particles on the concave fide than on the extenfion of them on the con-
vex fide ; and by fuppofing the elafticity of the elaftic gum to depend
more on the refiftance to the lateral comprefilion of its particles than
to the longitudinal extenfion of them. Neverthelefs in mufcular
contraiftion, as above obferved, there appears no difference in the ve-
locity or force of it at its commencement or at its termination ; from
whence we muft coAclude that animal contraction is governed by
laws of its own, and not by thofe of mechanics, chemiftry, magne-
tifm, or elcdricity.

1$: On

66 OF STIMULUS AND EXERTION. Sect. XII. i.

On thefe accounts I do not think the experiments conclufive,
which were lately publifhed by Galvani, Volta, and others, to {hew
a fimilitude between the fpirit of animation, which contrails the
mufcular fibres, and the electric fluid. Since the elcdric fluid may
adt only as a more potent ftimulus exciting the mufcular fibres into
aflion, and not by fupplying them with a new quantity of the fpirit
of life. Thus in a recent hemiplegia I have frequently obferved,
when the patient yawned and (Iretched himfelf, that the paralytic
limbs moved alfo, though they were totally difobedient to the will.
And when he was el"e(3:rified by paffing (hocks from the affefted hand
to the afFedted foot, a motion of the paralytic limbs was alfo produced.
Now as in the aft of yawning the mufclesof the paralytic limbs were
excited into aftion by the ftimulus of the irkfomenefs of a continued
pofture, and not by any additional quantity of the fpirit of life ; fo
we may conclude, that the paflage of the eledlric fluid, which pro-
duced a fimilar efFedl, afted only as a ftimulus, and not by fupplying
any addition of fenforial power.

If neverthelefs this theory fhould ever become eflablifhed, a ftimu-
lus mufl: be called an eduftor of vital ether; which ftimulus may
confift of fenfation or volition, as in the eledlric eel, as well as in the
appulfes of external bodies ; and by drawing off the charges of vital
fluid may occafion the contradion or motions of the mufcular fibres,
and organs of fenfe.

2. The immediate effe£l of the aflion of the fpirit of animation or
fenforial power on the fibrous parts of the body, whether it acts in
the mode of irritation, fenfation, volition, or aflbciation, is a con-
tra£tion of the animal fibre, according to the fecond law of animal
caufation. Se£t. IV. Thus the ftimulus of the blood induces the
contradion of the heart ; the agreeable tafte of a ftrawberry produces
the contraftion of the mufcles of deglutition ; the effort of the will
contracts the mufcles, which move the limbs in walking ; and by
aflbciation other mufcles of the trunk are brought into contraftion to

preferve

Sect. XII. i. OF STIMULUS AND EXERTION.

preferve the balance of the body. The fibrous extremities of the or-
gans of fenfe have been (hewn, by the ocular Tpedra in Seft. III. to
luffer fimilar contradion by each of the above modes of excitation ;
and by their configurations to conftitute our ideas.

3. After animal fibres have for fome time been excited into contrac-
tion, a relaxation fucceeds, even though the exciting caufe continues
to aft. In refpeiSt to the irritative motions this is exemplified in the
periftaltic contraftions of the bowels ; which ceafe and are renewed
alternately, though the ftimulus of the aliment continues to be uni-
formly applied ; in the fenfitive motions, as in flrangury, tenefmus,
and parturition, the alternate contradlions and relaxations of the muf-
cles exift, though the ftimulus is perpetual. In our voluntary ex-
ertions it is experienced, as no one can hang long by the hands, how-
ever vehemently he wills fo to do ; and in the aflbciate motions the
conftant change of our attitudes evinces the neceffity of relaxation to
thofe mufcles, which have been long in adion.

This relaxation of a mufcle after its contraftion, even though the
ftimulus continues to be applied, appears to arife from the expenditure
or diminution of the fpirit of animation previoufly refident in the muC-
cle, according to the fecond law of animal caufation in Seft. IV.
In thofe conftitutions, which are termed weak, the fpirit of anima-
tion becomes fooner exhaufted, and tremulous motions are produced,
as in the hands of infirm people, when they lift a cup to their mouths.
This quicker exhauflion of the fpirit of animation is probably owing
to a lefs quantity of it refiding in the ading fibres, which therefore
more frequently require a fupply from the nerves, which belong to
them.

4. If the fenforial power continues to aft, whether it ads in the
mode of irritation, fenfation, Volition, or afTociation, a new con-
traAion of the animal fibre fucceeds after a certain interval; which
in*:erval is of (horter continuance in weak people than in ftrong ones.
This is exemplified in the ftiaking of the hands of weak people, when

K 2 they

6,g OF STIMULUS AND EXERTION. Sect. XII. i,

they attempt to write. In a manufcript epiftle of one of my cor-
refpondents, which is written in a fmall hand, I obferved from four
to fix zigzags in the perpendicular ftroke of every letter, which
fhews that both the contraftions of the fingers, and intervals be-
tween them, muft have been performed in very (hort periods of
time.

The times of contraction of the mufcles of enfeebled people being
lefs, and the intervals between thofe contraftions being lefs alfo, ac-
counts for the quick pulfe in fevers with debility, and in dying ani-
mals. The fhortnefs of the intervals between one contraftion and
another in weak conftitutions, is probably owing to the general defi-
ciency of the quantity of the fptrft of animation, and that therefore
there is a lefs quantity of it to be received at each interval of the ac-
tivity of the fibres. Hence in repeated motions, as of the fingers in
performing on the harpfichord, it would at firft fight appear, that
fwiftnefs and ftrength were incompatible ; neverthelefs the fingle
contradion of a mufcle is performed with greater velocity as well as
with greater force by vigorous conftitutions, as in throwing a
javelin.

There is however another circumftance, which may often contri-
/|wte to caufe the quicknefs of the pulfe in nervous fevers, as in ani-
mals bleeding to death in the flaughter-houfc ; which is the deficient
quantity of blood ; whence the heart is but half diftended, and in con-
fequence fooner eontrads. See Seft. XXXII. 2. i.

Fl^we, muft not confound frequency of repetition with quicknefs
of motion, or the number of pulfations with the velocity, with which
the fibres, which conftitute the coats of the arteries, contraft them-
felves. For where the frequency of the pulfations is but feventy-five
in a minute, as in health ; the contrafting fibres, which conftitute the
fides of the arteries, may move through a greater fpace in a given
time, than where the frequency of pulfation is one hundred and fifty
in a minut«if as in fome fevers with great debility. For if in thofe

fevers

Sect. XII. i. OF STIMULUS AND EXERTION. 69

fevers the arteries do not expand themfelves in their diaftole to more
than half the ufual diameter of their diaftole in health, the fibres
which conftitute their coats, will move through a lefs fpace in a mi-
nute than in health, though they make two pulfations for one.

Suppofe the diameter of the artery during its fyftole to be one line,
and that the diameter of the fame artery during its diaftole is in health
is four lines, and in a fever with great debility only two lines. It fol-
lows, that the arterial fibres contraft iu health from a circle of twelve
lines in circumference to a circle of three lines in circumference, that
is they move through a fpnce of nine lines in length. While the ar-
terial fibres in the fever with debility would twice contradi from a
circle of fix lines to a circle oi three lines ; that is while they move
through a fpace equal to fix lines. Hence though the frequency of
pulfation in fever be greater as two to one, yet the Velocity of con-
tradlion in health is greater as nine to fix, or as three to two.

On the contrary in inflammatory difeafes with ftrength, as in the
pleurify, the velocity of the contradling fides of the arteries is much
greater than in health, for if we fuppofe the number of pulfations in
a pleurify to be half as much more than in health, that is as one hun-
dred and twenty to eighty, (which is about what generally happens
in inflammatory difeafes) and if the diameter of the artery in diaftole
be one third greater than in health, which I believe is near the truth,
the refult will be, that the velocity of the contraftile fides of the ar-
teries will be in a pleurify as two and a half to one, compared to the
velocity of their contraction in a ftate of health, for if the circum-
ference of the fyftole of the artery be three lines, v and the diaftole in
health be twelve lines in circumference, and in a pleurify eighteen
lines; and fecond:^s if the artery pulfates thrice in the difeafed ftato-
for twice in the healthy one,, k foUovvs, that the velocity of contrac-
tion in the difeafed ftate to that in the healthy ftate will be forty-five
to eighteen, or as two and a half to one,

4 Fronv

70 OF STIMULUS AND EXERTION. Sect. XII. i.

From hence it would appear, that if we had a criterion to deter-
mine the velocity of the arterial contraftions, it would at the fame
time give us their ftrength, and thus be of more fervice in diftinguifK.-
ing difeafes, than the knowledge of their fiequencj. As fuch a cri-
terion cannot be had, the frequency of pulfation, the age of the pa-
tient being allowed for, will in fome meafure aflift us to diftinguifli
arterial flrength from arterial debility, lince in inflammatory difeafes
with ftrength the frequency feidom exceeds one hundred and eighteen
or one hundred and twenty pulfations in a minute; unlefs under pe-
culiar circumftance, as the great additional ftimuli of wine or of ex-
ternal heat.

5. After a mufcle or organ of fenfe has been excited into contrac-
tion, and the fenlbrial power ceafes to ad, the laft fituation or con-
figuration of it continues ; unlefs it be difturbed by the a£lion of fome
antagonift fibres, or other extraneous power. Thus in weak or lan-
guid people, wherever they throw their limbs on their bed or fofa,
there they lie, till another exertion changes their attitude ; hence one
kind of ocular fpeftra feems to be produced after looking at bright
objects ; thus when a fire-ftick is whirled round in the night, there
appears in the eye a complete circle of fire ; the aflion or configuration
wf one part of the retina not ceafing before the return of the whirling
fij*e.

Thus If any one looks at the fetting fun for a (hort time, and then
covers his clofed eyes with his hand, he will for many feconds of time
perceive the image of the fun on his retina. A fimilar image of all
other bodies would remain fome time in the eye, but is effaced by the
eternal change of the motions of the extremity of this nerve in our
attention to other objeds. See Se6l. XVII. 1.3. on Sleep. Hence
the dark fpots, and other ocular fpedra, are more frequently attended
t«, and remain longer in the eyes of weak people, as after violent ex-
ercife, intoxication, or want of fleep*

6. A

Sect. XII. i. OF STIMULUS AND EXERTION. jt

6. A contraftion of the fibres fomewhat greater than ufual intro-
duces pleafurable fenfation into the fyftem, according to the fourtb
law of animal caulation. Hence the pleafure in the beginning of
drunkennefs is owing to the increafed aftion of the fyftem from the
ftimulus of vinous fpirit or of opium. If the contradlions be ftill
greater in energy or duration, painful fcnfations are introduced, as in
confequence of great heat, or cauftic applications, or fatigue.

If any part of the fyftem, which is ufed to perpetual aftivity, a»
the ftomach, or heart, or the fine veffels of the Ikin, a6ls for a time
with lefs energy, another kind of painful fenfation enfues, which is
called hunger, or faintnefs, or cold. This occurs in a lefs degree in
the locomotive mufcles, and is called wearyfomenefs. In the two-
former kinds of fenfation there is an expenditure of fenforial p ower^
in thefe latter there is an accumulation of it.

7. We have ufed the words exertion of fenforial power as- a general
term to exprefs either irritation, fenfation, volition, or affociation ;.
that is, to expreli the adlivity or motion of the fpirit of animation, at
the time it produces the contractions of the fibrous parts of the fyftem.
It may be fuppofed that there may exift a greater or lefs mobility of
the fibrous parts of our fyftem, or a propenfity to be ftimulated inta
contraiflion by the greater or lefs quantity or energy of the fpirit of
animation ; and that hence if the exertion of the fenforial power be in
its natural ftate, and the mobility of the fibres be increafed, the fame
quantity of fibrous contraftion \v\\\ be caufed, as if the mobility of
the fibres continues in its natural ftate^ aad the fenforial exertioa be
increafed.

Thus it may be conceived, tlvat in difeafes accompanied with,
ftrength, as in inflammatory fevers with arterial ftrength, that the
caufe of greater fibrous contraction may exift in. the increafed mobi-
lity of the fibres, whofe contractions are thence both, more forceable,
and more frequent. And that in difeafes attended with debility,, as
ilii nervous fevers, where the fibrous contractions are weaker, and.
J^rr more

78 OF STIMULUS AND EXERTION. Se€T.XII. i.

more frequent, it may be conceived that the caufe confifts in a de-
creafe of mobility of the fibres ; and that thofe weak conftitutions,
"which are attended with cold extremities and large pupils of the eyes,
may poflefs lels mobility of the contradtile fibres, as well as lefs quan^-
tity of exertion of the fpirit of animation.

In anfwer to this mode of reafoning it may be fnfficicnt to obferve,
that the contractile fibres confifl: of inert matter, and when the lea-
lorial power is withdrawn, as in death, they poflefs no power of mo-
tion at all, but remain in their laft ftate, whether of contraction or
relaxation, aiid muft thence derive the whole of this property from
the fpirit of ai^lmation. At the fame time it is not improbable, that
the moving fibrps of ftrong people may poflefs a capability of receiving
or containing aigreater quantity of the fpirit of animation than thofe
of weak people.? * "

In every coulSi'action of a fibre there is an expenditure of the fenfo-
rial power, or fpirit of animation ; and where the exertion of this
fenforial power has been for fome time increafed, and the mufcles or
organs of i'cnfe have in confequence a£ted with greater energy, its
propenfity to activity is proportionally lefiencd ; which is to be afcrib-
ed to the exhauftion or diminution of its quantity. On the contrary,
where there has been lefs fibrous contraction than ufual for a certain
time, the fenforial power or fpirit of animation becomes accumulated
in the inadtive part of the fyfliem. Hence vigour fucceeds refl:, and
hence the propenfity to aftion of all our organs of fenfe and mufcles
is in a fl:ate of perpetual fluctuation. The irritability for infl:ance of
the retina, that is, its quantity of fenforial power, varies every mo-
ment according to the brightnefs or obfcurlty of the objeCt laft beheld
compared with the prefent one. Th^ fame occurs to our fenfe of
heat, and to every part of our fyftem, which is capable of being ex-
cited into action.

When this variation of the exertion of the fenforial power becomes
much and permanently above or beneath the natural quantity, it be-

comefiF

Sect. XII. 2. OF STIMULUS AND EXERTION. 73'

comes a difeafe. If the irritative motions be too great or toolittle,
it {hews that the ftimulus of external things afFecl this fenforlal power
'■too violently or too inertly. If the fenfitive motions be too great or
too little, the caufe arifes from the deficient or exuberant quantity of
ienfation produced in confequence of the motions of the mufcular
fibres or organs of fenfe ; if the voluntary a£lions are difeafed the
caufe is to be looked for in the quantity of volition produced in con-
fequence of the deiire or averfion occaiioned by the painful or plea-
iurable fenfations above mentioned. And the difeafes of affociations
probably depend on the greater or lefs quantity of the other three fen-
forial powers by which they were formed.

From whence it appears that the propenfity to action, whether it
-be called irritability, fenfibility, voluntarily, or affociability., is only
another mode of expreffion for the quantity of fenforial power rcliding
in the organ to be excited. And that on the contrary the words in-
irritability and infenfibility, together with inaptitude to voluntary
and affociate motions, are fynonymous with deficiency of the quantity
of fenforial power, or of the fpirit of animation, refiding in the organs
io be excited,

II. Of fenforial 'Exirtian. . -

I. There are three circumflances to be attended to in the produc-
tion of animal motions. ifL The ftimulus. 2d. The fenforial power.
3d. The contractile fibre. ift. A ftimulus, external to the organ,
originally induces into a6lion the fenforial faculty termed irritation ;
this produces the contradlion of the fibres, which, if it be perceived at
all, introduces pleafure or pain ; w^hlch in their aftive ftate are termed
fenfation ; which is another fenforial faculty, and occafionally pro-
duces contra6lion of the fibres ; this pleafure or pain is therefore to be
confidered as another ftimulus, which may either aft alone or in con-
junftion with the former faculty of the fenforium termed irritation.

■ L This

74 OF STIMULUS AND EXERTION. Sect.XIL 3,

This new ftimulus of pleafure or pain either induces into aclion the
fenforial faculty termed fenfation, which then produces the contrac-
tion of the fibres ; or it introduces defire or averiion, which excite
into adion another fenforial faculty, termed volition, and may there-
fore be confidered as another ftimulus, which either alone or in con-
junction with one or both of the two former faculties of the fenforium
produces the contraction of animal fibres. There is another fenforial
power, that of aflbciation, which perpetually, in conjunction with
one or more of the above, and frequently fmgly, produces the con-
traction of animal fibres, and which is itfelf excited into aClion by the
previous motions of contracting fibres.

Now as the fenforial power, termed irritation, refiding in any par-
ticular fibres, is excited into exertion by the ftimulus of external
bodies aCling on thofe fibres; the fenforial power, termed fenfation,
refiding in any particiilar fibres is excited into exertion by the ftimulus
of pleafure or pain aCting on thofe fibres j the fenforial power, termed
volition, refiding in any particular fibres is excited into exertion by
the ftimulus of defire or averfion ; and the fenforial power, termed
aflbciation, refiding in any particular fibres, is excited into aClion by
the ftimulus of other fibrous motions, which had frequently preceded
.them. The word ftimulus may therefore be ufed without impro-
priety of language, for any of thefe four caufes, which excite the
four fenforial powers into exertion. For though the immediate caufe
of volition has generally been termed a motive ; and that of irritation
only has generally obtained the name oi Jihmdus ; yet as the imme-
diate caufe, which excites the fenforial powers of fenfation, or of af-
fociation into exertion, have obtained no general name, we fliall ufe
the word ftimulus for them all.

Hence the quantity of motion produced in any particular part of
the animal fyftem will be as the quantity of ftimulus and the quantity
of fenforial power, or fpirit of animation, refiding in the contracting
fibres. Where both thefe quantities are great, flrength is produced,

when

SECT.XIL2. OF STIMULUS AND EXERTION. 75

■when that word is applied to the motions of animal bodies. Where
-either of them is deficient, wcabiefs is produced, as applied to the
motions of animal bodies.

Now as the fenforial power, or fpirit of animation, is perpetually
exhatifted by the expenditure of it in fibrous contractions, and is per-
petually renewed by the fecretiou or produflion of it in the brain and
fpinal marrow, the quantity of animal ftrengfh muft be in a perpetual
ftate of fluduation on this account ; and if to this be added the un-
ceafing variation of all the four kinds of ftimulus above defcribed,
which produce the exertions of the fenforial powers, the ceafelefs vi-
ciffitude of animal ftrength becomes eafily comprehended.

If the quantity of fenforial power remains the fame, and the quan-
tity of ftimulus be leffened, a weaknefs of the fibrous contratStions
enfues, which may be denominated debility from defed'ofjlimulus. If
the quantity of ftimulus remains the fame, and the quantity of fen-
forial power be leffened, another kind of weaknefs enfues, which may
be termed debility frotn deje& of fenforial power ; the former of thefe
is called by Dr. Brown, in his Elements of Medicine, diredt debility,
and the latter indireft debility. The coincidence of fome parts of
this work with correfpondent dedudlions in the Brunonian Elementa
Medicina, a work (with fome exceptions) of great genius, mufl: be
confidered as confirmations of the truth of the theory, as they were
probably arrived at by different trains of reafoning.

Thus in thofe who have been expofed to cold and hunger there is a
deficiency of ftimulus. While in nervous fever there is a deficiency
of fenforial power. And in habitual drunkards, in a morning before
their ufual potation, there is a deficiency both of flimulus and of fen-
forial power. While, on the other hand, in -the beginning of intoxica-
tion there is an excefs of .ftimulus; in the hot-ach, after the hands
have been immerfed in fnow, there is a redundancy of fenforial
power ; and in inflammatory difeafes with arterial ftrength, there is
.an excefs of both..

L/ -2 Hence

76 OF STIMULUS AND- EXERTION. Sect. XIL z^.

Henee if the fenforial power be leffened, while the quantity of fti-
mulus remains the fame, aa in nervous fever, the frequency of repetition
of the arterial contraftions may continue, but. their force in refpeft to.
removing obftacles, as in promoting the circulation of the blood, or the
velocity of each contraftion^ will be diminifhed, that is, the animal,
flrength. will be leffened. And fecondly, if the quantity of fenforial.'
power be leffened,, and the ftimulus be increafed. to a certain degree,
as in giving opium in nervous fevers,, the arterial contraftions may be
performed more frequently than natural,, yet. with lefs flrength..

And, thirdly, if the fenforial power continues the. fame in refpe£l to^'
quantity, and the ftimulus be. fomewhat. diminifhed,, as m, going into a,
darkilh room, or into a coldifh bath,,fuppofe of about eighty degrees of.'
heat,, as Buxton-bath, a temporary weaknefs of the., affeded .fibres is^
induced, till an accumulation of fenforial power; gradually fucceeds,.,
and. counterbalances the deficiency, of ftimulus, . and then the bath i
ceafes to feel cold, and the room ceafes to appear dark ; becaufe the..
fibres of the fubcutaneous veffels, or of the organs of fenfe, ,adl with.^
their ufual energy.

A fet of mufcular fibres may thus be. ftimulated into violent ex^
ertion, that is, they may a£l frequently, and with their whole fen--
fbrial power, but may neverthelefs not adl ftrongly ; becaufe. the,,
quantity of their fenforial power wast originally fmall,.or was previ--
oufly exhaufted. Hence a ftimulus may be great, and the irritation .
in confequence a£t with its full force, as in the hot paroxifms of."
nervous fever ; but if the fenforial power, termed irritation, be fmall-.
in quantity, the force of the fibrous contradlions, and the times of.
their continuance in their contracted ftate, will be proportionally,
fmall.

In the fame manner in the hot paroxifm of putrid fevers, which,
are fhewn in Seft. XXXIII. to be inflammatory fevers with arterial-
debility, the fenforial power termed fenfation is exerted with great:
adivity, yet the fibrous contradions, which produce the circulation ,

3 ^'^\

S'Ecr.Xir. 2; OF STIMULUS AND EXERTION^. 77-

ef the blood, are performed without ftrength, becaufe the quanrity
of fetiforial power then refiding in that part of tlie fyftern is fmall.

Thus in irritative fever with arterial itrength, that is, wich ex-
cefs of fpirit of animation, the quantity of exertion during the hod
part of the paroxifm is to be eftimated from the quantity of ftimulus,-
and the qijantity of fenforial power. While in fenfitive (or inflam--
matory). fever with arterial (Irength, that is, with excefs of fpirit of
animation, the violent and forcible aftions of the vafcular fyftem-.
during the hot part- of the paroxifm are induced by the exertions of-
two fenforial' powers,, which are excited by two kindsof ftimulus.-
Thefe are the fenforial power of irritation excited by the ftimulus of-
bodies external to the moving fibres, and the fenforial power of fen--
fation excited. by the pain in .confequence of theincreafed contractions--
of thofe moving fibres; -

And in infane people in fome cafes the force of their mufcular ac--
tions will be ia proportion to the quantity of fenforial powerj which-
they poflefs, and the quantity of the ftimulus of deli re or averfion,
■which excites their vohtioa into acflioni At the fame time in other
cafes the ftimulus of pain or pleafure, and the ftimulus of external-
bodies, may excite into action ■the fenforial powers of fenfation and'
irritation, and thus add greater force to their mufcular adions.

a;- The application of the flimuluSj whether that ftimulus be fome
quality of external* bodies, or pleafure or paia^ or defire or averfion,
or a link of alTociation, excites, the correfpondent fenforial power into
a£tion; and this caufes the contraftion of the fibre. On thecontrac-^
tion of the fibre a part of the fpirit of animation becomes expended,:-
and the fibre ceafes to contract, though the ftimulus continues to be'
applied; till in a certain time the fibre having received a fupply oF"
fenforial pov/er is ready to contract again, if the ftimulus continues'
to be applied; If the ftimulus on the contrary be v/ithdrawn, the
fame quantity of quiefcent fenforial power becomes refident in the-
fibre as before its contradion ; as appears from th-e readinefs for ac-

tiou-

78 OF STIMULUS AND EXERTION. Sbct.XII. a.

tiou of the large Ipcomotive mufcles of the body ia a fliort time after
common exertion.

But in thofe mufcular fibres:, which are fubjefi; to conflant ftimu-
ius, as the arteries, glands, and capillary veflels, another phenomenon
occurs, if their accuflomed ftimulus be withdrawn; which is, that
the. fenforial power becomes accumulated in the contradlUe fibres,
owing to the want of its being perpetually expended, or carried away,
by their ufual unremitted contraftions. And on this account thofe
mufcular fibres become afterwards excitable into their natural actions
by a much weaker ftimulus ; or into unnatural violence of adion by
'their accuftomed ftimulus, as is feen in the hot fits of intermittent
fevers, which are in confequence of the previous cold ones. Thus
jthe minute veffels of the Ikin are conftantly ftimulated by the fluid
-matter of heat ; if the quantity of this ftimulus of heat be a while
diminifhed, as in covering the hands with fnow, the veflels ceafe to
:a6l, as appears from the palenefs of the Ikin ; if this cold applicatioa
-of fnow be continued but a fhort time, the fenforial power, which
had habitually been fupplied to the fibres, becomes now accumulated
in them, owino- to the want of its being expended by their accuftomed
contraftions. And thence a lefs ftimulus of heat will now excite
them into violent contra6tions.

If the quiefcence of fibres, which had previoufly been fubje£t to
perpetual ftimulus, continues a longer time; or their accuftomed
ftimulus be more completely withdrawn ; the accumulation of fenfo-
rial power becomes ftill greater, as in thofe expofed to cold and hun-
o-er ; pain is produced, and the organ gradually dies from the chemical
chano-es, which take, place in it ; or it is at a great diftance of time
reftored to a(ftion by ftimulus applied with great caution in fmall
quantity, as happens to fome larger animals and to many infefts,
which durino- the winter months lie benumbed with cold, and are
' faid to fleep, and to perfons apparently drowned, or apparently
frozen to death. Snails have been faid to revive by throwing them
T into

Sect. XII. 2. OF STIMULUS AND EXERTION. 79

into water after having been many years fhut up in the cabinets of
the curious ; and eggs and feeds in general are reftored to life after
many months of torpor by the ftimulus of warmth and moifture.

The inflammation of fchirrous tumours, which have long exifted
in a ftate of inaftion, is a procefs of this kind ; as well as the fenfibi-
lity acquired by inflamed tendons and bones, which had at their
formation a fimilar fenfibility, which had fo lono; lain dormant in their
uninflamed ftate.

3. If after long quiefcence from defeat of ftimulus the fibres,
which had previoufly been habituated to perpetual ftimulus, are again
expofed to but their ufual quantity of it; as in thofe who have fuf-
fered the extremes of cold or hunger ; a violent exertion of the af-
fefted organ commences, owing, as above explained, to the great
accumulation of fenforial power. This violent exertion not only di-
minifhes the accumulated fpirit of animation, but at the fame time
induces pleafure or pain into the fyftem, which, whether it be fuc-
ceeded by inflammation or not, becomes an additional ftimulus, and
adling along with the former one, produces flill greater exertions ;
and thus reduces the fenforial power in the contracting fibres beneath
its natural quantity.

When the fpirit of animation is thus exhaufted by ufelefs exer-
tions, the organ becomes torpid or unexcitable into aclion, and a
fe'cond fit of quiefcence fucceeds that of abundant adlivity. During
this fecond fit of quiefcence the fenforial power becomes again accu-
mulated, and another fit of exertion follows in train. Thefe viciffi-
tudes of exertion and inertion of the arterial fyftem conflitute the
paroxifms of remittent fevers ; or intermittent ones, when there is
an interval of the natural adlion of the arteries between the exacerba-
tions.

In thefe paroxifms of fevers, which confift of the libration of the
arterial fyftem between the extremes of exertion and quiefcence, either
the fits become lefs and lefs violent from the contradile fibres be-

comine

Sd of stimulus and exertion. Sect. XII. 3,

-coming lefs excitable to the flimul us by habit, that is, by becoming
accuftomed to it, as explained below XII. 3. i. or the whole fenfo-
rial power becomes exhaufled, and the arteries ceafe to beat, and the
patient dies in the- cold part of the paroxifm. Or feeondly, fo much
pain is introduced .into the fyftem by the violent contraftions of the
fibres, -that inflammation arifes, which prevents future cold fits by
expending a part of the fenforial power in the extenfion of old veffels
or the produftion of new ones; and thus preventing the too great ac-
cumulation or exertion of it in other parts of the fyftem ; or which
by the great increafeof ftimulus excites into great aftion the whole
glandular fyftem as well as the arterial, and thence a greater quantity
of fenforial power is produced in the brain, and thus its exhauftion ia
any peculiar part -of the fyftem ceafes to be afFeded.

4. Or thirdly, in confequence of the painful or pleafurable fenfa-
tion above mentioned, defire and averfion are introduced, and inordinate
volition fucceeds ; which by its own exertions expends fo much of the
fpirit of animation, that the two other fenforial faculties, or irritation
and fenfation, ad fo much feebler ; that the paroxifms of fever, or
that libration between the extremes of exertion and inadivity of the
arterial fyftem, gradually fubfides. On this account a temporary in-
sanity is a favourable fign in fevers, as 1 have had fome opportunities
efobferving.

III. Of repeated Sihmitm,

I. When a ftimulus is repeated more frequently tlian the expendi-
ture of fenforial power can be renewed in the afting organ, the effeft
of the ftimulus becomes gradually diminifhed. Thus if two grains of
opium be fwallowed by a perfon unufed to fo ftrong a ftimulus, all
the valcular fyftems in the body ad with greater energy, all the fe-
cretions and the abforption from thofe fecreted fluids are increafed in

quantity

Sect. XII. 3- OF STIMULUS AND EXERTION. Si

quantity ; and pleafure or pain are introduced into the fyftem, which
adds an additional ftimuhis to that already too great. After fome
hours the fenforial power becomes diminifl:;ed in quantity, expended
by the great activity of the lyftem; and thence, when the ftimulus
of the opium is withdrawn, the fibres will not obey their ufual de-
gree of natural ftimulus, and a confequent torpor or quiefcence fuc-
ceeds, as is experienced by drunkards, who on the day after a great
excefs of fpirituous potation feel indigeftion, head-ach, and general
debility.

In this fit of torpor or quiefcence of a part or of the whole of the
fyftem, an accumulation of the fenforial power in the affedled fibres
is formed, and occafions a fecond paroxyfm of exertion by the applica-
tion only of the natural ftimulus, and thus a libration of the fenforial
exertion between one excefs and the other continues for two or three
days, where the ftimulus was violent in degree; and for weeks in
fome fevers, from the ftimulus of contagious matter.

But if a fecond dofe of opium be exhibited before the fibres have
regained their natural quantity of fenforial power, its effect will be
much lefs than the former, becaufe the fpirit of animation or fen-
forial power is in part exhaufted by the previous excefs of exertion.
Hence all medicines repeated too frequently gradually lofe their
effeft, as opium and wine. Many things of difagreeable tafte at firll
ceafe to be difagreeable by frequent repetition, as tobacco; grief and
pain gradually diminilh, and at length ceaie altogether, and hence
life itfelf becomes tolerable.

Befides the temporary diminution of the fpirit of animation or fen-
forial power, which is naturally ftationary or refident in every livino-
fibre, by a fingle exhibition of a powerful flimulus, the contra6lile
fibres themfelves, by the perpetual application of a new quantity of
ftimulus, before they have regained their natural quantity of fenforial
power, appear to fufFer in their capability of receiving fo much as the
natural quantity of fenforial power ; and hence a permanent defici-

M ency

82 OF STIMULUS AND EXERTION. Sect. XII. -.

ency of fpirit of animation takes place, however long the ftimulus
may have been withdrawn. On this caiife depends the permanent
debility of thofe, who have been addicfted to intoxication, the general
weaknefs of old age, and the natural debility or inirritability of thofe,
who have pale fkins and large pupils of their eyes.

There is a curious phenomenon belongs to this place, which has
always appeared difficult of folution ; and that is, that opium or aloes
may be exhibited in fmall dofes at firfl, and gradually increafed to
very large ones without producing ftupor or diarrhoea. In this cafe,
though the opium and aloes are given in fuch fmall dofes as not to
produce intoxication or catharfis, yet they are exhibited in quantities
fufficient in fome degree to exhauft the fenforial power, and hence a
ftronger and a ftronger dofe is required; otherwife the medicine
would foon ceafe to adl at all.

On the contrary, if the opium or aloes be exhibited in a large dofe
at firft, fo as to produce intoxication or diarrhoea; after a few repe-
titions the quantity of either of them may be diminilhed, and they
will ftill produce this effeft. For the more powerful flimulus dif-
fevers the progreffive catenations of animal motions, defcribed in
Se£t. XVII. and introduces a new link between them ; whence every
repetition flrengthens this new aflbciation or catenation, and the fti-
mulus may be gradually decreafed, or be nearly withdrawn, and yet
the efFe6l fhall continue ; becaufe the fenforial pov/er of aflbciation or
catenation being united with the ftimuluSy increafes in energy with
every repetition of the catenated circle ; and it is by thefe means that
all the irritative aflbciations of motions are originally produced.

2. When a ftimulus is repeated at fuch diftant intervals of time,
that the natural quantity of fenforial power becomes completely re-
llored in the ailing fibres, it v/ill ad: vi'ith the fame energy as when
firft applied. Hence thofe who have lately accuftomed themfelves to
large dofes of opium by beginning with fmall ones, and gradually in-
creafing them, and repeating them frequently, as mentioned in the

preceding

Sbct.XII.j. of stimulus AND EXCRTION. 83

preceding paragraph ; if they intermit the ufe of it for a few days
only, nnuft begin again with as fmall dofes as they took at firfl:, other-
wife they will experience the inconveniences of intoxication.

On this circumftance depend the conftant unfailing effects of the
various kinds of flimulus, which excite into adlion all the vafcular
fyftems in the body ; the arterial, venous, abforbent, and glandular
veflels, are brought into perpetual unwearied aftion by the fluids,
which are adapted to Simulate them ; but thefe have the fenforial
power of affociatlon added to that of irritation, and even in fome de-
gree that of fenfation, and even of volition, as will be fpoken of in
their places ; and life itfelf is thus carried on by the production of fen-
Ibri.d power being equal to its wafte or expenditure in the perpetual
movement of the vafcular organization.

3. When a ftimuius is repeated at uniform intervals of time with
fuch diftances between them, that the expenditure of fenforial power
in the afting fibres becomes completely renewed, the efFedl is pro-
duced with greater facility or energy. For the fenforial power of
aflbciation is combined with the fenforial power of irritation, or,
in common language, the acquired habit affifls the power of the
flimulus.

This circumftance not only obtains in the annual and diurnal cate-
nations of animal motions explained in Sett. XXXVI. but in every
lefs circle of a£tions or ideas, as in the burthen of a fong, or the ite-
rations of a dance ; and conftitutes the pleafure we receive from re-
petition and imitation ; as treated of in Se6l, XXII. 2.

4. When a ftimulus has been many times repeated at uniform in-
tervals, fo as to produce the complete aftion of the organ, it may
then be gradually dimlniflied, or totally withdrawn, and the adlion
of the organ will continue. For the fenforial power of aflbciation
becomes united with that of irritation, and by frequent repetition be-
■comes at length of fufficient energy to carry on the new link ia

M 2 the

84 OF STIMULUS AND EXERTION. Sect.XII. 3.

the circle of adions, without the irritation which at firll intro-
duced it.

Hence, when the bark is given at ftated intervals for the cure of
intermittent fevers, if li.xtj grains of it be given every three hours for
the tvi'entj-four hours preceding the expefted paroxyfm, fo as to Si-
mulate the defedivc part of the fjftem into adtion, and by that means
to prevent the torpor or quiefcence of the fibres, which conftitutes the
cold fit; much lefs than half the quantity, given before the time at
which another paroxyfm of quiefcence would have taken place, will
be fufficient to prevent it ; becaufe now the fenforial power, termed
aflbciation, a6ls in a twofold manner, Firft, in refpedt to the period
of the catenation in which the cold fit was produced, which is now
diffevered by the ftronger ftimulus of the firfi: dofes of the bark ; and,
fecondly, becaufe each dofe of bark being repeated at periodical times,
has its efFe6t increafed by the fenforial faculty of aflbciation being com-
bined with that of irritation.'

Now, when fixty grains of Peruvian bark are taken twice a day,
fuppofe at ten o'clock and at fix, for a fortnight, the irritation ex-
cited by this additional ftimulus becomes a part of the diurnal circle
of adions, and will at length carry on the increafed adlion of the
fyftem without the afliftance of the ftimulus of the bark. On this
theory the bitter medicines, chalybeates, and opiates in appropri-
ated dofes, exhibited for a fortnight, give permanent ftrength to pale
feeble children, and other weak conftitutions.

5. When a defe£l of ftimulus, as of heat, recurs at certain diurnal
intervals, which induces fome torpor or quiefcence of a part of the
fyftem, the diurnal catenation of aftions becomes difordered, and a
new aflbciation with this link of torpid a£lion is formed ; qn the next
period the quantity of quiefcence will be increafed, fuppofe the fame
defed of fl:imulus to recur, becaufe' now the new aflbciation con-
5 fpires

Sect. XIL 3. OF STIMULUS AND EXERTION. 85

fpires with the defective irritation in introducing the torpid a£l:ion
of this part of the diurnal catenation. In this manner many fever-
fits commence, where the patient is for fome days indifpofed at cer-
tain hours, before the cold paroxifm of fever is completely formed.
See Sect. XVII. 3. 3. on Catenation of Animal IMotions.

6. If a ftimulus, which at firfi: excited the affe£led organ into fo
great exertion as to produce fenfation, be continued for a certain time,
it will ceafe to produce fenfation both then and when repeated, though
the irritative motions in confequence of it may continue or be re-
excited.

Many catenations of irritative motions were at firft fucceeded by
fenfation, as the apparent motions of objects when we walk part them,
and probably the vital motions themlelves in the early ftate of our ex-
igence. But as thofe fenfations were followed by no movements of
the fyllem in confequence of them, they gradually ceafed to be pro-
duced, not being joined to any fucceedlng link of catenation. Hence
contagious matter, which has for fome weeks ftimulated the fyftem
into great and permanent fenfation, ceafes afterwards to produce gene-
ral fenfation, or inflammation, though it may ftill induce topical irri-
tations. See Sea. XXXIII. 2. 8. XIX. 10.

Our abforbent iyftem then feems to receive thofe contagious mat-
ters, which it has before experienced, in the fame manner as It im-
bibes common moifture or other fluids ; that is, without being
thrown into fo violent a£tion as to produce fenfation ; the confe-
quence of which is an increafe of daily energy or activity, till inflam-
mation and its confequences fucceed.

7. If a ftimulus excites an organ into fuch violent contra£lions as to
produce fenfation, the motions of which organ had not ufually pro-
duced fenfation, this new fenforial power, added to the irritation oc-
cafioned by the ftimulus, increafes the adlivity of the organ. And if
this aftivity be catenated with the diurnal circle of aflions, an in-
creafing inflammation is produced ; as in the evening paroxyfms of

fmall-

U OF STIMULUS AND EXERTION. Sect.XIL 4.

fmall-pox, and other fevers with inflammation. And hence' fchirrous
tumours, tendons and membranes, and probably the arteries them-
felves become inflamed, when they are flrongly Simulated.

IV. Of S^t'rmulus greater than natural.

I. A quantity of ftimulus greater than natural, producing an in-
creafed exertion of fenforial power, whether that exertion be in the
r-mode of irritation, fenfation, volition, or aflbciation, diminiflies the
general quantity of it. This fa£t is obfervable in the progrefs of in-
toxication, as the increafed quantity or energy of the irritative mo-
tions, owing to the ftimulus of vinous fpirit, introduces much plea-
furable fenfation into the fyftem, and much exertion of mufcular or .
fenfual motions in confequence of this increafed fenfation; the volun-
tary motions, and even the aflbciate ones, become much impaired
or diminilhed ; and delirium and flaggering fucceed. See Se£l. XXI.
on Drunkennefs. And hence the great proftration of the flrength of
the locomotive mufcle-s -in fome fevers, is owing to the exhauftion
of fenforial power by the increafed aftion of the arterial fyftem.

In like manner a ftimulus greater than natural, applied to a part of
the fyftem, increafes the exertion of fenforial power in that part, and
diminiflies it in fome other part. As in the commencement of fcarlet
fever, it is ufual to lee great rednefs and heat on the faces and breafts
of children, while at the fame time their feet are colder than natural;
partial heats are obfervable in other fevers with debility, and are ge-
nerally attended with torpor or quiefcence of fome other part of the
iyftem. But thefe partial exertions of fenforial power are fometimes
attended with increafed partial exertions in other parts of the fyftem,
which fympathize with them, as the flufhing of the face after a full
■ meal. Both thefe therefore are to be afcribed to fyxn^z\.\\&t\c aflbci-

ations,

Sect. XII. 4. OF STIMULUS AND EXERTION. 87

ations, explained in Se£t. XXXV. and not to general exhauftion or
accumulation of fenforial power.

2. A quantity of ftimulus greater than natural, producing an in-
creafed exertion of fenforial power in any particular organ, diminiflies
the quantity of it in that organ. This appears from the contradions
of animal fibres being not fo eafily excited by a lefs ftimulus after the
organ has been fubjefted to a greater. Thus after looking at any lu-
minous objecSt of a fmall fize, as at the fetting fun, for a fhort time,
fo as not much to fatigue the eye, this part of the retina becomes lefs
fenfible to fmaller quantities of light ; hence when the eyes are turned
on other lefs luminous parts of the fky, a dark fpot is feen refembling
the fliape of the fun, or other luminous object which we laft behold.
See Sea. XL. No. 2.

Thus we are fome time before we can diftinguifh objedls in an
qbfcure room after coming from bright day-light, though the iris
prefently contrads itfelf. We are not able to hear wezk founds
after loud ones. And the ftomachs of thofe who have been much
habituated to the ftronger ftimulus of fermented or fpirituous liquors,
are not excited into due a£tion by weaker ones.

3. A quantity of ftimulus lomething greater than the laft men-
tioned, or longer continued, induces the organ into fpafmodic a£lion,
which ceafes and recurs alternately. Thus on looking for a time on
the fetting fun, fo as not greatly to fatigue the fight, a yellow fpec-
trum is feen when the eyes are clofed and covered, which continues
for a time, and then difappears and recurs repeatedly before it entirely
vanifhes. See Se£t. XL. No. 5. Thus the action of vomiting
ceafes and is renewed by intervals, although the emetic drug is
thrown up with the firft effort. A tenefmus continues by intervals
fome time after the exclufion of acrid excrement ; and the pulfations
of the heart of a viper are faid to continue fome time after it is cleared
from its blood.

7 III

88 OF STIMULUS AND EXERTION. SEcr.XII. 4.

In thefe cafes the violent contraftions of the fibres produce pain
according to law 4; and this pain conftitutes an additional kind or
quantity of excitement, which again induces the fibl'es into contrac-
tion, and which painful excitement is again renewed, and again in-
duces contradlions of the fibres with gradually diminifhing efFe£l.

4. A quantity of ftimulus greater than that laft mentioned, or
longer continued, induces the antagonift mufcles into fpafmodic ac-
tion. This is beautifully illuftrated by the ocular fpeilra defcribed
in Seft. XL. No. 6. to which the reader is referred. From thofe
experiments there is reafon to conclude that the fatigued part of the
retina throws itfelf into a contrary mode of aftion like ofcitation or
pandiculation, as foon as the ftimulus, which has fatigued it, is
withdrawn ; but that it ftill remains liable to be excited into adlioii
by any other colours except the colour with which it has been fa-
tigued. Thus the yawning and ftretching the limbs after a con-
tinued ailion or attitude feems occafioned by the antagonift mufcles
being ftimulated by their extenfion during the contradtions of thofe
in ailion, or in the fituation in which that a£tion laft left them.

5. A quantity of ftimulus greater than the laft, or longer conti-
nued, induces variety of convulfions or fixed fpafms either of the af-
fected organ or of the moving fibres in the other parts of the body.
In refpeft to the fpeftra in the eye, this is well illuftrated in No. 7
and 8, of Se£t, XL. Epile6tic convalfions, as the emprofthotonos
and.opifthotonos, with the cramp of the calf of the leg, locked jaw,
and other cataleptic fits, appear to originate from pain, as fome of
thele patients fcream aloud before the convulfion takes place ; which
feems at firft to be an efixDrt to relieve painful fenfation, and after-
wards an effort to prevent it.

In thefe cafes the violent contradlions of the fibres produce fo much
pain, as to conftitute a perpetual excitement ; and that in fo great a
degree as to allow but fmall intervals of relaxation of the con-

tradling

Sect. XII. 4. OF STIMULUS AND EXERTION. 8<>

traitlng fibres as in couvulhons, or no intervals at all as in fixed
fpafms.

6. A quantity of ftimulus greater than the lad, or longer con-
tinued, produces a paralylis of the organ. In many cafes this para-
lyfis is only a temporary effect, as on looking long on a fmall area of
bright red filk placed o.n a fheet of white paper on the floor in a ftrong
light, the r^d filk gradually becomes paler, and at length difappears ;
which evinces that a part of the retina, by being violently excited,
becomes for a time unaffedled by the ttimulus of that colour. Thus
cathartic medicines, opiates, poifons, contageous matter, ceafe to in-
fluence our fyftem after it has been habituated to the ufe of them,
except by the exhibition of increafed quantities of them ; our fibres
not only become iinaffeiSted by ftimuli, by which they have previ-
oufly been violently irritated, as by the matter of the fmall-pox or
meaflles ; but they alfo become unaffe£led by fenfation, where
the violent exertions, which difabled them, were in confequence
of too great quantity of fenfation. And laftly the fibres, M'hich
become difobedient to volition, are probably difabled by their too
violent exertions in confequence of too great a quantity of vo-
lition.

After every exertion of our fibres a temporary paralyfis fucceeds,
whence the intervals of all mufcular contraftions, as mentioned in
No. 3 and 4 of this Sedlion j the immediate caufe of thefe more per-
manent kinds of paralyfis is probably owing in the fame manner to
the too great exhauftion of the fpirit of animation in the affedted part;
fo that a ftronger ftimulus is required, or one of a different kind from
that, v^'hich occafioned thofe too violent contractions, to again excite
the affe£led organ into activity ; and if a flronger fi:imulus could be
applied, it muil: again induce paralyfis.

For thefe powerful flimuli excite pain at the fame time, that they
produce irritation ; and this pain not only excites fibrous motions by
its ftimulus, but it alfo produces volition ; and thus all thefe ftimuli

N , aftins:

90 OF STIMULUS AND EXERTION. Sect. XII. 5.

acting at the fame time, and fometlmes with the addition of their af-
fociations, produce fo great exertioQ as to expend the whole of the
fenforial power in the affedled fibres.

v. Of Stmulus lefs than natural,

I. A quantity of ftimuluslefs than natural, producing a decreased
exertion of fenforial power, occafions an accumulation of the general
quantity of it. This circumftance is obfervable in the haemiplagia,.
in which the patients are perpetually moving the mufcles, which are
"unafFefted. On this account we awake with greater vigour after
fleep, becaufe during fo many hours, the great ufual expenditure of
fenforial power in the performance of voluntary aftions, and in the
exertions of our organs of fenfe, in confequence of the irritations oc-
cafioned by external obje£ts had" been fufpended, andaconfequent ac-
cumulation had taken place.

In like manner the exertion of the fenforial power lefs than natural
in one part of the fyftem, is liable to produce an increafc of the ex-
ertion of it in fomc other part. Thus by the action of vomiting, in<
which the natural exertion of the motions of the flomach are de-
flroyed or diminlfhed, an increafed abforption of the pulmonary and
cellular lymphatics is produced, as is known by the increafed abforp-
tion of the fluid depofited in them in dropfica^l cafes. But thefe par-
tial quiefcences of fenforial power are alfo fometimes attended with,
other partial quiefcences, which fympathize with them, as cold and
pale extremities from hunger. Thefe therefore are to be afcribed to
the alTociations of iympathy explained in Se£t. XXXV. and not to the-
general accumulation of fenforial power.

2. A quantity of ftimulus lefs than natural, applied to fibres pre-
vioufly accuflomed to perpetual ftimulus, is fucceeded by acctimula-

tion

Sect. XII. 5. OF STIMULUS AND EXERTION. 91

tion of fenfoiial power in the affefted organ. The truth of this pro-
pofition is evinced, becaufe a ftimulus lefs than natural, if it be
fomevvhat greater than that above mentioned, will excite the organ
fo circumftanced into violent ailivity. Thus on a froity day with
wind, the face of a perfon expofed to the wind is at firrt: pale and
rhrunk ; but on turning the face from the wind, it becomes foon of
a glow with warmth and flufhing. The glow of the Ikin in emerg-
ing from the cold-bath is owing to the fame caufe.

It does not appear, that an accumulation of fenforial power above
the natural quantity is acquired by thofe mufcles, which are not fub-
je£t to perpetual flimulus, as the locomotive mufcles : thefe, after the
greateft fatigue, only acquire by reft their ufual aptitude to motion ;
whereas the vafciilar fyftem, as the heart and arteries, after a fhort
quiefcence, are thrown into violent a£tion by their natural quantity of
ftimulus.

Neverthelefs by this accumulation of fenforial power during the
application of decreafed ftimulus, and by the exhauftion of it during
.the-a6tion of increafed ftimulus, it is wifely provided, that the ac-
tions of the vafcular tnufcles and organs of fenfe are not much de-
ranged by fmall variations of ftimulus ; as the quantity of fenforial
power becomes in fome meafure inverfely as the quantity of fti-
mulus.

3. A <juantity of ftimulus lefs than that mentioned above, and
<:ontinued for fofme time, induces pain in the affe<5led organ, as the
pain of cold in the hands, when they are immerfed in fnow, is owing
to a deficiency of the ftimulation of heat. Hunger is a pain from the
deficiency of the ftimulation of food. Pain in the back at the com-
■jnencement of ague- fits, and the head-achs which attend feeble peo-
ple, are pains from defect of ftimulus, and are hence relieved by opi-
um, eflential oils, fpirit of wine.

As the pains, which originate from defe*^ of ftimulus, only occur
in thofe parts of the fyftem, which have been previoufly fubjedled to

N 3 perpetual

92 OF STIMULUS AND EXERTION. SECT.XIL5.

perpetual ftlmulus ; and as an accumulation of fenforial power is pro-
duced in the quiefcent organ along with the pain, as in cold ■ or
hunger, there is reafon to believe, that the pain is owing to the ac-
cumulation of fenforial power. For, in the locomotive mufcles, in.
the retina of the eye, and other organs of fenfes, no pain occurs from
the abfence of flimulus, nor any great accumulation of fenforial
power beyond their natural quantity, fince thefe organs have not-
been ufed to a perpetual fupply of it. There is indeed a greater ac-
cumulation occurs in the organ of vilion after its quiefcence, becaufe
it is fubjeft to more conftant ftimulus.

4. A certain quantity of ftimulus lefs than natural induces the
moving organ into feebler and more frequent contraftions, as men-
tioned in No. I. 4. of this. Seftion. For each contradion moving-
through a lefs fpace, or with lefs force, that is, with lefs expendi-
ture of the fpirit of animation, is fooner relaxed, and the fpirit of ani-
mation derived at each interval into the adling fibres being lefs, thefe
intervals likewife become fhorter. Hence the tremours of the hands^
of people accuftomed to vinous fpirit, till they take their ufual flimu-
lus ; hence the quick pulfe in fevers attended with debility, which;
is greater than in fevers attended with ftrength ; in the latter the:
pulfe feldom beats above 120 times in a minute, in the former it fre-
quently exceeds 140.

It muft be obferved, that in this and the two following articles the
decreafed aftion of the fyftem is probably more frequently occaiionedi
by deficiency in the quantity of fenforial power, than in the quantity
©f flimulus. Thus thofe feeble conflitutions which have large pupils
of their eyes, and all who labour under nervous fevers, feem to owe
their want of natural quantity of activity in the fyflem to the defici-.
ency of fenforial power ; fince, as far as can be feen, they frequently'
poffefs the natural quantity of flimulus.

5. A certain quantity of flimulus, lefs than that above mentioned,
inverts the order bf facceffive fibrous contraftions ; as in vomiting-

the

Sect. XII. 6. OF STIMULUS AND EXERTION. 93

the vermicular motions of the ftomach and duodenum are inverted,
and their contents ejected, which is probably owing to the exhauftion
of the fpirit of animation in the a£ling mufcles by a previous exceffive
flimulus, as by the root of ipecacuanha, and the confequent defedb
of fenforial power. The fame retrograde motions afFeft the whole
inteftinal canal in ileus ; and the oefophagus in globus hyftericus.
See this further explained in Sedt. XXIX. No, 11. on Retrograde
Motions^

I muft obferve, alfo, that fomething fimilar happens in the pro-
dudlion of our ideas, or fenfual motions, when they are too weakly-
excited ; when any one is thinking intenfely about one thing, and.
carelefsly converfing about another, he is liable to ufe the word of a
contrary meaning to that which he defigned,. as cold weather for hot
weather, fup^mer for winter.

6. A certain quantity of ftimulus, lefs than that above mentioned,
is fucceeded by paralyfis, firft of the voluntary and fenfitive motions,,
and afterwards of thofe of irritation and of affociation, which conili-
tutes death,.

VI. Cure of tncreafed Kxertlon..

J. The cure,, which nature has provided for the increafed exertion
©f any part of the fyftem, confifls in the confequent expenditure of
the fenforial power. But as a greater torpor follows this exhauftion of
fenforial power, as explained in the next paragraph, and a greater ex-
ertion fucceeds this torpor, the conftitution frequently finks under
tbefe increaiing librations between exertion and quiefcence; till at
length complete quiefcence, that is, death, clofes the fcene.

For, during the great exertion of the fyflem in the hot fit of fever^
aaincreafe of flimulus is produced fi'om the greater momentum ot^

the;

94 OF STIMULUS AND EXERTION. Sect. XII. 6.

the blood, the greater diftention of the heart and arteries, and the iti-
creafed produdtion of heat, by the violent adlions of tne fyftem oc-
cafioned by this augmentation of ftinnulus, the fenforial power be-
comes diminifhed in a few hours miich beneath its natural quantity,
the veffels at length ceafe to obey even thefe great degrees of llimulus,
as fhewn in Se6t. XL. 9. i, and a torpor of the whole or of a part of
the fyftem enfues.

Now as this fecond cold fit commences with a greater deficiency of
fenforial power, it is alio attended with a greater deficiency of ftixnu-
lus than in the preceding cold fit, that is, with lefs momentum of
blood, lefs diftention of the hearts On this account the fecond cold
fit becomes more violent and of longer duration than the firfi: ; and as
a greater accumulation of fenforial power mufl: be produced before the
fyftem of veflels will again obey the diminifhed ftimulus, it follows,
that the fecond hot fit of fever will be more violent than the former
-one. And that unlefs fome other caufes counteradl either the violent
exertions in the hot.^t, or the great torpor in the cold fit, life will
at length be extinguifhed by the expenditure of the whole of the
fenforial power. And from hence it appears, that the true means of
curing fevers mufl be fuch as decreafe the aftion of the fyftem in the
■hot fit, and increafe it in the cold fit ; that is, fuch as prevent the
too great diminution of fenforial power in the hot fit, and the too great
,accumuJation of it in the cold one.

2. Where the exertion of the fenforial powers is much increafed,
as in the hot-fits of fever or inflammation, the following are the ufual
means of relieving it. Decreafe the irritations by blood-letting, and
-other evacuations ; by cold water taken into the ftomach, or injedled
as an enema, or ufed externally ; by cold air breathed into the lungs,
and diifufed over the fkin ; with food of lefs ftimulus than the patient
lias been accuftomed to.

3. As a cold fit, or paroxyfm of inactivity of fome parts of the
iydem, generally precedes the hot fit, or paroxyfm of exertion, by

y which

Sect. XII. 7. OF STIMULUS AND EXERTION. 95

which the fenforial power becomes accumulated, this cold paroxyfm
ihould be prevented by ftimulant medicines and diet, as wine, opium,
bark, warmth, cheerfulnefs, anger, furprife.

4. Excite into greater adlion fome other part of the fy flem, by
which means the fpirit of animation may be in part expended, and
thence the inordinate adtions of the difeafed part may be lefl'ened.
Hence when a part of the fkin a£ls violently, as of the face in the
eruption of the fmall-pox, if the feet be cold they (hould be covered.
Hence the ufe of a blifter applied near a topical inflammation. Hence
opium and warm bath relieve pains both from excefs and defe6l of
ftimulus.

5. Firft increafe the general ftimulation above its natural quantity^
which may in fome degree exhauft the fpirit of animation, and then
decreafe the ftimulation beneath its natural quantity. Hence after
fiidorific medicines and warm air, the application of refrigerants may
have greaier efFedt, if they could be adminiftered without danger of
producing too great torpor of fome part of the lyftem ; as frequently
happens to people in health from coming out of a warm room into the
cold air, by which a topical inflammation iii confequenee of torpor of
the mucous membrane of the noflril is produced, and is termed.a colA
ill the head.

TIL Cure of decreafed. Exertio?u

I. Where the exertion of the fenforial powers is much d'eereafed^
as in the cold fits of fever, a gradual accumulation of the fpirit of
animation takes place ; as occurs in all cafes where inactivity or top-
por of a part of the fyftem exifts ; this accumulation of fenforial^
power increafes,. till ftimuli lefs than natural are fufficient to throw it

iutaj

96 OF STIiMULUS AND EXERTION. Sect.XII. 7.

into a£1:ion, then the cold fit ceafes ; and from the adion of the na-
tural ftimuli a hot onefucceeds with increafed aftivity of the whole
fjftem.

So in fainting fits, or fyncope, there is a temporary deficiency of
fenforial exertion, and a confequent quiefcence of a great part of the
iyftem. This quiefcence continues, till the fenforial power becomes
again accumulated in the torpid organs ; and then the ufual diurnal
ftimuli excite the revivefcent parts again into.adlion ^ but as this kind
.of quiefcence continues but a fliort time compared to the cold parox-
yfm of an ague, and lefs affe£ls the circulatory fyftem, a lefs fuper-
abundancy of exertion fucceeds in the organs previoufly torpid, and a
lefs excefs of arterial adlivity. See Se£t. XXXI V. i. 6.

2. In the difeafes occafioned by a defe6l of fenforial exertion, as in
cold fits of ague, hyfteric complaint, and nervous fever, the follow-
ing means are thofe commonly ufed. i. Increafe the ftimulatlon
above its natural quantity for fome weeks, till a new habit of more
energetic -contraftion of the fibres is eftablifhed. This is to be done
by wine, opium, bark, ^fleel, given at exa£l periods, and in appro-
priate quantities ; for if theie medicines be given in fuch quantity,
as to inducethe leaft degree of intoxication, a debility fucceeds from
the ufelefs exhauftion of fpirit of animation in confequence of too
great exertion of the mufcles or organs of fenfe. To thefe irritative
ftimuli fhould be added the fenfitive ones of cheerful ideas, hope,
affedion.

3. Change the kinds of ftlmulus. The habits acquired by the
conflitution depend on fuch nice circumftances, that when one kind
of fcimulus ceafes to excite the fenforial power into the quantity of
exertion neceffary to health, it is often fufficient to change the fti-
mnlus for another apparently fimilar in quantity and quality. Thus
when wine ceafes to ftimulate the conflitution, opium in appropriate
dofes fupplies the defedl^ and the contrary. This is alfo obferved in

the

Sect. XII. 7. OF STIMULUS AND EXERTION. 97

the efFedts of cathartic medicines, when one lofes its power, another,
apparently lefs efficacious, will fucceed. Hence a change of diet,
drink, and Simulating medicines, is often advantageous in difeafes of
debility.

4. Stimulate the organs, whofe motions are aflbciated with the
torpid parts of the fyftem. The adlions of the minute veffels of the
various parts of the external Ikin are not only aflbciated with each
other, but are ftrongly aflbciated with thofe of fome of the internal
membranes, and particularly of the flomach. Hence when the ex-
ertion of the ftomach is lefs than natural, and indigeftion and heart-
burn fucceed, nothing fo certainly removes thefe fymptoms as the
llimulus of a blifl:er on the back. The coldnefs of the extremities,
as of the nofe, ears, or fingers, are hence the befl indication for the
fuccefsful application of blifl:ers.

5. Decreafe the ftimulus for a time. By leflTening the quantity of heat
for a minute or two by going into the cold bath, a great accumulation
of fenforial power is produced ; for not only the minute veflels of the
whole external fkin for a time become inadive, as appears by their
palenefs ; but the minute veflels of the lungs lofe much of their ac-
tivity alfo by concert with thofe of the Ikin, as appears from the dif-
ficulty of breathing at firfl: going into cold water. On emergino-
from the bath the fenforial power is thrown into great exertion by
the ftimulus of the common degree of the warmth of the atmo-
Iphere, and a great produ£lion of animal heat is the confequence.
The longer a perfon continues in the cold bath the greater mufl: be
the prefent inertion of a great part of the fyftem, and in confequence"
a' greater accumulation of fenforial power. Whence M. Pome re-
commends fome melancholy patients to be kept from two to fix hours
in fpring-water, and in baths ftill colder.

6 Decreafe the ftimulus for a time below the natural, and then
increafe it above natural. The effeft of this procefs, improperly ufed,
is feen in giving much food, or applying much warmth, to thofe

O -who

98 OF STIMULUS AND EXERTION. Sect. XII. -j.

who have been previoufly expofed to great hunger, or to great cold.
The accumulated fenforial power is thrown into fo violent exertion,
that inflammations and mortifications fupervene, and death clofes the
cataftrophe. In many difeafes this method is the moft fuccefsful ;
hence the bark in agues produces more certain eftedt after the previ-
ous exhibition of emetics. In difeafes attended with violent pain,
opium has double the efFeft, if venefe6lion and a cathartic have been
previoufly ufed. On this feems to have been founded the fuccefsful
practice of Sydenham, who ufed venefeftion and a cathartic in chlo-
rofis before the exhibition of the bark, fteel, and opiates.

7. Prevent any unneceflary expenditure of fenforial power. Hence
in fevers with debility, a decumbent pofl:ure is preferred, with filence,
little light, and fuch a quantity of heat as may prevent any chill fen-
fation, or any coldnefs of the extremities. The pulfe of patients in
fevers with debility increafes in frequency above ten pulfations in a
minute on their rifing out of bed. For the expenditure of fenforial
power to preferve an ereft pofl:ure of the body adds to the general de-
ficiency of it, and thus afFe£ls the circulation.

8. The longer in time and the greater in degree the quiefcence or
inertion of an organ has been, fo that it ftill retains life or excitability,
the lefs ftimulus Ihould at firfl; be applied to it. The quantity of fli-
mulation is a matter of great nicety to determine,^ where the torpor
or quiefcence of the fibres has been experienced in a great degree^ or
for a confiderable time, as in cold fits, of the ague, in continued fevers-
with great debility, or in 'people famiflied at fea, or perifliing with
cold. In the two lafl; cafes, very minute quantities oi food fliould be;
firfl: fupplied, and very few additional degrees of heat. In the two
former cafes, but little ftimulus of wine or medicine, above what
they had been lately accuftomed to, fhould be exhibited, and this at
frequent and flated intervals, fo that the effe£l of one quantity may
be obferved before the exhibition of another.

If thefe circumfl:ances are not attended to, as the fenforial power

15 becomes

Sect. XII. 7. OF STIMULUS AND EXERTION, 9f

becomes accumulated in the qulefcent fibres, an inordinate exertion
takes place by the increafe of ftimulus ading on the accumulated
quantity of fenforial power, and either the paralyfis, or death of the
contradile fibres enfues, from the total expenditure of the fenforial
power in the afFedted organ, owing to this increafe of exertion, like
the debility after intoxication. Or, fecondly, the violent exertions
above mentioned produce painful fenfation, which becomes a new
ftimulus, and by thus producing inflammation, and increafing the
adivity of the fibres akeady too great, fooner exhaufts the whole of
the fenforial power in the a6ling organ, and mortification, that is,
the death of the part, fupervenes.

Hence there have been many inftances of people, whofe limbs have
been long benumbed by expofure to cold, who have loft them by
mortification on their being too haflily brought to the fire ; and of
others, who were nearly famiihed at fea, who have died foon after
having; taken not more than an ufual meal of food. I have heard of
two well-attefted inftances of patients in the cold fit of ague, who
have died from the exhibition of gin and vinegar, by the inflammation
which enfued. And in many fevers attended with debility, the un-
limited ufe of wine, and the wanton application of blifters, I believe,
has deftroyed numbers by the debility confequent to too great ftimu-
lation, that is, by the exhauftion of the fenforial power by its in-
ordinate exertion.

Wherever the leaft degree of intoxication exifts, a proportional de-
bility is the confequence; but there is a golden rule by which the
neceffary and ufeful quantity of ftimulus in fevers with debility may
be afcertained. When wine or beer are exhibited either alone or di-
luted with water, if the pulfe becomes flower the ftimulus is of a
proper quantity; and fhould be repeated every two or three hours,
or when the pulfe again becomes quicker.

In the chronical debility brought on by drinking fplrituous or fer-
mented liquors, there is another golden rule by which I have fuccefs-

O 2 fully

100 OF STIMULUS AND EXERTION. Sect. XII. 7.

fully direfted the quantity of fpirit which they may fafely leffen, for
there is no other means by which they can recover their health. It
(hould be premifed, that where the power of digeftion in thefe pa-
tients is totally deftroyed, there is not much reafon to expedl: a return
to healthful vigour. ' ^r-i.

I have diredted feveral of thefe patients to omit one fourth part of
the quantity of vinous fpirit they have been lately accuflomed to,
and if in a fortnight their appetite increafes, they are advifed to omit
another fourth part ; but if they perceive that their digeftion becomes
impaired from the want of this quantity of fpirituous potation, they are
advifed to continue as they are, and rather bear the ills they have,
than rilk the encounter of greater. At the fame time flefli-meat with
or without fpice is recommended, with Peruvian bark and fteel in
fmall quantities between their meals, and half a grain of opium or a
grain, with five or eight grains of rhubarb at night.

SECT.

Sect. XIII. r. OF VEGETABLE ANIMATION. loi

SECT. XIII.

OF VEGETABLE ANIMATION.

I. I. Vegetables are irritable, mimofa, dionaa mufcipula. Vegetable Jeer etions.

I. Vegetable buds are inferior animals^ are liable to greater or lejs irritability.

II. Stamens and fijlils of plants Jhew marks of Jenfibility. Ill, Vegetables poj-
Jefs fame degree of volition. IV. Motions of plants are ajfociated like thcfe of

animals. V. i. Vegetable JlruSlure like that of animals, their anthers and flig-
tnas are living creatures. Male-flowers of Vallifneria. i. Whether vegetables
poffejs ideas ? "They have organs offenje as of touch andjmell, and ideas of exter-^
nal things?

I. 1. THE fibres of the vegetable world, as well as thofe of the
animal, are excitable into a variety of motion by the irritations of ex-
ternal objects. This appears particularly in the mimofa or fenfitive
plant, whofe leaves contrail on the flightefl injury ; the dion^a muf-
cipula, which was lately brought over from the marfhes of America,
prefents us with another cui-ious inftance of vegetable irritability ; its
leaves are armed with fpines on their upper edge, and are fpread on
the ground around the ftem ; when an infedl creeps on any of them
in its paflage to the flower or feed, the leaf Ihuts up like a fteel rat-
trap, and deftroys its enemy. See Botanic Garden, Part II. note on
Silene.

The various fecretions of vegetables, as of odour, fruit, gum,
refin, wax, honey, feem brought about in the fame manner as in the
glands of animals : the taftelefs moifture of the earth is converted by
the hop-plant into a bitter juice ; as by the caterpillar in the nut-

ihell

lOTi OF VEGETABLE ANIMATION. Sect. XIII. i.

fhell the fweet kernel is converted into a bitter powder. While the
power of abforption in the roots and barks of vegetables is excited
into aflion by the fluids applied to their mouths like the lafteals and
lymphatics of animals.

2. The individuals of the vegetable world may be confidered as in-
ferior or lefs perfect animals ; a tree is a congeries of many living
buds, and in this refpedl refembles the branches of coralline, which
are a congeries of a multitude of animals. Each of thefe buds of a
tree has its proper leaves or petals for lungs, produces its viviparous
or its oviparous offspring in buds or feeds; has its own roots, which
extending down the ftem of the tree are interwoven with the roots
of the other buds, and form the bark, which is the only living part
of the ftem, is annually renewed, and is fuperinduced upon the
former bark, which then dies, and with its ftagnated juices gradually
hardening into wood forms the concentric circles, which we fee ia
blocks of timber.

The following circumftances evince the individuality of the buds of
trees. Firft, there are many trees, whofe whole internal wood is
perifbed, and yet the branches are vegete and healthy. Secondly,
the fibres of the barks of trees are chiefly longitudinal, refembling
roots, as is beautifully feen in thofe prepared barks, that were lately
brought from Otaheita. Thirdly, in horizontal wounds of the bark
of trees, the fibres of the upper lip are always elongated downwards
like roots, but thofe of the lower lip do not approach to meet them.
Fourthly, if you wrap wet mofs round any joint of a vine, or cover
it with moifl earth, roots will fhoot out from it.^ Fifthly, by the
inoculation or engrafting of trees many fruits are produced from one
ftem. Sixthly, a new tree is produced from a bi"anch plucked from
an old one, and fet in the ground. Whence it appears that the buds
of deciduous trees are fo many annual plants, that: the bark is a con-
texture of the roots of each individual bud ; and that the internal wood

Sect. XIII. 5. OF VEGETABLE ANIMATION. 103

is of no other ufe but to fupport them in the air, and that thus they
refemble tiie animal world in their individuality.

The irritability of plants, like that of animals, appears liable to be
increafed or decreafed by habit ; for thofe trees or fhfnbs, which are
brought from a colder climate to a warmer, put out their leaves and
bloflbms a fortni2;ht fooner than the indigenous ones.

Profeffor Kalm, in his Travels in New York, obferves that the
apple-trees brought from England bloffom a fortnight fooner than the
native ones. . In our country the fhrubs, that are brought a degree
or two from the north, are obferved to fiourilli better than thofe,
which come from the fouth. The Siberian barley and cabbage are
faid to grow larger in this climate than the {imilar more fouthern ve-
getables. And our hoards of roots, as of potatoes and onions, ge-
minate with lefs heat in fpring, after they have been accuflomed to
the winter's cold, than in autumn after the fummer's heat.

II. The flamens and piftils of flower-s fhew evident marks of fen-
fibility, not only from many of the ftamens and fome piilils approach-
ing towards each other at the feafon of impregnation, but from many
of them clofing their petals and calyxes during the cold parts of the
day. For this cannot be afcribed to irritation, becaufe cold means a
defeft of the ftimulus of heat ; but as the want of accuflomed flimuli
produces pain, as in coldnefs, hunger, and thirfl of animals, thefe
motions of vegetables in clofing up their flowers mufl be afcribed to
the difagreeable fenfation, and not to the irritation of cold. Others
clofe up their leaves during darknefs, which, like the former, cannot
be owing to irritation, as the irritating material is withdrawn.

The approach of the anthers in many flowers to the fligmas, and
of the piftils of fome flowers to the anthers, mufl be afcribed to the
paflion of love, and hence belongs to fenfation, not to irritation.

III. That the vegetable world poflefles fome degree of voluntary
powers, appears from their necefiity to fleep, which we have fhewn
in Sect. XVIII. to confifl: in the temporary abolition of voluntary

power.

I04 OF VEGETABLE ANIMATION. Sect. XIII. 5.

power. This voluntary power feems to be exerted in the circular
movement of the tendrils of vines, and other climbing vegetables ;
or in the efforts to turn the upper furface of their leaves, or their
flowers to the light.

IV. The affociations of fibrous motions are obfervable in the ve-
getable world, as well as in the animal. The divifions of the leaves
of the fenfitive plant have been accuftomed to contraft at the fame
time from the abfence of light ; hence if by any other circumflance,
as a flight flroke or injury, one divifion is irritated into contraftion,
the neighbouring ones contract alfo, from their motions being affoci-
ated with thofe of the irritated part. So the various ftamina of the
clafs of fyngenefia have been accuftomed to contract together in the
evening, and thence if you ftimulate one of them with a pin, accord-
ing to the experiment of M. Colvolo, they all contract from their ac-
quired affociations.

To evince that the collapfing of the fenfitive plant is not owing to
any mechanical vibrations propagated along the whole branch, when
a fingle leaf is ftruck with the finger, a leaf of it was flit with fliarp
fciffors, and fome feconds of time paffed before the plant feemed fen-
fible of the injury; and then the whole branch collapfed as far as the
principal ftem: this experiment was repeated feveral times with the
leaft poffible impulfe to the plant.

V. I. For the numerous circumftances in which vegetable buds
are analogous to animals, the reader is referred to the additional notes
at the end of the Botanic Garden, Part i. It is there fliewn, that
the roots of vegetables refemble the la£leal fyftem of animals ; the
fap-veffels in the early fpring, before their leaves expand, are analo-
gous to the placental veffels of the foetus ; that the leaves of land-
plants refemble lungs, and thofe of aquatic plants the gills of fifli ;
that there are other fyftems of veffels refembling the vena portarum
of quadrupeds, or the aorta of fifli ; that the digeftive power of ve-
getables is fimilar to that of ainimals converting the fluids, which they

abforb,

Sect.XIII. 5- OF VEGETABLE ANIMATION. 105

abforb, into fugar ; that their feeds refemble the eggs of animals,
and their buds and bulbs their viviparous offspring. And, laftly,
that the anthers and ftigmas are real animals, attached indeed to their
parent tree like polypi or coral infe£ts, but capable of fpontaneous
motion ; that they are afFe<Sted with the paflion of love, and furnifhed
with pov/ers of reproducing their fpecies, and are fed with honey like
the moths and butterflies, which plunder their nedtaries. See Bota-
nic Garden, Part I. add. note XXXIX.

The male flowers of vallifneria approach ftill nearer to apparent
animality, as they detach themfelves from the parent plant, and
float on the furface of the water to the feniale ones. Botanic Garden,
Part II, Art. Vallifneria. Other flowers of the claffes of monecia and
diecia, and polygamia, difcharge the fecundating farina, which float-
ing in the air is carried to the ftigma of the female flowers, and that
at confiderable diftances. Can this be affected by any fpecific attrac-
tion ? or, like the diffulion of the odorous particles of flowers, is it
left to the currents of winds, and the accidental mifcarriages of it
countera£led by the quantity of its production. ?

2. This leads us to a curious enquiry, whether vegetables. have
ideas of external things ? As all our ideas are originally received by
our fenfes, the queflion may be changed to, whether vegetables
poflefs any organs pf fenfe ? Certain it is, that they polTefs a fenfe of
heat and cold, another of moifture and drynefs, and another of licrht
and darknefs ; for they ciofe their petals occafionally from the pre-
fence of cold, moillure, or darknefs. And it has been already
Ihewn, that thefe anions cannot be performed Amply from irritation,
becaufe cold and darknefs are negative quantities, and on that ac-
.count fenfation or volition are implied, and in confequence a fenfo-
rium or union of their nerves. So when we go into the lio-ht we
contrail the iris ; not from any flimulus of the light on the fine
mufcles of the iris, but from its motions being aflbciated with the
fenfation of too much light on the retina: which could not take

P place

io6 OF VEGETABLE ANIMATION. Sect. XIII. 5-,

place without a feaforium: or center of union of the nerves of the
iris with thofe of vifion. See Botanic Garden, Part I. Canto 5.
I. 440. note,

Befides thefe organs of fenfe, which diftinguifh cold, moifturei
and darknefs, the leaves of mimofa, and of dionaea, and of drofera,
and the ftamens of maay flowers, as of the berbery, and the numerous
clafs of fyngenefia, are fenfible to mechanic impaft, that is, thej
polTefs a fenfe of touch, as well as a common fenforium ; by the
medium of which their mufcles are excited into adlion. Laftly, in
many flowers the anthers, when mature, approach the ftigma, ia
others the female organ approaches to the male. In a plant of coliin-
fonia, a branch of which is now before me, the two yellow ftamens-
are about three eights of an inch high,, and diverge from each other,
at an angle of about fifteen degrees, the purple flyle is half an inch,
high, and in fome flowers is now applied to the flamen. on the right
hand, and in others to that of the left ; and will, I fuppofe, change
place to-morrow in thofe,, where the anthers have not yet efFufed their
powder.

I afk, by what means are the anthers in many ffowers, and ffigmas
in other flowers, diredbed to find their paramours ? How do either of
them know, that the other exifts in their vicinity? Is this curious kind
of ftorge produced by mechanic attradtion, or by the fenfation of love ?
The latter opinion is fupported by the ftrongeff analogy, becaufe a
reproduilion of the fpecies is the confequence ; and then another organ
of fenfe muft be wanted to dire6t thefe vegetable amourettes to find
each other, one probably analogous to our fenfe of fmell, which ia
the animal world direds the new-born infant to its fource of nou-
rifhment, and they may thus poflefs a faculty of perceiving as well
as of producing odours.

Thus, befides a kind of tafte at the extremities of their roots, fimi-
lar to that of the extremities of our ladeal veflels, for the purpofe of
felecting their proper food ; and befides different kinds of irritability

refiding

Sect. XIII. c. OF VEGETABLE ANIMATION, 107

Tcfiding in the various glands, which feparate honey, wax, rcfin, and
other juices from their blood ; vegetable life feems to poffefs an organ
of fenfe to diftinguifli the variations of heat, another to diftinguifh
the varying degrees of moifture, another of light, another of touch,
and probably another analogous to our fenfe of fmell. To thefe nauft
^be added the indubitable evidence of their paffion of love, and I think
we may truly conclude, that they are furniflied with a common fen-
forium belonging to each bud, and that they muft occafionaliy repeat
thofe perceptions either in their dreams or waking hours, and confe-
quently poffefs ideas of fo many of the properties of the external world,
and of their own exiftence.

P2 SECT.

io8 PRODUCTION OF IDEAS, Sect. XIV. i.

SECT. XIV.

OF THE PRODUCTION OF IDEAS.

I. Of materid and immaterial heings. DoSirine of St. Paul: II. \. Of the Jenfe
of touch. Of folidity. i. Of figure. Motion. Time. Place. Sface.
Number. 3. Of the penetrability of matter. 4. S-pir-it of animation poffejfes
, folidity, figure, vifihility, iBc. Of fpirits and angels. 5. The exiftence of ex-
ternal things. III. Of vifton. IV. Of hearing. V. Of fmell and tafte.
VI. Of the organ offenfe by which we perceive heat and cold, not by thefenfe of
touch. VII. Of the fenfe of extenfion, the whole of the locomotive mufcles may be
confideredasoneorganoffenfe. VIII . Of the fenfes of hunger, thirft, want of
frejh air, fuckling children, and liift. IX. Of many other organs offenfe belong-
ing to the glands. Of painful fenfations from the excefs of light, prejfure, heat,
itching, cauftics, and eleSiricity.

I. PHILOSOPHERS have been much perplexed to underftaiid, in
what manner we become acquainted with the external world ; info-
much that Dr. Berklj even doubted its exiftence, from having ob-
ferved (as he thought) that none of our .ideas refemble their cor^
refpondent objefts. Mr. Hume afferts, that our belief depends on the
greater diftinftnefs or energy of our ideas from perception ; and Mr.
Reid has lately contended, that our belief of external obje(5'£s is an in-
nate principle neceffarily joined with our perceptions.

So true is the obfervation of the famous Malbrancli, '* that our
fenfes are not given us to difcover the eflences of things, but to ac-
quaint us with the means of preferving our exiftence," (L. I. ch. v.)
a melancholy refleclion to philofophers !

Some philofophers have divided all created beings into material and

immaterial:

Sect. XIV. 2. PRODUCTION OF IDEAS. 109

immaterial : the former including all that part of being, which obeys
the mechanic laws of aftion and reaftion, but which can begin no
motion of itfelf; the other is the caufe of all motion, and is either
termed the power of gravity, or of fpecific attra£lion, or the fpirit of
animation. This immaterial agent is fuppofed to exift in or with
matter, but to be quite dillinft from it, and to be equally capable of
exiftence, after the matter, which now poffeffes it, is decompofed.

Nor is this theory ill fupported by analogy, fince heat, eledricity,
and magnetifm, can be given to or taken from a piece of iron ; and
muft therefore exift, whether feparated from the metal, or combined
wath it. From a parity of reafoning, the fpirit of animation would
appear to be capable of exifting as well feparately from the body as
with it.

I beg to be underftood, that I do not wifh to difpute about words,
and am ready to allow, that the powers of gravity, fpecific attra6tion,
ele£lricity, magnetifm, and even the fpirit of animation, may confift
of matter of a finer kind ; and to believe, with St. Paul and Mal-
branch, that the ultimate caufe only of all motion is immaterial, that
is God. St. Paul fays, " in him we live and move, and have our
being;" and, in the 15th chapter to the Corinthians, diftinguifhes
between the pfyche or living fpirit, and the pneuma or reviving
fpirit. By the words fpirit of animation or fenforial power, I mean
only that animal life, which mankind poffefles in common with brutes,
and in fome degree even with, vegetables, and leave the confideration
of the immortal part of us, which is the objed of religion, to thofe
who treat of revelation.

II. I. Of the Senfe of touch.

The firft ideas we become acquainted with, are thofe of the
fenfe of touch ; for the foetus muft experience fome varieties of agi-
tation-

no PRODUCTION OF IDEAS. Sect.XIV.z;

tation, and exert fome mufcular adlion, in the woaib ; and may with
great probability be luppofed thus to gain fome ideas of its own figure,
of that of the uterus, and of the tenacity of the fluid, that furrounds
it, (as appears from the fa3:s mentioned in the fucceeding Section
upon Inftinft.)

Many .of .the organs of fenfe are confined -to a fmall part of the
body, as th^ noftrils, ear, or eye, whilft the fenfe of touch is dif-
fufed over the whole ikin, but exifts with a more exquifite degree of
delicacy. at the extremities of the fingers and thumbs, and in the lips.
The fenfe of touch is -thns very com modioufly difpofed for the pur-
pofe of encompafling fmaller bodies, <ind for adapting itfelf to the in-
equalities of larger ones. The figure of fmall bodies feems to be
learnt by children by their lips as much as by their fingers ; on which
account they put every new objedl to their mouths, when they are
fatiated with food, as well as when they are hungry. And puppies
feem to learn their ideas of figure principally by the lips in their mode
of play.

We acquire our tangible ideas of obje6ls either by the fimple pref-
fure of this organ of touch againft a folid body, or by moving our
organ of touch along the furface of it. In the former cafe we learn
the length and breadth of the objedl by the quantity of our organ of
touch, that is impreffed by it: in the latter cafe we learn the length
and breadth of objefts by the continuance of their preffure on our
moving organ of touch.

It is hence, that we are very flow in acquiring our tangible ideas,
and very flow in recolleding them ; for if I now think of the tangible
idea of a cube, that ia, if I think of .its figure, a:nd of the folidity of
every part of that figure, I muft conceive myfeilf as pafling my fingers
■ over it, and feem in fome meafure to feel the idea, as I formerly did
the impreflion, at the ends of them, and am thus very .flo.w in diP
tinftly recoUefting it.

When a body compreffes any part of our fenfe of touch, what hap-
pens ?

Sect. XIV. 2. PRODUCTION OF IDEAS. iii

pens r' Firft, this part of our fenforium undergoes a mechanical
compreffion, which is termed a ftimulus ; fecondly, an idea, or con-
tradion of a part of the organ of feufe is excited ; thirdly, a motion
of the central parts, or of the whole fenforium, which is termed fen-
fation, is produced; and thefe three conftitute the perception of
foliditv.

2. O/Fip^re, Motion, time y Place, Space, Number.

No- one will deny, that the medulla of the brain and nerves has a
certain figure ; which, as it is difFufed through nearly the whole of
the body, mufl have nearly the figure of that body. Now it follows,
that the fpirit of animation, or living principle, as it occupies this me-
dulla, and no other part, (which is evinced by a great variety of cruel
experiments on living animals,) it follows, that this fpirit of anima-
tion has alio the fame figure as the medulla above defcribed. I ap-
peal to common fenfe ! the fpirit of animation aits, Where does it
adt ? It a6ls wherever there is the medulla above mentioned ; and
that whether the limb is yet joined to a living animal, or whether it
be recently detached from it ; as the heart of a viper or frog will re-
new its contraftions, when pricked with a pfn, for many minutes of
time after its exieftion from the body. — Does it a<£l any where elfe ?
— No ; then it certainly exifts in this part of fpace, and no where
elfe ; that is, it hath figure ; namely, the figure of the nervous
fyftem, which is nearly the figure of the body. When the idea of
folidity is excited, as above explained, a part of the extenfive organ of
touch is compreffed by fome external body, and this part of the fen-
forium fo compreffed exactly refembles in figure the figure of the
body that compreffed it. Hence, when we acquire the idea of foK-

dity.

112 PRODUCTION OF IDEAS. Sect. XIV. 2.

dity, we acquire at the fame time the idea of figure ; and this idea
of figure, or motion of a part of the organ of touch, exaftly refem-
bles in its figure the figure of the body that occafions it ; and thus
exaftly acquaints us with this property of the external world.

Now, as the whole univerfe with all its parts poffeffes a certain
form- or figure, if any part of it moves, that form or figure of the
whole is varied : hence, as motion is no other than a perpetual vari-
ation of figure, our idea of motion is alfo a real refemblance of the
motion that produced it.

It may be faid in objedlion to this definition of motion, that an
ivory globe may revolve on its axis, and that here will be a motion
without change of figure. But the figure of the particle x on one
fide of this globe is not the fatne figure as the figure of y on the
other fide, any more than the particles themfelves arc the fame,
though they are Jimilar figures ; and hence they cannot change
place with each other without difturbing or changing the figure of
the whole.

Our idea of time is from the fame fource, but is more abflra6ted,
as it includes only the comparative velocities of thefe variations of
figure; hence if it be alked. How long was this book in print-
ing ? it may be anfwered, WhillT: the fun was pafllng through
Aries.

Our idea of place includes only the figure of a group of bodies,
not the figures of the bodies themfelves. If it be alked where is Not-
tinghamftiire, the anfwer is, it is furrounded by Derbyfhire, Lincoln-
fliire, and Leicefterfhire ; hence place is our idea of the figure of one
body furrounded by the figures of other bodies.

The idea of space is a more abftradled idea of place excluding the
group of bodies.

The idea of number includes only the particular arrangements, or
diftributions of a group of bodies, and is therefore only a more ab-

ilradted

Sect.XIV. 2. PRODUCTION OF IDEAS. 113

flra6led idea of the parts of the figure of the group of bodies ; thus
when I fay England is divided into forty counties, I only fpeak of
certain divifions of its figure.

Hence arifes the certainty of the mathematical faiences, as they ex-
plain thefe properties of bodies, which are exactly refembled by our
ideas of them, whilft we are obliged to colleft almoft all our other
knowledge from experiment ; that is, by obferving theelFecls exerted
by one body upon another.

Of the Penetrability of Matter.

The impoffibility of two bodies exifling together in the fame fpace
cannot be deduced from our idea of folidity, or of figure. As foon as
we perceive the motions of objedls that furround us, and learn that,
we polTefs a power to move our own bodies, we experience, that
thofe objects, which excite in us the idea of folidity and of figure, op-
pofe this voluntary movement of our own organs ; as whilft I endea-
vour to comprefs between my hands an ivory ball into a fpheroid.
And we are hence taught b}'' experience, that our own body and thofe,
which we touch, cannot exifl in the fame part of fpace.

But this by no means demonftrates, that no two bodies can exift
together in the fame part of fpace. Galilaeo in the preface to his
works feems to be of opinion, that matter is not impenetrable ; Mr.
IVIichel, and Mr. Bofcowich in his Theoria. Phllof. Natur. have
efpoufed this hypothefis : which has been lately publifhed by Dr.
Prieftley, to whom the world is much indebted for fo many impor-
tant difcoveries in fcience. (Hift. of Light and Colours, p. 391.) The
uiiinterrupted pafTage of light through tranfparent bodies, of the elec-
tric 2ether through metallic and aqueous bodies, and of the magnetic
effluvia through all bodies, would feem to give fome probabihty to this

Q^ opinion.

114 PRODUCTION OF IDEAS. Ssct.XIV. 2.

opinion. Hence it appears, that beings mayexift vvithout poffeffing
the property of folidity, as well as they can exift: without poffeffing
the properties, which excite our fmell or tafte, and can thence occupy
fpace without detruding other bodies from it ; but we cannot be-
come acquainted with fuch beings by our fenfe of touch, any more
than we can with odours or flavours without our fenfes of fmell and
tafte.

But that any being can exift without exifting in fpace, is to my
ideas utterly incomprehenfible. My appeal is to common fenfe. To
be implies a when and a where ; the one is comparing it with the mo-
tions of other beings, and the other with their iituations.

If there was but one obje6t, as the whole creation may be confider-
ed as one objeft, then I cannot alk where it exifts ? for there are no
other objefls to compare its fituation with. Hence if any one denies,
that a being exifts in fpace, he denies, that there are any other
beings but that one ; for to anfwer the queftion, " Where does it
exift ?" is only to mention the fituation of the objedls that fur-
round it.

In the fame manner if it be alked — " When does a being ^xift ?"
The anfwer only fpecifies the fucceffive motions either of itfelf, or of
other bodies ; hence to fay, a body exifts not in time,, is to fay, that
there is, or was, no motion in the world.

4. Of the Spirit of Animation.

But though there may exift beings in the univerfe, that have not
the property of folidity ; that is, which can poffefs any part of fpace,
at the fame time that it is occupied by other bodies ; yet there may
be other beings, that can affume this property of folidity, or difrobe
themfelves of it occafionally, as we are taught of ipirits, and of an-
gels ;

Sect.XIV. 2. PRODUCTION OF IDEAS. 115

gels; and it would feem, that the spirit of animation mud be
endued with this property, otherwife how could it occafionally give
motion to the limbs of animals ? — or be itfelf ftimulated into motion
by the obtrufions of furrounding bodies, as of light, or odour ?

If the fpirit of animation was always neceffarily penetrable, it could
not influence or be influenced by the folidity of common matter ; they
would exift together, but could not detrude each other from the part
of fpace, where they exifl ; that is, they could not communicate mo-
tion, to each other. No two things can injiuence or ajf'ecl each other.,
which have not fome property common to both of them ; for to influence
or afFe6t another body is to give or communicate fome property to it,
that it had not before ; but how can one body give that to another,
which it does not poffefs itfelf? — The words imply, that they raufl
agree in having the power or faculty of poffefling fome common pro-
perty. Thus if one body removes another from the part of fpace,
that it poflefles, it muft have the power of occupying that fpace
itfelf: and if one body communicates heat or motion to another,
it follows, that they have alike the property of poffefling heat or
motion.

Hence the fpirit of animation at the time it communicates or re-
ceives motion from folid bodies, mufl: itfelf poffefs fome property of
folidity. And in confequence at the time it receives other kinds of
motion from light, it mufl: poffefs that property, which light pof-
feffes, to communicate that kind of motion ; and for which no lan-
guage has a name, unlefs it may be termed Vifibility. And at the
time it is fliimulated into other kinds of animal motion by the particles
of fapid and odorous bodies affe£ling the fenfes of tafl:e and fmell, it
mufl: refemble thefe particles of flavour, and of odour, in poffefling
fome fimilar or correfpondent property ; and for which language has
no name, unlefs we may ufe the words Saporofity and Odoroflty for
thofe common properties, which are poffeffed by our organs of tafle
and fmell, and by the particles of fapid and odorous bodies; as the

0^2 words

ii6 PRODUCTION OF IDEAS. Sect, XIV. 2,

words Tangibility and Audibility may exprefs the common property
poffefied by our organs of touch, and of hearing, and by the folid
bodies, or their vibrations, which afFe6l thofe organs.

5. Finally, though the figures of bodies are in truth refemblcd by
the figure of the part of the organ of touch, which is Simulated into
motion ; and that organ refembles the folid body, which Simulates .
it, in its property of folidity ; and though the fenfe of hearing re-
fembles the vibrations of external bodies in its capability of being fti-
mulated into motion by thofe vibrations ; and though our other
organs of fenfe referable the bodies, that flimulate them, in their ca-
pability of being flimulated by them ; and we hence become ac-
quainted with thefe properties of the external world ; yet as we can-
repeat all thefe motions of our organs of fenfe- by the efforts of voll^
tion, or in confequence of the fenfation of pleafure or pain, or by their-
alFociation with other fibrous motions, as happens in our reveries or ia
fleep, there would ftill appear to be fome difficulty in demonfbrating
the exiftence of any thing external to us.

In our dreams we cannot determine this circumftance, becaufe our.
power of volition is fufpended, and the flimuli of external objects
are excluded ; but in our waking hours we can compare our ideas
belonging to one fenfe with thofe belonging to anothei", and can thus
diftinguifh the ideas occafioned by irritation from thofe excited by
fenfation, volition, or affociation. Thus if the idea of the fweetnefs
of fugar fhould be excited in our dreams, the whitenefs and hardhefs
of it occur at the fame time by afibciation ; and we believe a material
lump of fugar prefent before us. But if, in our waking hours, the
idea of the fweetnefs of fugar occurs to us, the flimuli of furround-
ing objefts, as the edge of the table, on which we prefs, or green
colour of the grafs, on which we tread, prevent the other ideas of
the hardnefs and whitenefs of the fugar from being exerted by affoci-
ation. Or if they fhould occur, we voluntarily compare them with
the irritative ideas of the table or grafs above mentioned, and deteft

their

Sect.XIV. J. PRODUCTION OF IDEAS. ri;

their fallacy. We can thus diftinguifh the ideas caufed by the ftimuli
of external objefts from thofe, which are introduced by affjciation,
fenfation^ or volition ; and. during our waking hours can thus acquire
a knowledsfe of the external world. Which neverthelefs we canziot
do in our dreams, becaufe we have neither perceptions of external
bodies, nor the power of volition to enable us to compare them; with
the ideas of imas;inatievii.

nr. Of infion.

O^R eyes obferve a dilterence of colour, or of fhade, in the pro*
minences and depreflions of objefts, and that thofe (hades uniformly
var}% when the fenfe of touch, obferves any variation. Hence when
the retina becomes- ftimulated by colours or fhades of light in a certain
form, as in a circular fpot ; we know by experience, that this is a
fign, that a tangible body is before us ; and that its figure is refembled
by the miniature figure of the part of the organ, of vil]on,.that is thus
ftimulated.

Here whilft the ftimulated part of the retina refembles exadlv the
vifible figure of the whole in miniature, the various kinds of flimuli
from different colours mark the vifible figures of the minuter parts ;:.
and by habit we inftantly recall the tangible figures.

Thus when a tree is the obieft of fight, a part of the retina re-
fembling a flat branching figure is ftimulated by various fliades of co-
lours ; but it is by fuggeflion, that the gibbofity of the tree, and the-
mofs, that fringes its trunk, appear before us. Thefeare ideas of fuo--
geftion, which we feel" or attend to, affociated with the motions of the
retina, or irritative ideas, which we do not attend to.

So that though our vifible ideas refemble in miniature the outline
of the figure of coloured bodies, in other refpeds they ferve only as

a laii-

ii8 PRODUCTION OF IDEAS. SECT.XIV.4.

a language, which by acquired affociations introduce the tangible
ideas of bodies. Hence it is, that this fenfe is fo readily deceived by
the art of the painter to our amufement and inflrudion. The reader
will find much very curious knowledge on this fubjedt in Bifhop Berk-
ley's Effay on Vifion, a work of great ingenuity.

The immediate obje6t however of the fenfe of vifion is light ; this
fluid, though its velocity is fo great, appears to have no perceptible
mechanical imp ulfe, as was mentioned in the third Section, but feems
to flimulate the retina into animal motion by its tranfmiffion through
this part of the fenforium : for though the eyes of cats or other
animals appear luminous in obfcure places ; yet it is probable, that
none of the light, which falls on the retina, is refleded from it,
but adheres to or enters into combination with the choroids coat be-
hind it.

The combination of the particles of light with opake bodies, and
therefore with the choroide coat of the eye, is evinced from the heat,
which is given out, as in other chemical combinations. For the fun-
beams communicate no heat in their paffage through tranfparent bodies,
with which they do not combine, as the air continues cool even in the
focus of the largefl burning-glaffes, which in a moment vitrifies a
particle of opaque matter.

IV. Of the Organ of Hearing.

It is generally believed, that the tympanum of the ear vibrates
mechanically, when expofed to audible founds, like the firings of one
mufical inflrument, when the fame notes are ftruck upon another-
Nor is this opinion improbable, as the mufcles and cartilages of the
larynx are employed in producing variety of tones by mechanical vi-
bration : fo the mufcles and bones of the ear feem ada.pted to increafe

Sect. XIV. 4." PRODUCTION OF IDEAS. 119

or diminifli the ten fi on of the tympanum for the purpofes of fimilar
mechanical vibrations.

But it appears from diffedion, that the tympanum is not the im-
mediate organ of hearing, but that like the humours and cornea of
the eye, it is only of ufe to prepare the object for the immediate organ.
For the portio mollis of the auditory nerve is not fpread upon the
tympanum,, but upon the veftibulum, and cochlea, and femicircular
canals of the ear ; while between the tympanum and the expanfion
of the auditory nerve the cavity is faid by Dr. Cotunnus and Dr.
Meckel to be filled with water ; as they had frequently obferved by
freezing the heads of dead animals before they diffecled them; and water
being a more denfe fluid than air is much better adapted to the pro-
pagation of vibrations. We may add, that even the external openino-
of the ear is not abfolutely neceflary for the perception of found : for
fome people, who from thefe defefts would have been completely
deaf, have diilinguiftied acute or grave founds by the tremours of a
ftick held between their teeth propagated along the bones of the head,
(Haller. Phyf. T. V. p. 295.)

Hence it appears, that the immediate organ of hearing is not affe£led
by the particles of the air themfelves,,but is Simulated into animal
motion by the vibrations of them. And it is probable from the loofe
bones, which are found in the heads of fome fifhes, that the vibra-
tions of water are fenfible to the inhabitants of that element by a
fimilar organ.

The motions of the atmofphere, which we become acquainted with
by the fenfe of touch, are combined with its folidity, weight, or vis
inertiae; whereas thofe, that are perceived by this organ, depend alone
on its elafticity. But though the vibration of the air is the immediate
objed of the fenfe of hearing, yet the ideas, we receive by this fenfe,
like thofe received from light, are only as a language, which by ac-
quired aflbciations acquaints us with thofe motions of tangible bodies,
3. which J

I20 PRODUCTION OF IDEAS. Sect. XIV. 6.

which depend on their elaflicity ; and which we had before learned
bj our fenfe of touch.

V. Of Smell and of tap.

The objefts of fmell are diflblved in the fluid atmofphere, and
thofe of tafte in the faliva, or other aqueous fluid, for the better dif-
fufing them on their refpeftive organs, which feem to be ftimulated
into animal motion perhaps by the chem.ical affinities of thefe particles,
which conftitute the fapidity and odorofity of bodies with the nerves-
of fenfe, which perceive them.

Mr. Volta has lately obferved a curious circumftance relative to our
fenfe of tafte. If a bit of clean lead and a bit of clean filver be fepa-
rately applied to the tongue and palate no tafl:e is perceived ; but by
applying them in contaft in refpedt to the parts out of the mouth,
and nearly fo in refpeft to the parts, which are immediately applied to
the tongue and palate, a faline or acidulous tafte is perceived, as of a
fluid like a ftream of eleftricity pafling from one of them to the other.
This new application of the fenfe of tafte deferves further invefti^a-
tion, as it may acquaint us with new properties of matter.

VI. Of the Senfe of Heat.
y

There are many experiments in chemical writers, that evince the
exiftence of heat as a fluid element, which covers and pervades all
bodies, and is attradted by the folutions of fbme of them, and is de-
truded from the combination of others. Thus from the combinations
of metals with acids, and from thofe combinations of animal fluids,

which

Sect.XIV.6. production of ideas. 121

which are termed fecretions, this fluid matter of heat is given out
amougft the neighbouring bodies ; and in the folutions of falts in wa-
ter, or of water in air, it is abforbed from the bodies, that furround
them ; whilft in its facihty in pafllng through metallic bodies, and its
difficulty in pervading refins and glafs, it relembles the properties of
the eledlric aura ; and is like that excited by friftion, and feems like
that to gravitate amongft other bodies in its uncombined ftate, and to
find its equilibrium.

There is no circumftance of more confequence in the animal eco-
nomy than a due proportion of this fluid of heat ; for the digeftion of
our nutriment in the flomach and bowels, and the proper qualities o£
all our fecreted fluids, as they are produced or prepared partly by animal
and partly by chemical procefles,' depend much on the quantity of
heat ; the excefs of which, or its deficiency, alike gives us pain,
and induces ns to avoid the circumftances that occadon them. And
in this the perception of heat effentially differs from the perceptions
of the fenfe of touch, as we receive pain from too great preflure of
folid bodies, but none from the abfence of it. It is hence probable,
that nature has provided us with a fet of nerves for the perception of
this fluid, which anatomifts have not yet attended to.

There may be fome difficulty in the proof of this aflertion ; if we
look at a hot fire, we experience no pain of the optic nerve, though
the heat along with the light mufl be concentrated upon it. Nor
does warm water or warm oil poured into the ear give pain to the
organ of hearing ; and hence as thefe organs of fenfe do not perceive
fmall exceflTes or deficiences of heat ; and as heat has no greater ana-
logy to the folidity or to the figures of bodies, than it has to their
colours or vibrations ; there feems no fufficient reafon for our afcrib-
ing the perception of heat and cold to the fenfe of touch ; to which it
has generally been attributed, either becaule it is diffufed beneath the
whole {km like the fenfe of touch, or owing to the inaccuracy of our
obfervations, or the defedt of our Iang;uag;es.

R The

122 PRODUCTION OF IDEAS. S£ct.XIV.7;^

There is another circumftance would induce us to believe, that the
perceptions of heat and cold do not belong to the organ of touch ;
lince the teeth, which are the leaft adapted for the perceptbns of fo-
lidity or figure, are the moil fenfible to heat or cold ; whence we are,
forewarned from fwallowing thofe materials, whofe degree of coldnefs
or of heat would injure our ftomachs.

The following is an extraO: from a letter of Dr. R. W. Darwin„
of Shrewfbury, when he was a ftudent at Edinburgh. " I made an,
experiment yefterday in our hofpital, which much favours your opi-
nion, that the fenfation of heat and of touch depend on different feta
of nerves. A man who had lately recovered from a fever, and was
flill weak, was feized with violent cramps in his legs and feet ; which,
were removed by opiates,, except that one of his feet remained infeu--
fible. Mr. Ewart pricked him with a pin in five or fix places, and
the patient declared he did not feel it in the leafl, nor was he fenfible
of a very fmart pinch. I then held a red-hot poker at fome diftance,
and brought it gradually nearer till it came within three inches, when
he afferted that he felt it quite diftindly. I fuppofe fome violent ir-^
ritation on the nerves of touch, had caufed the cramps, and had left
them paralytic ; while the nerves of heat, having fuffered no increafed
ftimulus, retained their irritability,"

VII. Of the Senfe of Extenfioni

The organ of touch is properly the fenfe of preffure, but the mufr
cular fibres themfelves conftitute the organ of fenfe, that feels ex-
tenfion. The fenfe of preffure is always attended with the ideas of
the figure and folidity of the object, neither of which accompany our
perception of extenfion. The whole fet of mufcles, whether they are
hollow ones, as the heart, arteries, and inteilines, or longitudinal

ones

Sect. XIV. 7- PRODUCTION OF IDEAS. 123

ones attached to bones, contra(fi: themfelves, whenever they are fti-
mulated by forcible elongation ; and it is obfervable, that the white
mufcles, which conftitute the arterial iyftcm, feem to b'e excited
into contraclion from no other kinds of ilimulus, according to the
experiments of Haller, And hence the violent pain in fonie inflam-
mations, as in the paronychia, obtains immediate relief by cuttino-
the membrane, that was ftretched by the tumour of the fubjacent
parts.

Hence the whole mufcular fvftem mav be conGdered as one orsan
of fenfe, and the various attitudes of the bodv, as ideas belonsine to
this organ, of many of which we are hourly confcious, while many
others, like the irritative ideas of the other fenfes, are performed with-
out our attention.

When the mufcles of the heart ceafe to aft, the refluent blood
again diftends or elongates them ; and thus irritated they contract
as before. The fame happens to the arterial fyftem, and I fuppofe
to the capillaries, inteftines, and various glands of the body.

When the quantity of urine, or of excrement, diftends the bladder,
or reftum, thofe parts contra(5t, and exclude their contents, and
many other mufcles by affociation act along with them ; but if thefe
evacuations are not foon complied with, pain is produced by a little
further extenlion of the mufcular fibres : a fimilar pain is caufed in
the mufcles, when a limb is much extended for the redudlion of dif-
located bones ; and in the punifhment of the rack : and in the pain-
ful cramps of the calf of the leg, or of other mufcles, for a greater
degree of contra£lion of a mufcle, than the movement of the two
bones, to which its ends are affixed,, will admit of, muft give fimi-
lar pain to that, which is produced by extending it beyond its due
length. And the pain from punftures or incifions arifes from the dif-
lention of the fibres, as the knife paffes through them ; for it nearly
ceafes as foon as thedivifion is completed.

R 2 All

^*v-

124 PRODUCTION OF IDEAS. Sect. XIV. 8.

All thefe motions of the mufcles, that are thus naturally excited
by the flimulus of diflending bodies, are alfo liable to be called into
ftrong atflion by their catenation, with the irritations or fenfations
produced by the momentum of the progrefiive particles of blood in
the arteries, as in inflammatory fevers, or by acrid fubftances- oit
other fenfible organs, as in the ftrangury, or tenefmus,. or cholera.

We (hall conclude this account of the fenfe of extenfion by obferv-
ing, that the- want of its object is- attended with a difagreeable fenfa-
tion, as well as the excefs of it. In thofe hollow mufcles, which
have been accuftomed to it, this difagreeable fenfation is called faint-
nefs, emptinefs, and finking ; and, when it arifes to a certain degree,
is attended with fyncape, or a total quiefcence of all motions, but the
internal irritative ones,, as happens from fudden lofs of blood, or in the.;
operation of tapping in the dropfy...

VIII^ Of the Appetites (^Hunger, Thir/i, Heat,. Extenfion,. the want:
of frejh Air^ animal hove,, and the Suckling, of Children..

Hunger is moft. probably perceived by thofe numerous ramifica-
tions of nerves that arc feen about the upper opening of. the ftomach;
and third by the nerves about the fauces, and.thetopof the gula..
The ideas of thefe fenfes are few in the generality of mankind, but-
are more numerous in thofe, who by difeafe, . or indulgence, defire .
particular kinds of foods or liquids.

A fenfe of heat has already been fpoken of, which. may with pra^-
priety be called an appetite,,, as we painfully defire it, when it is de-
ficient in quantity.

The fenfe of extenfion maybe ranked amongft thefe appetites,,
unce the deficiency of its objeft gives difagreeable fenfation; when
this happens in the arterial fyftem, it is called faintnefs,.and feems to

7 • bear

Sect.XIV. 8. PRODUCTION OF IDEAS. 125

bear fome analogy ta hunger and to cold ; which like it are attended
with emptinefs of a part of the vafcular fy/lem.

The fenfe of want of frefli air has not been attended to, but is as
diflin£l as the others, and the £rft perhaps that we experience
after our nativity ; from the want of the objedl of this fenfe many
difeafes are produced, as the jail-fever, plague, and other epidemic
maladies. Animal love is another appetite, which occurs later in
life,, and the females of ladliferous animals have another, natural inlet
of pleafure or pain from the fuckling their offspring. The want of,
which either owing, to the death of their progeny, or to the fafhiori of
their country, has been fatal to many of the fex. The males have.
alfo peroral glands,, which are frequently turgid with a thin milk at
their nativity, and are furnifhed with nipples, which ere£l on titillar
tion.like thofe of the female ; but which feem now to be of no fur-
ther ufe, owing perhaps to fome change which thcfe animals have
undergone in the gradual progreffion of the formation of the earth,
and of all that it inhabit..

Thefe feven laft mentioned fenfes may properly be termed appetites,,
as they differ from thofe of touch, fight, hearing, tafte, and fmell,.
in this refpedl ; that they are affedted with pain as well by the defedl-
of their obje£ls as by the excefs of them, which is not fo in the latter..
Thus cold and hunger give us pain, as well as an excefs of heat or.
fatiety i but it is not fo with darknefs and filence. ,

IX. Before we conclude this Sefl'ion on the organs of fenfe, we
muft obferve, that, as far as we know, there are many more fenfes,
than have been here mentioned, as every gland feems to be influenced
to feparate from the blood, or to abforb from the cavities of the body, .
or from the atmofphere, its appropriated fluid, by the itimulus of
that fluid on the living gland ; and not by mechanical capillary ab-
forption, nor by chemical affinity. Hence it appears, that each of:

thefe

126 PRODUCTION OF IDEAS. Sect. XIV. 9,

thefe glands muft have a peculiar organ to perceive thefe irritations,
but as thefe irritations are not fucceeded by fenfation, they have not
acquired the names of fenfes.

However when thefe glands are excited into motions ftronger thaa
ufual, either by the acrimony of their fluids, or by their own irrita-
bility being much increafed, then the fenfation of pain is produced in
them as in all the other fenfes of the body ; and thefe pains are all of
different kinds, and hence the glands at this time really become each
a different organ of fenfe, though »thefe different kinds of pain have
acquired no names.

Thus a great excefs of light -does not give the idea of light but of
■pain 4 as in forcibly opening the eye when it is much inflamed. The
-great excefs of prefTure or diilention, as when the point of a pin is
-preffed upon our flein, produces pain, (and when this pain of the
ienfe of touch is flighter, it is termed itching, or tickling,) without
any idea of folidity or of figure : an excefs of heat produces fmarting,
of cold another kind of pain ; it is probable by this fenfe of heat the
pain produced by cauflic bodies is perceived, and of eledlricity, as all
thefe are fluids, that permeate, diftend, or decompofe the parts that
&el thera.

S E C T.

SecT.XV.u CLASSES OF IDEAS, 127

SECT. XV^.

OF THE CLASSES OF IDEAS,.

t. I. Ideas received in tribes. 2. We comhme them further, or aiJiraSf from ihefe
tribes. 3. Co7n;^lex ideas. 4. Compounded ideas. 5. Simple ideas, modes,
Jubfiances, relations, general ideas. 6. Ideas of reflexion. 7. Memory and
imagination imperfeSlly defined. Ideal prefence. Memorandum-rings. II. \. Ir-
ritative ideas. Perception. 1. Serfttive ideas, imagination. 3. Voluntary
ideas, recolleSlion. 4. Affociated ideas, fuggejlion. III. \. Definitions of per-
ception, memory. 2. Reafoning, judgtnent, doubting, dijlinguijhing, comparing,
J. Invention. 4. Confcioufnefs. ^. Identity. 6,. Lapfe of time, 7. Free-
tvHL

°L AS theconftituent elements of tKe materiar world are only per-
ceptible to our organs of fenfe in a ftate of combination ; it follows,
that the ideas or fenfual motions excited by them, are never received
fingly, but ever with a greater or lefs degree of combination. So the
colours of bodies or their hardnefies occur with their figures : every
fmell and tafte has its degree of pungency as well as its peculiar fla-
vour : and each note in mulic is combined with the tone of fome in-
ftrument. It appears from hence, that we can be fenfible of a num-
ber of ideas, at the fame time, fuch as the whitenels, hardnefs, and
coldnefs, of a fnow-ball, and can experience at. the fame time many
irritative ideas of furrounding bodies, which we do not attend to, as
mentioned in Se£lion VII. 3. 2, But thofe ideas which belong to the
fame fenfe, feem to be more eafily combined into fynchronous tribes,,
than thofe which were not received by the fame iti\{c, as we can

128 CLASSES OF IDEAS. Sect. XV. .i.

more eafily think of the whitenefs and figure of a lump of fugar at
the fame time, than the whitenefs and fweetnefs of ir.

2, As thefe ideas, or fenfual motions, are thus excited with greater
or lefs degrees of combination ; fo we have a power, when we repeat
•them either by our volition or fenfation, '-to increafe or diminifli this
degree of combination, that is, to form compounded ideas from thoie,
which were more iimple; and *abfl:ra6l ones from thofe, which were
more complex, when they were firfl excited; that is, we can repeat
a part or the whole of thofe feiifuai motions, which did confbitute our
ideas of perception ; and the repetition of which now coxiftitutes our
ideas of recoUedlion, or of imagination.

•3. Thofe ideas, which we repeat without change of the quantity
of -that combination, with which we firft received them^ are called
complex ideas, as when you recolieft Weftn.infter Abbey, or the
planet Saturn : but it muft be obferved, that thefe complex ideas,
■thus re-excited by volition, fenfation, or aflbciation, are feldom per-
fe€t copies of their correfpondent perceptions, except in our dreams,
where other external objefts do not detraft our attention.

4. Thofe ideas, which are more complex than the natural obje£ts
that firft excited them, have been called compounded ideas, as when
we think of a fphinx, or griffin.

5. And thofe that are lefs complex than the correfpondent natural
objefts, have been termed abftradted ideas : thus fweetnefs, and white-
nefs, and folidity, are received at the fame time from a lump of fugar,
yet I can recolleft any of thefe qualities without thinking of the
•others, that were excited alons: with them.

When ideas are {o far abftracled as in the above example, they have
been termed fimple by the writers of metaphyfics, and feem indeed to
be more complete repetitions of the ideas or fenfual motions, originally
excited by external obje(fls.

Other claffes of thefe ideas, where the abftradlion has not been fo
great, ha.ve been termed, by Mr. Locke, modes, fubftances, and re-
lations.

Sect. XV. r. CLASSES OF IDEAS. 129

lations, but they feem only to differ in their degree of abflrafbion from
the complex ideas that were at firft excited; for as thefe complex or
natural ideas are themfelves imperfeft copies of their correfpondent
perceptions, fo thefe abftradl; or general ideas are only ftill more im-
perfedl copies of the fame perceptions. Thus when I have feen an
objedi but once, as a rhinoceros, my abflrait idea of this animal is the
fame as my complex one. I may think more or lefs diftindly of a
rhinoceros, but it is the very rhinoceros that I faw,. or fome part or
property of him, which recurs to my mind.

But when any clafs of complex objefts becomes the fubje6t of con-
verfation, of which I have feen many individuals, as a caftle or an
army, fome property or circumftance belonging to it is peculiarly al-
luded to; and then I feel in my own mind, that my abflradl idea of
this complex obje£t is only an idea of that part, property, or attitude
of it, that employs the prefent converfation, and variesvvith every
fentence that is fpoken concerning it. So if any one fhould fay,
" one may fit upon a horfe fafer than on. a camel," my abftraft idea
of the two animals includes only an outline of the level back of. the
one, and the gibbofity on the back of the other. What noife. is that
in the ftreet? ? — Some horfes trotting over the pavement.. H&re my
idea of the horfes includes principally thefhape aad motion of their
legs. So alfo the abftrad ideas of goodnefs and courage are fl:ill
more imperfe£l reprefentations- of the objeds they were received
from ; for here we abfiracl the material parts.,, arid recoiled only the
qualities;

Thus we abftrad fo much from fome of our complex ideas, that
at length it becomes difficult to determine of what perception they
partake ; and; in. many inftances our. idea feems to be no other than of
the fouad or letters of the word, that ftands -for the collective tribe,
of which we are faid to have arLabUraded idea,, as noun, verb, chi-
maera, apparition.

S 6. Ideas

13^ CLASSES OF IDEAS. Ssct.XV. w

6. Ideas have been divided into thofe of perception and thofe of
reflexion, but as whatever is perceived mufl be external to the
organ that perceives it, all our ideas muft originally be ideas of per-
ception.

7. Others have divided our ideas into thofe of memory, and thofe
of imagination ; they have faid that a recolledion of ideas in the order
they were received eonftitutes memory, and without that order ima-
gination ; but all the ideas of imagination, excepting the few that are
termed fimple ideas, are parts of trains or tribes in the order they
were received : as if I think of a fphinx, or a griffin, the fair face,
bdfom, wings, claws, tail, are all complex ideas in the order they
were received : and it behoves the writers, who adhere to this de-
finition, to determine, how fmall the trains muft be, that (hall be
called imagination ; and how great thofe, that {hall be called memory.

Others have thought that the ideas of memory have a greater viva-
city than thofe of imagination : but the ideas of a perfon in fleep, or
.in a waking reverie, where the trains connefted with fenfation are un-
interrupted, are more vivid and diftind than thofe of memory, fo that
they cannot be diftinguiflied by this criterion.

The very ingenious author of the Elements of Criticifm has de-
fcribed what he conceives to Tse a fpecies of memory, and calls it ideal
prefence ; but the inftances he produces are the reveries of fenfation,
and are therefore in truth connexions of the imagination, though they
are recalled in the order they were received.

The ideas conne£led by aflociation are in common difcourfe attri-
buted to.memory, as we talk of memorandum-rings, and tie a knot
-on our handkerchiefs to brino; ibmethino; into our minds at a diftance
of time. And a ichool-boy, w<ho can repeat a thoufand unmeaning
lines in Lilly's Grammar, is faid to have a good memory. But thefe
■have been already (hewn to belong to the clafs of aflociation j and are

rtermed ideas of fuggeftion.

H. Laftly,

Sect.XV. 3. CLASSES OF IDEAS. 131

11. Laftly, the method already explained of claffing ideas into thofe
excited by irritation, fenfation, volition, or aflbciation, we hope will
be found more convenient both for explaining the operations of the
mind, and for comparing them with thofe of the body ; and for the
illuftration and the cure of the difeafes of both, and which we fhall
here recapitulate. '

1. Irritative ideas are thofe, which are preceded by irritation, which
is excited by objefts external to the organs of fenfe : as the idea of
that tree, which either I attend to, or which I fhun in walking near
it without attention. In the former cafe it is termed perception, in
the latter it is termed fimply an irritative idea.

2» Senfitive ideas are thofe, which are preceded by the fenfation of
pleafure or pain ; as the ideas, . which conilitute our dreams or reve-
ries, .this is called imagination. .

3. Voluntary ideas are thofe, which are preceded : by voluntary
exertion, as when I repeat the alphabet backwards : this is called re-
GolleiTtion.

4. Aflbciate ideas are thofe, which are preceded by other ideas or
raufcular motions, as when we think over or repeat the alphabet by
rote in its ufual order j or fin g a tune we are accuftomed to; this is
sailed fuggeftion.

IIL I. Perceptions fignify thofe ideas, which are preceded by ir-
ritation and fucceeded by the fenfation of pleafure or pain, for what-
ever excites eur attention interefts us ; that is, it is accompanied with
pleafure or pain ; however flight may be the degree or quantity of
either of them.

The word memory includes two clafles of ideas, either thofe which
are preceded by voluntary exertion, or thofe which are fuggefted by
their aflbciations with other ideas.

2. Rcafoning is that operation of the ienforium, by which we ex-
cite two or many tribes of ideas ; and then re-excite the ideas, in •
which they differ, or correfpond- If we determine this difference, it

S 2 is

132 CLASSES OF IDEAS. Sect.XV. 3.

is called judgment ; if we in vain endeavour to determine it, it is called
doubting.

If we re-excited the ideas, in which they difFer, it is called dif-
tinguifliing. If we re- excite thofe in which they correfpond, it is
called comparing.

3. Invention is an operation of the fenforium, by which we volun-
tarily continue to excite one train of ideas, fuppofe the defign of
raifing water by a machine ; and at the fame time attend to all other
ideas, which are connedted with this by every kind of catenation ;
and combine or feparate them voluntarily for the purpofe of obtaining
fome end.

For we can create nothing new, we can only combine or feparate
the ideas, which we have already received by our perceptions : thus
if I wifh to reprefent a monfler, I call to my miiid the ideas of every
thing difagreeable and horrible, and combine the naftinefs and glut-
tony of a hog, the .ftupidity ai^ obftinacy of an afs, with the fur and
awkwardnels of a bear, and call the new combmation Caliban. Yet
fuch amonfter may exiil in nature, as all his attributes are parts of
nature. So when I wifli to reprefent every thing, that is excellent,
and .amiable ; when I combine benevolence with cheerfulnefs, wif-
■dom, knowledge, tafte, wit, beauty of perfon, and elegance of
manners, and aflbciate them in one lady as a pattern to the world,
it is called invention ; yet fuch a perfon may exift, — fuch a perfoa

does exift ! — It is , who is as much a monfter as

Caliban.

4. In refpe£t to confcioufnefs, we are only confcious of our ex-
iftence, when we think about it ; as we only perceive the lapfe of
time, when we attend to it ; when we are bufied about other objeds,
neither the lapfe of time npr the confcioufnefs of our own exiftence
can occupy our attention. Hence, when we think of our own ex-
iftence, we only excite abftradled or reflex ideas (as they are termed),
of our principal pleafures or pains, of our defires or averfions, or of the

figure

Sect. XV. 3- CLASSES OF IDEAS. .133

figure, folidity, colour, or other properties of our bodies, and call that
aft of the lenforium a confcioufnefs of our exiftence. Some philofo-
phers, I believe it is Des Cartes, has faid, " I think, therefore I exift."
But this is not right reafoning, becaufe thinking is a mode of exiftence;
and it is thence only faying, " I exift, therefore I cxift." For there
are three modes of exiftence, or in the language of grammarians three
kinds of verbs. Firft, (imply I am, or exift. Secondly, I am acting,
or exift in a ftate of adivity, as I move. Thirdly, I am fuffering, or
exift in a ftate of being adted upon,, as I am moved. The when, and
the where, as applicable to this exiftence, depends on the fucceffive
motions of our own or of other bodies ; and on their refpeftive fitua-
tions, as fpoken of Sed. XIV. 2. 5.

5. Our identity is known by our acquired habits or catenated trains
of ideas and mufcular motions ; and perhaps, when we compare in-
fancy with old age, in thofe alone can our identity be fuppoled to exift.
For what elfe is there of fimilitude between, the firft fpeck of living
entity and the mature man ? — every deduction of reafoning, every fen-
timent or paflion, with every fibre of the corporeal part of our lyftem,
has been fubjeft almoft to annual mutation ; while fome catenations
alone of our ideas and mufcular a£lions have continued in part un-
changed.

By the facility, with which we can in our waking hours voluntarily
produce certain fucceffive trains of ideas, we know by experience,
that we have before reproduced them ; that is, we are confcious of a
time of our exiftence previous to the prefent time ; that is, of our iden-
tity now and heretofore. It is thefe habits of aftion, thefe catenations
of ideas and mufcular motions, which begin with life, and only ter-
minate with it ; and which we can in fome meafure deliver to our
pofterity ; as explained in Se£l. XXXIX.

6. When the progreflive motions of external bodies make a part of
our prefent catenation of ideas, we attend to the lapfe of time ; which
appears the longer, the more frequently we thus attend to it ; as when

t34 CLASSES OF IDEAS. Sect.XV. 3^.

we expe£l fomething at a certain hour, which much interefts us,,
whether it be an agreeable or difagreeable event ;. or when we count
the paffiiig feconds on a flop- watch.

When an idea of our own perfon, or a reflex idea of our pleafures-
and pains, delires and averiions, makes a part of this catenation, it is
termed confcioufnefs ; and if this idea of confcioufnefs makes a part of
a catenation, which we excite by recolledion, and know by the facility-
with which we excite it, that we have before experienced it,, it is.
called identity, as explained above^

7. In refpeft to freewill, it is certain, that we cannot will to think
of a new train of ideas, without previoufly thinking of the firft link of:
it; as I cannot will to think of a black fwan, without previoufly think-
ino- of a black fvvan. But if I now think of a tail, I can voluntarily
recolle£l all animals, which have tails; m^ will is fo far free, that t
can purfue the ideas linked to this idea of tail, as far as my knowledge
of the fubjed extends ; but to will without motive is to will without
defire or averfion; which is as abfurdas to feel without pleafure or'pain;
they are both folecifms in the terms. So far are we governed by the
catenations of motions, which affeft both the body and the mind of
man, and which begin with our irritability, and end with it.

SECT.

Sect. XVI. I. OF INSTINCT. 155

SECT. XVI.

OF INSTINCT.

HAUD EQTJIDEM CREDO, QUIA SIT DIVINITU3 ILLIS
INGENIUM, AUT RERUM FATO PRUDENTIA MAJOR.

VIRG. GEORG. L. I. 415,

I. Infi'tuSltve anions defined. Of connate paffions. II. Of the fenjations and mot ions
of the fcetus in the womb. III. Some animals are more ferfeSfly fanned than
others before nativity. Of learning to walk. IV. Ofthefwallowing, breath-
ing, fucking, pecking, and lapping of young animals. V. Of the fenfe of fmell,
and its ufes to animals. Why cats do not eat their kittens. VI. Of the accu-
racy of fight in mankind, and their fenfe of beauty. Of the fenfe of touch in ele-
phants, monkies, beavers, men. VII. Of natural language. VIII. The
origin of natural language ; i. the language of fear ; 1. of grief; 2-Oftefider
pleafure; 4. offerenepleafure; 5. of anger ; 6. of attention. IX. Artificial
language of turkies, hens, ducklings, wagtails, cuckoos, rabbits, dogs, and
nightingales. X. Ofmufic; of tooth-edge; of a good ear; of architeSiure.
XI. Of acquired knowledge ; of foxes, rooks, feildfares, lapwings, dogs, cats,
horfes, crows, and pelicans. XII. Of birds of paff age, dormice, fnakes, hats,
Jwallows, quails, ringdoves, fare, chafjinch, hoopoe, chatterer, hawfinch, crofs-
hill, rails and cranes. XIII. Of birds nefts; of the cuckoo; of fwallows nefts ;
of the taylor bird. XIV. Of the old foldier ; of haddocks, cods, and dogfijh ;
cf the remora; of crabs, herrings, and falmon. XV. Of Jpidsrs, caterpillars,
antSy and the ichneumon. XVI. i. Of locufts, gnats; 1. bees; 3. dormice,
fits, worms, ants, and wafps. XVIL Of the faculty that difiinguifhes man
from the brutes.

I. ALL thofe internal motions of animal bodies, which contribute

to digeft their aliment, produce their fecretions, repair their injuries,

or increafe their growth, are performed without our attention t)r con-:

8 -fcioufnefs.

136 , OF INSTINCT. Sect.XVLz.

fcioufnefs. They exift as well In our fleep, as in our waking hours,
as well in the foetus during the time of geftation, as in the infant
after nativity, and proceed with equal regularity in the vegetable as
in the animal lyftem. Thefe motions have been fliewn in a former
part of this work to depend on the irritations of peculiar fluids, and as
they have never been clafled amongffc the inftindlive adlions, of animals^
are precluded from our prefent difquifition.

But all thofe adlions of men or animals, that are attended with con-
fcioufnefs, and feem neither to have been diredted by their appetites,
taught by their experience, nor deduced from obfervation or tradition,
have been referred to the power of inftindt. And this power has been
explained to be a divine fomething, a kind of infpiration ; whilft the
poor animal, that pofiefies it, has been thought little better than a
machine 1

The irkfomenefs, that attends a continued attitude of the body,, or
the fiains, that we receive from heat, cold, hunger, or other injuri-
ous circumftances, excite w^ to general locomotion : and our fenfes are
fo formed and eonftituted by the hand of nature, that certain obj.e(Sts
prefent us with pleafure, others with pain, and we are induced to ap-
proach and embrace thefe, to avoid and abhor thofe, as fuch fenfa-
tions direft us.

Thus the palates of fome animal's are gratefully affedted by the
raaftication of fruits, others of grains, and others of flefh ; and they
are thence inftigated to attain, and to coi^^furae thofe materials j. and
are furnifhed with powers of mufcular motion, and of digeftion pro-
per for fuch purpofes.

Thefe fenjatiom znd. dejires conftitute a part of our lyftem, as our
mufcles and bo?ies conftitute another part : and hence they may alike
be termed natural or connate ; but neither of them can properly be
termed inftin&ive : as the word inftin6t in its ufual acceptation refers
only to the aciions of animals, as above explained : the origiii of thefe
a.^io7i$ is the fubjed of our prefent enquiry.

The

Sect. XVI. 2. OF INSTINCT. i-^-]

The reader is intreated carefully to attend to this dehnition of /«-
fiinciive anions, left by ufing the word inftiuft without adjoining any
accurate idea to it, he may not only include the natural delires of love
and hunger, and the natural fenfations of pain or pleafure, but the
figure and contexture of the body, and the faculty of reafon itfelf un-
der this general terna.

11. We experience fome fenfations, and perform fome aclions before
our nativity; the fenfations of cold and warmth, agitation and reft,
fulnefs and inanition, are inftances of the former ; and the repeated
ftruggles of the limbs of the foetus, which begin about the middle of
geftation, and thofe motions by which it frequently wraps the um-
bilical chord around its neck or body, and even fometimes ties it on
a knot ; are inftances of the latter. Smellie's Midwifery, (Vol. I.
p. 182).

By a due attention to thefe circumflances many of the adions of
young animals, which at firfl fight feemed only referable to an inex-
plicable inftinfl:, will appear to have been acquired like all other ani-
mal aftions, that are attended with confcioufnefs, by the repeated
efforts of our mufcles under the conduEi of our fenfations or defres.

The chick in the fhell begins to move its feet and legs on the fixth
day of incubation (Mattreican, p. 138); or on the feventh day,
(Langley) ; afterwards they are feen to move themfelves gently in
the liquid that furrounds them, and to open and fhut their mouths,
(Harvei, de Generat. p. 62, and 197. Form de Poulet. ii. p. 129).
Puppies before the membranes are broken, that involve them, are
feeu to move themfelves, to put out their tongues, and to open and
Ihut their mouths, (Harvey, Gipfon, Riolan, Haller). And calves
lick themfelves and fwallow many of their hairs before their nativity:
which however puppies do not, (Swammerden, p. ^\(). Flemyng
Phil. Tranf. Ann. 1755. 42). And towards the end of geftation, the
foetus of all animals are proved to drink part of the liquid in which
they fwim, (Haller. Phyfiol. T. 8. 204). The white of egg is found

T in

138 OF INSTINCT. SECT.XVL3.

ill the mouth and gizzard of the chick, and is nearly or quite con-
fumed before it is hatched, (Harvei de Generat. 58). And the hquor
amnii is found in the mouth and ftomach of the human foetus, and of
calves ; and how elfe fhould that excrement be produced in the in-
teftines of all animals, which is voided in great quantity foon after
their birth ; Gipfon, Med. Eflays, Edinb. V. i. 13. Halleri Phyfiolog*
T. 3. p. 318. and T. 8). In the ftomach of a calf the quantity of
this liquid amounted to about three pints, and the hairs amongft it
were of the fame colour with thofe on its Ikin, (Blafii Anat. Animal,
p. m. 1 22). Thefe fadls are attefted by many other writers of credit,
beiides thofe above mentioned.

III. It has been deemed a furprifing inftance of inftin£t, that calves
and chickens Ihould be able to walk by a few efforts almoft immedi-
ately after their nativity : whilft the human infant in thofe countries
where he is not incumbered with clothes, as in India, is five or fix
months, and in our climate almoft a twelvemonth,, before he caa
fafely ftand upon his feet.

The ftruggles of all animals in the womb muft refemble their mode-
of fwimming, as by this kind of .motion they can beft change their
attitude in water. But the fwimming of the calf and chicken re-
fembles their manner of walking, which they have thus in part ac-
quired before their nativity, and hence accomplifh it afterwards with
very few efforts, whilft the fwimming of the human creature re-
fembles that of the frog, and totally differs from his mode of
walking.

There is another clrcumftance to be attended to in this af?air, that
not only the growth of thofe peculiar parts of animals, which are firft
wanted to fecure their fubfiftence, are in general furtheft advanced
before their nativity : but fomc animals come into the world more
completely formed throughout their whole fyftem than others : and
are thence much forwarder in all their habits of motion. Thus the
colt, and the lamb, are much more perfefl animals than the blind

3 • P"PP7>

Sect. XVI. 4. OF INSTINCT. 139

puppy, and the naked rabbit ; and the chick of the pheafant, and the
partridge, has more perfeft plumage, and more perfedi eyes, as well
as greater aptitude to locomotion, than the callow neftlings of the
dove, and of the wren. The parents of the former only fiiid it ne-
ceffary to fliew them their food, and to teach them to take it up ;
whilft thofe of the latter are obliged for many days to obtrude it into
their gaping mouths.

IV. From the fa£ts mentioned in No. 2. of this Seftlon, it is evinced
that the foetus learns to fwallow before its nativity ; for it is feen to
open its mouth, and its ftomach is found filled with the liquid that fur-
rounds it.- It opens its mouth, either infligated by hunger, or by the
irkfomenefs of a continued attitude of the mufcles of its face-j the
liquor amnii, in which it fwims, is agreeable to its palate, as it con-
fiilis of a nourifliing material, (Haller Phyf. T. 8. p. 204). It is
tempted to experience its tafle further in the mouth, and by a few
efforts learns to fwallow, in the fame manner as we learn all other
animal aflions, which are attended with confcioufnefs, hy the repeated
efforts of our mufcles under the conduct of our fenfations or volitions.

The infpiratlon of air into the lungs is fo totally different from
that of fwallowing a fluid in which we are immerfed, that it cannot
be acquired before our nativity. But at this time, when the circula-
tion of the blood is no longer continued through the placenta, that
fuffocating fenfation, which we feel about the precordia, when we
are in want of frefh air, difagreeably affe6ts the infant : and all the
mufcles of the body are excited into a£tion to relieve this oppreffion ;
thofe of the breaft, ribs, and diaphragm are found to anfwer this pur-
pofe, and thus refpiration is difcovered, and is continued throughout
our lives, as often as the oppreffion begins to recur. Many infants,
both of the human creature, and of quadrupeds, ftruggle for a minute
after they are born before they begin to breathe, (Haller Phyf. T.S.
p. 400. ib. pt. 2. p. i). Mr. Buffon thinks the action of the dry air
upon the nerves of fmell of new-born animals, by producing an en^

T 2 deavour

I40 OF INSTINCT. Sect.XVI. 4;

deavour to fneeze, may contribute to induce this firll: infpiration, and
that the rarefa61:ion "of the air by the warmth of the lungs contributes
to induce expiration, Hift. Nat. Tom. 4. p. 174. Which latter it
may efFedl by producing a difagreeable fenfation by its delay, and a
confequent effort to relieve it. Many children fneeze before they
refpire, but not all, as far as I have obferved, or can learn- frora
others.

At length, by the direction of its fenfe of fmell, or by the officious
care of its mother, the young animal approaches the odoriferous rill
of its future nourifliment, already experienced to fwallow. But in
the a(5t of fwallowing, it is neceffary nearly to clofe the mouth,
whether the creature be immerfed in the fluid it is about to drink, or
not : hence, when the child firft attempts to fuck, it does not (light-
ly comprefs the nipple between its lips, and fuck as an adult perfon
would do, by abforbing the milk ; but it takes the whole nipple into
its mouth for this purpofe, compreffes it between its gums, and thus
repeatedly chewing (as it were) the nipple, preffes out the milk ; ex-
adlly in the fame manner as it is drawn from the teats of cows by
the hands of the milkmaid. The celebrated Harvey obferves, that
the foetus in the womb mufi: have fucked in a part of its nourifhment,
becaufe it knows how to fuck the minute it is born, as any one may
experience by putting a finger between its lips, and becaufe in a few
days it forgets this art of fucking, and cannot without fome difficulty
again acquire it, (Exercit. de Gener. Anim. 48). The fame obferva.-
tion is made by Hippocrates.

A little further experience teaches the young animal to fuck by ab^
forption, as well as by compreffion ; that is, to open the cheft as in
the beginning of refpiration, and thus to rarefy the air in the mouth,
that the prefliire of the denfer external atmofphere may contribute to
force out the milk.

The chick yet in the fhell has learnt to drink by fwallowing a part
of the white of the egg for its food; but not having experienced how

Sect. XVI. 5- OF INSTINCT. 141-

to take up and fvvallow folid feeds, or grains, is eith&r taught by rhe
felicitous induftry of its mother; or by many repeated attempts is
enabled at length to diftinguifli and to fwallow this kind of nutri-
ment.

And puppies, though they know how to fuck like other animals
from their previous experience in fwallowing, and in refpiration ; yet
are theylong in acquiring the art of lapping with their tongues, which
from the flaccidity of their cheeks, and length of their mouths, is after-
wards a more convenient way for them to take in Vv'ater.

V. The fenfes of fmell and tafte in many other animals greatly ex-
cel thofe of mankind, for in civilized fociety, as our vi6luals are ge-
iierally prepared by others, and are adulterated with fait, fpice, oil,
and'empyreuma, we do not hefitate about' eating whatever is fetbefore
us, and negledl to cultivate thefe fenfes: whereas other animals try
every morfel by the fmell, before they take it into their mouths, and
by the tafte before they fwallow it : and are led not only each to his
proper nourifhment by this organ of fen fe, but it alfo at a maturer age
dire6ts them- in the gratification of their appetite of love. Which may
be further underftood by confidering the fympathies of thefe parts de-
fcribed in Clafs IV. 2. 1.7. While the human animal is direded to
the objedl of his love by his fenfe of beauty, as mentioned in-No. Vli
of this Sedion. Thus Virgil. Georg. III. 230.-

Nonne vides, ut tota tremor pertentat equorum
Corpora, fi tantum notas odor attulit auras ?
Nonne canis nidum veneris nafutus odore
Quarit, et erranti trahitur fublambere lingua ?
Refpuit at guftum cupidus, labiifqne retraftis
Elevat OS, trepidanfque novis percutitur asftris,-
Inferit et vivum felici vomere femen. —
Quam tenui file cscos adneftit amores
Dofta: Venus, vitseque monet renovare favillam !

Anon.

The

143 OF INSTINCT. Sect.XVL 6.

The following curious experiment is related by Galen. " On dif-
fering a goat great with young I found a briik embryon, and having
detached it from the matrix, and fnatching it away before it faw its
dam, I brought it into a certain room, where there were many veflels,
fome filled with wine, others with oil, fome with honey, others with
milk, or fome other liquor; and in others were grains and fruits; we
firfi: obfervcd the young animal get upon its feet, and walk ; then it
fhook itfelf, and afterwards fcfatched its fide with one of its feet : then
we faw it fmelling to every one of thefe things, that were fet in the
room ; and when it had fmelt to them all, it drank up the milk."
L,. 6. de locis. cap. 6.

Parturient quadrupeds, as cats, and bitches, and fows, are led by
their fenfe of fmell to eat the placenta as other common food ; why
then do they not devour their whole progeny, as is reprefented in an
antient emblem of Time ? This is faid fometimes to happen in the
xinnatural ftate in which we confine fows ; and indeed nature would
feem to have endangered her offspring in this nice circumflance ! But
at this time the flimulus of the milk in the tumid teats of the mother
excites her to look out for, and to defire fome unknown circumftance
to relieve her. At the fame time the fmell of the milk attracts the
exertions of the young animals towards its fource, and thus the de-
lighted mother difcovers a new appetite, as mentioned in Seft. XIV. 8.
and her little progeny are led to receive and to communicate pleafure
by this moft beautiful contrivance.

VI. But though the human fpecies in fome of their fenfations are
much inferior to other animals, yet the accuracy of the fenfe of touch,
which they pofTefs in fo eminent a degree, gives them a great fuperi-
ority of underflanding; as is well obferved by the ingenious Mr. Buf-
fon. The extremities of other animals terminate in horns, and hoofs,
and claws, very unfit for the fenfation of touch ; whilft the human
hand is finely adapted to encompafs its objedt with this organ of
fenfe.

The

Sect. XVI. 6. O F 1 N S T 1 N C T. 143

The elephant is indeed endued with a fine fenfe of feeling- at the
extremity of his probofcis, and hence has acquired much more accu-
rate ideas of touch and of fight than mod other creatures. The two
following inftances of the fagacity of thefe animals may entertain the
reader, as they were told me by fome gentlemen of diflin£t obferva-
tion, and undoubted veracity, who had been much converfant with
our eaflern fettlements. Firft, the elephants that are ufed to carry
the baggage of our armies, are put each under the care of one of the
natives of Indoftan, and whilft himfelf and his wife go into the woods
to colle6l leaves and branches of trees for his food, they fix him to the
ground by a length of chain, and frequently leave a child yet unable
to walk, under his protedtion : and the intelligent animal not only de-
fends it, but as it creeps about, when it arrives near the extremity of
his chain, he wraps his trunk gently round its body, and brings it
again into the centre of his circle. Secondly, the traitor elephants
are taught to walk on a narrow path between two pit-falls, which are
covered with turf, and then to go into the woods, and to feduce the
wild elephants to come that way, who fall into thefe wells, whilft he
paffes fafe between them : and it is univerfally obferved, that thofe
wild elephants that efcape the fnare, purfue the traitor with the ut-
moft vehemence, and if they can overtake him, which fometimes hap-
pens, they always beat him to death.

The monkey has a hand well enough adapted for the fenfe of touch,
which contributes to his great facility of imitation; but in taking ob-
je£ls with his hands, as a ftick or an apple, he puts his thumb on the
fame fide of them with his fingers, inftead of counteradling the pref-
fure of his fingers with it : from this neglect he is much flower in ac-
quiring the figures of objedls, as he is lefs able to determine the dif-
tances or diameters of their parts, or to diftinguifli their vis inertias
from their hardnefs. Helvetius adds, that the fhortnefs of his life, '
his being fugitive before mankind, and his not inhabiting all climates,
combine to prevent his improvement. (De TEfprit. T. i . p.) There

■144 . -CsF "INSTINCT. Sect/XVI. 6,

is however at this time an old monkey (hewn in Exeter Change,
London, who having loft his teeth, when nuts are given him, takes
a flone into his hand, and cracks them with it one by one ; thus ufing
tools to effedc his purpofe like mankind.

The beaver is another animal that makes much ufe of his hands,
and if we may credit the reports of travellers, is pofleffed of amazing
ingenuity. This however, M. BufFon affirms, is only where they
exift in large numbers, and in countries thinly peopled with men ;
while in France in their folitary ftate they fhew no uncommon in-
genuity.

Indeed all the quadrupeds, that have collar-bones, (claviculae) \ife
their fore-limbs in fome meafure as we ufe our hands, as the cat,
fquirrel, tyger, bear and lion; and as they exercife the fenfe of touch
more univerfally than other animals, fo are they more fagacious in
watching and furprifmg their prey. All thofe birds, that ufe their
claws for hands, as the hawk, parrot, and cuckoo, appear to be more
docile and intelligent ; though the gregarious tribes of birds have more
acqviired knowledge.

Now as the images, that are painted on the retina of theeye, are no
other than figns, which recall to our imaginations the objects we had
before examined by the organ of touch, as is fully demonftrated by
Dr. Berkley in his treatife on vifion ; it follows that the human crea-
ture has sreatlv more accurate and diflinft fenfe of vifion than that of
any other animak Whence as he advances to maturity he gradually
acquires a fenfe of female beauty, which at this time diredls him to the
object of his new paffion.

•Sentimental love, as difringuiflied from the animal paflion of that
name, with which it is frequently accompanied, confifts in the
defire or fenfation of beholding, embracing, and faluting a beautiful
obje£l.

The charadleriftic of beauty therefore is that it is the objeft of love?
and though many other objeds ^re in common language called beauti-
ful.

Sect.XVI.6. of instinct. 145

ful, yet they are only called fo metaphorically, and ought to be termed
agreeable. A Grecian temple may give us the pleafurable idea of
fublimity, a Gothic temple may give us the pleafurable idea of va-
riety, and a modern houfe the pleafurable idea of utility; mufic and
poetry may infpire our love by aflbciation of ideas ; but none of thefe,
except metaphorically, can be termed beautiful, as we have no \vi(h
to embrace or falute them.

Our perception of beauty confifts in our recognition by the fenfe of
vifion of thofe objedls, firft, which have before infpired our love by
the pleafure, which they have afforded to many of our fenfes ; as to
our fenfe of warmth, of touch, of fm.ell, of tafte, hunger and thiril ;
and, fecondly, which bear any analogy of form to fuch objecls.

When the babe, foon after it is born into this cold world, is applied
to its mother's bofom ; its fenfe of perceiving warmth is firft agree-
ably affefted ; next its fenfe of fmell is delighted with the odour
of her milk ; then its tafte is gratified by the flavour of it ;• after-
wards the appetites of hunger and of thirft afford pleafure by the pof-
fefiion of their objedts, and by the fubfequent digeftion of the ali-
ment; and, laftly, the fenfe of touch is delighted by the foftnefs and
fmoothnefs of the milky fountain, the fource of fuch variety of hap-
pinefs.

All thefe various kinds of pleafure at length become aiTociated with
the form of the mother's breaft ; which the infant embraces with its
hands, preffes with its lips, and watches with its eyes ; and thus ac-
quires more accurate ideas of the form of its mother's bofom, than of
the odour and flavour or warmth, which it perceives by its other
fenfes. And hence at our maturer years, when any objedl of vifion is
prefented to us, which by its waving or fpiral lines bears any fimili-
tude to the form of the female bofom, whether it be found in a iand-
fcape with foft gradations of rifing and defcending furface, or in the
forms of fome antique vafes, or in other works of the pencil or the
chiflel, we feel a general glow of delight, which feems to influence all
our lenfes ; and, if the objeft be not too large, we experience an at-

U traction

146 OF INSTINCT.. Sect.XVI. 7.

traction to embrace It with our arms, and to falute it with our lips,
as we did in our early infancy the bofom of our mother. And thus
we find, according to the ingenious idea of Hogarth, that the waving
lines of beauty were originally taken from the temple of Venus.

This animal attraction is love ; which is a fenfation, when the ob-
jeft is prefent ; and a defire, when it is abfent. Which conflitutes-
the pureft fource of human felicity, the cordial drop in the otherwife
vapid cup of life, and which overpays mankind for the care and la-
bour, which are attached to the pre-eminence of his fituation above
other animals.

It fliould have been obferved, that colour as well as form fometimes
enters into our idea of a beautiful objed, as a good complexion for in-
ftance, becaufe a fine or fair colour is in general a fign of health, and
conveys to us an idea of the warmth of the obje£t ; and a pale
countenance on the contrary gives an idea of its being cold to the
touch.

It was before remarked, that young animals ufe their lips to dif-
tinguifh the forms of things, as well as their fingers, and hence we
learn the origin of our inclination to falute beautiful objedls with our

lips.

VII. There are two ways by which we become acquainted with
the paffiohs of others : firft, by having obferved the effects of them,
as of fear or anger, on our own bodies, we know at fight when others
are under the influence of thefe afFedlons. So when two cocks are
preparing to fight, each feels the feathers rife round his own neck,
and knows from the fame fign the difpofition of his adverfary: and
children long before they can fpeak, or underfi:and the language of
their parents, may be frightened by an angry countenance, or foothed
by fmiles and blandifhments.

Secondly, when we put ourfelves into the attitude that any paffiou
naturally occafions, we foon in fome degree acquire that pafiion ;
hence when thofe that fcold indulge themfelves in loud oaths, and

violent

Sect. XVI. 8. OF INSTINCT. 147

violent anions of the arms, they increafe their anger by the mode of
expreffing themfeh^es: and on the contrary the counterfeited fmile of
pleafure in difagreeable company foon brings along jvith it a portion
of the reality, as is well illuflrated by Mr. Burke. (Effay on the Su-
blime and Beautiful.)

This latter method of entering into the paffions of othere is ren-
dered of very extenfive ufe by the pleafure we take in imitation,
which is every day prefented before our eyes, in the a£lions of chil-
dren, and indeed in all the cufloms and fafliions of the world. From
this our aptitude to imitation, arifes what is generally underilood by
the word fympathy fo well explained by Dr. Smith of Glafgow.
Thus the appearance of a cheerful countenance gives us pleafure, and
of a melancholy one makes us Ibrrowful. Yawning and fometlmes
vomiting are thus propagated by fympathy, and fome people of deli-
cate fibres, at the prefence of a fpeftacle of mifery, have felt pain in
the fame parts of their own bodies, that were difeafed or mangled in
the other. Amongft the writers of antiquity Ariftotle thought this
aptitude to imitation an effential property of the human fpecies, and
■calls man an imitative animal. To ^uov fAi[4,ai^Bvov.

Thefe then are the natural figns by which we underhand each
other, and on this flender bafis is built all human language. For
without fome natural figns, no artificial ones could have been invented
■or underftood, as is very ingenioufly obferved by Dr. Reid. (Inquiry
into the Human Mind.)

VIII. The origin of this unlverfal language is a fubje^l of the high-
eft curiofity, the knowledge of which has always been thought utterly
inacceffible. A part of which we fhall however- here attempt.

Light, found, and odours, are unknown to the foetus in the womb,
which, except the few fenfatlons and motions already mentioned,
fleeps away its time infenfible of the bufy world. But the moment he
arrives into day, he begins to experience many vivid pains and plea-
fures ; thefe are at the fame time attended with certain mufcular mo-

U 2 tions.

148 OF INSTINCT. Sect. XVI. 8.

tions, and from this their early, and individual aflbciation, they ac-
quire habits of occurring together, that are afterwards iadilToluble.

I . Of Fear.

As foon as the young animal is born, the firft important fenfations,
that occur to him, are occafioned by the oppreffion about his pre-
cordia for want of refpiration, and by his fudden tranfition from ninety-
eight degrees of heat into fo cold a climate. — He trembles, that is, he
exerts alternately all the mufcles of his body, to enfranchife himfelf
from the oppreffion about his bofom, and begins to breathe with fre-
quent and fliort refpirations ; at the fame time the cold contrails his
red Ikin, gradually turning it pale ; the contents of the bladder and of
the bowels are evacuated : and from the experience of thefe firft dif-
agreeable fenfations the paffion of fear is excited, which is no other
than the expe£tation of difagreeable fenfations. This early aflbciation
of motions and fenfations perfifts throughout life ; the paffion of fear
produces a cold and pale Ikin, with tremblings, quick refpiration,
and an evacuation of the bladder and bowels, and thus conftitutes the
natural or univerfal language of this paffion.

On obferving a Canary bird this morning, January 28, 1772, at
the houfe of Mr. Harvey, near Tutbury, in Derbyffiire, I was told
it always fainted away, when its cage was cleaned, and defired to fee
the experiment. The cage being taken from the ceiling, and its
bottom drawn out, the bird began to tremble, and turned quite white
about the root of his bill : he then opened his mouth as if for breath,
and refpired quick, flood ftraighter up on his perch, hung his wings,
fpread his tail, clofed his eyes, and appeared quite fliffand cataleptic
for near half an hour, and at length with much trembling and deep
refpirations came gradually to himfelf.

5 2.0/

Sect. XVI. 8. OF INSTINCT, 149

2. Of Grief .

That the internal membrane of the noflrils may be kept always
moift, for the better perception of odours, there are two canals, that
condudl the tears after they have done their office in moiftening and
cleaning the ball of the eye into a fack, which is called the lacrymal
fack; and from which there is a duft, that opens into the noftrils :
the aperture of this du£l is formed of exquifite fenfibility, and when
it is ftimulated by odorous particles, or by the drynefs or coldnefs of the
air, the fack contradls itfelf, and pours more of its contained moifture
on the organ of fmell. By this contrivance the organ is rendered
more fit for perceiving fuch odours, and is preferved from being in-
jured by thofe that are more ftrong or corrofive. Many other recep-
tacles of pecuhar fluids difgorge their contents, when the ends of their
dufts are ftimulated ; as the gall bladder, when the contents of the
duodenum ftimulate the extremity of the common bile duel : and the
falivary glands, Avhen the termination of their du6ls in the mouth are
excited by the ftimulus of the food we mafticate. Atque vellculse fe-
minales fuum exprimunt fluidum glande penis fricata.

The coldnefs and drynefs of the atmofphere, compared with the
warmth and moifture, which the new-born infant had juft before
experienced, difagreeably affedts the aperture of this lacrymal fack ;
the tears, that arc contained in- this fack, are poured into the noftrils,
and a further fupply is fecreted by the lacrymal glands, and difFufed
upon the eye-balls ; as is very vifible in the eyes and noftrils of chil-
dren foon after their nativity. The fame happens to us at our ma-
turer age, for in fevere frofty weather, fnivelling and tears are pro-
duced by the coldnefs and drynefs of the air.

But the lacrymal glands, which feparate the tears from the blood,
are fituated on the upper external part of the globes of each eye ; and,

when

150 OF INSTINCT, Sect. XVI. 8.

whea a greater quantity of -tears are wanted, we contraft the fore-
head, and bring down the eye-brows, and ufe many other diflortions
of the face, to comprefs thefe glands.

Now as the fufFocating fenfation, that produces refpiration, is re-
moved almofi: as foon as perceived, and does not recur again : this
difagreeable irritation of the lacrymal dudls, as it muft frequently
recur, till the tender organ becomes ufed to variety of odours, is one
■of the firft pains that is repeatedly attended to: and hence throughout
our infancy, and in many people throughout their lives, all difagree-
able fenfations are attended with fnivelling at the nofe, a profufion
of tears, and fome peculiar diftortions of countenance : according to
the laws of early aflbciation before mentioned, which conflitutes the
natural or univerfal lang^iage of grief.

You may affure yourfelf of the truth of this obfervation, if you
will attend to what pafles, when you read a diftrefsful tale alone ;
before the tears overflow your eyes, you will invariably feel a titilla-
tion at that extremity of the lacrymal dud, which terminates in the
noftril, then the compreffion of the eyes fucceeds, and the profufion
of tears.

Linnaeus aflerts, that the female bear fheds tears in grief; the fame
-has been faid of the hind, and fome other animals.

3. Of Tender PJeafure.

The firfl: moft lively impreffion of pleafure, that the infant enjoys
after its nativity, is excited by the odour of its mother's milk. The
organ of fmell is irritated by this perfume, and the lacrymal fack
empties itfelf into the noftrils, as before explained, and an increafe of
tears is poured into the eyes. Any one may obferve this, when very
young infants are about to fuck ; for at thofe early periods of life, the
S fenfation

Sect.XVL 8. OF INSTINCT. 151

fenfation afFefts the organ of fmell, much more powerfully, than
after the repeated habits of fmelluig has inured it to odours of common
ftrength : and in our adult years, the flronger fmells, though they
are at the fame time agreeable to us, as of volatile fpirits, continue to
produce an increafed fecretion of tears.

This pleafing fenfation of fmell is followed by the early affection of
the infant to the mother that fuckles it, and hence the tender feelings
of gratitude and love, as well as of hopelefs grief, are ever after joined
with the titillation of the extremity of the lacrymal du6ls, and a pro—
fufion of tears.

Nor is it fingular, that the lacrymal fack fhould be Influenced by
pleafing ideas, as the fight of agreeable food produces the fame effedt
on the falivary glands. Ac dum vidimus infomniis lafcivae puellae ii--
mulacrum tenditur penis.

Lambs fhake or wriggle their tails, at the time when they fitii.'
fuck, to get free of the hard excrement, which had been long lodged
in their bowels. Hence this becomes afterwards a mark of pleafure in
them, and in dogs-, and other tailed animals. But cats gently extend
and contracl their paws when they are pleafed, and purr by drawing,
in their breath, both which refemble their manner of fucking, and
thus become their language of pleafure, for thefe animals having col-
lar-bones ufe their paws like hands when they fuck, which dogs and
Iheep do not. J

4. Of Serene Pleafure^

In the a£lion of fucking, the. lips of the infant are clofed around
the nipple of its mother, till he has filled his ftomach, and the plea-
fure occafioned by the ftimulus of this grateful food fucceeds. Then
the fphinfter of the mouth, fatigued by the continued adion of fuck-
ing*-

152 OF INSTINCT. Sect.XVI. 8.

ing, is relaxed ; and the antagonift mufcles of the face gently a£ling,
produce the fmile of pleafure : as cannot but be feen by all who are
converfant with children.

Hence this fmile during our lives is aflbciated with gentle pleafure;
it is vifible iu kittens, and puppies, when they are played with, and
tickled; but more particularly marks the human features. For in
children this expreflion of pleafure is much encouraged, by their imi-
tation of their parents, or friends i who generally addrefs them with
a fmiling countenance : and hence fome nations are more remarkable
for the gaiety, and others for the gravity of their looks.

5. Of Anger.

The actions that conftitute the mode of fighting, are the immediate
language of anger in all animals ; and a preparation for thefe a£lions
is the natural language of threatening. Hence the human creature
clenches his fift, and flernly furveys his adverfary, as if meditating
where to make the attack ; the ram, and the bull, draws himfelf
fome fteps backwards, and levels his horns ; and the horfe, as he
fights by ftriking with his hinder feet, turns his heels to his foe, and
bends back his ears, to liften out the place of his adverfary, that the
threatened blow may not be inefFeftual.

6. Of Attention.

The eye takes in at once but half our horizon, and that only in the
day, and our fmell informs us of no very diftant objeds, hence we
confide principally in the organ of hearing to apprize us of danger :

when

Sect. XVI. 9. O F I N S T I N C T. " 153

when we hear any the fraallefl: found, that we cannot innmediately
account for, our fears arc alarmed, we fufpend our fleps, hold every
mufcle flill, open our mouths a little, erecl our ears, and liften to
gain further information : and this by habit becomes the general
language of attention to objefts of light, as well as of hearing ; and
even to the fucceffivc trains of our ideas.

The natural language of violent pain, which is exprefled by writh-
ing the body, grinning, and fcreaming ; and that of tumultuous
pleafure, exprefled in loud laughter ; belong to Se6tion XXXIV. on
Difeafes from Volition.

IX. It muft have already appeared to the reader, that all other ani-
mals, as well as man, are polfefled of this natural language of the
paflions, exprefled in figns or tones; and we fhall endeavour to evince,
that thofe animals, which have preferved themfelves from being en-
flaved by mankind, and are aflbciated in flocks, are alfo poflTefled of
feme artificial language, and of fome traditional knowledge.

The mother-turkey, when fhe eyes a kite havering high in air,
has either feen her own parents thrown into fear at his prefence, or
has by obfervation been acquainted with his dangerous defigns upon
her young. She becomes agitated with fear, and ufes the natural
language of that paflion, her young ones catch the fear by imitation,
and in an.inftant conceal themfelves in the grafs.

At the fame time that fhe fhews her fears by her gefture and de-
portment, (he ufes a certain exclamation, Koe-ut, Koe-uf, and the
young ones afterwards know, when they hear this note, though they
do not fee their dam, that the prefence of their advei-fary is denounced,
and hide themfelves as before.

The wild tribes of birds have very frequent opportunities of know-
ing their enemies, by obferving the defl:ru6lion they make^mong their
progeny, of which every year but a fmall part efcapes to maturity :
but to our domefl:ic birds thefe opportunities fo rarely occur, that
their knowledge of their diflant enemies muft frequently be de-

X livered

1 54 OF INSTINCT. Sect. XVL 9,

livered by tradition in the manner above explained, through many
generations.

This note of danger, as well as the other notes of the mother-
turkey, when fhe calls her flock to their flood, or to fleep under her
wings, appears to be an artificial language, both as expreffed by the
mother, and as underftood by the progeny. For a hen teaches this
language with equal eafe to the ducklings, (lie has hatched from fup-
pofitious eggs, and educates as her own cfTspring : and the wagtails.,
or hedge-fparrows, learn it from the young cuckoo their fofter nurf-
ling, and fupply him with food long after he can fly about, whenever
they hear his cuckooing, which Linneus tells us, is his call of hun-
ger, (Syft. Nat.) And all our demeflic animals are readily taught to
come to us for food, when we ufe one tone of voice, and to fly from
our anger, when we ufe another.

Rabbits, as they cannot eafily articulate founds, and are formed
into focieties, that live under ground, have a very different method of
giving alarm. When danger is threatened, they thump on the
ground with one of their hinder feet, and produce a found, that can
be heard a great way by animals near the furface of the earth, which
would feem to be an artificial fign both from its fmgularity and its
aptnefs to the {ituation of the animal.

The rabbits on the ifland of Sor, near Senegal, have white fieih,
and are well tafl:ed, but do not burrow in the earth, fo that we may
fufpe6L their digging themfelves houfes in this cold climate is an ac-
quired art, as well as their note of alarm, (Adanfon's Voyage to
Senegal).

The barking of dogs is another curious note of alarm, and would
feem to be an acquired language, rather than a natural lign : for " in
the ifland of Juan Fernandes, the dogs did not attempt to bark, till
fome European dogs were put among them, and then they gradually
begun to imitate them, but in a ilrange manner at iirft, as if they
*vere learning a thing that was not natural to them," {Voyage to

South

&f.cT.XVI. lo. OF INSTINCT. 155

South America by Don G. Juan, and Don Ant. de Ulloa. B. 2.
c. 4). -

J^innsus alfo obferves, that thedogs of South America do not bark
at Grangers, (Syft. Nat.) And the European dogs, that have bten
carried to Guinea,, are faid in three or four generations to ceafe to bark,,
and only howl, like the dogs that are natives of that coaft, (World
Difplayed, Vol. XVII. p. 2-6.)

A circumftauce not difhmilar to this,, and equally curious, is menr
tioned by Kircherus. de Mufurgia, in his Chapter de Lufciniis.
" That the young nightingales, that are hatched under other birds,
never fing till they are inftruited by the company of other nightin-
gales.." And Jon (Ion afSrms, that the nightingales that vifit Scot-
land,, have not the fame harmony as thofe of Italy, (Pennant's Zoo-
logy, o6tavo, p. 255); which would lead us to fufpecSl that the fing-
ing of birds, like human niufic, is an artificial, language rather than a
natural expreffion. of paffion.

X. Our mufic like our language, is perhaps entirely confrituted of
artificial tones,, which by habit fuggeft certain agreeable paffions.
For the fame combination of notes and tones do not excite devotion,
love, or poetic melancholy in a native of Indoftan and of Europe.
And " the Hi2;hlander has the lame warlike ideas annexed to the
found of a bagpipe (an inllrument which an EnglLfhman derides), 33
the Engliftiman has to that of a trumpet or fife," (Dr. Brown's
Union of Poetry and Mufic, p. 58.) So " the mufic of the Turks
is very different from the Italian, and the people of Fez and Morocco
have again a different kind, which to us appears very rough and hor-
rid, but is highly pleafing to them," (L' Arte Armoniaca a, Giorgio
Antoniotto). Hence we fee why the Italian opera does not delioht
an untutored Englifhman ; and why thofe, who are unaccuftomed^:o
mufic, are more pleafed with a tune, the fecond or third time they
hear it, than the firfl. For then the fame melodious train of founds'
excites the naelancholy,, they had learned from the foug; or the fame

X a. vivid

15$ OF INSTINCT. Sect. XVI. lo.

vivid combination of them recalls all the mirthful ideas of the dance
and company.

Even the founds, that were once difagreeable to us, may by habit
be afibciated with other ideas, fo as to become agreeable. Father
Lafitau, in his account of the Iroquois, fays " the mufic and dance
of thofe Americans, have fomething in them extremely barbarous,
Avhich at firft difgufls.- We grow reconciled to them by degrees,
and in the end partake of them with pleafure, the favages themfelves
3.re fond of them to diftradlion,^' (Moeurs des Savages, Tom. ii.)

There are indeed a few founds, that we very generally aflbcia-te
with agreeable ideas, as the whiftling of birds, or purring of animals,
that are delighted ; and fome others, that we as generally affociate
with difagreeable ideas, as the cries of animals in pain, the hifs of
fome of them in anger, and the midnight howl of beafts of prey. Yet
we receive no terrible or fublime ideas from the lowing of a cow, or
the braying of an afs. Which evinces, that thefe emotions are
owing to previous afibciations. So if the rpmbling of a carriage in
the ftreet be for a moment miftaken for thunder, we receive a fub-
lime fenfatlon, which ceafes as foon as we know it is the noife of a
coach and fix.

There are otbier difagreeable founds, that are faid to fet the teeth
on edge; which, as they have always been thought a neceffary elFedl
of certain difcordant notes, become a proper fubjeft of our enquiry.
Every one in his childhood has repeatedly bit a part of the glafs or
earthen vefTel, in which his food has been given him, and has thence
had a very difagreeable fenfation in the teeth, which fenfation was de-
figned by nature to prevent us from exerting them on objeils harder
than themfelves. The jarring found produced between the cup and
the teeth is always attendant on this difagreeable fenfation : and ever
after when fuch a found is accidentally produced by the conflidl of
two hard bodies, we feel by aflbciatiou of ideas the concomitant dif-
agreeable fenfation in our teeth.

Others

Sect. XVI. lo. OF INSTINCT, 157

• Others have in their infancy frequently held the corner of a filk
handkerchief in their mouth, or the end of the velvet cape of their
coat, whilft their companions in play have plucked it from them, and
have criven another difagreeable fenfation to their teeth, which has
afterwards recurred on touching thofe materials. And the light of a
knife drawn along a china plate, though no found is excited by k,
and even the imagination of fuch a knife and plate fo fcraped together,
I know by repeated experience will produce the fame difagreeable
fenfation of the teeth.

Thefe circumftances indifputably prove, that this fenfation of the •
tooth-edge is owing to affociated ideas; as it is equally excitable by
iight, touch, hearing, or imagination.

In refpeil to the artificial proportions of found excited by mufical
inftruments, thofe, who have early in life affociated them with agree-
able ideas, and have nicely attended to diftinguifh them from each
■other, are faid to have a good ear, in that country where fuch pro-
portions are in fafhion : and not from any fuperior perfection in the
organ of hearing, or any inftindlive fympathy between certain found?
and paffions.

I have obferved a child to be exquifitely delighted with mufic, and
who could with great facility learn to ling any tune that he heard
diftindly, and yet whofe organ of hearing was fo imperfe6l, that it
was neceflary to Ipeak louder to him in common converfation than to
others.

Our mulic, like our architedlure, feems to have no foundation in
nature, they are both arts purely of human creation, as they imitate
nothing. And the profelTors of them have only claffed thofe circum-
ftances, that are moft agreeable to the accidental tafte of their a^e, or
country; and have called it Proportion. But this proportion muft
always fluftuate, as it refts on the caprices, that are introduced into
our minds by our various modes of education. And thefe fluftuations

"4 of

^SS OF INSTINCT. Sect. XVI. ir.

of tafte mui> become more frequent in the prefent age, where mzn-
kuKl have eafranchifed tliemfelves from the blind obedience to the
rules of antiquity in perhaps every fcience, but that of architefture.
See Sea. XIL No.- 7. 3.

XI. There are many articles of knowledge, which the animals ia
cultivated countries feem to learn very early in their lives, either
from each other, or from experience, or obfervation :. one of the moft
general of thefe is to avoid mankind.. There is fo great a refemblance
iu the natural language of the paflions of. all animals, that we gene-
rally know, when they are in apacific,^. or in a malevolent humour,
they hav.e the fame knowledge of us ; and hence we can fcold thena
from us.by fome tones and geftures, and could poffibly attrad them
to u& by others, if they were not already apprized of our general ma-
levolence towards them. Mr. Gmelin, Profeffor at Peterfb,urg, afr
jfures us,^ that in his journey into Siberia, undertaken by order of the
Emprefs of Ruffia, he favv foxes, that expreffed. no. fear of himfelf or
companions, but permitted him to come quite near them, having
never feen the human creature before. And Mr. Bongainville. relates,
that at his arrival at th.e Malouine^, or Falkland's Iflands,. which were
not inhabited by men, all the animals came about himfelf and his
people; th€ fowls fettling upon their heads and fhoulders, and the
quadrupeds running about their feet. From the difficulty of acquir-
ing the confidence of old animals, and the eafe of. taming young ones^
it appears that the fear, they all conceive at the fight of mankind,, is.
an acquired article of knowledge..

This knowledge is more nicely underftood- by rooks, who are
formed into focieties,. and build, as it were, cities over our heads.;
they evidently diftinguifh, that the danger is greater when a man is
armed with a gun. Every one has feen this, who in the fpring of
the year has walked under a rookery with a gun in his hand: the in-
habitants of the trees rife on their wings,, and feream to the unfledged

young

Sect. XVI. M. OF INSTINCT. 159

young to fhrink into their nefts froKi the fight of the enemy. The
vulgar obferving this circumftance fo uniformly to occur, aflert that
rooks can irnell gun-powder.

The fieldfairs, (tardus pilarus) which breed in Norv/ay, and come
hither in the cold feafon for our winter berries; as they are affociated
in flocks, and are in a foreign country, have evident marks of keeping
a kind of watch, to remark and announce the appearance of danger.
On approaching a tree, that is covered with them, they continue fear-
lefs till one at the extremity of the bu(h rifing on his wings gives a
loud and peculiar note of alarm, when they all immediately fly, ex-
cept one other, who continues till you approach ftill nearer, to cer-
tify as it were the reality of the danger, and then -he alfo flies off re-
peating the note of alarm.

And -in the woods about Senegal there is a -bird called uett-uett
by the negroes, and fquallers by the French, which, as foon as they
fee a man, fet up a loud fcream, and keep flying round him, as if their
intent was to warn other birds, which upon hearing the cry im-
mediately take wing. Thefe birds are the bane of fportfmen, and
frequently put me into a paflion, and obliged me to flioot them,
(Adanfon's Voyage to Senegal, 78). For the fame intent the
lelfer birds of our climate feem to fly after a hawk, cuckoo, or
owl, and fcream to prevent their companions from being furprifed
by the g-eneral enemies of thcmfelveg, or of their eggs and pro-
geny.

But the lapwing, (charadrius pluvialis Lin.) when her unfledged
offspring run aboet the marfhes, where they were hatched, not only
gives the note of alarm at the approach of men or dogs, that her
young may conceal themfelves; but flying and fcreaming near the
adverfary, fhe appears more folicitous and impatient, as he recedes
from her family, and thus endeavours to miflead him, and frequently
fucceeds in her defig.n. Thefe laft inflances are fo appofite to the (itu-
ation, rather than to the natures of the creatures, that ufe them ; and

are

i6o OF INSTINCT. Sect.XVI. ii.

are fo fimilar to the aftions of men in the fame circumftances, that we
cannot but believe, that they proceed from a fimilar principle.

On the northern coafl: of Ireland a friend of mine faw above a
hundred crows at once preying upon mufcles ; each crow took a
mufcle up into the air twenty or forty yards high, and let it fall oiv
the ftones, and thus by breaking the fhell, got poffeflion of the ani-
mal.— A certain philofopher (I think it was Anaxagoras) walking
along the fea-(hore to gather fhells, one of thefe unlucky birds mif-
taking his bald head for a ftone, dropped a fhell-fifti upon it, and
killed at once a philofopher and an oyfler.

Our doraeflic animals, that have fome liberty, are alfo pofleffed of
fome peculiar traditional knowledge : dogs and cats have been forced
into each other's fociety, though naturally animals of a very different
kind, and have hence learned from each other to eat the knot- grafs, .
when they are fick, to promote vomiting. I have feen a cat miftake
the blade of barley for this grafs, which evinces it is an acquired know^-
ledge. They have alfo learnt of each other to cover their excrement"
and urine; — about a fpoonful of water was fpilt upon my hearth from
the tea-kettle, and I obferved a kitten cover it with afiies. Hence
this muft alfo be an acquired art, as the creature miftook the applica-
tion of it.

To preferve their fur clean, and efpecially their whifkers, cats
wa(h their faces, and generally quite behind their ears, every time-
they eat. As they cannot lick thofe places with their tongues, they
firft wet the infide of the leg with faliva, and then repeatedly wafli
their faces with it, which mull originally be an effedl of reafoning,
becaufe a means is ufed to produce an effe£t ; and feems afterwards to
be taught or acquired by imitation, like the greatefl part of human
arts.

Mr. Leonard, a very intelligent friend of mine, faw a cat catch, a
trout by darting upon it in a deep clear water at the mill at Weaford,
near Lichfield. The cat belonged to Mr. Stanley, who had often

fee^

Sect. XVI. II. O F I N S T I N C T. i6i

feen her catch fifh ia the fame manner in fummer, when the mill-pool
was drawn fo low, that the fifli could be fecn. I have heard of other
cats taking fifh in Ihallow water, as they flood on the bank. This
feems a natural art of taking their prey in cats, which their acquired
delicacy by domeflication has in general prevented them from ufing,
though their defire of eating fifh continues in its original ftrength.

Mr. White, in his ingenious Hiftory of Selbourn, was witnefs to a
cat's fuckling a young hare, which followed her about the garden,
and came jumping to her call of affeftion. At Elford, near Lich-
field, the Rev. Mr. Sawley had taken the young ones out of a hare,
which was Ihot ; they were alive, and the cat, who had juft lofl: her
own kittens, carried them away, as it was fuppofed to eat them ; but
it prefently appeared, that it was affedlion not hunger which incited
her, as fhe fuckled them, and brought them up as their mother.

Other inflances of the miftaken application of what has been
termed inftin£l may be obferved in flies in the night, who miftaking
a candle for day-light, approach and perlfh in the flame. So the pu-
trid fmell of the ftapelia, or carrion-flower, allures the large flefh-fly
to depofit its young worms on its beautiful petals, which perifii there
for want of nourifliment. This therefore cannot be a neceflary in-
ftin£l, becaufe the creature miftakes the application of it.

Though in this country horfes fhew little veftiges of policy, yet in
the deferts of Tartary, and Siberia, when hunted by the Tartars they
are feen to form a kind of community, fet watches to prevent their
being furprifed, and have commanders, who direct, and haften their
flight. Origin of Language, Vol.1, p. 212. In this country, where
four or five horfes travel in a line, the firfl always points his ears for-
ward, and the laft points his backward, while the intermediate ones
feem quite carelefs in this refped: ; which feems a part of policy to
prevent furprife. As all animals depend moft on the ear to apprize
them of the approach of danger, the eye taking in only half the ho-
rizon at once, and horfes poflefs a great nicety of this fenfe ; as ap-

Y pears

i62 OF INSTINCT. Sect'. XV-L-m

pears from their mode of fighting mentioned No, 8. 5, of this Sedion,
as well as by commoa obfervation.

Ifhere are Ibme'parts of a horfeVw-hich he cannot convenient])^ rub-,
vvlien they'it&h!,' as about the flioulder, wHich he-'can neither- bite
\vith his teeth/ nor' fcratch with his hind foot ; when this part itches,
he goes to another horle, and gently bites him in the part which he
wifhes to be' bitten, which is immediately done by his intelligent
friend. I once obferved a young foal tbiis bite its large mother, -who
did not thbofeto drop-the grafs fhe hadiin her mouth, and'rubbed her
nofe againfi the foal's neck inftead of biting it ; which evinces that
flie knew the defign of her progeny, and was not governed by a ne-
ceffary infiinft t6 Hte wliere fhe was bitten. o

Many of our fhrubs, which would otherwife afford an agreeable
food to horfes, are armed with thorns or prickles, which fecure them
from thofe animals ; as the holly, hawthorn, goofeberry,' gorfe. la
the extenfive moorlands of Staffordfliire, the horfes have learnt to
ftamp upon a gorfe-bufh with one of their fore-feet for a minute to-
gether, and wiien the points are broken, they eat it without injury.
Which is an art other horfes in the fertile parts of the county do not
poffefs, and prick their mouths till they bleed, if they are induced by-
hunger or caprice to attempt eating gorfe.

Swine have a fenfe of touch as well as of fmell at the end of their
nofe, which they ufe as a hand, both to root up the foil, and to turn
over and examine objefts of food, fomewhat like the probofcis of an
elephant. As they require ftielter from the cold in this climate, they
have learnt to colled ftraw in their mouths to make their neft, when
the wind blows cold ; and it o call their companions by repeated cries
■to aifift in the work, and add to their warmth by their numerous bed-
fellows. Hence thefe anihaals, which are efteemed fo unclean, have
alfo lear-n'ed never to befoul their dens, where they have liberty, with
their own excrement ; an art, Vvhich cows and horfes, which have
open hovels to run into, have-.neve" acquired, I have obferved great

fagacity

SfiCT.XVI. II. OF INSTINCT. 163

fagacity in fwlne ; but the (hort lives we allow thetn,^ and their ge-
neral confinement, prevents their improvement, which might pro-
bably be.otherwife greater than that of dogs.

Inftances of the fagacity aiid knowledge of animals are very nu-
merous to every obferver, and their docility in learning various arts- ,
from mankind, evinces that they may learn fimilar arts from their
own fpecies, and thus be poffeffed of much acquired and traditional,
knowledge..

A dog whofe natural prey is fheep, is taught by mankind, not
only to leave them unmolefled, but to guard them ; and to hunt, to
fet, or to deftroy other kinds of animals, as birds, or vermin ; and in-
ibme countries to catch filh, in others to find truffles, and to pradifa
a great variety of tricks ;. is it more furprifing that the crows fhould
teach each other^ that the hawk can catch lets birds, by the fuperio;:
fwiftnefs of his wing, and if two of them foUov/ him, till he fucceeda
ki; his d.elign,- that they can by force Ihafe a part of the capture?.'
This I have formerly obierved with attention and aflonifliment.

There is one kind of pelican mentioned by Mr. Oibeck, one of
Linnasus's travelling pupils (the pelicanus aquilus),. whofe food is
filTi; and which it takes from other birds,, becaufe it is not formed to
catch them itldf ; hence it is called by the Englifh a Man- of- war- bird.
Voyage to China, p. 88. There are many other interefling anec-
dotes of the pelican and cormorant, colleded from authors of the befl
authority, in a well-managed Natural Hiftory for.ChildlTn, pubhflied
by Mr. Galton. Johnl'on. London..

And the following narration from the very accurate Monf, Adan*
fon, in his Voyage to Senegal, may gain credit with the reader : as his
employment in this country was iblely to make obfervations in natu-
ral hiftory. On the river Niger, in his road to the ifland Griel, he
faw a great number of pelicans, or wide throats. " They moved
wi:h great flate like fwans upon the water, and are the largefl bird
oext to thfi oftrich j the bill of the one I killed was upwards of a foot

y a and

i64 OF INSTINCT. Sect. XVI. 12;

and half long, and the bag faftencd underneath it held two and twenty-
pints of water. They fw im in flocks, and form a large circle, which
they contrail afterwards, driving the fifh before them with their
legs: when they fee the fifh in fufficient number confined in this
fpace, they plunge their bill wide open into the water, and (hut it
again with great quicknefs. They thus get fi{h into their throat-
bag, which they eat afterwards on fhore at their leifure." P. 247.

XII. The knowledge and language of thofe birds, that frequently
change their climate with the feafons, is ftill more extenfive: as they
perform thefe migrations in large focietles, and are lefs fubjeft to the
power of man, than the refident tribes of birds. They are faid to
follow a leader during the day, who is occafionally changed, and to
keep a continual cry during the night to keep themfelves together.
It is probable that thefe emigrations were at firft undertaken as acci-
dent direded, by the more adventurous of their fpecies, and learned
from one another like the difcoveries of mankind in navigation. The
following circumftances flrongly fupport this opinion.

I. Nature has provided thefe animals, in the climates where they
are produced, with another refource : when the feafon becomes too
cold for their conftitutions, or the food they were fupported with
ceafes to be fupplied, I mean that of fleeping. Dormice, fnakes,
and bats, have not the means of changing their country ; the two
former from the want of wings, and the latter from his being not
able to bear the light of the day. Hence thefe animals are obliged to
make ufe of this refource, and fleep during the winter. And thofe
fwallows that have been hatched too late in the year to acquire their
full ftrength of pinion, or that have been maimed by accident or
difeafe, have been frequently found in the hollows of rocks on the fea
coafts, and even under water in this torpid ftate, from which they
have been revived by the warmth of a fire. This torpid ftate of fwal-
lows is teflified by innumerable evidences both of antient and modern
names. Ariftotle fpeaking of the fwallows fay?, " They pafs into

warmer

Sect.XVI. 12. OF INSTINCT. 165

warmer climates in winter, if fuch places are at no great diflancc; if
they are, they bury themfelves in the climates where they dwell,"
(8. Hift. c. 16. See alfo Derham's Phyf. Theol. v. ii. p. i yy.)

Henpe their emigrations cannot depend on a neceffary inftinft, as the
emigrations themfelves are not necejfary !

2. When the weather becomes cold, the fwallows in the neigh-
bourhood affemble in large flocks; that is, the unexperienced attend
thofe that have before experienced the journey they are about to un-
dertake : they are then feen fome time to hover on the coaft, till there
is calm weather, or a wind, that fuits the dire<Slion of their flight.
Other birds of paflage have been drowned by thoufands in the fea, or
have fettled on fhips quite exhaufled with fatigue. And others, either
by miftaking their courfe, or by diftrefs of weather, have arrived in
countries where they were never feen before : and thus are evidently
fubje<ft to the fame hazards that the human fpecies undergo, in the
execution of their artificial purpofes.

3. The fame birds are emigrant from fome countries and not fo
from others : the fwallows were feen at Goree in January by an in-
genious philofopher of my acquaintance, and he was told- that they
continued there all the year; as the warmth of the climate was at all
feafons fufficient for their own conftitutions, and for the produ£lion of
the flies that fupply them with nourifliment. Herodotus fays, that in
Libya, about the fprings of the Nile, the fwallows continue all tjie
year. (L. 2.)

Quails (tetrao corturnix, Lin.) are birds of paflTage from the coafl
of Barbary to Italy, and have frequently fettled in large flioals on fhips
fatigued with their flight. (Ray, Wifdom of God, p. 129. Derham
Phyfic. Theol. v. ii. p. 178.) Dr. Ruflel, in his Hiftory of Aleppo,
obferves that the fwallows vifit that country about the end of Febru-
ary, and having hatched their young difappear about the end of July ;
and returning again about the beginning of Odober, continue about a
fortnight, and then again difappear. (P. 70.)

When

OF INSTINCT., SEeT.XVL 12.

When my late friend Dr. Chambres, of Derby, was on the ifland
of Caprea in tlie bay of Naples, he was informed that great flights 06
quails annually fettle on that ifland about the beginning of May, ins
their paflage from Africa to Europe. And that they always come;
when the fouth-eaft wind blows, are, fatigued when they refl on this,
ifland,, and are taken in fuch amazing quantities and fold to the Con-
tinent, that the inhabitants pay the biflaop his ftipend out. of the pro-
fits arifing from the fale of them.

• The flights of thefe birds acrofs the Mediterranean are recorded'near
three thoufand years ago. " There went forth a wind from the.
Lord and brought quails from the fea, and let them fall upon the
camp, a day's journey round about it, and they were two cubits above,
the earth," (Numbers, chap. ii. ver. 31.)

In. our country, Mr. Pfennant informs us, that fome quails migrate^,
and others only remove from the internal parts of the ifland to the-
coafts, (Zoology, odavo, 210.) Some of the ringdoves and fl:area
breed here, others migrate, (ibid. 510, 511.) And the flender billed
fmall birds do not all quit thefe kingdoms in the winter, though the
diflKculty of procuring the worms and infects,, that they feed on, fup-
plies the fame reafon for migration to them all, (ibid. 511.)

Linn^us has obferved;, that in Sweden the female chaffinches quit-
that country in September, migrating into Holland, and leave their
mates behind till their return in fpring. Hence he has called them
Fringilla caelebs, (Amaen. Acad. ii. 42. iv. 595.) Now in our, cUt
mate both fexes of them are perennial birds. And Mr. Pennant ob-
ferves that the hoopoe, chatterer, • hawfinch, and crofsbill, migrate
into England fo rarely, and at fuch uncertain times, as not to deferve
to be ranked among our bi;rds.of paflTage, (ibid. 511.)

The water fowl, as geefe and ducks, are better adapted for long
migrations, than the other tribes of birds, as, when the weather is
calm, they can not only reft themfelves, or fleep upon the ocean, but

poffibly procure fome kind of food from it.

Henca

Sect. XVI. i^: OF INSTINCT. 167

Hence in Siberia, as foon as the lakes are fcozen, the water fowl,
which are very, numerous, all difappear, and are fuppofed to fly to
-warraer climates, except the rail, . vvfhich, from its inabihty for lopg
flights, probably fleeps,. like our bat, in their winter. The fqilpvy;-
ing account from the Journey of Profeflbr Gmelin, may entertain the
reader. " In the neighbourhood of Krafnoiark, amongft many other
emigrant water fowls, we obferved a great number of rails, which
when purfued never took flight, but endeavoured to efcape by run-
ning. We enquired how thefe birds, that could not fly, could retire
into other countries in the winter, and were told, both by the Tar-
tars and Affanians, that they well knew thofe birds could not alone
pafs into other countries : but when the crains (les grues) retire in
autumn, each one takes a rail (un rale) upon his back, and carries
Iiim to a warmer climate."

rn:;.

'Recapitulation,

1 . All birds of paffage can exifl in the climates, where they arc
produced.

2. They are fubje£l in their migrations to the fame accidents and
difficulties, that mankind are fubjedl to in navigation.

3. The fame fpecies of birds migrate from fome countries, and are
refident in others.

From all thefe circumftances it appears that the migrations of birds
are not produced by a neceffary inftinft, but are accidental improve-
ments, like the arts among mankind, taught by their cotemporaries,
or deliver-ed by tradition from one generation of them to another.

XIII. In that feafon of the year which fupplies the nourifhment
proper for the expeded brood, the birds enter into a contract of mar-
riage, and with joitit labour conftrudt a bed for the reception of their

offspring.

i68 OF INSTINCT. ^ect.XVI. ij.

ofFspring. Their choice of the proper feafon, their contra6l:s of mar-
riage, and the regularity with which they conftrud: their nefts, have
in all ages excited the admiration of naturalifts ; and have always been
attributed to the power of inftinft, which, like the occult qualities
of the antient philofophers, prevented all further enquiry. We (hall
confider them in their order.

'^heir Choke of the Seafon.

Our domeftiG birds, that are plentifully fupplied throughout the
year with their adapted food, and are covered with houfes from the
inclemency of the weather, lay their eggs at any feafon: which
evinces that the fpring of the year is not pointed out to them by a
neceflary ixiflinfl:.

Whilfl: the wild tribes of birds choofe this time of the year from
their acquired knowledge, that th^ mild temperature of the air is more
convenient for hatching their eggs, and is foon likely to fupply that
kind of nourifliment, that is wanted for their young.

If the genial warmth of the fpring produced the paffion of love, as-
it expands the foliage of trees, all other animals fliould feel its influ-
ence as well as birds : but, the viviparous creatures, as they fuckfe
their young, that is, as they previoully digefl the natural food, that
it may better fuit the tender flomachs of their ofFspring, experience
the influence of this paflion at all feafons of the year, as cats and
bitches. The graminivorous animals indeed generally produce their
young about the time when grafs is fupplied in the greateft plenty,
but this is without any degree of exa£tnefs> as appears from our cows>
Iheep, and hares, and may be a part of the traditional knowledge,
which they learn from the example of their parents.

their

Sect.XVI. i> OF INSTINCT. 169

^he'ir ContraBs of Marriage.

- Their mutual paffion, and their acquired knowledge, that their
joint labour is neceffary to procure fuftenance for their numerous fa-
mily, induces the wild birds to enter into a contra6t of marriage,
which does not however take place among the ducks, geefe, and
fowls, that are provided with their daily food from our barns.

An ingenious philofopher has lately denied, that animals can enter
into contrafts, and thinks this an effential difference between them
and the human creature: — but does not daily obfervation convince us,
that they form contra£ts of friendfhip with each other, and with
mankind ? When puppies and kittens play together, is there not a
tacit contrad, that they will not hurt each other ? And does not your
favorite dog expedl you fliould give him his daily food, for his fer^ices
and attention to you ? And thus barters his love for your protedtion ?
In the fame manner that all contrails are made amongft men, that do
not underftand each others arbitrary language.

^je Conjiru&ion of their Nejls.

I. They feem to be inftrudled how to build their nefls from their
obfervation of that, in which they were educated, and from their
knowledge of thofe things, that are moft agreeable to their touch in
refped to warmth, cleanlinefs, and {lability. They choofe their
fituations from their ideas of fafety from their enemies, and of fhelter
from the weather. Nor is the colour of their nefts a circumftance
unthought of ; the finches, that build in green hedges, cover their
habitations with green mofs ; the fwallovv or martin, that builds

Z againfl

I7Q OF INSTINCT.' S^ciir.SV.jr.:!^?

againft rocks and houfes, covers her's with clay, whilfl the lark
choofes vegetable ftraw nearly of the colour of the ground fhe inha-
bits : by this contrivance, they are all lefs liable to be difcovered by
their adverlaries.

2. Nor are the neftsof the fame fpecies of bii'ds con ft rubied always
of the fanne materials, nor in the faoie form ; which is another cir-
cumftance that afcertains, that they are led by dbfervation.

In the trees before Mr. Levet's houfe in Lichfield, there are an-
nually nefts built by fparrows, a bird which ufually builds under the
tiles of houfes, or the thatch of barns. Not finding fuch convenient
lituations for their nefts, they build a covered .neft bigger than a man's
head, with an, opening like a mouth at the fide, refembling that of a
magpie, except that it is built with flraw and hay, and lined with
feathers, and fo nicely managed as to be a defence againft both wind
and rain.

So the jackdaw (corvus monedula) generally builds in church-
fleeples, or under the roofs of high houfes; but at Selbourn, in
Southamptonfhire, where towers and fteeples are not fufficiently nu-
merous, thefe fame birds build in forfaken rabbit burrows. See a cu-
rious account of thefe fubterranean nefts in White's Hiftory of Sel-
bourn, p. 59. Can the fkilful change of archite£lure in thefe birds
and the fparrows above mentioned be governed -by inftinft ? Then
they muft have two inftin(fts, one for common, and the other for
extraordinary occafions.

I have feen green worfted in a neft, which no where exifts in na-,
ture : and the down of thifiles in thofe nefts, that were by fome ac-
cident conftrudled later in the fummer, which material could not be
procured for the earlier nefts : in many different climates they cannot
procure the fame materials, that they ufe in ours. And it is well?
known, that the canary birds, that are propagated in this country, and-
the finches, that are kept tame, will build their nefts of any flexile
4 materiaisj

Sect.XVI. 15. OF INSTINCT. 171

materials, that are given them. Plutarch, in his Book on Rivers,
fpeaking of the Nile, fays, " that the fwallows collect a material,
when the waters recede, with which they form nefts, that are im-
pervious to water." And in India there is a fwallow that collects a
glutinous fubftance for this purpofe, whofe neft: is efculent, and
efteemed a principal rarity amongft epicures, (Lin, Syfl. Nat.) Both
thefe muft be conftru£led of very different materials from thofe ufed
by the fwallows of our country.

In India the birds exert more artifice in building their nefts on ac-
count of the monkeys and fnakes : fome form their penfile nefls in the
fhape of a purfe, deep and open at top ; others with a hole in the
fide; and others, flill more cautious, with an entrance at the very
bottom, forming their lodge near the fummit. But the taylor-bird
will not ever trufl its neft to the extremity of a tender twig, but
makes one more advance to fafety by fixing it to the leaf itfelf. It
picks up a dead leaf, and fews it to the fide of a living one, its [lender
bill being its needle, and its thread fome fine fibres ;the^ lining con-
fifls of feathers, golTamer, and down ; its eggs are white, the colour
of the bird light yellow, its length three inches^ its weight three iix-
teenths of an ounce ; fo that the materials of the neft, and the weight
of the bird, are not likely tq draw down an habitation fo (lightly fuf-
pended. A nefl of this bird is preferved in the Britifh Mufeum, (Pen-
nant's Indian Zoology). This calls to one's mind the Mofaic ac-
coynt of the origin of mankind^ the firfl dawning of art there afcribed
tolhem, is that of fewing leaves together. For many other curious,
kinds tif nefts fee Natural Hiftory for Children, by Mr. Galton.
Johnfon. London. Part I. p. 47. Gen. Oriolus.

3. Thofe birds that are brought up by our care, and have had
little communication with others of their own fpecies, are very de-
feftive in this acquired knowledge; they are not only very awkward
in the cohftru£!ion of their, nefts, but generally fcatter their eggs in
various parts of the room or cage, where they are confined, and feldom

Z 2 - produce

J72 OF INSTINCT. Sect. XVI. 13.

produce young ones, till, by failing in their firfl: attempt, they have
learnt fomething from their own obfervation.

4. During the time of incubation birds are faid in general to tura
their eggs every day ; fome cover them, when they leave the neft, as
ducks and geefe; in fome the male is faid to bring food to the female,
that fhe may have lefs occafion of abfence, in others he is faid to take
her place, when fhe goes in queft of food ; and all of them are faid to
leave their eggs a fhorter time in cold weather than in warm. In Se-
negal the oftrich fits on her eggs only during the night, leaving them
in the day to the heat of the fun ; but at the Cape of Good Hope,
where the heat is lefs, fhe fits on them day and night.

If it fhould be alked, what induces a bird to fit weeks on its firft
eggs unconfcious that a brood of young ones will be the product?
The anfwer muft be, that it is the fame pafilon that induces the hu-
man mother to hold her offspring whole nights and days in her fond
arms, and prefs it to her bofom, unconfcious of its future growth
to fenfe and manhood, till obfervation or tradition have informed
her.

5. And as many ladies are too refined to nurfe their own children,
and deliver them to the care and provifion of others ; fo is there one
inftance of this vice in the feathered world. , The cuckoo in fome parts
of England, as I am well informed by a very diftinft and ingenious
gentleman, hatches and educates her own young j whilft in other
parts fhe builds no neft, but ufes that of fome lefler bird, generally
either of the wagtail, or hedge fparrow, and depofiting one egg in it,,
takes no further care of her progeny.

As the Rev. Mr. Stafford v^'as walking in Glofop Dale, in the Peak
of Derbyihire, he faw a cuckoo rife from its neft. Theneft was on
the ftump of a tree,. that had been fome time felled, among fome chipS;
that were in part turned, grey, fo as much ta-refernble the colour of
the bird, in this neft were two young cuckoos : tying a ftring about
the leg of one of thera^ he pegged the other end of it to the ground,

and

SkcT.XVI. 14. OF INSTINCT. 173;

and very frequently for many days beheld the old cuckoo feed thefe her-
young, as he flood very near them.

Nor is this a new obfervation, though it is entirely overlooked by
the modern natuialifts, for Ariftotle fpeaking of the cuckoo, aflerts
that £he fometimes builds her neft among broken rocks, and on high
mountains, (L. 6. H. c. r.) but adds in another place that fhe gene-
rally poffeffcs the nefl: of another bird, (L. 6. H. c. 7.) And Ni-
phus fays that cuckoos rarely build for themfelves, moft frequently
laying their eggs in the nefts of other birds, (Gefner, L. 3. de
Cuculo.)

The Philofopher who is acquainted with thefe fadls concerning the
cuckoo, would feem to have very little /-ffl/o^himfelf, if he could
imagine this negledt of her young to be a neceflary injiintll

XIV. The deep recefTes of the ocean are inaccefiible to mankind,
which prevents- us from having much knowledge of the arts and go-
vernment of its inhabitants;

1. Gnc of the baits ufed by the fiilierman is an animal called an Old
Soldier, his fize and form are fomewhat like the craw-fifh, with this
difference, that his tail is covered with a tough membrane inftead of
a fhell ; and to obviate this defe£l, he feeks out the uninhabited fhell
of fome dead filh, that is large enough to receive his tail, and carries
it about with him as part of his clothhig or armour.

2. On the coafts about Scarborough, where the haddocks, cods,,
and dog-fifh, are in great abundance, the fifhermen univerfally be-
lieve that the dog-fifh make a line, or femicircle, to encompafs a-
fhoal of haddocks and cod, confining them within certain limits near -
the (hore, and eating them as occafion requires. For the haddocks
and cod are always found near the fhore without any dog-fiih among"
them, and the dog-fifh further off without any haddocks or cod ; and
yet the former are known to prey upon the latter,, and .'in: fome years
devour fuch immenfe quantities as to render this filhery more expenfive
than profitable, .

3.. The..

174 OF INSTINCT. Sect. XVI. 14.

3. The remora, when he wifhes to remove his fituation, as he is
a very flow fwimmer, is content to take an outfide place on whatever
conveyance is going his way ; nor can the cunning animal be tempted
to quit his hold of a fhip when flie is failing, not even for the lucre of
a piece of pork, left it fhould endanger the lofs of his paflage : at
other times he is eafily caught with the hook.

4. The crab-fifli, like many other teftaceous animals, annually
changes its {hell ; it is then in a foft ftate, covered only with a mucous
membrane, and conceals itfelf in holes in the fand or under weeds ;
at this place a hard fhelled crab always ftands centinel, to prevent the
fea infeds from injuring the other in its defencelefs fl:ate ; and the
iifliermen from his appearance know where to find the foft ones,
which they ufe for baits in catching other fifh.

And though the hard, fhelled crab, when he is on this duty, ad-
vances boldly to meet the foe, and will with difficulty quit the field;
yet at other times he flievvs great timidity, and has a wonderful fpeed
in attempting his efcape ; and, if often interrupted, will pretend
■death like the fpider, and watch an opportunity to fink himfelf into
the fand, keeping only his eyes above. My ingenious friend Mr.
Burdett, who favoured me with thefe accounts at the time he was
iorveying the coafts, thinks the commerce between the fexes takes
;place at this time, and infpires the courage of the creature.

5. The Ihoals of herrings, cods, haddocks, and other fi{h, which
approach our fiiores at certain feafons, and quit them at other feafons
without leaving one behind ; and the falmon, that periodically fre-
quent our rivers, evince, that there are vagrant tribes of fifh, that
perform as regular migrations as the birds of paffage already men-
tioned.

6. There is a catara£l on the river LifFey in Ireland about nine-
teen feet high : here in the falmon feafon many of the inhabitants
amufe themfelyes in obferving thefe fifh leap up the torrent. They
dart themfelves quite out of the water as they afcend, and frequently

fall

Sect. XVI. 15- O F I N S T I N C T. 175

fall back many times before they fnrmount it, and bafkets made of
twigs are placed near the edge of the ftream to catch them in their
fall.

I have obferved, as I have fat by a fpout of water, which defcends
from a flone trough about two feet into a ftream below, at particular
feafons of the year, a great number of little fifli called minums, or
pinks, throw themfelves aboi.it twenty times their own length out of
the water, expelling to get into ihe trough above.

This evinces that the ftorgee, or attention of the dam to provide
for the offspring,' is ftrongly exerted amongft the nations of fifh,.
■where it would fe'eni to be the moft neglected ; as thefe falmon can-
not be fuppofed to attempt fo difficult and dangerous a tafk without
being confcious of the purpofe or end of their endeavours.

It is further remarkable, that moft of the old falmon return to the
fea before it is proper for the young (hoals to attend therri, yet that a.
few old ones continue in the rivers fo late, that they become perfeftly
emaciated by the inconvenience of their fituation, and this apparently
to guide or to protect the unexperienced brood.

Of the fmaller water animals we have flill lefs knowledge, who
neverthelefs probably pofTefs many fuperior arts ; fome of thefe are
mentioned in Botanic Garden, P. I. Add. Note XXVII. and XXVIIL.
The nympha of the water-moths of our rivers, which cover them-
felves with cafes of Uraw, gravel, and fhell, contrive to make their
habitations nearly in equilibrium with the water -,- when too heavy,,
they add a bit of wood or ftraw ; when too light, a bit of gravel.
Edinb. Tranf.

All thefe circumftances bear a near refemblance to the deliberate ac-
tions of human reafon.

XV. We have a very imperfed acquaintance with the various
tribes of infefts : their occupations, manner of life, and even the
number of their fenfes, differ from our own, and from each other ;
but there is reafon to imagine, that thofe which goffefs the fenfe of

touch.

176 OF INSTINCT. Sect.XVI. 15.

-touch in the moft exquifite degree, and whofe occupations require the
moll conftant exertion of their powers, are indued with a greater
proportion of knowledge and ingenuity.

The fpiders of this country manufacture nets of various form?,
adapted to various fituations, to arreft the flies that are their food ;
and fome of them have a houfe or lodging-place in the middle of the
net, well contrived for warmth, fecurity, or concealment. There
is a large Ipider in South America, who conftrufts nets of fo flrong a
texture as to entangle fmall birds, particularly the humming bird.
And in Jamaica there is another fpider, who digs a hole in the earth
obUquely downwards, about three inches in length, and one inch in
diameter, this cavity flie hnes with a tough thick web, which when
taken out refembles a leathern purfe : but what is moft curious, this
houfe has a door with hinges, like the operculum of fome fea (hells ;
and herfelf and family, who tenant this neft, open and fliut the door,
whenever they pafs or repafs. This hiflory was told me, and the
:neft with its operculum (hewn me by the late Dr. Butt of Bath, who
was fome years phyfician in Jamaica.

The produ£lion of thefe nets is indeed a part of the nature or con-
formation of the animal, and their natural ufe is to fupply the place
of wings, when (he wi(hes to remove to another (ituation. But when
(he employs them to entangle her prey, there are marks of evident
defio-n, for (he adapts the form of each net to its (ituation, and
ftrengthens thofe lines, that require it, by joining others to the middle
■of them, and attaching thofe others to diftant objeds, with the fame
individual art, that is ufed by mankind in fupporting the mafts and
extending the fails of (hips. This work is executed with more ma-
thematical exaftnefs and ingenuity by the field fpiders, than by thofe
in our houfes, as their conftrudions are more fubjefted to the injuries
,of dews and tempefts.

Belides the ingenuity (hewn by thefe httle creatures in taking their
.prey, the circumftance of their counterfeiting death, when they are

pu]t

Sect. XVL 15. O F I N S T I N C T. 177

put into terror, is truly wonderful ; and as foon as the objed of terror
is removed, they recover and run away. Some beetles are alfo faid to
poffefs this piece of hypocrify.

The curious webs, or chords, conrtruded by fome young cater-
pillars to defend themfelves from cold, or from infefts of prey; and
by filk-worms and fome other caterpillars, when they tranfmigrate
into aurelite or larvae, have defervedly excited the admiration of the
inquifitive. But our ignorance of their manner of life, and even of
the number of their fenfes, totally precludes us from underflanding
the means by which they acquire this knowledge.

The care of the falmon in choofing a proper (ituation for her fpawn,
the fl:ru6lure of the nefts of birds, their patient incubation, and the
art of the cuckoo in depofiting her egg in her neighbour's nurfery,
are inftances of great fagacity in thofe creatures : and yet they are
much inferior to the arts exerted by many of the infe6t tribes on llmi-
lar occafions. The hairy excrefcences on briars, the oak apples, the
blafted leaves of trees, and the lumps on the backs of cows, are fitu-
ations that are rather produced than chofen by the mother infe6l for
the convenience of her offspring. The cells of bees, wafps, fpiders,
and of the various coralline infefts, equally aftonifli us, whether we
attend to the materials or to the architecture.

But the condu£l of the ant, and of fome fpecies of the ichneumon
fly in the incubation of their eggs, is equal to any exertion of human
fcience. The ants many times in a day move their eggs nearer the
furface of their habitation, or deeper below it, as the heat of the
Aveather varies ; and in colder days lie upon them in heaps for the
purpofe qf incubation : if their manfion is too dry, they carry them
to places where there is moifture, and you may diftindly fee the little
worms move and fuck up the water. When too much moifture. ap-
proaches their neft, they convey their eggs deeper in the earth, or to
fome other place of fafety. (Swammerd, Epil. ad Hlil:. Infects, p.
153. Phil. Tranf. No. 23. Lowthrop. V. 2. p. 7.)

A a There

178 OF INSTINCT. Sect.XVI. 16.

There is one fpecies of ichneumon-fly, that digs a hole in the earth,
and carrying into it two or three living caterpillars, depofits her eggs,
and nicely doling up the neft leaves them there ; partly doubtlefs to
affift the incubation, and partly to fupply food to her future young,
(Derham. B. 4. c. 13. Ariftotle Hift. Animal, L. 5. c. 20.)

A friend of mine put about fifty large caterpillars collefted from
cabbages on fome bran and a few leaves into a box, and covered it
with gauze to prevent their efcape. After a few days we faw, from
more than three fourths of them, about eight or ten little caterpillars
of the ichneumon-fly come out of their backs, and fpin each a fmall
cocoon of filk, and in a few days the large caterpillars died. This fmall
fly it feems lays its egg in the back of the cabbage caterpillar, which
when hatched preys upon the material, which is pi"oduced there for
the purpofe of making fllk for the future neft of the cabbage cater-
pillar; of which being deprived, the creature wanders about till it
dies, and thus our gardens are preferved by the ingenuity of this cruel
fly. This curious property of producing a filk thread, which is com-
mon to fome fea animals, fee Botanic Garden, Part I. Note XXVII.
atid is defigned for the purpofe of their transformation as in the filk-
worm, is ufed for conveying themfelves from higher branches to lower
ones of trees by fome caterpillars, and to make themfelves temporary
nefts or tents, and by the fpider for entangliag his prey. Nor is it
ftrange that fo much knowledge fhould be acquired by fuch fmall ani-
mals ; fince there is reafon to imagine, that thefe infefts have the fenfe
of touch, either in their probofcis, or their autennas, to a great degree
of perfeftion ; and thence may pofTefs, as far as their fphere extends,^
as accurate knowledge, and as fubtle invention, as the difcoverers of
human arts.

XVI. I. If we were better acquainted with the hiflories of thofe
infe£ls that are formed into focietles, as the bees, wafps, and ants, I
make no doubt but we fhould find, that their arts and improvements
are not fo fimilar and uniform as they now appear to us, but that they

arofe

SficT.XVr. i6. OF INSTINCT. 179

arofe in the fame manner from experience and tradition, as the arts of
our own fpecies ; though their reafoning is from fewer ideas, is bufied
about few-er obje£ls, and is exerted with lefs energy.

There are fome kinds of infefts that migrate like the birds before
mentioned. The locufl of warmer chmates has fometimes come over
to England ; it is fhaped like a grafshopper, with very large whigs,
and a body above an inch in length. It is mentioned as coming into
Egypt with an eail: wind, " The Lord brought an eaft wind upon
the land all that day and night, and in the morning the eafr wind
brought the locufts, and covered the face of the earth, fo that the
land was dark," Exod. x. 13. The migrations of thefe infedls are
mentioned in another part of the fcripture, " The locufts have no
king, yet go they forth all of them in bands," Prov. xxx. 27.

The accurate Mr. Adanfon, near the river Gambia in Africa, was
witnefs to the migrration of thefe infefts. " About eio;ht in the
morning, in the month of February, there fuddenly arofe over our
heads a thick cloud, which darkened the air, and deprived us of the
rays of the fun. We found it was a cloud of iocufls raifed about
twenty or thirty fathoms from the ground, and covering an extent of
feveral leag^ues ; at length a fhower of thefe infe£ls defcended, and
after devouring every green herb, while they refled, again refumed
their flight. This cloud was brought by a ilrong eaft-wind, and was
all the morning in pafTing over the adjacent country." (Voyage to
Senegal, 158.)

In this country the gnats are fometimes feen to migrate in clouds,
like the muiketoes of warmer climates, and our fwarms of bees fre-
quently travel many miles, and are faid in North America always to
fly towards the fouth. The prophet Ifaiah has a beautiful allufion to
thefe migrations, " The Lord fhall call the fly from the rivers of
Egypt, and fliall hifs for the bee that is in the land of Aflyria,"
Ifa. vii. 18. which has been lately explained by Mr. Bruce, in his tra-
vels to difcover the fource of the Nile.

A a 3 . 2, I

1 8o O F I N S T 1 N C T. Sect. XVL r 6,

2. I am well informed that the bees that were carried into Barba-
does, and other weftern iflands, ceafed to lay up any honey after the
firfl year, as they found it not ufeful to them : and are now become very
troublefome to the inhabitants of thofe iflands by infefling their fugar-
houfes ; b\it thofe in Jamaica continue to make honey^ as the cold
north winds, or rainy feafons of that ifland, confine them at home for
feveral weeks together. And the bees of Senegal, which differ from
thofe of Europe only in fize, make their honey not only fuperior to
ours in delicacy of flavour, but it has this Angularity, that it never
concretes, but remains liquid as fyrup, (Adanfon). From fome
obfervations of Mr. Wildman, and of other people of veracity, it ap-
pears, that during the fevere part of the winter feafon for weeks to-
gether the bees are quite benumbed and torpid from the cold, and do
not confume any of their provifion. This ftate of fleep, like that of
fwallows and bats, feems to be the natural refource of thofe creatures
in cold climates, and the making of honey to be an artificial improve-
ment.

As the death of our hives of bees appears to be owing to their being
kept fo warm, as to require food when their ftock is exhaufted; a
very obferving gentleman at my requefl: put two hives for many
weeks into a dry cellar, and obferved, during all that time, they did
not confume any of their provifion, for their weight did not decreafe,
as it had done when they were kept in the open air. The fame ob-
fervation is made in the Annual Regifter for 1768, p. 113. And the
Rev. Mr, White, in his Method of preferving Bees, adds, that thofe
on the north fide of his houfe confumed lefs honey in the winter than
thofe on the fouth fide.

There is another obfervation on bees well afcertained, that they at
various times, when the feafon begins to be cold, by a general mo-
tion of their legs as they hang in clufl'ers produce a degree of warmth,
which is eafily perceptible by the hand. Hence by this ingenious cx-

5 ertion.

Sect. XVI. 1 5. OF INSTINCT. i8i

ertion, they for a long time prevent the torpid ftate they would na-
turally fall into.

According to the late obfervations of Mr. Hunter, it appears that
the bee's- wax is not made from the duft of the anthers of flowers,
which they bring home on their thighs, but that this makes what is
termed bee-bread, and is ufed for the purpofe of feeding the bee-mag-
gots ; in the fame manner butterflies live on honey, but the previous
caterpillar lives on vegetable leaves, while the maggots of large flies
require flefh for their food, and thofe of the ichneumon fly require
infeds for their food. What induces the bee who Uves on honey to
lay up vegetable powder for its young ? What induces the butterfly
to lay its eggs on leaves, when itfelf feeds on honey ? What induces
the other flies to feek a food for their progeny different from what
they confume themfelves ? If thefe are not deduftions from their own
previous experience or obfervation, all the a£lions of mankind mufl be
refolved into inflindt.

3. The dormoufe confumes but little of its food during the rigour
of the feafon, for they roll themfelves up, or fleep, or lie torpid the
greateft part of the time ; but on warm funny days experience a fhort
revival, and take a little food, and then relapfe into their former
ftate." (Pennant Zoolog. p. 67.) Other animals, that fleep in winter
without laying up any provender, are obferved to go into their winter
beds fat and flrong, but return to day-light in the fpring feafon very
lean and feeble. The common flies fleep during the winter without
any provifion for their nourifhment, and are daily revived by the
warmth of the fun, or of our fires. Thefe whenever they fee light
endeavour to approach it, having obferved, that by its greater vicinity
they get free from the degree of torpor, that the cold produces ; and
are hence induced perpetually to burn themlelves in our candles : de-
ceived, like mankind, by the mifapplication of their knowledge.
Whilft many of the fubterraneous in lefts, as the common worms,
feem to retreat fo deep into the earth as not to be enlivened or awak-
ened

i82 OF INSTINCT. Sect.XVI. i6.

€ned by the dittereuce of our winter days ; and flop up their holes
with leaves or ftraws, to prevent the frofts from injuring them, or
the centipes from devouring them. The habits of peace, or the ftra-
ta^ems of war, of thele lubterranean nations are covered from our
view ; but a friend of mine prevailed on a diftreffed ^^'orm to enter
the hole of another worm on a bowling-green, and he prefently re-
turned much wounded about his head. And I once faw a worm rife
haftily out of the earth into the funftiine, and obferved a centipes
hanging at Its tail ; the centipes nimbly quitted the tail, and feizing
the worm about its middle cut it in half with its forceps, and preyed
vpon one part, while the other efcaped. \\'hich evinces thev have
dellgn in flopping the mouths of their habitations.

4. The wafp of this country fixes his habitation under ground,
that he may not be affected with the various changes of our climate ;
but in Tatr.aica he hangs it on the bough of a tree, where the feafons
are lefs fevere. He weaves a very curious paper of vegetable fibres to
cover his neil, which is conflrucled on the fame principle with that
of the bee, but with a different material ; but as his prey confifts of
flefli, fruits, and infects, which are perifhable commodities,- he can
lav up no provender for the winter.

M. de la Loubiere, in his relation of Siam, fays, " That in a part
of that kino"dom, which lies open to great inundations, all the ants
make their fettlements upon trees ; no ants' nefts are to be feen any
where elfe." Whereas in our country the ground is their only fitu-
ation. From the fcriptural account of thefe iiafe£ls, one might be
led to fufpecl, that in fome climates they lay up a provifion for the
winter. Ori^en affirms the fame, (Cont. Celf. L. 4.) But it is gene-
rally beheved that in this country they do not, (Prov. vi. 6. xxx. 25.)
The white ants of the coaft of Africa make themfelves pyramids eight
or ten feet high, on a bafe of about the fame width, with a fmooth
furface of rich clay, exceflively hard and well built, which appear at a
diftance like an afiemblage of the huts of the negroes, (Adanfon;.

The

Sect. XVI. 17- OF INSTINCT. 1S5

The hiftory of thefe have beea lately well defcribed in the Philofoph.
Tranfactions, under the name of termes, or termites. Thefe differ
very much from the nefls of our large ant ; but the real hiftory of
this creature, as well as of the wafp, is yet very imperfectly
known.

Wafps are faid to catch large fpiders, and to cut oft their legs, and
carry their mutilated bodies to their young, Dicl. Raifon. Tom, I.
p. 152.

One circumftance I fhall relate which fell under my own eye,
and fhewed the power of reafon in a walp, as it is exercifed among
men. A wafp, on a gravel walk, had caught a fly nearly as large as
himfelf ; kneeling on the ground I obferved him feparate the tail and
the head from the body part, to which the wings were attached. He
then took the body part in his paws, and rofe about two feet from the
ground with it ; but a gentle breeze "wafting the wings of the fly
turned him round in the air, and he fettled again with his prey upon
the gravel. I then diftintSly obferved him cut off with his mouth,
firft one of the wings, and then the other, after which he flew away
with it unmolefted by the wind.-

Go, thou fluggard, learn arts and induftry from the bee, and from
the ant !

Go, proud reafoner, and call the worm thy fifter !

XVII. Ccnclufim.

It was before obferved how much the fuperior accuracy of our
fenfe of touch contributes to increafe our knowledge ; but it is the
greater energy and activity of the power of vohtion (as explained in
the former Sedions of this work) that marks ma^ikind, and has given
him the empire of the world.

There

i84 OF INSTINCT. Sect. XVI. 17.

There is a criterion by which we may diftinguifli our voluntary a6ls
or thoughts from thofe that are excited by our fenfations : " The
former are always employed about the means to acquire pleafureable ob-
jecls, or to avoid painful ones : while the latter are employed about
tl^Q poJfeJfio?i of thofe that are already in our power."

If we turn our eyes upon the fabric of our fellow animals, we find
they are fupported with bones, covered with Ikins, moved by muf-
cles; that they poffefs the fame fenfes, acknowledge the fame appetites,
and are nouriflied by the fame aliment with ourfelves ; and we fhould
hence conclude from the flrongeft analogy, that their internal faculties
were alfo in fome meafure fimilar to our own.

Mr. Locke indeed publifhed an opinion, that other animals poffeffed
no abflradl or general ideas, and thought this circumftance was the
barrier between the brute and the. human world. But thefe abftradled
ideas. have been fince demonftrated by Bifhop Berkley, and allowed by
Mr. Hume, to have no exigence in nature, not even in the mind of
their inventor, and we are hence neceffitated to look for fome other
mark of diftindlion.

The ideas and aftions of brutes, like thofe of children, are almoft
perpetually produced by their prefent pleafures, or their prefent pains;
and, except in the few inflances that have been mentioned in this
Sedlion, they feldom bufy themfelves about the means of procuring
future blifs, or of avoiding future mifery.

Whilft the acquiring of languages, the making of tools, and the
labouring for money ; which are all only the 7neans of procuring plea-
fure: and the praying to the Deity, as another means to procure hap-
pinefs, are charadteriflic of human nature.

SECT.

Sect.XVII. I. CATENATION OF MOTIONS. 185

SECT. XVII.

THE CATENATION OF MOTIONS.

I. I. Catenations of animal motion. 1. Are produced by irritations j hy/enfationsy
by volitions. 3. They continue fome time after they have been excited. Cauje
cf catenation. 4. 7Ve can then exert our attention on other objeSls. 5. Many
catenations of motions go on together. 6. Some links of the catenations rfmotio7is
may be left out -without difuniting the chain. 7. Interrupted circles of motion
continue confufedly till they come to the part of the circle, where they tuere dif~
turbed. 8. Weaker catenations an dijfevered by fironger. 9. Then new cate-
vations take place. 10. Much effort prevents their reuniting. Impediment of
fpeech. 1 1. Trains more eafily dijfevered than circles. 1 2. Sleep defh-oys vo-
lition and external flimulus. II. Inftances of various catenations in a young
lady playing on the harpfichord. III. i. JVhat catenations are the flrongefl.
1, Irritations joined with affociations form flrongefl connexions. Vital motions.
3. New links with increajed force, cold fits of fever produced. 4. New links
with decreafed force. Cold hath. 5. Irritation joined with Jenfation. Inflam-
matory fever. IVhy children cannot tickle themfelves. 6. Volition joined with
Jenfation. Irritative ideas of found become Jenjible. 7. Ideas of imagination dij-
fevered by irritations, by volition, prodiiSlion ofjicrprije.

I. I. TO Inveftigate with precifion the catenations of animal mo-
tions, it would be well to attend to the manner of their produdion ;
but we cannot begin this difquilitlon early enough for this purpofe, as
the catenations of motion feem to begin with life, and are only ex-
tinguifhable with it. We have fpoken of the power of irritation, of
fenfation, of volition, and of affociation, as preceding the fibrous

B b motions:

1 86 CATENATION OF MOTIONS. Sect..XV1T. k-

motions; we now ftep forwards, and confider, that converfely they
are in their turn preceded by thofe motions ; and that all the fuc-
ceffive trains or circles of our aftions are compofed of this twofold^
concatenation. Thofe we fliall call trains of a£lion, which continue-
to proceed without any flated repetitions ; and thofe circles of adtion,
when the parts of them return at certain periods,, though the trains,,
of which they confift, are not exaflly fimilar. The reading an epic-
poem is a train of actions; the reading a fong with a chorus. at equal
diftances in the meafure conftitutes fo many circles of action.

2. Some catenations of animal motion are produced by reiterated;
fucceffive irritations, as when we learn to repeat the alphabet in its
order by frequently reading the letters of it. Thus the vermicular-
motions of the bowels were originally produced by the fucceffive ir-
ritations of the paffing aliment ; and the fucceffion of anions of the
auricles and ventricles of the heart was originally formed by fucceffive
ftimulusof the blood, thefe afterwards become part of the diurnal eir-^
cles of animal aftions, as appears by the periodical returns of hunger,,
and the quickened pulfe of weak people in the evening-
Other catenations of animal motion are gradually acquired by fuc-
ceffive agreeable fenfations,. as in learning a favourite fong or dance ;,
others by difagreeable fenfations, as in coughing or niftitation ; thefe
become affociated by frequent repetition, and afterwards compofe parts-
of o-reater circles of a£lion like thofe above mentioned*

Other catenations of motions are gradually acquired by frequent vo-
luntary repetitions ; as when we deliberately learn to march,, read,,
fence, or any mechanic art, the motions of many of our mufcles be-
come gradually linked together in trains,, tribes^ or circles of adlion..
Thus when any one at firft begins to ufe the tools in turning wood or
metals in a lathe, he wills the motions of his hand or fingers,, tillat
length thefe aftions become fo conneded with the effeft, that he-
fcems only to will the point of the ehiflel. Thefe are caufed by vo-

•J lltion>

Sect.XVU.i. catenation of motions. 187

lition, connected by affoclation like thofe above defcribed, and after-
wards become parts of our diurnal trains or circles of aftion.

3. All thefe catenations of animal motions are liable to proceed
fome time after they are excited, unlefs they are difturbed or impeded
by other irritations, fenfations, or volitions ; and in many inftances
in fpite of our endeavours to ftop them; and this property of animal
motions is probably the caufe of their catenation. Thus when a child
revolves fome minutes on one foot, the fpeiStra of the ambient objefts
appear to circulate round him fome time after he falls upon the
ground. Thus the palpitation of the heart continues fome time after'
the obje^l of fear, which occaiioned it, is removed. The blufh of
ihame, which is an excefs of fenfation, and the glow of anger, which
is an excefs of volition, continue fome time, though the affefted per-
fon finds, that thofe emotions were caufed by miftaken fafts, and en-
deavours to extinguilh their appearance. See Sedl. XII. i. 5.

4. When a circle of motions becomes conneded by frequent repe-
titions as above, we can exert our attention ftrongly on other obje(9:s,
and the concatenated circle of motions will neverthelefs proceed io.
due order ; as whilft you are thinking on this fubject, you ufe variety,
of mufcles in walking about your parlour, or iu fitting at your writ-
ing-table.

5. Innumerable catenations of motions may proceed at the fame
time, without incommoding each other. Of thefe are the motions
of the heart and arteries ; thofe of digeftion and glandular fecretion ;
of the ideas, or fenfual motions ; thofe of progrefiion, and of fpeak-
ing ; the great annual circle of axftions fo apparent in birds in their
times of breeding and moulting ; the monthly circles of many female

. animals ; and the diurnal circles of fleeping and waking, of fulnefs
and inanition.

6. Some links of fuccefCve trains or -of fyachronous tribes of aftioa
may be left out without disjoining the whole. Such are our ufuai
trains of recolledion ; after havina; travelled through an entertainin*

B b 2 country.

i88 CATENATION OF MOTIONS. Sect.XVII.i.

country, and viewed many delightful lawns, rolling rivers, and echo-
ing rocks ; in the recollection of our journey we leave out the many
diftrifts, that we croffed, which were marked with no peculiar plea-
fure. Such alfo are our complex ideas, they are catenated tribes of
ideas, which do not perfedtly refemble their correfpondent perceptions,
becaufe fome of the parts are omitted.

7. If an interrupted circle of aftions is not entirely diffevered, it
will continue to proceed confufedly, till it comes to the part of the
circle, where it was interrupted.

The vital motions in a fever from drunkenncfs, and in other peri-
odical dileafes, are inftances of this circumftance. The accidental in-
ebriate does not recover himfelf perfedly till about the fame hour on
the fucceeding day. The accuftomed drunkard is difordered, if he
has not his ufual potation of fermented liquor. So if a confiderable-
part of a connected tribe of adlion be difturbed, that whole tribe goes
on with confufion, till the part of the tribe affected regains its ac-
cuftomed catenations. So vertigo produces vomiting, and a great fe-
cretion of bile, as in fea-ficknefs, all thefe being parts of the tribe of
irritative catenations.

8. Weaker catenated trains may be diflevered by the fudden ex-
ertion of the ftronger. When a child firft attempts to walk acrofs a
room, call to him, and he inftantly falls upon the ground. So while
I am thinking over the virtues of my friends, if the tea-kettle fpurt
out fome hot water on my flocking ; the fudden pain breaks the
weaker chain of ideas, and introduces a new group of figures of its
own. This circumflance is extended to fome unnatural trains of ac-
tion, which have not been confirmed by long habit ; as the hiccough,
or an ague-fit, which are frequently curable by furprife. A young
lady about eleven years old had for five days had a contraftion of one
mufcle in her fore arm, and another in her arm, which occurred four
©r five times every minute ; the mufcles were feen to leap, but with-
out bending the arm. To countcradl this new morbid habit, an ifTue

3 was

Sect.XVII. I. CATENATION OF MOTIONS. 189

was placed over the convulfed mufcle of her arm, and an adhefive
plafter wrapped tight like a bandage over the whole fore arm, by
which the new motions were immediately deftroyed, but the .means
were continued fome weeks to prevent a return.

9. If any circle of adions is diffevered, either by omiffion of fome
of the links, as in fleep, or by infertion of other links, as in furprife,
new catenations take place in a greater or lefs degree. The laft link
of the broken chain of a<Sions becomes connefted with the new mo-
tion which has broken it, or with that which was nearefl the link
omitted ; and thefe new catenations proceed inftead of the old ones.
Hence the periodic returns of ague-fits, and the chimeras of our
dreams.

10. If a train of a(5lions is diffevered, much effort of volition or
fenfation will prevent its being reftored. Thus in the common im-
pediment of fpeech, when the affociation of the motions of the muf-
cles of enunciation with the idea of the word to be fpoken is difor-
dered, the great voluntary efforts, which diftort the countenance,
prevent the rejoining of the broken affociations. See No. II. 10. of
this Sedion. It is thus likewife obfervable in fome inflammations of
the bowels, the too ftrong efforts made by the mufcles to carry for-
wards the offending material fixes it more firmly in its place, and
prevents the c;3re. So in endeavouring to recal to our memory fome
particular word of a fentence, if we exert ourfelves too ffrongly about
it, we are lefs likely to regain it.

11. Catenated trains or tribes of aftion are eafier diffevered than
catenated circles of a£lion. Hence in epileptic fiits the iynchronous
conneded tribes of acflion, which keep the body eredV, are diffevered,
but the circle of vital motions continues undifturbed.

12. Sleep deftroys the power of volition, and precludes the ftimull
of external obje6ls, and thence diffevers the trains, of which thefe are
a part ; which confirms the other catenations, as thofe of the vital

motions.

1,90 CATENATION OF MOTIONS. Sect.XVILi.

motions, fecretions, and abforptions ; and produces the new trains c^-
ideaa, which conftitute our dreanis.

IT. r. All the preceding circumftances of the catenations of animd-
■motions will be more clearly underftood by the following example of
a perfon learning mufic ; and when we recolleft the variety of me-
chanic arts, which are performed by affociated trains of mufcular ac-
tions-catenated with the efFe(!ls they produce, as in knitting, netting,
weaving ; and the greater variety of affociated trains of ideas caufed
or catenated by volitions or fenfations, as in our hourly modes of rea-
soning, or imagining, or recollefting, we fhall gain fome-idea of the
innumerable catenated trains and circles ef aflion, which form the
' tenor of our lives, and which began, and will only ceafe entirely with
them.

2. When a young lady begins to learn mufic, fhe voluntarily ap-
rplies herfelf to the charadters of her mufic-book, and by many repe-
titions endeavoursto catenate them with the proportions of found, of
which they are fymbols. The ideas excited by the mufical charac-
ters are {\awly connedled with the keys of the harpfichord, and much
effort is neceffary to produce every note with the proper finger, and in
its due place and time ; till at length a train of voluntary exertions
becomes catenated with certain irritations. As the various notes by
frequent repetitions become connedled in the order, in which they
-are produced, a new catenation of fenfitive exertions becomes mixed
with the voluntary ones above defcribed; and not only the mufical
'fymbols of crotchets and. quavers, but the auditory notes and tones at
the fame time, become fo many fucceffive or fynchronous links in this
circle of catenated adlions.

At leno-th the motions of her fingers become catenated with the
mufical charaders; and thefe no fooner ftrike the eye, than the finger
^reffes down the key without any voluntary attention between them j
the adivity of the hand being conneded with the irritation of the

ifi^ure

SE€T.XVrL2. CATENATION OF MOTIONS. rpi

figure or place of the mufical fjmbol on the retina ; till at length by
frequent repetitions of the fame tune the movements of her fingers in
playing, and the mufcles of the larynx in finging, become affociated
with each, other, and form part of thofe intricate trains and circles of
catenated motions, according with the fecond article of the preceding
propofitions in No. i. of this Sedlion.

3» Befides the facility, which by habit attends the execution of
this mufical performance, a curious circumftance occurs, which is,
that when our young mufician has began a tune, (he finds herfelf in-
clined to continue it ; and that even when fhe is carelcfsly finging
alone without attending to her own fong; according with the third
preceding article.

4. At the fame time that our young performer continues to play
with great exadnefs this accuftomed tune, fhe can bend her mind,
and that intenfely, on fome other objedt, according with the fourth,
article of the preceding propofitions.

The manufcript copy of this work was lent to many of my friends-
at different times for the ptirpofe of gaining their opinions and criti-
cifms on many parts of it, and I found the following anecdote writ-
ten with a pencil oppofite to this page, but am. not certain by whom,
" I remember feeing the pretty young a<flrefs, who fucceeded Mrs..
Arne in the performance of the celebrated Padlock, rehearfe the mu.^
fical parts at her harpfichord under the eye- of her mafter with great
tafte and accuracy ; though I obferved her countenance full of emo-
tion, which I could not account for; at laft fiie luddenly burft into
tears;, for flie had all this time been eyeing a beloved canary bird,,
fuffering great agonies, which at that inftant fell dead from its
perch.""

5. At the fame time many other catenated circles of action are
going on in the perfon of our fair miifician, as well as the motions of
her fingers, fuch as the vital motions, refpiration, the movements of

her

i9» CATENATION OF MOTIONS. Sect. XVII. 2.

her eyies and eyelids, and of the uitricate mufcles of vocality, accord-
ing with the fifth preceding article.

d. If by any ftrong impreflion on the mind of our fair raufician fhe
lhou4d be interrupted for a very inconfiderabJe time, Ihe can ftill con-
tinueher performance, according to the fixth article.

7. If however this interruption be greater, though 'the chain^of ac-
tions be not diflevered, it proceeds confufedly, and our young per-
former continues indeed to play, but in a hurry without accuracy and
elegance, till fhe begins the tune again, according to the feventh of
the preceding articles.

8. But if. this interruption be ftill greater, the circle of axSions be-
comes entirely drflTevered, and flie finds herfelf immediately under the
neceflity to begin over again to recover the lofl catenation, according
to the eighth preceding article.

,9. Or in trying to recover it fhe will fing fome diilbnant notes,
or flrike fome improper k«ys, according to the ninth j)receding
a-rticle.

10. A very remarkable thing attends this breach of catenation, if
the performer has forgotten fome word oFher fong, the more energy
of mind fhe ufes about it, the more diflant is fhe.from regaining it.;
and artfully- employs her mind in part on fome other obje£l, or endea-
vours.to dull its perceptions, continuing to repeat, as it were inconfci-
oufly, the former part of the fong, that fhe remembers, in hopes to
regain the loft connexion.

For if the aftivity of the mind itfelf be more energetic, or takes its
attention more, than the connecting word, which is wanted.; it will
not perceive the (lighter link of this lofl word ; as who liflens to a
feeble found, mufl be very filent and motionlefs ; fo that in this cafe
the very vigour of the mind itfelf feems to .prevent it from regaining
the lofl catenation, as well as the too great exertion in endeavouring to
regain it, according to the tenth preceding article.

Sect.XVII.2. catenation of motions. 193

We frequently experience, when we are doubtful about the fpelUng
of a word, that the greater voluntary exertion we ufe, that is the
inore intenfely we think about it, the further are we from regaining
the loft aflociatiou between the letters of it, but which readily recurs
M'hen we have become carelefs about it. In the fame manner, after
having for an hour laboured to recoUedl the name of fome abfent per-
foh, it fhall feem, particularly after fleep, to come into the mind as it
were fpontaneoufly; that is, the word we are in fearch of, was joined
to the preceding one by affociation J this affociation being diffevered,
we endeavour to recover it by volition ; this very aftion of the mind
ftrikes our attention more, than the faint link of affociation, and wc
find it impoffible by this means to retrieve the loft word. After Deep,
when volition is entirely fufpended, the mind becomes capable of per-
ceiving the fainter link of afibciation, and the word is regained.

On this circumftance depends the impediment of fpeech before
mentioned; the firft fyllable of a word is caufable by volition, but the
remainder of it is in common converfation introduced by its aflbcia-
tions with this firft fyllable acquired by long habit. Hence when the
mind of the ftammerer is vehemently employed on fome idea of am-
bition of fhining, or fear of not fucceeding, the aflbeiations of the mo-
tions of the mufcles of articulation with each other become diflevered
by this greater exertion, and he endeavours in vain by voluntary ef-
forts to rejoin the broken affociation. For this purpofe he continues
to repeat the firft fyllable, which is caufable by volition, and ftrives in
vain, by various dift-ortions of countenance, to produce the next links,
which are fubje6t to affociation. See Clafs IV. 3. i. i .

II. After our accomplifhed mufician has acquired great variety of
tunes and fongs, fo that fome of them begin to ceafe to be eafily re-
collefted, ftie finds progreffive trains of mufical notes more frequently
forgotten, than thofc which are compofed of reiterated circles, ac-
cording with the eleventh preceding article.

Co 12. To

J94 CATENATION OF MOTIONS. SECT.XVIL3.

12. To finifh our example with the preceding articles we mufl: at
length fuppofe, that our fair performer falls afleep over her harpfi-
chord ; and thus by the fufpeafion of volition, and the exclufion of ex-
ternal ftimuli, fhe diffevers the trains and circles of her mufical ex-
ertions.

III. I. Many of thefe circuniftances of catenations of motions re-
ceive an eafy explanation from the four following confequences to the
feventh law of animal caufation in Se6l. IV. Thefe are, firft, that
thofe fucceflions or combinations of animal motions, whether they
Were united by caufation, affociation, or catenation, which have been
moft frequently repeated, acquire the ftrongeft connexion. Secondly,
that of thefe, thofe, which have been lefs frequently mixed with
other trains or tribes of motion, have the ftrongeft connexion.
Thirdly, that of thefe, thofe, which were firft formed, have the
ftrongeft connexion. Fourthly, that if an animal motion be excited
fey more than one caufation, affociation, or catenation, at the fame
time, it will be performed with greater energy.

2. Hence alfo we underftand, why the catenations of irritative mo-
tions are more ftrongly connedled than thofe of the other claffes,
where the quantity of unmixed repetition has been equal ; becaufe
they were firft formed. Such are thofe of the fecerning and abforbent
fyftems of veffels, where the aftion of the gland produces a fluid,
which ftimulates the mouths of its correfpondent abforbents. The
affociated -motions feem to be the next moft ftrongly united, from
their frequent repetition j and where both thefe circumftances unite,
as in the vital motions, their catenations are indiffoluble but by the
deftruftion of the animal.

3. Where a new link has been introduced into a circle of adlions
by fome accidental defedl of ftimulus ; if that defeft of ftimulus be
repeated at the fame part of the circle a fecond or a third time, the
defective motions thus produced, both by the repeated defed of fti-
8 niuli>s

Sect.XVII.^. catenation of ^IOTIONS. 195

mulus and by their catenation with the parts of the circle of a£lions,
will be performed with lefs and lefs energy. Thus if any perfon is
expofed to cold at a certain hour to-daj^, fo long as to render fome
part of the fyflem for a time torpid ; and is again expofed to it at the
fame hour to-morrow% and the next day; he will be more and more
afFeded by it, till at length a cold fit of fever is completely formed,
as happens at the beginning of many of thofe fevers, which are called
nervous or low fevers. Where the patient has flight periodical fhiver-
ings and palenefs for many days before the febrile paroxifm is com-
pletely formed.

4. On the contrary, if the expofure to cold be for fo fhort a time
as not to induce any confiderable degree of torpor or quiefcence and
is repeated daily as abov.e mentioned, it lofes its effect more and more
at every repetition, till the conftitution can bear it without inconveni-
ence, or indeed without being confcious of it. As in walking into the
cold air in frofly weather. The fame rule is applicable to increafed
ftimulus, as of heat, or of vinous fpirit, within certain limits, as is
applied in the two laft paragraphs to Deficient Stimulus, as is further
explained in Se£t. XXXVI. on the Periods of Difeafes.

5. Where irritation coincides with fenfation to produce the fame
catenations of motion, as in inflammatory fevers, they are excited
with ftill greater energy than by the irritation alone. So when chil-
dren expert to be tickled in play, by a feather lightly pafled over the
lips, or by gently vellicating the foles of their feet, laughter is moft
vshemently excited ; though they can ftimulate thefe parts with their

'own fingers unmoved. Here the pleafureable idea of playfulnefs co-
incides with the vellication ; and there is no voluntary exertion ufed
to diminifti the fenfation, as there would be, if a child Ihould endea-

-vour to tickle himfelf. See Seft. XXXIV. i. 4.

6. And laftly, the motions excited by the junftion of voluntary
exertion with irritation are performed with more energy, than thole

C c 2 hv

196 CATENATION OF MOTIONS. Sect.XVII.j.

by irritation fingly ; as when we liften to fmall noifes, as to the tick-
ing of a watch in the night, we perceive the moil weak founds, that
are at other times unheeded. So when we attend to the irritative
ideas of found in our ears, which are generally not attended to, we
can hear them ; and can fee the fpeilra of obje£ts, which remain in
the eye, whenever wc pleafe to exert our voluntary power in aid of
thofe weak a6lions of the retina, or of the auditory nerve.

7. The temporary catenations of ideas, which are caufed by the
fenfations of pleafure or pain, are eafily diflevered either by irritations,
as when a fudden noife difturbs a day-dream ; or by the power of vo-
lition, as when we awake from deep. Hence in our waking hours,
whenever an idea occurs, which is incongruous to our former expe-
rience, we inflantly diffever the train of imagination by the power
of volition, and compare the incongruous idea with our previous
knowledge of nature, and rejeft it. This operation of the mind has
not yet acquired a fpecific name, though it is exerted every minute
of our waking hours ; unlefs it may be termed intuitive ana-
logy. It is an a£l of reafoning of which we are unconfcious except
from its efFe6ls in preferving the congruity of our ideas, and bears the
fame relation to the fenforial power of volition, that irritative ideas,
of which we are inconfcious except by their effetfls, do to the fenfo-
rial power of irritation ; as the former is produced by volition without
our attention to it, and the latter by irritation without our attention
to them.

If on the other hand a train of imagination or of voluntary ideas are
excited with great energy, and paffing on with great vivacity, and be-
come diflevered by fome violent ftimulus, as the difcharge of a piflol
near one's ear, another circumftance takes place, which is termed
SURPRISE ; which by exciting violent irritation, and violent fenfation,
employs for a time the whole fenforial energy, and thus difl'evers the
paffing, trains of ideas, before the power of volition has time to com-
pare

Sect. XVII. 3- CATENATION OF MOTIONS. 197

pare them with the ufual phenomena of nature. In this cafe fear is
generally the companion of furprife, and adds to our embarralTment,
as every one experiences in fome degree when he hears a noife in the
dark, which he cannot inftantly account for. This catenation of fear
with furprife is owing to our perpetual experience of injuries from
external bodies in motion, unlefs we are upon our guard againft them.
See Sea. XVIII. 17. and XIX. 2.

Many other examples of the catenations of animal motions are ex-
plained in Sed. XXXVI, on the Periods of Difeafes,

SECT.

io8, OF SLEEP. Sect.XVIILu

SECT. XVIIL

OF SLEEP.

I. Volition is Jufpended in Jleep. i. Senfation continues. Dreams p-event delirium
and inflammation. 3. Nightmare. 4. Ceajelejs flow of ideas in dreams,
5. Wejeem to receive them by thejenjes. Optic nerve perfeRly Jenfible in fleep^
Eyes lejs dazzled after dreaming of vifible objects. 6. Reverie, belief. 7. Hoia
we diftinguifh ideas from perceptions. 8. Variety offcenery in dreams, excellence
cf the fenfe of vijion. 9. Novelty of combination in dreams. 10. DiftinEfnefs
'Of imagery in dreams. 11. Rapidity of tranfaBion in dreams. 12. Of mcafur-
ing time. Of dramatic time and place. Why a dull play induces fleep, and an
interefting one reverie. 13. Confcioufnefs of our exiflence and identity in d.r earns „.
14. How we awake fometimes fuddenly, fometimes frequently, n^. Irritative
motions continue in fleep, internal irritations are fucceeded byferfation. Senftbility
-increafes during fleep, and irritability. Morning dreams. V^hy epilepfies occur
in fleep. Ecftacy of children. Cafe of convtdfions in fleep. Cramj.\ why pain-
ful. Afthma. Morning fvoeats. Increafe of heat, Increafe ■ of urine in fleep.
Why more liable to take cold in fleep. Catarrh from thin night-caps. WJjy we
feel chilly at the' approach of fleep, and at waking in the open air. 16. Why
the gout commences infle-ep. Secretions are more copious in fleep, young animals
and plants grow more in fleep. 17. Incoiflflency of dreams. Abftnce of furprife
■in dreams. 1 8 . Why we forget fame dreams and not others. 1 9. Sleep-
talkers awake with furprife. 20. Remote caufes of Jleep. Atmofphere zoilh
■lefs oxygC'ie. Compreflion of the brain in fpina bifida. By whirling on an hori-
zontal wheel. By cold, 11. Definition of fle^p,

I. THERE are four fituations of our fyftem, which in their mo-
clerate degrees are not ufually termed dileafes, and yet abound with
-many very curious and inftruftive phenomena; thcfc are fleep , re-

■ver-ie.

Sect.XVIII. I. OF SLEEP. rp^i-

vcrie, vertigo, druiikeniiefs. T iefe we (hall previoufly confider,
before we ftep forwards to develop the caufes and cures of difeafes
with the modes of the operation of medicines.

As all thofe trains and tribes of animal motion, which arefubjefted
to volition, were the lalT: that were cauftd, their connexion is weaker
than that of the other clafles ; and there is a peculiar circumftance at-
tending this caufation, which is, that it is entirely lulpended during
deep; \vhilft the other claffes of motion, which are more immediate-
ly neceffary to life, as thole cauied by uiternal ftimuli, for inftaiice
the pulfations of the heart and arteries, or thofe catenated with plea-
furable fenfation, as the powers of digeftion, continue to ftrengthen
their habits without interruption. Thus though n>an in his fleeping
ftate is a much lefs perfe6l animal, than in his waking hours; and,
though he confumes more than one third of his life in this his irra-
tional fituatlon ; yet is the wildom of the Author of nature manifefl
even in this feeming imperfeftion of his work !

The truth of this affertion with reipe£t to the large mufcles of the
body, which are concerned in locomotion, is evident ; as no one ia
perfedl fanity walks about in his flsep, or performs any dom.eflic of-
fices : and in refpeft to the mind, we never exercife our reafon or re-
CoUedtion in dreams ; we may fometimes ieem diftradled between con-
tending paflions, but we never compare their objects, or deliberate
about the acquifition of thole objeds, if our fleep is perfe£l. And
though many fynchronous tribes or fucceflive trains of ideas may re-
prefent the houfes or walks, which have real exiftence, yet are they
here introduced by their connexion with our fenlations, and are ia
truth ideas of imagination, not of recolle6lion.

2. For our fenfations of pleafure and pain are experienced with,
great vivacity in our dreams ; and hence all that motley group of ideas,
which are caufed by them, called the ideas of imagination, with their
various aflbciated trains, are in a very vivid manner a£ted over in the
fenforium ; and thefe fometimes call into aclion the larger mufcles,

which.

2 00 OF SLEEP. Sect.XVIII.j.

which have been much affociated with them ; as appears- from the
muttering fentences, which fome people utter ia tlieir dreams, and
from the obfcure barking of fleeping dogs, and the motions of their
feet and noflrils.

This perpetual flow of the trains of ideas, which conftltute our
dreams, and which are caufed hy painful or pleafureable fenfation>
might at firft view be conceived to be an ufelefs expenditure of fen-
foriai pow^er. But it has been fliewn, that thofe motions, which are
perpetually excited, as thofe of the arterial fyftem by the ftimulus of
the blood, are attended by a great accumulation of fenforial power,
after they have been for a time fufpended ; as the hot-fit of fever is
the confequence of the cold one. Now as thefe trains of ideas caufed
by fenfation are perpetually excited during our waking hours, if they
were to be fufpended in fleep like the voluntary motions, (which are
exerted only by intervals during our waking hours,) an accumulation
of fenforial power would follow j and on our awaking a delirium
would fupervene, fince thefe ideas caufed by fenfation would be pro-
duced with fuch energy, that we (hould miftake the trains of ima-
gination for ideas excited by irritation ; as perpetually happens to
people debilitated by fevers on their firft awaking; for in thefe fevers
with debility the general quantity of irritation being diminiflied, that
of fenfation is increafed. In like manner if the aftions of the flomach,
inteflines, and various glands, which are perhaps in part at leafl
caufed by or catenated with agreeable fenfation, and which perpetual-
ly exift during our waking hours, were like the voluntary motions
fufpended in our deep; the great accumulation of fenforial power,
which would neceffarily follow, would be liable to excite inflamma-
tion in them.

3. When by our continued poflure in {leep, fome uneafy fenfa-
tions are produced, we either gradually awake by the exertion of vo-
lition, or the mufcles connefted by habit with fuch fenfations alter
the pofition of the body; but where the fleep is uncommonly pror
. S . found,

SECT.XVI1I.4.S- OF SLEEP. zoi

found, and thofe uneafy fenfations great, the difeafe called the incu-
bus, or nightmare, is produced. Here the defire of moving the
body is painfully exerted, but the power of moving it, or volition, is
incapable of adion, till we awake. Many lefs dlfagreeable ftruggles
ill our dreams, as when v^^e wifh in vain to fly from terrifying objeils,
conftitute a flighter decree of this difeafe. In awakinsf from the
nightmare I have more than once obferved, that there was no diforder
in my pulfe ; nor do I believe the refpiration is laborious, as feme
have affirmed. It occurs to people whofe fleep is too profound, and
fome dlfagreeable fenfation exifls, which at other tinies would have
awakened them, and have thence prevented the difeafe of nightmare;
as after great fatigue or hunger with too large a fupper and wine,
which occafion our ileep to be uncommonly profound. See No. 14,
of this Section.

4. As the larger mufcles of the body are much more frequently
excited by volition than by fenfation, they are but feldom brought
into -action in our fleep: but the ideas of the mind are by habit much
more frequently connedled with fenfation than with volition ; and
hence the ceafekfs fiow of our ideas in dreams. Every one's experi-
ence will teach him this truth, for we all daily exert much voluntary
mufcular motion : but few of mankind can bear the fatigue of much
voluntary thinking.

5. A very curious circumftance attending thefe our fleeping ima-
ginations is, that we feem to receive them by the fenfes. The muf-
cles, which are fubfervientto the external organs of fenfe, are con-
nected with volition, and ceafe to 2.St in fleep ; hence the eyelids are
clofed, and the tympanum of the ear relaxed; and it is probable a
iimilarity of voluntary exertion may be neceflary for the perceptions
of the other nerves of fenfe ; for it is obferved that the papilla; of the
tongue can be feen to become ere<3:ed, when we attempt to tafte any
•thing extremely grateful. Hewfoa Exper. Enquir. V. 2. 186. Albini
Annot, Acad. L. i. c. 15.. Add to this, that the immediate organs

D d of

202 O F S L E E P. Sect. XVIII. 5.

of fenfe have no objefts to excite them in the darknefs and filence of
the night ; but their nerves of fenfe neverthelefs continue to poffefs
their perfed activity fubfervient to all their numerous fenfitive con-
nexions. This vivacity of our nerves of fenfe during the time of
fleep is evinced by a circumftance, vi'hich almoft every one mufl at
fome time or other have experienced ; that is, if we fleep in the day-
light, and endeavour to fee fome objed in our dream, the light is ex-
ceedingly painful to our eyes; and after repeated fl:ruggles we lament
in our fleep, that we cannot fee it. In this cafe I apprehend the eye-
lid is in fome degree opened by the vehemence of our fenfations; and,
the iris being dilated, the optic nerve fhews as great or greater fen-
libility than in our waking hours. See No. 15. of this Se6lion,

When we are forcibly waked at midnight from profound fleep, ouir

eyes are much dazzled with the light of the candle for a minute or

two, after there has been fufficient time allowed for the coatraflioa

of the iris; which is owing to the accumulation of fenforial power ia

the organ of vifiou during its flate of lefs adlivity. But when we

have dreamt much of vifible objedls, this accumulation of fenforial

power in the organ of vifion is leflened or prevented, and we~ awake

in the morning without being dazzled with the hght, after the iris

has had time to contraft itfelf. This is a matter of great curiofity,

and may be thus tried by any one in the day-light. Clofe your eyes,

and cover them with your bat ; thiiik for a minute on a tune, which

you are accufl:omed to, and endeavour to fmg it with as little adtivity

of mind as poflible. Suddenly uncover and open your eyes, and ia

one fecond of time the iris will contrail itfelf, but you will perceive

the day more luminous for feveral feconds, owing to the accumulatioa

of fenforial power in the optic nerve.

Then again clofe and cover your eyes, and think intenfely on a
cube of ivory two inches diameter, attending firfl to the north and
fouth fides of it, and then to the other four fides of it j then get a
clear image in your mind's eye of all the fides of the fame cube co-
Loured

Sect. XVIII. 6. OF SLEEP. 203

loured red; and then of it coloured green; and then of it coloured
blue ; laftly, open your eyes as in the former experiment, and after
the firft: fecond of time allowed for the contra6lion of the iris, you
will not perceive any increafe of the light of the day, or dazzling ;
becaufe now there is no accumulation of fenforial power in the optic
nerve ; that having been expended by its adlion in thinking over vi-
fible objeds.

This experiment Is not eafy to be made at firft, but by a few pa-
tient trials the fadt appears very certain ; and (hews clearly, that our
ideas of imagination are repetitions of the motions of the nerve, which
were originally occafioned by the flimulus of external bodies j becaufe
they equally expend the fenforial power in the organ of fenfe. See
Sed. III. 4. which is analogous to our being as much fatigued by
thinking as by labour.

6. Nor is it in our dreams alone, but even in our waking reveries,
and in great efforts of invention, fo great is the vivacity of our ideas,
that we do not for a time diftinguifh them from the real prefence of
fubftantial objects ; though the external organs of fenfe are open, and
furrounded with their ufual ftimuli. Thus whilft I am thinking over
the beautiful valley, through which I yefterday travelled, I do not
perceive the furniture of my room : and there are fome, whofe wak-
ing imaginations are fo apt to run into perfecfl reverie, that in their
common attention to a favourite idea they do not hear the voice of
the companion, who accofts them, unlefs it is repeated with unufual
energy.

This perpetual miftake in dreams and reveries, where our ideas of
imagination are attended with a belief of the prefence of external ob-
jects, evinces beyond a doubt, that all our ideas are repetitions of the
motions of the nerves of fenfe, by which they were acquired ; and
that this belief is not, as fome late phllofophers contend, an inftin<5t
neceffarily connefted only with our perceptions,

D d 2 7. A

204 OF SLEEP. . SECT.XVm. 7. 8.

7. A curious queftion demands our attention in this place ; as we
do not dlftinguiOi in our dreams and reveries between our perceptions^
of external obje<fls, and our ideas of them in their abfence, how da
we diftinguifh them at any time I In a dream, if the fweetnefs of
fugar occurs to my imagination, the whitenefs and hardnefs of it,.
which were ideas ufually coane£led with the fweetnefs, immediately
follow in the train ; and I believe a material lump of fugar prefent
before my fenfes: but in my waking hours, if the fweetnefs occurs
to my imagination, the flimulus of the table to my hand, or of th&
window to my eye, prevents the other ideas of fehe hardnefs and
whitenefs of the fugar from, fucceeding ; and- hence I perceive the
fallacy, and difbelieve the exigence of objecfts correfpondeat to thofe.
ideas, whofe tribes or trains- are broken by the ftimulus of other ob-.
jeds. And further in our waking hours,, we frequently exert our
volition in comparing prefent appearances with fuch, as we have
tiiually obferved; and thus correal the errors of one fenfe by our ge-
neral knowledge of nature by intuitive analogy. See Se6t. XVII.
3. 7. Whereas in dreams* the power of volition is fufpended, we can
recollect and compare our prefent ideas with none, of our acquired
knowledge, and are hence incapable of obferving^ any abfurdities ia
them.

By this criterion we diftinguilh our waking from our fleeping.
hours, we can voluntarily recolle£t our fleeping ideas, when we are
awake, and compare them with, our waking ones ; but we cannot in
our fleep vohtntarily recolle£l our waking ideas at all.

8. The vaffc variety of fcenery, novelty of combination, and dif-
tin£lnefs of imagery, are other curious circumftances of our fl^eeping
imaginations. The variety of fcenery feems to arife from the fupe-
I'ior aftivity and excellence of our fenfe of viiion j which in an inftant
xuifolds to the mind extenfive fields of pleafurable ideas ; while the
other fenfes colle<£l their obj'edts flowly, and with little combination ;

3 add

Sect.XVIII. 9- lo. ir. OF SLEEP. 205

add to this, that the ideas, which this organ prefents us with, are
more frequently connefted with our fenlation than thofe of any
other.

9. The great novelty of combination is owing to another circum-
flance ; the trains of ideas, which are carried on in our waking
thoughts, are in our dreams diflevered in a thouiand places by the
fufpeniion of volition, and the abfence of irritative ideas, and are
hence pei"petually falling into new catenations. As explained in Seel.
XVI. 1.9. For the power of volition is perpetually exerted during
our waking hours in comparing our paffing trains of ideas with our
acquired knowledge of nature, and thus forms many intermediate links
in their catenation. And the irritative ideas excited by the ftimulus
of the objefts,, with which we are furrounded, are every moment in-
truded upon us, and form other links of our unceafing catenations of
ideas.

10. The abfence of the {limuli of external bodies, and of volition,.
in our dreams renders the organs of fenfe liable to be more ftrongly af-
fefted by the powers of fenfation, and of affociatlon. For our defires-
or averiions, or the obtrufions of furrounding bodies, diflever the
fenfitive and aflbciate tribes of ideas in our waking hours by intro-
ducing thofe of irritation and volition amongfl them.. Hence pro-
ceeds the fuperiordifHnftnels of pleafureable or painful imagery in our
fleep; for we recal the figure and the features of a long loft friend,
whom we loved, in our dreams with much more accuracy and viva-
city than in our waking thoughts. This circum.ftance contributes to
prove, that our ideas of imagination are reiterations of thofe motions
of our organs of fenfe, which were excited by external objedls ; be-
caufe while we are expofed to the flimuli of prefent objedts, our ideas
of abfent obj efts cannot be fo diftinftly formed.

1 1. The rapidity of the fucceffion of tranfa£tions in our dreams is
almoft inconceivable ;. infoniuch that, . when we are accidentally
awakened by the jarring of a door, which is opened into our bed-
chamber,.

2o6 OF SLEEP. Sect. XVIII. 12.

chamber, we fometimes dream a whole hiftory of thieves or fire in
the very inftant of awaking.

During the fufpenfion of volition we cannot compare our other
ideas with thofe of the parts of time in which they exift ; that is, we
cannot compare the imaginary fcene, which is before us, with thofe
changes of it, which precede or follow it ; becaufe this aft of com-
paring requires recolle6lion or voluntary exertion. Whereas in our
waking hours, we are perpetually making this comparifon, and by
that means our waking ideas are kept confiftent with each other by
intuitive analogy^ but this comparifon retards the fucceffion of them,
by occafioning their repetition. Add to this, that the tranfadlions of
our dreams confifl chiefly of vifible ideas, and that a whole hiftory of
thieves and fire may be beheld in an inllant of time like the figures in
a picture.

12. From this incapacity of attending to the parts of time in our
dreams, arifes our ignorance of the length of the night ; which, but
from our conftant experience to the contrary, we ihould conclude was
but a few minutes, when our fleep is perfedl- The fame happens in
our reveries; thus when we are pofleffed with vehement joy, grief,
or anger, time appears fhort, for we exert no volition to compare the
prefent fcenery with the paft or future ; but when we are compelled
to perform thofe exercifes of mind or body, which are unmixed with
pafiion, as in travelling over a dreary country, time appears long ;
for our defire to finifh our journey occafions us more frequently to
compare our prefeat fituation with the parts of time or place, which
are before and behind us.

So when we are enveloped in deep contemplation of any kind, or
in reverie, as in reading a very interefting play or romance, we mea-
fure time very inaccurately ; and hence, if a play greatly affedls our
paffions, the abfurdities of paffing over many days or years, and of
perpetual changes of place, are not perceived by the audience; as is
-experienced by every one, who reads or fees fome plays of the im-
mortal

Sect. XVIII. 12. OF SLEEP. 207

mortal Shakefpear ; but it is neceflary for inferior authors to obferve
thofe rules of the •fftdocvov and v^ivov inculcated by Ariftotle, becaufe
their works do not intereft the paffions fufficiently to produce com-
plete reverie.

Thofe works, however, whether a romance or a fermon, which
do not intereft us fo much as to induce reverie, may neverthelefs in-
cline us to fleep. For thofe pleafureable ideas, which are prefented to
us, and are too gentle to excite laughter, (which is attended with in-
terrupted voluntary exertions, as explained Seft. XXXIV. i. 4.) and
which are not accompanied with any other emotion, which ufually
excites fome voluntary exertion, as anger, or fear, are liable to pro-
duce fleep ; which confifts in a fufpenlion of all voluntary power.
But if the ideas thus prefented to us, and intereft our attention, are
accompanied with fo much pleafureable or painful fenfation as to ex-
cite our voluntary exertion at the fame time, reverie is the confe-
qucnce. Hence an interefting play produces reverie, a tedious one
produces fleep : in the latter we become exhaufted by attention, and
are not excited to any voluntary exertion, and therefore fleep ; in the
former we are excited by fome emotion, which prevents by its pain
the fufpenfion of volition, and in as much as it intercfts us, induces
reverie, as explained in the next Sedlion.

But when our fleep is imperfed, as when we have determined to
rife in half an hour, time appears longer to us than in moft other litu-
ations. Here our folicitude not to overfleep the determined time in-
duces us in this imperfed fleep to compare the quick changes of ima-
gined fcenery with the parts of time or place, they would have taken
up, had they real exiftencei and that more frequently than in our
waking hours ; and hence the time appears longer to us : and I make
no doubt, but the permitted time appears long to a man going to the
gallows, as the fear of its quick lapfe will make him think frequently
about it»

13. As

2oB OF SLEEP, SECT.XVIIL13.14.

13. As we gain our knowledge of time by comparing the prefent
fcenery with the paft and future, and of place by comparing the fitu-
ations of objedxs with each other; fo we gain our idea of confcioufnefs
by comparing ourfelves with the fcenery around usj and of identity
by comparing our prefent confcioufnefs with our pall: confcioufnefs :
as we never think of time or place, but when we make the compa-
rifons above mentioned, fo we never think of confcioufnefs, but
Vv'hen we compare our own exiftence with that of other objects ; nor
of identity, but when we compare our prefent and our paft confci-
oufnefs. Hence the confcioufnefs of our own exiftence, and of our
identity, is owing to a voluntary exertion of our minds: and on that
account in our complete dreams we neither meafure time, are fur-
prifed at the fudden changes of place, nor attend to our own ex-
iftence, or identity; beeaufe our power of volition is fufpended. But
all thefe circumftances are more or lefe obfervable in our incomplete
ones ; for then we attend a little to the lapfe of time, and the changes
of place, and to our own exiftence; and even to our identity of per-
fon; for a lady feldom dreams, that fl^ is a. foldierj nor a man, that
ihe is brought to bed-

14. As long as our fenfations only excite their fenfual motions, or
ideas, our fleep continues found; but as foon as they excite defires or
averfions, our fleep becomes imperfect; and when that defire or aver-
sion is fo ftrong, as to produce voluntary motions, we begin to awake;
the larger mufcles of the body are brought into a<3;ion to remove that
irritation or fenfation, which a continued pofture has caufed; we
ftretch our limbs, and yawn, and our fleep is thus broken by the ac-
cumulation of voluntary power.

Som_etimes it happens, that the zd: of waking is fuddenly pro-
duced, and this foon after the commencement of fleep; which is oc-
cafioned by fome fenfation fo difagreeable, as inflantaneoufly to ex-
cite the power of volition; and a temporary adion of all the voluntary

motions

Sect. XVIII. 15. O F S L E E P. 209

motioas fuddenly fucceeds, and we ftart a>vak.e. This is fometimes
accompanied with loud noife in the ears, and with rome degree of fear ;
and when it is in great excefs, fo as to produce continued convulfive
motions of thofe mufcles, which are generally fubfervient to volition,
it becomes epilepfy : the fits of which in feme patients generally com-
mence during fleep. This differs from the night-mare defcribed in
No. 3. of this Se(flion, becaufein that the difagreeable fenfation is not
fo great as to excite the power of volition into action ; for as foon as
that happens, the difeafe ceaies.

Another circumftance, which fometimes awakes people foon after
the commencement of their fleep, is where the voluntary power is al-
ready fo great in quantity as almoft to prevent them from falling
afleep, and then a little accumulation of it foon again awakens them ;
this happens in cafes of infanity, or where the mind has been lately
much agitated by fear or anger. There is another circumftance ia
which fleep is likewife of fhort duration, which arifes from great de-
bility, as after great over-fatigue, and in fomc fevers, where the
ftrength of the patient is greatly dirpiniflied, as in thefe cafes the pulfe
intermits or flutters, and the refpiration is previoufly affefted, it feems
to originate from the want of fome voluntary efforts to facihtate re-
fpiration, as when we are awake. And is further treated of in Vol. II.
Clafs L 2. I. 2. on the Difeafes of the Voluntary Power. Art. Spm-
nus interruptus.

15. We come now to thofe motions which depend on irritation.
The motions of the arterial and glandular fyfl:ems continue in our fleep,
proceeding flower indeed, but flronger and more uniformly, than in
our waking hours, when they are incommoded by external fl:imuli, or
by the movements of volition ; the motions of the mufcles fubfervient
to refpiration continue to be fliimulated into adlion, and the other in-
ternal fenfes of hunger, thirfl, and lufl:, are not only occafionally ex-
cited in our fleep, but their irritative motions are fucceeded by their
afuai feafations, and make a part of the farrago of our dreams. Thefe

E e fenfations

2IO ^ OF SLEEP. S^cT.XVIIL 15.

fenfations of the want of air, of hunger, thirfl, and hi ft, in our dreams^,
contribute to prove, that the nerves of the external fenfes are alfo
alive and excitable in our fleep ; but as the ftimuli of external objedts
are either excluded from th^m by the darknefs and filence of the
night, or their accefs to them is prevented by the fufpenfion of vo-
lition, thefe nerves of fenfe fall more readily into their connexions
with fenlation aiid with affociation ; becaufe much fenforial power,
which during the day was expended in moving the externaKorgans of
fenfe in confequence of irritation from external ftimuli', or in conffe-
quence of volition, becomes now n\ fome degree accumulated, and
renders the internal or immediate organs of fenfe more ealily excitable
by the other fenforial powers. Thus ia refpe£t to the eye, the irrita-
tion from external ftimuli, and the power of volition during our wak-
ing.hours, elevate the eye-lids, adapt the aperture of the iris to the
quantity of light, the focus of the eryftalline humour, and the angle
of the optic axifes to the diftance of the objedt, all which perpetual
aftivity during the day expends much fenforial power, which isfaved
during our fleep.

Hence it appears, that not only thofe parts of the fyftem, whicH
are always excited by internal ftimuli, as the ftomach, inteftinal canal,
bile-du£ls, and the various glands, but the organs of fenfe alfo may
be more violently excited into adion by the irritation from internal
ftimuli, or by fenfation, during our fleep than in our waking hours ;
becaufe during the fufpenfion of volition, there is a greater quantity
of the fpirit of animation to be expended by theother fenforial powere.
On this account our irritability to internal ftimuli, and our fenfibility
to pain or pleafure, is not only greater in fleep, but increafes as our
fleep is prolonged. Whence digeftion and fecretion are performed
better in fleep, than in our waking hours, and' our dreams in the
morning have greater variety and vivacity, as our fenfibility increafes,
than at night when we firft lie down. And hence epileptic fits,
whiph are always occafioned by fome difagreeable fenfation, fo fre-
quently

Sect.XVIIL 15. OF SLEEP. 211

quently attack thofe, who are fubjeft to them, in then- fleep ; becaufe
at this time the fyftem is more excitable by painful fenfation in con-
lequence of intei^nal ftimuh ; and the power of volition is then fud-
denly exerted to relieve this pain, as explained Seft. XXXIV. i. 4.

There is a difeafe, which frequently afteds children in the cradle,
"which is termed ecftafy, and feems to confift in certain exertions to
relieve painful fenfation, in which the voluntary power is not fo fiir
excited gs totally to awaken them, and yet is fufficient to remove
the difagreeable fenfation, which excites it ; in this cafe changing the
poflure of the child frequently relieves it.

I have at this time under my care an elegant young man about
twenty-two years of age, who feldom Heeps more than an hour with-
out experiencing a convulfion fit ; which ceafes in about half a mi-
nute without any fubfequent ftupor. Large dofes of opium only
prevented the paroxyfms, fo long as they prevented him from flecping
by the intoxication, which they induced. Other medicines had no
efFeft on him. He was gently awakened every half hour for one
night, but without good efFeft, as he foon (lept again, and the fit re-
turned at about the fame periods of time, for the accumulated fenfo-
rial power, which occafioned the increaled fenflbility to pain, was not
thus exhaufted. This cafe evinces, that the fenfibiUty of the fyflem
to internal excitation increafes, as our fleep is prolonged ; till the paiii
thus occafioned produces voluntary exertion ; which, when it is in
its ufual degree, only awakens us ; but when it is more violent, it
occafions convulfions.

The cramp in the calf of the leg is another kind of convulfion,
which generally commences in fleep, occalloned by the continual in-
creafe of irritability from internal flimuli, or of lenfibility, during
that flate of our exiflence. The cramp is a violent exertion to re-
lieve pain, generally either of the Ikin from cold, or of the bowels,
as in fome diarrhoeas, or from the mufcles having been previoufly
overftretched, as in walking up or down fleep hills. But in thei^

E e 2 convulfions

:ii2 OF SLEEP. Sect.XVIIL 15.

convulfions of the mufcles, which form the calf of the leg, the con-
tradtion is fo violent as to occaiion another pain in confequence of
their own too violent contraftion ; as foon as the original pain, which
caufed the contrai£tion, is removed. And hence the cramp, or fpafm,
of thefe mufcles is continued without intcrmiffion by this new pain,
unlike the alternate convulfions and remiffions in epileptic fits. The
reafon, that the contradlion of thefe mufcles of the calf of the leg is
more violent during their convulfion than that of others, depends on
the weaknefs of their antagoniil: mufcles; for after thefe have been
contra6ted in their ufual aftion, as at every flep in walking, they are
again extended, not, as moft other mufcles are, by their antagoniflis,
but by the weight of the whole body on the balls of the toes ; and
that weight applied to great mechanical advantage on the heel, that is,
on the other end of the bone of the foot, which thus a£ts as a lever.

Another difeafe, the periods of which generally commence during
our deep, is the ailhma. Whatever may be the remote caufe of pa-
roxyfms of afthma, the immediate caufe of the convulfive refpiration,
whether in the common ailhma, or in what is termed the convulfive
afthma, which are perhaps only different degrees of the fame difeafe,
mufl be owing to violent voluntary exertions to relieve pain, as in other
convulfions ; and the increafe of irritability to internal ftimuli, or of
fenfibility, during fleep mufl occafion them to commence at this time.

Debilitated people, who have been unfortunately accuflomed to
great ingurgitation of fpirituous potation, frequently part with a great
quantity of water during the night, but with not more than ufual in
the day-time. This is owing to a beginning torpor of the abforbent
fyftem, and precedes anafarca, which commences in the day, but is
cured in the night by the increafe of the irritability of the abforbent
fyftem during deep, which thus imbibes from the cellular membrane
the fluids, which had been accumulated there during the day ; though
it is poflible the horizontal pofition of the body may contribute fome-
thing to this purpofe, and alfo the greater irritability of fome branches

Sect. XVIII. id. O F 6 L E E P. 213

of the abforbent veflels, which open their mouths in the cells of the
cellular membrane, than that of other branches.

As foon as a perfon begins to fleep, the irritability and fenfibility of
the fyftem begins to increafe, owing to the fufpenlion of volition and
the exckiiion of external ftimuli. Hence the adions of the veflels in
obedience to internal ftimulation become ftronger and more energetic,
though lefs frequent in refpedt to number. And as many of the fe-
cretions are increafed, fo the heat of the fyftem is gradually increafed,
and the extremities of feeble people, which had been cold during the
day, become warm. Till towards morning many people become fo
warm, as to find it neceflary to throw off fome of their bed-clothes,
as foon as they awake ; and in others fweats are fo liable to occur to-
wards morning during their fleep.

Thus thofe, who are not accufl:omed to fleep in the open air, are
very liable to take cold, if they happen to fall afleep on a garden
bench, or in a carriage with the window open. For as the fy ftem is
warmer during fleep, as above explained, if a current of cold air affects
any part of the body, a torpor of that part is more effedlually pro-
duced, as when a cold blafl of air through a key-hole or cafement
falls upon a perfon in a warm room. In thofe cafes the afredled part
poflefles lefs irritability in refpedt to heat from its having previoufly
been expofed to a greater ftimulus of heat, as in the warm room, or
during fleep ; and hence, when the fl:imulus of heat is diminiflied, a
torpor is liable to enfue ; that is, we take cold. Hence people who
fleep in the open air, generally feel chilly both at the approach of
fleep, and on their awaking ; and hence many people are perpetually
fubjeft to catarrhs if they fleep in a lefs warm head-drefs, than that
which they wear in the day.

16. Not only the fenforial powers of irritation and of fenfation, but

that of aflbciatioii alfo appear to a6l with greater vigour during the

fufpenlion of volition in fleep. It will be fliewn in another place,

that the gout generally firfl: attacks the liver, and that afterwards an

3 inflammatioo

2f4 OF SLEEP. Sect. XVIII. 1^.

inflammation of the ball of the great toe commences by aflbciation,
and that of the liver ceafes. Now as this change or metaftafis of the
adlivityof the fyftem generally commences in fleep, it follows, that
thefe affociations of motion exift with greater energy at that time ;
that is, that the fenforial faculty of aflbciation, like thofe of irritation
and of fenfation, becomes in fome meafure accumulated during the
fufpenfion of volition.

Other affociate tribes and trains of motions, as well as the irritative
and fenfitive ones, appear to be increafed in their aftivity during the
fufpenfion of volition in fleep. As thofe which contribute to circu-
late the blood, and to perform the various fecretions ; as well as the
aflTociate tribes and trains of ideas, which contribute to fumifli the
perpetual ftreams of our dreaming imaginations.

In fleep the fecretions have generally been fuppofed to be diminifh-
ed, as the expe6torated mucus in c-oughs, the fluids difoharged in di-
arrhoeas, and in falivation, except indeed the fecretion of fweat,
which is often vifibly increafed. This error feems to have arifen from
attention to the excretions rather than to the fecretions. For the fe-
cretions, except that of fvveat, are generally received into refervoirs,
as the urine into the bladder, and the mucus of the inteftines and
lungs into their refpeflive cavities ; but th-efe refervoirs do not ex-
clude thefe fluids immediately by their ftimulus, but require at the
fame time fome voluntary efforts, and therefore permit them to re-
main during fleep. And as they thus continue longer in thofe re-
ceptacles in our fleeping hours, a greater part is abforbed from them,
and the remainder becomes thicker, and fometlmes in lefs quantity,
though at the time it was fecreted the fluid was in greater quantity
than in our waking hours. Thus the urine is higher coloured after
long fleep ; which fhews, that a greater quantity has been fecreted,
and that more of the aqueous and faline part has been reabforbed, and
the earthy part left in the bladder ; hence thick urine in fevers fliews

only

Sect. XVIII. 17- OF SLEEP. zi5

only a greater a6lion of the veflels which fecrete it in the kidneys, and
of thofe which abforb it from the bladder.

The fame happens to the mucus expedlorated in coughs, which is
thus thickened by abforption of its aqueous and faline parts; and the
fame of thefeces of the inteftines. From hence it appears, and from
what has been faid in No. 15 of this Sedtion concerning the iucreafe
of irritability and of fenfibility during deep, that the fecretions are in
general rather increafed than diminiihed during thefe hours of our ex-
iflence ; and it is prob;ibIe that nutrition is almoft entirely performed
in deep ; and that young animals grow more at this time than in their
waking hours, as young plants have long fince been obferved to grow
more in the night, which is their time of fleep.

17. Two other remarkable cireumftancea of our dreaming ideas are
their inconfiflency, and the total abfencc of furprife. Thus we feem
to be prefent at more extraordinary metamorphofes of animals or trees,
than are to be met with in the fables of antiquity ; and appear to be
tranfported from place to place, which feas divide, as quickly as the
changes of fcenery are performed in a play-houfe ; and yet are not
fenfible of their inconfijftency, nor ia the leaft degree afFeded with
furprife.

We muft confider this circumftance more minutely. In our wak-
ing trains of ideas, thofe that are inconfiftent with the ufual order of
nature, fo rarely have occurred to us, that their connexion is the
flighteft of all others: hence, when a confiftent train of ideas is ex-
hauiled, we attend to the external ftimuli, that ulually furround us,
rather than to- any inconfiftent idea, which might other wife prefent
itfelf : and if an inconfiftent idea fhould intrude itfelf, we immediately
compare it with the preceding one, and voluntarily rejeil the train it
would introduce ; this appears further in the Sedlion on Reverie, in
which ftate of the mind external ftimuli are not attended to, and yet
the ftreams of ideas are kept confiftent by the efforts of volition. But
as our faculty of volition is fufpended, and all external ftimuli are ex-
cluded

2i6 OF SLEEP, Sect.XVIII. 1S.19.

eluded in deep, this {lighter connexion of ideas takes place ; and the
train is faid to be inconfiftent ; that is, diffirailar to the ufual order of
nature.

But, when any confident train of fenfitive or voluntary ideas is
flowing along, if any external ftimulus afFefts us fo violently, as to in-
trude irritative ideas forcibly into the mind, it difunites the former
train of ideas, and we are afFe£led with furprife. Thefe ftimuli of
unufual energy or novelty not only difunite our common trains of
ideas, but the trains of mufcular motions alfo, which have not been
long eftabliflied by habit, and difturb thofe that have. Some people
become motionlefs by great furprife, the fits of hiccup and of ague
have been often removed by it, and it even affetSts the movements of
the heart, and arteries ; but in our fleep, all external fliniuli arc
excluded, and in confequence n© furprife can exift. See Seftioii

XVII. 2>-l'

18. We frequently awake with pleafure from a dream, which has
delighted us, without being able to recollect the tranfaftions of it 4
iinlefs perhaps at a diftance of time, fome analogous idea may intro-
duce afrefh this forgotten train : and in our waking reveries we fome-
times in a moment lofe the train of thought, but continue to feel the
glow of pleafure, or the depreflion of fpirits, it occafioned : whilfi: at
other times we can retrace with eafe thefe hiflories of our reveries and
dreams.

The above explanation of furprife throws light upon this fubjedL
When we are fuddenly awaked by any violent ftimulus, the furprife
totally difunites the trains of our fleeping ideas from thefe of our wak-
ing ones ; but if we gradually awake, this does not happen ; and we
readily unravel the preceding trains of imagination.

19. There are various degrees of furprife ; the more intent we are
upon the train of ideas, which vs/'e are employed about, the more vio-
lent muft be the ftimulus that interrupts them, and the greater is the
degree of furprife. I have obferved dogs, who have flept by the fire,

and

Sect. XVIII. 20. O F S L E E P. 217

and by their obfcure barking and ftruggling have appeared very intent
on their prey, that (hewed great furprife for a few feconds after their
awaking by looking eagerly around them ; which they did not do at
other times of waking. And an intelligent friend of mine has re-
marked, that his lady, who- frequently fpeaks much and articularly
in her fleep, could never recolle£l her dreams in the morning, when
this happened to her: but that when fhe did not fpeak in her deep,
(he could always recolle£l them.

Hence, when our fenfations aft fo ftrongly in fleep as to influence
the larger raufcles, as in thofe, who talk or ftruggle in their dreams ;
or in thofe, who are aitecled with complete reverie (as dcfcribed in
the next Seflion), great furprile is produced, when they awake ; and
thefe as well as thofe, who are completely drunk or delirious, totally
forget afterwards their imaginations at thofe times.

20. As the immediate cauie of fleep confifts in the fufpenfion of vo-
lition, it follows, that whatever diminishes the general quantity of
fenforial power, or derives it from the faculty of volition, will ccn-
ilitute a remote cauie of fleep ; fuch as fatigue from mufcular or men-
tal exertion, which diminifhes the general quantity of fenforial power;
or an increafe of the fenlitive motions, as by attending to foft mufic,
v/bich diverts the fenforial power from the faculty of volition ; or
laftly, by increafe of the irritative motions, as by \^"lne, or food, or
warmth ; which not only by their expenditure of fenforial pov/er di-
minifh the quantity of volition ; but alio by their producing pleafurc-
able fenfations (which occalion other mufcular or fenfual motions in
confequence), doubly decreafe the voluntary power, and thus more
forceably produce fleep. See Sect. XXX1\\ i. 4.

Another method of inducing fleep is delivered in 'a very ingenious
work lately publifhed by Dr Beddoes. Who, after lamenting that
opium frequently occaiions reflilefliiefs, thinks, " that in mofl: cafes
it v.'ould be better to induce fleep by the abfl:raaion of Itimuli, than
by -exhaufl:ing the excitability;" and adds, " upon this principle we

F f could

2i8 ^ OFSLEEP. Sect. XVIII. 20.

could not have a better foporific than an atmofphere with a diminifh-
ed. proportion of oxygene air, and that common air might be admitted
after the patient was aflcep." (Obferv. on Calculus, &c. by Dr. Bed-
does. Murray.) If it ihould be found to be true, that the excitability
of the fyftem depends on the quantity of oxygene abforbed by the.
lungs in refpiration according to the theory of Dr. Beddoes, and of
M. Girtanner, this idea of deeping in an atmofphere with lefs oxygene
in its compofition might be of great fervice in epileptic cafes, and in
cramp, and even in fits of the afthma, where their periods commence
from the increafe of irritability during fleep.

Sleep is likewife faid to be induced by mechanic preffure oix
the brain in the cafes of fpina bifida. Where there has been a de-
feO. of one of the vertebrae of the back, a tumour is protruded in con-
fequencej and, whenever this tumour has been comprefled by the hand,
fleep is faid to be induced, becaufe the whole of the brain both within:
the head and fpine becomes comprefled by the retroceffion of the fluid
within the tumour. But by what means a compreflion of the brain
induces fleep has not been explained, but probably by diminifliing the
fecretion of fenforial power, and then the voluntary motions become
fafpended prevloufly to the irritative ones, as occurs in moft dying
perfons.

Another way of procuring fleep mechanically was related to me by
Mr. Brindley, the famous canal engineer, who was brought up tO'
the bufinefs of a raill-wright ; he told me, that he had more than
once feen the experiment of a man extending himfelf acrofs the large
flone of a corn-mill, and that by gradually letting the ftone whirlj.
the man fell afleep, before the flone had gained its full velocity, and
he fuppofed would have died without pain by the continuance or in-
creafe of the motion. In this cafe the centrifugal motion of the head
and feet muft accumulate the blood in both thofe extremities of the
body, and thus comprefs the brain.

Laftly, we fliould mention the application of cold j which, when

3 ^"

Sect. XVIII. 21. OF SLEEP. 219

in a lefs degree, produces watchfulnefs by the pain it occafions, and
the treniulous convuKions of the fubcutaneous mufcles; but when it
is applied in great degree, is faid to produce fleep. To explain this
efFedl it has been faid, that as the veffels of the Ikin and extremities
become firft torpid by the want of the ftimulus of heat, and as thence
lefs blood is circulated through them, as appears from their palenefs,
a greater quantity of blood poured upon the brain produces fleep by
its compreilion of that organ. But I fhould rather imagine, that the
fenforial power becomes exhaufled by the convulhve adlions in confe-
quence of the pain of cold, and of the voluntary exercife previoufly
ufed to prevent it, and that the fleep is only the beginning to die, as
the fufpenfion of voluntary power in lingering deaths precedes for many
hours the extinclion of the irritative motions.

21. The following are the charafteriftic circumftances attendino-
perfe6l fleep.

1. The power of volition is totally fufpended.

2. The trains of ideas caufed by fen fat ion proceed with greater fa-
cility and vivacity ; but become inconfiftent with the ufuai order of
nature. The mufcular motions caufed by fenfation continue; as
thofe concerned in our evacuations during infancy, and afterwards in
digeflion, and in priapifmus.

3. The irritative mufcular motions continue, as thofe concerned in
the circulation, in fecretion, in refpiration. But the irritative fenfual
motions, or ideas, are nDt excited ; as the immediate organs of fenfe
are not ftimulated into adlion by external objedis, which are excluded
by the external organs of fenfe ; which are not in fleep adapted to their
reception by the power of volition, as in our waking hours.

4. The aflibciate motions continue ; but their firfl link is not ex-
cited into adion by volition, or by external flimuli. In all refpcfls,
except thofe above mentioned, the three laft fenforial powers are
fomewhat increafed in energy during the fufpenfion of volition, owing
^o the confequent accumulation of the fpiritt)f animation.

Ff2 -SECT.

220 OF REVERIE. Sect. XIX. i.

SECT. XIX..

- OF REVERIE.

I. Various degrees of reverie, i. Sleep-walkers, Cafe of a young lady.. Great
furfrife at awaking. And total forgetfulnefs of what pajfed in reverie. 3. No
Jufpenfton of volition in reverie. 4. Senjitive motions continue, and are confiflent.
5. Irritative motions continue,, hut .are not fucceeded by fenfation. 6. Volition
neceffary for the perception of feeble imprefftons. 7. Affociated motions continue.-
8. Nerves offenfe are irritable infleep,. but not in reverie. 9. Somnambuli are
not afleep. Contagion received but once. 10. Definition of reverie.^

I. WHEN we are employed, with great fenfation of pleafure, or
with great efforts of volition, in the purfuit of fome intercfting train
of ideas, we ceafe to be confcious of our exiftence, are inattentive to
time and place, and do not diftinguifli this train- of fenfitive and vo*
luntary ideas from the irritative ones excited by the prefence of exter-
nal obje£ls, though our organs of fenfe are furrounded with their ac-
cuftomed ftimuli, till at length this interefting train of ideas becomes
exhaufted, or the appulfes of external objefts are applied with unufual
violence, and we return with furprife,. or with. regret, into the com-
mon track of life. This is termed reverie or ftudium.

In fome conftitutions thefe reveries continue a confiderable time,
and are not to be removed without greater difficulty, but are experi-
enced in a lefs degree by us all ; when, we attend earneftly to the ideas
excited by volition or fenfation, with their affociated connexions, but
are at the fame time confcious at intervals of the flimuli of furround-
ing bodies. Thus in being prefent at a play, or in reading a romance,

fome

Sect. XIX. 2. OF REVERIE. 2c-r

fome perfons are fo totally abforbed as to forget tlielr ufual time of
fleep, and to negledl their meals ; while others are faid to have been
fo involved in voluntary ftudy as not to have heard the dlfcharge of
artillery; and there is a ftory of an Italian politician, who could think
£b intenfely on other fubjefts, as to be infenfible to the torture of the
rack..

From hence it appears, that thefe catenations of ideas and mufcular
motions,, which form the trains of reverie, are compofed both of vo-
luntary and fenfitive aflbciations of them ; and that thefe ideas differ
from thofe of delirium or of fleep, as they are kept confident by the
power of volition ; and they differ alfo from the trains of ideas belono--
ing to infanity, as they are as- frequently excited by fenfation as by
volition.. But laflly, that the whole fenforial. power is fo emploved
on thefe trains of complete reverie, that like the violent efforts of vo-
lition, as in convuliions or inlanity; or like the great activity of the
irritative motions in drunkennefs ; or of the fenfitive motions in de-
lirium j. they preclude all fenfation confequent to extenoal flimulus.

2. Thole perfons, who are faid to walk in their fleep, are affefted
with reverie to fo great a degree, that it becomes a formidable difeafe;
the effence of which confifls in the inaptitude of the mind to attend to
external- flimuli. Many hiflories of this difeafe have been publifhed by
medical writers >. of which there is a very curious one in the Lau-
fanne TranfaxSlions. lihall here fubjoin an account of fuch. a cafe,
with its cure, for the better illufliration of this fubjedt.

A very ingenious and elegant young lady, with light eyes and hair,
about the age of feventeen, in other refpecls well, was fuddenly
feized foon after her ufual menftruation with this very wonderful ma-
lady. The difeafe began with vehement convulfions of almoft every
mufcle of her body,, with great but vain efforts to vomit,, and the
raofl: violent hiccoughs,, that can be conceived: thefe were fucceeded
in about an hour with a fixed fpafm ; in which one hand was applied
to her head, and. the other to fupport it : in about half an hour thefe

ceafed.

322 OF REVERIE. Sect.XIX. 2.

'Ceafed, and the reverie began fuddenly, and was at firft manifeft by
the look of her eyes and countenance, which feemed to exprefs at-
tention. Then fhe converfed aloud with imaginary perfons with her
eyes open, and could not for about an hour be brought to attend to
the ftimulus of external objedls by any kind of violence, which it was
proper to ufe: thefe fymptoms returned in this order every day for
five or fix weeks.

Thefe converfations were quite confident, and we could under-
hand, what fhe fuppofed her imaginary companions to anfwer, by
the continuation of her part of the difcourfe. Sometimes (he was
angry, at other times (hewed much wit and vivacity, but was mod
■frequently inclined to melancholy. In thefe reveries (he fometimes
fung over fome mufic with accuracy, and repeated whole pages from
the Engli(h poets. In repeating fome lines from Mr. Pope's works
(he had forgot one word, and began again, endeavouring to recoUedl
it ; when (he came to the forgotten word, it was (liouted aloud in her
ear, and this repeatedly, to no purpofe ; but by many trials (he at
length reo;ained it herfelf.

Thefe paroxyfms were terminated with the appearance of inex-
preffible furprife, and great fear, from which fhe was fome minutes
in recovering herfelf,- calling on her (after with great agitation, and
very frequently underwent a repetition of convulfions, apparently from
the pain of fear. See Sed. XVII. 3. 7.

After having thus returned for about an hour every day for two or
three weeks, the reveries feemed to become lefs complete, and fome
of their circumftances varied ; fo that fhe could walk about the room
. in them without running againft any of the furniture ; though thefe
motions were at firft very unfteady and tottering. And afterwards
fhe once drank a di(h of tea, when the whole apparatus of the tea-
table was fet before her ; and expreffed fome fufpicion, that a medi-
cine was put into it, and once feemed to fmell of a tuberofe, which
was in flower in her chamber, and deliberated aloud about breaking it

from

Sect.XIX. 3.4- OF REVERIE. 223

from the ftem, faying, '* it would make her fifter fo charmingly
angry." At another time in her melancholy moments (he heard the
found of a paffing bell, " I wifh I was dead," flie cried, liflening to
the bell, and then taking off one of her flioes, as flie fat upon the
bed, " I love the colour black," fays (he, " a little wider, and a
little longer, even this might make me a coffin !" — Yet it is evident,
fhe was not fenfible at this time, any more than formerly, of feeing
or hearing any perfon about her ; indeed when great light was thrown
upon her by opening the fliutters of the window, her trains of ideas
feemed lefs melancholy; and when 1 have forcibly held her hands, or
covered her eyes,, fhe appeared to grow impatient, and would fay,, fhe
could not tell what to do, for fhe could neither fee nor move. In all
thefe circumftances her pulfe continued unaffe£]!ed as in health. And
when the paroxyfm was over, fhe could never recolle£l a fingle idea
of what had pafled in it.

This aftonifhing dlfeafe, after the ufe of many other medicines and
applications in vain, was cured by very large dofes of opium given
about an hour before the expedted returns of the paroxyfms ; and after
a few relapfes, at the intervals of three or four months, entirely dif-
appeared. But fhe continued at times to have other fymptoms of
epilepfy.

3. We fliall only here confider, what happened during the time of
her reveries, as that is our prefent fubjedl; the fits of convulfion be-
long to another part of this treatife. Se£l. XXXIV. 44.

There feems to have been no fufpenfion of volition during the fits
©f reverie, becaufe fhe endeavoured to regain the lofb idea in repeating
the lines of poetry, and deliberated about breaking the tuberofe, and
fufpefted the tea to have been medicated.

4. The ideas and mufcular movements depending on fenfation v/ere
exerted with their ufual vivacity, and were kept from being incon-
fiftent by the power of volition, as appeared from her whole conver-
fation^ and was explained in Se£l, XVII. 3. 7. and XVIII. 16.

5. The

224 OF REVERIE. Sect. XIX. 5. 6.

5. The ideas and motions dependant on irritation during the firft
weeks of her difeafe, whilft the reverie was complete, were never
fucceeded by the fenfation of pleafure or pain j as flie neither faw,
heard, nor felt any of the furrounding objeds. Nor was it certain
that any irritative motions fucceeded the flimulus of external objefts,
till the reverie became lefs complete, and then fhe could walk about
the room without running againfl the furniture of it. Afterwards,
when the reverie became dill lefs complete from the ufe of opium,
fome few irritations were at times fucceeded by her attention to them..
As when ihe fmelt at a tuberofe, and drank a difh of tea, but this
only when flie feemed voluntarily to attend to them.

6. In common life when we liften to diftant founds, or wifli to
diftinguifh objects in the night, we are obliged ftrongly to exert our
volition to difpofe the organs of fenfe to perceive them, and to fup-
prefs the other trains of ideas, which might interrupt thefe feeble fen-
fations. Hence in the prefent hiftory the flrongeft ftimuli were not
perceived, except when the faculty of volition was exerted on the
organ of fenfe ; and then even comm.on ftimuli were fometimes per-
ceived : for her mind was fo ftrenuoufly employed in purfuing its own
trains of voluntary or fenlitive ideas, that no common ftimuli could fo
far excite her attention as to difunite them ; that is, the quantity of
volition or of fenfation already exifting was greater than any, which
could be produced in confequence of common degrees of ftimulation.
But the few ftimuli of the tuberofe, and of the tea, which fhe did
perceive, were fuch, as accidentally coincided with the trains of
thought, which were paffmg in her mind; and hence did not dif-
unite thofe trains, and create furprife. And their being perceived at
all was owing to the power of volition preceding or coinciding with
that of irritation.

This explication is countenanced by a faft mentioned concerning a
fomnambulift in the Laufanne Tranfaftions, who fometimes opened
his eyes for a (hort time to examine, where he was, or where his ink-
pot

Sect. XIX. 7.8.9. OF REVERIE. 225

pot flood, and then fliut them again, dipping his pen into the pot
every now and then, and writing on, but never opening his eyes af-
terwards, although he wrote on from line to line regularly, and cor-
redled fome errors of the pen, or in fpelling : lb much eafier was it
to him to refer to his ideas of the pofitions of things, than to his per-
ceptions of them.

7. The aflbciated motions perfifled in their ufual channel, 'as ap-
peared by the combinations of her ideas, and the ufe of her mufcles,
and the equality of her pulfe ; for the natural motions of the arterial
iyftem, though originally excited like other motions by flimulus,
feem in part to continue by their ailbciation with each other. As the
heart of a viper pulfates long after it is cut out of the body, and re-
moved from the ftimulus of the blood.

8. In the feet ion on fleep, it was obferved that the nerves of fenfe
are equally alive and fufceptible to irritation in that ftate, as when we
are awake ; but that they are fecluded from flimulating objects, or
rendered unfit to receive them : but in complete reverie the reverfe
happens, the immediate organs of fenfe are expofed to their ufual fli-
muli; but are either not excited into adlion at all, or not into fo great
a£bion, as to produce attention or fenfation.

The total forgetfulnefs of what paffes in reveries ; and the furprife
on recovering from them, are explained in Section XVIII. 19. and in
Seaion XVII. 3. 7.

9. It appears from hence, that reverie is a difeafe of the epileptic
or cataleptic kind, fince the paroxyfms of this young lady always be-
gan and frequently terminated with convuliions ; and though in its
greateft degree it has been called fomnambulation, or fleep- walking,
it is totally different from fleep; becaufe the effential charafter of
fleep conlifts in the total fufpenfion of volition, which in reverie is
not affedled ; and the eflential chara6ler of reverie confifls not in the
abfence of thofe irritative motions of our fenfes, which are occafioned
by the flimulus of external obje£ls, but in their never being produc-

G g tivc

226 OF REVERIE. Sect. XIX. lo.

tive of fenfation. So that during a fit of reverie that ftrange event
happens to the whole fyftem of nerves, which occurs only to fome
particular branches of them in thofe, who are a fecond time expofed
to the adtton of contagious matter. If the matter of the fmall-pox be
inferted into the arm of one, who has previoufly had that difeafe, it
will ftimulate the wound, but the general fenfation or inflammation
of the fyftem does not follow, which conftitutes the difeafe. See Se£t.
XII. 7. 6. XXXIII. 2. 8.

10. The following is the definition or character of complete reverie.
I. The irritative motions occafioned by internal ftimuli continue,
thofe from the ftimuli of external objedls are either not produced at
all, or are never fucceeded by fenfation or attention, unlefs they are
at the fame time excited by vohtion. 2. The fenfitive motions con-
tinue, and are kept confiftent by the power of volition. 3. The vo-
luntary motions continue undifturbed. 4. The aflbciate motions con-
tinue undifturbed.

Two other cafes of reverie are related in Se£lion XXXIV. 3. which
further evince, that reverie is an effort of the mind to relieve fome
painful fenfation, and is hence allied to convulfion, and to infanity.

SECT.

Sect.XX.i. of vertigo. 227

SECT. XX.

OF VERTIGO-
IT. We determine oiir ferpendicularity hy the apparent motions of objeSfs. A pe-rfon
hood-winked cannot walk in a firaight line. Dizzinejs on looking from a tower y
in a room flained. with uniform lozenges, on riding over J?iow. 1. Dizzinejs
from moving ohjeSfs. A whirling wheel. Fluctuations of a river. Experiment
with a child. 3. Dizzinefs from our own motions and thofe cf other objects.
Riding over a broad fir earn. Sea-ficknejs. 5. Of turning round on one foot.
Dervijes in'Tia'key. Attention of the mind prevents flight fea-fuknefs. After a
voyage ideas of vibratory motions are fiill perceived on fhore. 6. Ideas cojitinue
Jome time after they are excited. Circumfiances of turning on one foot, Jlanding on
a tower, and walking in the dark explained. 7. Irritative ideas of apparent mo-
tions. Irritative ideas of founds. Batthnent of the found of bells and organ-pipes.
Vertiginous noife in the head. Irritative motions of the flomach, intefiines, and
glands. 8. Symptoms that accompany vertigo. Why vomiii?ig comes on in fir ekes
of the palfy. By the motion of a fhip. By injuries en the head. Why motion
makes fick people vomit. 9. Why drunken people are vertigi-nous. IVhy a
jlor,e in the ureter, or lile-duSl, produces vomiting, i o. Wloy after a voyage
ideas of vibratory motions are perceived on fhore. 1 1. Kinds of vertigo and their
cure. 12. Definition of vertigo.

I. IN learning to walk we judge of the dlflances of the objeds,
which we approach, by the eye ; and by obferving their perpendicu-
larity determine our own. This circumftatice not having been at-
tended to by the writers on vifion, the difeafe called vertigo or dizzi-
nefs has been little underftood.

G g 2 When

ziS OF VERTIGO. - Sect. XX. i,'

When any perfon lofes the power of mufcular action, whether he
is ere£t or in a fitting pofture, he finks down upon the ground ; as is
{een. in fainting fits, and other inftances of great debility. Hence it
follows, that fome exertion of mufcular power is neceflkry to preferve
our perpendicular attitude. This is performed by proportionally ex-
erting the antagonift mufcles of the trunk, neck, and limbs ; and if
at any time in our locomotions we find ourfelves inclining to one fide,
we either reftore our equilibrium by the efforts of the mufcles on the
other fide, or by moving one of our feet extend the bafe, which we
reft upon, to the new center of gravity.

But the moft eafy and habitual manner of determining our want of
perpendicularity, is by attending to the apparent motion of the objedls
within the fphere of diftindl vifion ; for this apparent motion of ob-
je£ls, when we incline from our perpendicularity, or begin to fall, is
as much greater than the real motion of the eye, as the diameter of
the fphere of diftind vifion is to our perpendicular height.

Hence no one, who is hood- winked, can walk in a fi:raight line
for a hundred fteps together ; for he inclines fo greatly, before he is
warned of his want of perpendicularity by the fenfe of touch, not
having the apparent motions of ambient obje£ls to meafure this incli-
nation by, that he is neceflltated to move one of his feet outwards, to-
the right or to the left, to fupport the new centre of gravity, and thus
errs from the line he endeavours to proceed in.

For the fame reafon many people become dizzy, when they look
from the fummit of a tower, which is raifed much above all other ob-
jedls, as thefe objeds are out of the fphere of diftindl vifion, and they
are obliged to balance their bodies by the lefs accurate feelings of their
mulcles.

There is another curious phenomenon belonging to this place, if
the circumjacent vifible obje£ts are fo fmall, that we do not diftingulfh
their minute parts ; or fo fimilar, that we do not know them from
each other ; we cannot determine our perpendicularity by them. Thus

ill

Sect.XX.2.3. of vertigo. 229

in a room hung with a paper, which is coloured over with fimilar
fmall black lozenges or rhomboids, many people become dizzy ; for
when they begin to fall, the next and the next lozenge fucceeds upon
the eye ; which they miftake for the firft, and are not aware, that
they have any apparent motion. But if you fix a Iheet of paper, or
draw any other figure, in the midft of thefe lozenges, the charm
ceafes, and no dizzinefs is perceptible. — The fame occurs, when we
ride over a plain covered with fnow without trees or other eminent
objefts.

2. But after having compared vifible objefls at reft with the fenfe
of touch, and learnt to diftinguifh their fliapes and fhades, and to
meafure our want of perpendicularity by their apparent motions, we
come to confider them in real motion. Here a new difficulty occurs,
and we require fome experience to learn the peculiar mode of motion
of any moving obje6ts, before we can make ufe of them for the pur-
pofes of determining our perpendicularity. Thus fome people become
dizzy at the fight of a whirling wheel, or by gazing on the fluctua-
tions of a river, if no fleady obie6ls are at the fame time within the
fphere of their diftin<5t vifion ; and when a child firft can fland ere6l
upon his legs, if you gain his attention to a white handkerchief fleadi-
ly extended like a fail, and afterwards make it undulate, he inftantly
lofes his perpendicularity, and tumbles on the ground.

3. A fecond difficulty we have to encounter is to diftinguifh our
own real movements from the apparent motions of objects. Our
daily pra£lice of walking and riding on horfeback foon inftruds us
with accuracy to difcern thefe modes of motion, and to afcribe the
apparent motions of the ambient objects to ourfelves ; but thofe,
which we have not acquired by repeated habit, continue to confound
us. So as we ride on horfeback the ti^ees and cottages, which occur
to us, appear at reft; we can meafure their diftances with our eye,
and regulate our attitude by them ; yet if we carelefsly attend to dif-
tant hills or woods through a thin hedge, which is near us, we ob-

ferve

230

OF VERTIGO. SECT.XX.4.-5.

ferve the jumping and progreffive motions of them; as this is iii-
creafed by the paiala>i of thefe objects ; which we have not habituated
ouffeh'es to attend to. When firft an European mounts an elephant
iixteen feet high, an ■ whofe mode of motion he is not accuftomed to,
the obje£ls feem to undulate, as he pafles, and he frequently becomes
fick and vertiginous, as I am well informed. Any other unufual move-
ment of our bodies has the fame effeft, as riding backwards in a coach,
fwinging on a rope, turning round fvi'iftly on one leg, fcating on the
ice, and a thoufand others. So after a patient has been long confined
to his bed, when he firft attempts to walk, he finds himfelf verti-
ginous, and is obliged by pradlice to learn again the particular modes
of the apparent motions of objedls, as he walks by them.

4. A third difficulty, which occurs to us in learning to balance
ourfelves by the eye, is, when both ourfelves and the circumjacent
objefls are in real motion. Here it is necefi'ary, that we fliould be
habituated to both thefe modes of motion in order to preferve our per-
pendicularity. Thus on horfeback we accurately obferve another
perfon, whom we meet, trotting towards us, without confounding
his jumping and progreflive motion with our own, becaufe we have
been accuftomed to them both ; that is, to undergo the one, and to
fee the other at the fame time. -But in riding over a broad and fluc-
tuating ftream, though we are well experienced in the motions of our
horfe, we are liable to become dizzy from our inexperience in that of
the water. And when firft we go on fhip-board, where the move-
ments of ourfelves, and the movements of the large waves are both
new to us, the vertigo is almoft unavoidable with the terrible ficknefs,
which attends it. And this I have been affured has happened to fe-
veral from being removed from a large fliip into a fmall one ; and
again from a fmall one into a man of war.

5. From the foregoing examples it is evident, that, when we are

furrounded with unufual motions, we lofe our perpendicularity: but

there are fome peculiar circumftances attending this efFedl of moving

5 objeds.

Sect.XX.5. of vertigo. 231

obje(5ts, which we come now to mention, and fhall hope from the re-
cital of them to gain fome infight into the manner of their produc-
tion.

When a child moves round quick upon one foot, the circumjacent
objeds become quite indiftin6l, as their diftance increafes their appa-
rent motions ; and this great velocity confounds both their forms,
and their colours, as is feen in whirhng round a many coloured wheel;
he then lofes his ufual method of balancing himfelf by vifion, and be-
gins to ftagger, and attempts to recover himfelf by his mufcular feel-
ings. This daggering adds to the inftability of the vifible obje6ls by
giving a vibratory motion befides their rotatory one. The child then
drops upon the ground, and the neighbouring objeds feem to con-
tinue for fome feconds of time to circulate around him, and the earth
under him appears to librate like a balance. In fome feconds of time
thefe fenfations of a continuation of the motion of objeds vanifh ; but
if he continues turning round fomewhat longer, before he falls, lick-
neis and vomiting are very liable to fucceed. But none of thefe cir-
cumftanccs afFe£l thofe who have habituated themfelyes to this kind
of motion, as the dervifes in Turkey, amongfl whom thefe fwift
gyrations are a ceremony of religion.

In an open boat pafling from Leith to Kinghorn in Scotland, a fud-
den change of the wind fhook the undiftended fail, and ftopt our boat;
from this unufual movement the paffengers all vomited except my-
felf. I obferved, that the undulation of the (hip, and the inftability
of all vifible obje£ls, inclined me ftrongly to be lick ; and this conti-
nued or increafed, when I doled my eyes, but as often as I bent my
attention with energy on the management and mechanifm of the ropes
and fails, the ficknefs ceafedj and recurred again, as often as I re-
laxed this attention ; and I am afibred by a gentleman of obfervation
and veracity, that he has more than once obferved, when the veffel
has been in immediate danger, that the fea-ficknefs of the paffengers

has

232 OF VERTIGO. Sect.XX.6.

has inflantaneoufly ceafed, and recurred again, when the danger was
over.

'Thofe, who have been upon the water in a boat or fliip fo long,
that they have acquired the neceflary habits of motion upon that un-
liable elem;ent, at their return on land frequently think in their reve-
ries, or between fleeping and waking, that they oblerve the room,
they fit in, or fome of its furniture, to librate like the motion of the
veflel. This I have experienced myfelf, and have been told, that
after long voyages, it is fome time before thefe ideas entirely vanifh.
The fame is obfervable in a lefs degree after having travelled lome
days in a ftage coach, and particularly when we lie down in bed, and
compofe ourfelves to fleep; in this cafe it is obfervable, that the rat-
tling noife of the coach, as well as the undulatory motion, haunts us.
The drunken vertigo, and the vulgar cuftom of rocking children,
will be confidered in the next Sedion.

6, The motions, which are produced by the power of volition,
may be immediately ftopped by the exertion of the fame power on the
antagonift mufcles ; otherwife thefe with all the other claffes of mo-
tion continue to go on, fome time after they are excited, as the pal-
pitation of the heart continues after the objed; of fear, which occafion-
ed it, is removed. But this circumftance is in no clafs of motions
more remarkable than in thofe dependent on irritation ; thus if any
one looks at the fun, and then covers his eyes with his hand, he wili
for many feconds of time, perceive the image of the fun marked oii
his retina : a fimilar image of all other vifible objedls would remain
fome time formed on the retina, but is extinguiflied by the perpetual
change of the motions of this nerve in our attention to other objects.
To this muft be added, that the longer time any movements have
continued to be excited without fatigue to the organ, the longer will
they continue fpontaneoufly, after the excitement is withdrawn : as
the talle of tobacco in the mouth after a perfoa has beea fmoaking it.

This

Sect.XX.6. of vertigo. 2^-3

This tafte remains fo ftrong, that it a perfon continues to draw air
tliraugh a tobacco pipe in the dark, after having been finoklng feme
time, he cannot diftinguifh whether his pipe be lighted or not.

From thefe two confiderations it appears, that the dizzinefs felt in
the head, after feeing objefts in unufual motion, is no other than a
continuation of thetnotions of the optic nei^ve excited by thofe obje<9:s,
and which engage our attention. Thus on turning round oa one
foot, the vertigo continues for fome feconds of time after the perfou
is fallen on the ground ; and the longer he has continued to revolve,
the longer will continue thefe fucceffive motions of the parts of the
optic nerve.

Any one, who ftands alone on the top of a high tower, if he has
not been accuftomed to balance hlmfelf by objects placed at fuch dlf-
tances and with fuch inclinations, begins to flagger, and endeavours
to recover himfelf by his mufcular feelings. During this time the
apparent motion of objedls at a dlftance below him is very great, and
the impreffions of thefe apparent motions continue a little time after
he has experienced them ; and he is perfuaded to incline the contrary
way to countera£l their efFefts ; and either immediately falls, or ap-
plying his hands to the building, ufes his mufcular feelings to preferve
his perpendicular attitude, contrary to the eiToneous perfualions of his
eyes. Whilfl: the perfon, who walks in the dark, flaggers, but with-
out dizzinefs ; for he neither has the fenfation of moving objeds to
take off his attention from his mufcular feelings, nor has he the fpec-
tra of thofe motions continued on his retina to add to his coafulion. '
It happens indeed fometimes to one {landing on a tower, that the
idea of his not having room to extend his bafe by moving one of his
feet outwards, when he begins to incline, fuperadds fears to his other
inconveniences ; which like furprife, joy, or any great degree of fen-
fation, enervates him in a moment, by employing the whole fenfb-
rlal power, and by thus breaking all the affoclated trains and tribes of
motion.

H h 7. The

234 OF VERTIGO.. Sect.XX.^.

7. The irritative ideas of obje£ls, whilft we are awake^ are per-
petually prefent to our fenfe of light ; as we view the furaiture of our
rooms, or the ground, we tread upon, throughout the whole day with"
out attending to it. And as our bodies are never at perfedt reft during,
our waking hours, thefe irritative ideas of objedk are at'tended per-
petually with irritative ideas of their apparent motions- The ideas of
apparent motions are always irritative ideas,, becaufe we never attend^
to them, whether we attend to the objedls themfelves,. or to their
real motions, or to neither. Hence the ideas of the apparent motions
of objedls are a complete circle of irritative ideas,, which continue;
throughout the day.

Alfo during all our waking hours, there Is a perpetual conflifedi
found of various bodies, as of tJie wind in our rooms, the fire, dis-
tant converfations, mechanic bufinefs ; this continued buzz, as we
are feldom quite motionlefs, changes its loudnefs perpetually, like tb^
found of a bell ; which rifes and falls as long as it continues, and;
feems to pulfate on the ear. This any one may experience by turning
himfelf round near a waterfall ;: or by ftriking a glafs bell, and then
moving the direftion of its mouth towards the ears, or frosn them, as
long as its vibrations continue. Hence this undulation of indiflindt
found makes another concomitant circle of irritative ideas, which con-
tinues throughout the day..

We hear this undulating found,, when we are perfe£lly at reft ouf-
felves, from other fonorous bodies befides bells ; as from two organ-
pipes, which are nearly but not quite in unifon,. when they are
founded together. When a bell is ftruck, the circular form is changed
into an eliptic one 1 the longeft axis of which, as the vibrations con-
tinue, moves round the periphery of the bell ; and when either axis
of this elipfe is pointed towards our ears, the found is louder ; and
lefs when the intermediate parts of the elipfe are oppofite to us. The
vibrations of the two organ-pipes may be compared to Nonius's rule ;
the found is louder, when they coincide, and lefs at the intermediate
3 times.

Sect.XX.8. 9. OF VERTIGO. 235

times. But, as the found of bells is the moft familiar of thofe founds,
which have a confiderable battement, the vertiginous patients, who
attend to the irritative circles of founds above defcribed, generally com-
pare it to the noife of bells.

The periftaltic motions of our ftomach and Inteftines, and the
fecretions of the various glands, are other circles of irritative motions,
fome of them more or lefs complete, according to our abflinence or
latiety-.

So that the irritative ideas of the apparent motions of objeds., the
irritative battements of founds, and the movements of our bowels and
glands compofe a great circle of irritative tribes of motion : and when
one confiderable part of this circle of motions becomes interrupted,
the whole proceeds in confufion, as defcribed in SeQion XVII. i. 7,
on Catenation of Motions.

8. Hence a violent vertigo, from whatever caufe it happens, is 0-5-
nerally attended with undulating noife in the head, perverfions of the
motions of the ftomach and duodenum, unufual excretion of bile and
gaftic juice, with much pale urine, fometimes with yellownefs of the
Ikin, and a difordered fecretion of almoft every gland of the body, till
at length the arterial fyftem is affefted, and fever fucceeds.

Thus bilious vomitings accompany the vertigo occafioned by the
motion of a fhip; and when -the brain is rendered vertiginous by a
paralytic afFedlion of any part of the body, a vomiting generally en-
fues, and a great difcharge of bile: and hence great injuries of the
head from external violence are fucceeded with bilious vomitino-s,
and fometimes with abfceffes of the liver. And hence, when a pa-
tient is Inclined to vomit from other cauies, as in fome fevers, any
motions of the attendants in his room, or of himfelf when he is raifed
or turned in his bed, prefently induces the vomiting by fuperaddino- a
degree of vertigo.

9. And converfely-it is very \ifual with thofe, whofe ftomachs are
affeded from internal caufes, to be afflided with vertigo, and noife

H h 2 in

^^h OF VERTIGO. S'ECT.XX. lo.

in the head ; fuch is the vertigo of drunken people, which continues,
when their eyes are clofed, and themfelves in a recumbent poflure,.
as well as when they are in an ereft pofture, and have their eyes
open. And thus the irritation of a ftone in the bile-du6t, or in the
ureter, or an inflammation of any of the inteftines, are accompanied
with vomitings and vertigo.

In thefe cafes the irritative motions of the ftomach, which are in
general not attended to, become fo changed by fome unnatural fti-
nuilus, as to become uneafy, and excite our fenfation or attention.
And thus the other irritative trains of motions, which are affociated
with it, become difordered by their fympathy. The fame happens,
when a piece of gravel flicks in the ureter, or when fome part of the
inteftinal canal becomes inflamed. In thefe cafes the irritative muf-
cular motions are firft difturbed by unufual flimulus, and a difordered
adion of the fenfual motions, or dizzinefs enfues. While in fea-
{icknefs the irritative fenfual motions, as vertigo, precedes ; and the
difordered irritative mufcular motions, as thofe of the ftomach in vo-
miting, follow.

IQ. When thefe irritative motions are diikirbed, if the degree be
not very great, the exertion of voluntary attention to any other obje6t,
or any fudden fenfation, will disjoin thefe new habits of motion.
Thus fome drunken people have become fober immediately, when
any accident has flrongly excited their attention; and fea-ficknefs has.
vanifhed, when the fiiip has been in danger. Hence when our at-
tention to other obje6ts is mofl: relaxed, as juft before we fall afleep,
or between our reveries when awake, thefe irritative ideas of motion
and found are mod liable to be perceived ; as thofe, who have been at
fea, or have travelled long in a coach, feem to perceive the vibrations
of the ihip, or the rattling of the wheels, at thefe intervals; which
ceafe afain, as foon as they exert their attention. That is, at thofe
intervals they attend to the apparent motions, and to the battement
of founds of the bodies around them, and for a monaent miflake them
7 fe^

Sect.XX. ir. OF VERT IG a. 237

for thofereal motions of the fliip, and noife of wheels, which they had
lately been accuftomed to : or at thefe intervals of reverie, or on the
approach of fleep, th-efe fuppofed motions or founds may be produced
entirely by imagination.

We may conclude from this account of vertigo, that fea-ficknefs is
not an effort of nature to relieve herfelf, but a neceflary confequence
of the aflbciations or catenations of animal motions. And may thence
infer, that the vomiting, which attends the gravel in the ureter, in-
flammations of the bowels, and the commencement of fome fevers,
has a fimilar origin, and is not always an effort of the vis medicatrix
natur£e. But where the adtion of the organ is the immediate confe-
quence of the flimulating caufe, it is frequently exerted to diflodge
that ftimulus, as in vomiting up an emetic drug ; at other times,
the adion of an organ is a general effort to relieve pain, as in couvul-
lions of the locomotive mufcles ; other adlions drink up and carry on
the fluids, as in abforption and fecretion ; all which- may be termed ef-
forts of nature to relieve, or to preferve herfelf.

1 1 . The cure of vertigo will frequently depend on our previoufly
inveftigating the caufe of it, which from what has been delivered
above may originate from the diforder of any part of the great tribes
of irritative motions, and of the afTociate motions catenated with them.

Many people, when they arrive at fifty or fixty years of age, are af-
fected with flight vertigo; which is generally but wrongly afcribed to
indigeflion, but in reality arifes from a beginning defedl of their fight ;,
as about this time they alib find it neceflary to begin to ufe fpe6tacles,
when they read fmall prints, efpecially in winter, or by candle light,
but are yet able to read without them during the fummer days, when
the light is flronger. Thefe people do not fee objefts fo diflinctly as
formerly, and by exerting their eyes more than ufual, they perceive
the apparent motions of objects, and confound them with the real
motions of them ; and therefore cannot accurately balance themfelves
fo as eafily to preferve their perpendicularity by them>

That

238 OF VERTIGO. Sect. XX. I r.

That is, the apparent motions of obje6ts, which are at reft, as we
move by them, (hould only excite irritative ideas : but as thefe arc
now become lefs diftindt, owing to the beginning imperfeftion of'
our fight, we are induced voluntarily to attend to them ; and then thefe
apparent motions become fucceeded by fenlation; and thus the other
parts of the -trains of irritative ideas, or irritative mufcular motions,
become difordered, as explained above. In thefe cafes of flight vertigo
I have always promifed my patients, that they would get free from
it in two or three months, as they fhould acquire the habit of ba-
lancing their bodies by lefs diftilift objedls, and have feldom been mif-
taken in my prognoftic^'

There is an auditory vertigo, which is called a nolfe in tlie head,
explained in No. 7. of this feftion, which alfo is very liable to afFe£t
people in the advance of life, and is owing to their hearing lefs per-
fedly than before. This is fometimes called a ringing, and fometimes
a finging, or buzzing, in the ears, and is occalioned by our firft ex-
periencing a difagreeable fenfation from our not being able diftinftly
to hear the founds, we ufed formerly to hear diftindtly. And this
difagreeable fenfation excites defire and confequent volition ; and
when we voluntarily attend to fmall indiftiixSl founds, even the whifper-
ing of the air in a room, and the pulfations of the arteries of th^^ear
are fucceeded by fenfation ; which minute founds ought only to have
produced irritative fenfual motions, or \jnperceived ideas. See Section
XVII. 3. 6. Thefe patients after a while lofe this auditory vertigo,
by acquiring a new habit of not attending voluntarily to thefe indi-
ftind: founds, but contenting themfelves with the lefs accuracy of their
fen fe of hearing.

Another kind of vertigo begins with the difordered a£tion of fome

irritative mufcular motions, as'thofeof the ftomach from nitoxication,

or from emetics; or thofe of the ureter, from the ftimulus of a ftune

lodged in it; and it is probable, that the difordered motions of fome of

the great congeries of glands, as of thofe which form the liver, or of

the

Sect.XX.I2. of VERTIGa 239

the inteftinal canal, may occafiou vertigo in confequence of their mo-
tions beins: affociated or catenated with the great circles of irritative
motions ; and from hence it appears,- that the means of cure muft be
adapted to the caufe.

To prevent fea-ficknefs it is probable, that the habit of fwinging
for a week or two before going on fhipboard might be of fervice.
For the vertigo from failure of fight, fpe£lacles may be ufed. For
the auditory vertigo, sether may be dropt into the ear to Simulate the
part, or to diflblve ear-wax, if fuch be a part of the caufe.^ For the
vertigo arifing from indigeflion, the peruvian bark and a blifter are re-
commended. And for that owing to a flone in the ureter, venefec-
tion, cathartics-, opiates, fal foda aerated.

1 2. Definition of vertigo. i. Some of the irritative fenfual, or
mufcular motions, which were iifually not fucceeded by fenfation, are
in this difeafe fucceeded by fenfation ; and the trains or circles of mo-
tions, which were ufually catenated with them, are interrupted, or
inverted, or proceed in confufion. 2. The fenfitive and voluntary
motions continue undiflurbed. 3. The afTociate trains or circles of
motions continue; but their catenations with fome of the irritative
motions are difordered, or inverted, or dilTevered..

SECT.

'240 OF DRUNKENNESS. Sect.XXI. i.

SECT. XXI.

OF DRUNKENNESS.

I. Sleep from Jatiety of hunger. From rocking children. From uniform founds.
2. Intoxication from common food after fatigue and inanition. 3. From wine
or opium. Chilnejs after meals. Vertigo. Why pleajure is produced by in-
toxication, and by fwinging and rocking children. And why pain is relieved
by if. 4. Why drunkards fiagger and flammer, and are liable to weep. 5. And
become delirious, fleepy, and fiupid. 6. Or make pale urine and vomit. 7, Ob~
jeSis are feen double. 8. Attention of the mind diminifloes drunkennejs. 9.
Dijordered irritative motions of all the Jenfes. 10. Difeafes from drunken-
vefs. II. Definition of drunkennefs.

I. IN the (late of nature when the fenfe of hunger is appeafed by
the ftimulus of agreeable food, the bufinefs of the day is over, and-
the human favage is at peace with the world, he then exerts little
attention to external objefts, pleafing reveries of imagination fuc-
ceed, and at length fleep is the refult : till the nourifhment which he
has procured, is carried over every part of the fyftem to repair the in-
juries of action, and he awakens with frefh vigour, and feels a renewal
of his fenfe of hunger.

The juices of fome bitter vegetables, as of the poppy and the lauro-
cerafus, and the ardent fpirit produced in the fermentation of the
fuo'ar found in vegetable juices, are fo agreeable to the nerves of the
ftomach, that, taken in a fmall quantity, they inftantly pacify the
fenfe ©f hunger ; and the inattention to external flimuii with the re-
veries

Sect.XXI. 2.3. OF DRUNKENNESS. 241

veries of imagination, and fleep, fucceeds, in the fame manner as when
the flomach is tilled with other lefs intoxicatina: food.

This inattention to the irritative motions occafioned by external fli-
tnuli is a very important circumftance in the approach of fleep, and
is produced in young children by rocking their cradles: during which
all vifible objects become indiftinft to them. An uniform foft re-
peated found, as the murmurs of a gentle current, or of bees, are
faid to produce the fame effeft, by prefenting indiftincl ideas of in-
confequential founds, and by thus ftealing our attention from other
obje£ls, whilfh by their continued reiterations they become familiar
themfelves, and we ceafe gradually to attend to any thing, and fleep
enfues.

2. After great fatigue or inanition, when the ftomach is fuddenly
filled with flefli and vegetable food, the inattention to external fti-
muli, and the reveries of imagination, become fo confpicuous as to
amount to a degree of intoxication. The fame is at any time pro-
duced by fuperadding a httle wine or opium to our common meals;
or by taking thefe,feparately in confiderable quantity; and this more
efEcacioufly after fatigue or inanition ; becaufe a lefs quantity of any
fllmulating material will excite an organ into energetic a6lIon, after it
has lately been torpid from defedl of Itimulus ; as obje6ts appear more
luminous, after we have been in the dark; and becaufe the fufpenfi6n
■of volition, which is the immediate caufe of fleep, is fooner induced,
after a continued voluntary exertion has in part exhaufled the fenforial
power of volition ; in the fame manner as we cannot contrad a flno-le
mufcle long together without intervals of inadion.
' 3. In the beginning of intoxication we are inclined to fleep, as men-
tioned above, but by the excitement of external circumftances, as of
nolfe, light, bufinefs, or by the exertion of volition, we prevent the
approaches of it, and continue to take into our flomach greater quan-
tities of the inebriating materials. By thefe means the irritative
movements of the ftomach are excited into greater adlion than is na-

I i tural ;

243 OF DRUNKENNESS. SECT.XXL3.

tural ; and in confequence all the irritativ^e tribes and trains of mo-
tion, which are catenated with thena, become fufceptible of ftronger
aftion fiom their accuftomed flimuli ; becaufe thefe motions are ex-
cited both by their ufual irritation, and by their affociation with the
increafed aftions of the ftoraach and lafteals. Hence the Ikin glows,
and the-heat of the body is increafed, by the more energetic aftion of
the whole glandular fyflem ; and pleafure is introduced in confequence
of thefe increafed motions from internal ftimulus. According to
Law, 5. Se^. IV. on Animal Caufation.

From this great increafe of irritative motions from internal flimu-
lus, and the increafed fenfation introduced into the fyftem in confe-
quence ; and fecondly, from the increafed fenfitive motions in confe-
quence of this additional quantity of fenfation, fo much fenforial power
is expended, that the voluntary power becomes feebly exerted, and
the irritation from the ftimulus of external objects is lefs forcible ;
•the external parts of the eye are not therefore voluntarily adapted to
the diftances of objects, whence the apparent motions of thofe objeds
either are feen double, or become too indiftind for the purpofe of ba-
lancing the body, and vertigo is induced.

Hence we become acquainted with that very curious circumftance,
why the drunken vertigo is attended with an increafe of pleafure ; for
the irritative ideas and motions occafioned by internal ftimulus, that
were not attended to in our fober hours, are now juft fo much in-
<;reafed as to be fucceeded by pleafureable fenfation, in the fame man-
tier as the more violent motions of our organs are fucceeded by painful
fenfation. And hence a greater quantity of pleafureable fenfation is
introduced into the conftitution ; which is attended in fome people
with an increafe of benevolence and good humour.

If the apparent motions of objects is much increafed, as when we
revolve on one foot, or are fwung on a rope, the ideas of thefe ap-
parent motions are alfo attended to, and are fucceeded with pleafure-
able fenfation, till they become familiar to us by frequent ufe. Hencq

children

S£CT.XXI.4. OF DRUNKENNESS. 243

children are at firft delighted with thefe kinds of exercife, and with
riding, and failing, and hence rocking young children inclines them
to fleep. For though in the vertigo froni intoxication the irritative
ideas of the apparent motions of objeds are indiftinft from their de-
creafe of energy : yet in the vertigo occafioned by rocking or fwing-
ing the irritative ideas of the apparent motions of objects are increafed
in energy, and hence they induce pleafure into the fyftem, but are
equally indiflinft, and in confequence equally unfit to balance our-
felves by. This addition of pleafure precludes defire or averfion, and
in. confequence the voluntary power is feebly exerted, and on this ac-
count rocking young children inclines them to fleep.

In what manner opium and wine a6l in relieving pain is another
article, that well deferves our attention. There are many pains that
originate from defeft as well as from excefs of ftimulus; of thefe are
thofe of the fix appetites of hunger, thirft, luft, the want of heat, of
diftention, and of frefti air. Thus if our cutaneous capillaries ceafe to
a£t from the diminilhed ftimulus of heat, when we are expofed to
cold weather, or our ftomach is uneafy for want of food ; thefe are
both pains from defe£t of ftimulus, and in confequence opium, which
Simulates all the moving fyftem into increafed adlion, muft relieve
them. But this is not the cafe in thofe pains, which arife from excefs
of ftimulus, as in violent inflammations: in thefe the exhibition of
opium is frequently injurious by increafing the a<Sion of the lyftem
already too- great, as in inflammation of the bowels mortification is
often produced by the ftimulus of opium. Where, however, no fuch
bad confequences follow; the ftimulus of opium, by increafing all the
motions of the fyftem, expends fo much of the fenforial power, that
the adlions of the whole fyftem foon become feebler, and in confe-
quence thofe which produced the pain and inflammation.

4. When intoxication proceeds a little further,, the quantity of
pleafureable fenfation is fo far increafed, that all defire ceafes, for there
is no pain, in the fyftem to excite it. Hence the voluntary exertions

I i 2 are

244 'OF DRUNKENNESS. Sect.XXI. 5.6.

are diminiflied, ftaggering and ftammering fucceed j and the trains of
ideas become more and more inconfiftent from this defedt of voluntary-
exertion, as explained in the fedlions on fleep and reverie, whilft
thofe paffions which are vinmixed with volition are more vividly felt,
and fliewn with lefs referve ; hence pining love, or fuperftitious fear,
and the maudling tear dropped on the remembrance of the mofl trifling
diftrefs.

5. At length all thefe circumftances are increafed; the quantity of
pleafure introduced into the fyflrem by the increafed irritative mufcu-
lar motions of the whole fanguiferous, and glandular, and abforbent
fyftems, becomes fo great, that the organs of fenfe are more forcibly
excited into aftion by this internal pleafureable fenfation, than by the
irritation from the ftimulus of external objefts. Hence the drunkard
ceafes to attend to external ftimuli, and as volition is now alfo fufpend-
cd, the trains of his ideas become totally inconfiftent as in dreams, or
delirium : and at length a ftupor fucceeds from the great exhauflion of
fenforial power, which probably does not even admit of dreams, and
in which, as in apoplexy, no motions continue but thofe from internal
ftimuli, from fenfation, and from aflbciation.

6. In other people a paroxyfm of drunkennefs has another termina-
tion ; the inebriate, as foon as he begins to be vertiginous, makes pale
■urine in great quantities and very frequently, and at length becomes
fick, vomits repeatedly, or purges, or has profufe fweats, and a tem-
porary fever enfues with a quick ftrong pulfe. This in fome hours is
fucceeded by fleep; but the unfortunate bacchanalian does not perfeftly
recover himfelf till about the fame time of the fucceeding day, when
his courfe of inebriation began. As fhewn in SeiSl. XVII. i. 7. on
Catenation. The temporary fever with ftrong pulfe is owing to the
fame caufe as the glow on the Ikin mentioned in the third paragraph
of this Sedlion : the flow of urine and ficknefs arifes from the whole
fyftem of irritative motions being thrown into confufion by their .aflb-
ciations with each other; as in fea-licknefs, mentioned in Sed. XX.4.

Sect. XXI. 7- 8. 9- OF DRUNKENNESS. 245

on Vertigo; and which is more fully explained in Se£lion XXIX. on
Diabetes.

7. In this vertigo from internal caufes we fee objects double, as two
candles inftead of one, which is thus explained. Two lines drawn
through the axes of our two eyes meet at the objeifl we attend to :
this angle of the optic axes increafes or diminifhes \\'ith the lefs or
greater diftances of objedls. All objefts before or behind the place
where this angle is formed, appear double ; as any one may obferve
by holding up a pen between his eyes and the candle ; when he looks
attentively at a fpot on the pen, and carelefsly at the candle, it will
appear double; and the reverfe when he looks attentively at the candle
and carelefsly at the pen ; fo that in this cafe the mufcles of the eye,
like thofe of the limbs, ftagger and are difobedient to the expiring ef-
forts of volition. Numerous objeds are indeed fometimes feen by the
inebriate, occafioned by the refractions made by the tears, which ftand
■upon his eye-lids.

8. This vertigo alfb continues, when the inebriate lies in his bed,
in the dark, or with his eyes clofed ; and this more powerfully than
when he is eredt, and in the light. For the irritative ideas of the ap-
parent motions of obje£ls are now excited by irritation from internal
flimulus, or by affociation with other irritative motions; and the in-
ebriate, like one in a dream, believes the objedls of thefe irritative mo-
tions to be prefent, and feels himfelf vertiginous. I have obferved in

f this fituation, fo long as my eyes and mind were intent upon a book,
the ficknefs and vertigo ceafed, and were renewed again the moment
I difcontinued this attention ; as was explained in the preceding ac-
count of fea-ficknefs. Some drunken people have been know^n to be-
come fober inftantly from fome accident, that has flrongly excited
their attention, as the pain of a broken bone, or the news of their
houfe being on fire.

9. Sometimes the vertigo from internal caufes, as from intoxica-
tion, or at the beginning of fome fevers, becomes fo univerfal, that

4 the

246 OF DRUNKENNESS. Sect. XXI. lo.

the irritative motions which befong to other organs of fetife are fuc-
ceeded by fenfatiou or attention, as well as thofe of the eye. The
vertiginous noife in the ears has been explained in Section XX. on
Vertigo. The tafte of the faUva, which in general is not attended
to, becomes perceptible, and the patients complain of a bad tafte ia
their mouth.

The common fmells of the furroundingair fometimes excite the at-
tention of thefe patients, and bad fmells are complained of, which to
other people are imperceptible. The irritative motions that belong-
to the fenfe of preffure, or of touch, are attended to, and the patient
conceives the bed to librate, and is fearful of falling out of it. The
irritative motions belonging to the fenfes of diflention, and of heat,,
like thofe above mentioned, become attended to at this time:: hence
we feel the pulfation of our arteries all over us, and compkin of heat,
or of cold, in parts of the body where there is no accumulation or di-
minution of aftual heat. All which are to be explained, as in the laft
paragraph, by the irritative ideas belonging to the various fenfes being
now excited by internal ftimuli, or by their afiociations with other ir-
ritative motions. And that the inebriate, like one in a dream, be-
lieves the external objefts, which ufually caufed thefe irritative ideas,,
to be' now prefent.

lo, The difeafes in confequence of frequent inebriety, or of daily
taking much vinous fpirit without inebriety, confift in the paralyfis,
which is liable to fucceed violent Simulation. Organs, whofe adions
are aflbciated with others, are frequently more afFefted than the organ-,,
which is Simulated into too violent adHon. See Seft. XXIV. 2. 8,
Hence in drunken people it generally happens, that the fecretory veflels
of the liver become firft paralytic, and a torpor with confequent gall-
ftones or fchirrus of this vifcus is induced with concomitant jaundice j
otberwife it becomes inflamed in confequence of previous torpor, and
this inflammation is frequently transferred to a more fenfible part, which.
is aflbciated with it, and produces the gout, or the rofy eruption of

7 ^he

Sect. XXI. fo. OF DRUNKENNESS. 247

the face, or fdme other leprous eruption on the head, or arms, or leo-s.
Sometimes the ftomach is firfi: aftefted, and paralyfis of the lacteal
ijltem is induced; whence a total abhorrence from flefli-food, and
general emaciation. In others the lymphatic fyftem is afFecled with
paraljfis, and dropfy is the confequence. In fome inebriates the tor-
por of the liver produces pain without apparent fchirrus, or gall-ftones,
or inflammation, or confequent gout, and in thefe epilepfy or infanity
are often the confequence. All which will be more fully treated of
in the courfe of the work.

I am well aware, that it is a common opinion, that the gout is as
frequently owing to gluttony in eatings as to intemperance in drink-
ing fermented or fpirituous liquors. To this I anfwer, that I have
feen no perfon afflicted with the gout, who has not drank freely of
fermented liquor, as wine and water, or fmall beer ; though as the
difpolition to all the difeafes, which have originated from intoxication,
is in fome degree hereditary, a lefs quantity of fpirituous potation w'lU
induce the gout in thofe, who inherit the difpofition from their pa-
rents. To which I muft add, that in young people the rheum.atjiibj is
frequently miftaken for the gout.

Spice is feldom taken in fuch quantity as to do any material injury
to the fyflem, flefh-meats as well as vegetables are the natural diet of
mankind ; with thefe a glutton may be crammed up to the throat,
and fed fat like a flailed ox ; but he will not be difeafed, unlefs he adds
fpirituous or fermented liquor to his food. This is well known in the
diflilleries, where the fwine, which are fattened by the fpirituous fe-
diments of barrels, acquire difeafed livers. But mark what happens
to a man, who drinks a quart of wine or of ale, if he has not been
habituated to it. He lofes the ufe both of his limbs and of his under-
flanding! He becomes a temporary idiot, and has a temporary ftroke
of the palfy ! And though he flowly recovers after fome hours, is it
not reaibnable to conclude, that a perpetual repetition of fo powerful
a poifon muft at length permanently affedl him ? — If a perfon acciden-
tal! v

248 OF DRUNKENNESS. SecT.XXI.ir,

tally becomes intoxicated by eating a few muflirooms of a peculiar
kind, a general alarm is excited, and he is faid to be poifoned, and
emetics are exhibited ; but fo familiarifed are we to the intoxication
from vinous fpirit, that it occafions laughter rather than alarm.

There is however confiderable danger in too haftily difcontinuing
the ufe of fo ftrong a ftimulus, left the torpor of theXyftem, or para-
lyfis, fliould fooner be induced by the omiflion than by the continu-
ance of this habit, when unfortunately acquired. A golden rule for
determining the quantity, which may with fafety be difcontinued, is
delivered in Seft. XII. 7. 8.

II. Definition of drilnkennefs. Many of the irritative motions are
much increafed in energy by internal ftimulation.

2. A great additional quantity of pleafureable fenfation is occafioned
by this increafed exertion of the irritative motions. And many fenfi-
tive motions are produced in confequence of this increafed fenfation.
■ 3. The aflbciated trains and tribes of motions, catenated with the
increafed irritative and fenfitive motions, are difturbed, and proceed
in confufion.

4. The faculty of volition is gradually impaired, whence proceeds
the inftability of locomotion, inaccuracy of perception, and incon-
liftency of ideas ; and is at length totally fufpended, and a temporary
apoplexy fucceeds.

SECT.

Sect. XXII. u REPETITION AND IMITATION. 249

SECT. XXII.

OP PROPENSITY TO MOTION, REPETITION AND IIvIITATlON.

L Accumulation of Jenjorial power in hemiplagia^ in Jleep, in cold fit of fever, in
the locomotive mufcles, in the organs of fenfe. Produces propenftty to alfion.
II. Repetition by three Jenforial powers. In rhimes and alliterations, in mufic,
dancing, architeSfure, landjcape-painting, leauty. III. i. Perception confifts
in imitation. Four kinds of imitation. i. Voluntary. Dogs taught to dance.
3. Senfitive. Hence fympathy, and all our virtues. Contagious matter of vene-
real ulcers, of hydrophobia, of jail-fever, of fmall-pox, produced by imitation,
and the fex of the embryon. 4. Irritative imitation. 5. Imitations refolvable
into ajfociations-.

I. I. IN the hemiplagia, when the limbs on Oiie fide have loft
their power of voluntary motion, the .patient is for many days per-
petually employed in moving thofe of the other. 2. When the vo-
luntary power is fufpended during fleep, there commences a ceafelefs
flow of feiifitive motions, or ideas of imagination, which compofe our
dreams, 3. When in the cold fit of an intermittent fever fome parts
of the fyftem have for a time continued torpid, and have thus ex-
pended lefs than their u^ual expenditure of fenforial power ; a hot fit
fucceeds, with violent adltioii of thofe velTels, which had previoufly
been quiefcent. All thefe are explained from an accumulation of
lenforial power during the inaftivity of fome part of the fyftem.

Befides the very great quantity of fenforial power perpetually pro-
duced and expended in moving the arterial, venous, and glandular

K k fyftems,

250 REPETITION AND IMITATION. Sect. XXII. 2.

fyftems, with the various organs of digeftion, as defcribed in Se«Slion
XXXII. 3. 2. there is alfo a conftant expenditure of it by the ac-
tion of our locomotive mufcles and organs of fenfe. Thus the thick-
nefs of the optic nerves, where they enter the eye, and the great ex-
panfion of the nerves of touch beneath the whole of the cuticle,
evince the great confumption of fenforial power by thefe fenfes. And
our perpetual mufcular a£llons in the common offices of life, and in
conftantly preferving the perpendicularity of our bodies during the
day, evince a confiderable expenditure of the fpirit of animation by
our locomotive mufcles. It follows, that if the exertion of thefe
organs of fenfe and mufcles be for a while intermitted, that fome
quantity of fenforial power muft be accumulated, and a propenfity to
adivity of fome kind enfue from the increafed excitability of the
fyftem. Whence proceeds the irkfomenefs of a continued attitude,
and of an indolent life.

However fmall this hourly accumulation of the fpirit of animation
may be, it produces a propenfity to fome kind of aftion ; but it never-
thelefs requires either defire or averfion, either pleafure or pain, or
fome external ftimulus, or a previous link of aflbciation, to excite the
fyftem into activity; thus it frequently happens, when the mind and
body are fo unemployed as not to poflefs any of the three firft kinds
of ftimuli, that the laft takes place, and confumes the fmall but per-
petual accumulation of fenforial power. Whence fome indolent pea-»
pie repeat the fame verfe for hours together, or hum the fame tune.
Thus the poet :

Onward he trudged, not knowing what he foughtj
And whiftled, gs he went, for want of thought.

II. The repetitions of motions may be at firft produced either by
volition, or by fenfation, or by irritation, but they foon become eafier
to perform than any other kinds of a£lion, becaufe they foon become
affociated together, according to Law the feventh, Sedion IV. on

Animal

Sect. XXII. 2. REPETITION AND IMITATION. 25!

Animal Caufation. And becaufe their frequency of repetition, if as
much fenforial power be produced during every reiteration as is ex-
pended, adds to the facility of their production.

If a ftimulus be repeated at uniform intervals of time, as defcribed
in Sedl. XII. 3. 3. the aftion, whether of our mufcles or organs of
feiife, is produced with flill greater facility or energy; becaufe the
fenforial power of affociation, mentioned above, is combined with the
fenforial power of irritation ; that is, in common language, the ac-
quired habit affifts the power of the ftimulus.

This not only obtains in the annual, lunar, and diurnal catenations
of animal motions, as explained in Se£l. XXXVI. which are thus
performed with great facility and energy ; but in every lefs circle of
a£lions or ideas, as in the burthen of a long, or the reiterations of a
dance. To the facility and diftindlnefs, with which we hear founds
at repeated intervals, we owe the pleafure, which we receive from
mufical time, and from poetic time ; as. defcribed in Botanic Garden,
P. 2. Interlude 3. And to this the pleafure we receive from the
rhlmes and alliterations of modern verification ; the fource of which
without this key would be difficult to difcover. And to this likewife
fhould be afcribed the beauty of the duplicature in the perfecfl tenfe
of the Greek verbs, and of fome Latin ones, as tango tetegi, mordeo
momordi.

There is no variety of notes referable to the gamut in the beating
of the drum, yet if it be performed in mufical time, it is agreeable to
our ears ; and therefore this pleafureable fenfation muft be owing to
the repetition of the divifions of the founds at certain intervals of time,
or mufical bars. Whether thefe times or bars are dlftinguilhed by a
paufe, or by an emphafis, or accent, certain it is, that this diftindtion
is perpetually repeated ; otherwife the ear could not determine inftant-
ly, whether the fucceflions of found were in common or in triple time.
In common time there is a divifion between every two crotchets, or

K k 2 other

2.52 REPETITION AND IMITATION. Sect. XXII. z,

other notes of equivalent time ; though the bar in written mufic is.
put after every fourth crotchet, or notes equivalent in time; in triple
time the divifion or bar is after every three crotchets, or notes equi^
valent; fo that in common time the repetition recurs more frequently
than in triple time. The grave or heroic verfes of the Greek and,
Latin poets are written in common time ; the French heroic verfes,
and Mr. Anftie's humorous verfes in his bath guide, are written in
the fame time as the Greek and Latin verfes, but are one bar fhorter.
The Englifh grave or h«roic verfes, are meafured. by triple time, as.
Mr. Pope's tranflation of Homer..

But befides thefe little circles of mufical time, there are the greater
returning periods, and the ftill more diftant chorufes, which, like the
rhimes at the ends of verfes, owe their beauty to repetition; that is,
to the facility and diflinftnefs with which we perceive founds, which
we expedl to perceive, or have perceived before ;. or in the language
of this work, to the greater eafe and energy with which o\xt organ, is
excited by the combined fenforial powers of affociation and irritation,
than by the latter fingly.

A certain uniformity or repetition of parts enters the very compo-
fition of harmony. Thus two oftaves neareft to each other in. the
fcale cemmence their vibrations together after every fecond vibration
of the higher one. And where the firfl, third, and fifth compofe a
chord the vibrations concur or coincide frequently, though lefs fo
than in the two odaves. It is probable that thefe chords bear fome
analogy to a mixture of three alternate colours in the fun's fpeftrum
feparated by a prifm.

The pleafure we receive from a melodious fuccefiion of notes refer-
able to the gamut is derived from another fource,' viz. to the pandi-
culation or counteradtion of antagonift fibres. See Botanic Garden,
P. 2. Interlude 3. If to thefe be added our early aflbciations of agree-
able ideas with certain proportions of found, I fuppofe, from thefe

three

Sect. XXII. 5. REPETITION AND IMITATION. 253-

three fources fprings all the deUght of mufic, fo celebrated by ancient
authors, and fo enthufiafticaUy cultivated at prefent. See Sedl. XVL
No. 10. on Inftinft.

This kind of pleafure arifing from repetition, that is from the faci-
lity and diftindlnefs, with which we perceive and underftand repeated
fenfations, enters into all the agreeable arts ; and when it is carried tO'
excefs is termed formality. The art of dancing like that of mulic de-
pends for a great part of the pleafure, it affords,, on repetition ; ar-
chitefture, efpecially the Grecian, confi-fts of ©ne part being a repe-
tition of another ; and hence the beauty of the pyramidal outline in
landfcape-painting ; where one fide of the pi£ture may be faid in fome
meafure to balance the other.. So. univerfally does repetition contribute
to our pleafure in the fine arts, that beauty itfelf has been defined by
fome writers to conliU in a due combination of uniformity and variety.
See Sea. XVI. 6.

III. I. IvJ^n is termed by A..riftotle an imitative animal;: this pro-
penfity to imitation not only appears in the adions of children, but in-
all the cuftoms and fafhions of the world; many thoufands tread ini
the beaten paths of others, for one who traverfes regions of his own
difcov.ery. The origin of this propenfity to imitation has not, that I
recoUedl, been deduced from any known principle; when any a6lion
prefenfes itfelf to the view of a child, as of whetting a knife, or thread-
ing a needle, the parts of this a£lion in refpeifl of time, motion, fi--
gure, is imitated by a part of the retina of his eye; to perform this-
a«Stioh therefore with his hands is eafier to him than to invent anv
new aftion, becaufe it confifts in repeating with another fet of fibres^
viz. with the moving mufcles, what he had jufi; performed by fome
partsof the retina ; jull a^ in dancing we transfer the times of mo-
tion from the adions of the auditory nerves to the mufcles of the
limbs. Imitation therefore confifts of repetition, which we have
Ihewn above to be the eafiefl: kind of animal adion, and which we-

3 perpetually

^54 REPETITION AND IMITATION. Sect.XXII, 3.

perpetually fall into, when we poffefs an accumulation of fenforial
power, which is not otherwife called into exertion.

It has been fliewn, that our ideas are configurations of the organs
of fenCe, produced originally in confequence of the ftimulus of exter-
nal bodies, x-^nd that thefe ideas, or configurations of the organs of
fenfe,- refemble in fome property a correfpondent property of external
matter; as the parts of the fenfes of fight and of touch, which are
excited into aftion, refemble in figure the figure of the ftimulating
body; and probably alfo the colour, and the quantity of denfity,
^vhich they perceive. As explained in Seft. XIV. 2. 2. Hence it ap-
pears, that our perceptions themfelves are copies, that is, imitations
of fome properties of external matter ; and the propenfity to imitation
is thus interwoven with our exiftence, as it is produced by the ftimuli
of external bodies^ and is afterwards repeated by our volitions and fen-
fations, and thus conftitutes all the operations of our minds.

2. Imitations refolve themfelves into four kinds, voluntary, fenfi-
tive, irritative, and aflbciate. The voluntary imitations are, when
•we imitate deliberately the aftions of others, either by mimicry, as in
afting a play, or in delineating a flower ; or in the common actions of
our lives, as in our drefs, cookery, language, manners, and even in
our habits of thinking.

Not only the greatefl part of mankind learn all the common arts of
life by imitating others, but brute animals feem capable of acquiring
knowledge with greater ■ facility by imitating each other, than by any
methods by which we can teach them ; as dogs and cats, when they
are fick, learn of each other to eat grafs ; and I fuppofe, that by
making an artificial dog perform certain tricks, as in dancing on his
hinder legs, a living dog might be eafily induced to imitate them;
and that the readieft way of inftrufting dumb animals is by pradtifing
them with others of the fame fpecies, which have already learned the
arts we wifh to teach them. The important ufe of imitation in ac-

5 quiring

Sect. XXII. 3. REPETITION AND IMITATION. 255

quiring natural language is mentioned in Sedion XVI. 7. and 8. on
Inftina.

3. The fenfitive imitations are the immediate confequences of plea-
fure or pain, and thefe are often produced even contrary to the efforts
of the will. Thus many young men on feeing cruel furgical opera-
tions become fick, and fome even feel pain in the parts of their ovfii
bodies, which they fee tortured or wounded in others ; that is, they
in fome meafure imitate by the exertions of their own fibres the vio-
lent a£lions, which they witnefled in thofe of others. In this cafe a
double imitation takes place, firft the obferver imitates with the ex-
tremities of the optic nerve the mangled limbs, which are prefent be-
fore his eyes ; then by a fecond imitation he excites fo violent a6tion
of the fibres of his own limbs as to produce pain in thofe parts of his
own body, which he faw wounded in another. In thefe pains pro-
duced by imitation the effect has fome fimilarity to the caufe, which
diftinguillies them from thofe produced by aflbciation ; as the pains of
the teeth, called tooth-edge, which arc produced by aflbciation with
difagreeable founds, as explained m Se£l. XVI. 10.

The efFe£l of this powerful agent, imitation, in the moral world,
is mentioned in Se£l. XVI. 7. as it is the foundation of all our intel-
ledual fympathies with the pains and pleafures of others, and is in
confequence the fource of all our virtues. For in what confifls our
fympathy with the miferies, or with the joys, of our fellow creatures,
but in an involuntary excitation of ideas in fome meafure fimilar or
imitative of thofe, which we believe to exift in the minds of the per-
fons, whom we commiferate or congratulate?

There are certain concurrent or fucceffive adions of fome of the
glands, or other parts of the body, which are poflefled of fenfation,'
which become intelligible from this propenfity to imitation. Of
thefe are the production of matter by the membranes of the fauces, or
by the Ikin, in confequence of the venereal difeafe previoufly affeding

the

±se REPETITION AND IMITATION. Sect. XXII. 3.

the parts of generation. Since as no fever is excited, and as neither
the blood of. fuch patients, nor even the matter from ulcers of the
throat, or from cutaneous ulcers, will by inoculation produce the ve-
nereal difeafe in others, as obferved by Mr. Hunter, there is reafon
to conclude, that no contagious matter is conveyed thither by the
blood-vefiels, but that a milder matter is formed by the adlions of the
fine vefl'els in thofe membranes imltatins; each other. See Seftion
XXXIII. 2. 9. In this difeafe the actions of thefe veffels producing
ulcers on the throat and ikin are imperfedt imitations of thofe pro-
ducing chanker, or gonorrhoea ; fince the matter produced by them
is not infeftious, while the imitative a<3:ions in the hydrophobia ap-
pear to be perfedt refemblances, as they produce a material -equally in-
fedlious with the original one, which induced them.

The contagion from the bite of a mad dog differs from other con-
tasious materials, from its being; communicable from other animals to
mankind, and from many animals to each other ; the phenomena at-
tending the hydrophobia are in fome degree explicable on the fore-
going theory. The infe£tious matter does not appear to enter the
circulation, as it cannot be traced along the courfe of the lymphatics
from the wound, nor is there any fwelling of the lymphatic glands,
nor does any fever attend, as occurs in the fmall-pox, and in many
other contagious difeafes ; yet by fome unknown procefs the difeafe is
^communicated from the wound to the throat, and that many months
after the injury, fo as to produce pain and hydrophobia, with a fecre-
tion of infeftious faiiva of the fame kind, as that of the mad dog,
which inflicted the wound.

This fubje£t is very intricate. — It would appear, that by certain
morbid a£lions of the falivary glands of the mad dog, a peculiar kind
of faiiva is produced; which being inftilled into a wound of another
animal ftimulates the cutaneous or mucous glands into morbid a£lions,
but which are ineffedlual in refpeft to the production of a fimilar con-
tagious

Sect.XXIT.4. repetition and imitation. 25;

taglous material ; but the fallvary glands by irritative fympathy are
thrown into firailar aftion, and produce an infedlious faliva fimilar to
that inftilled into the wound.

Though in many contagious fevers a material fimilar to that which
produced the difeafe, is thus generated by imitation ; yet there are
other infeftious materials, which do not thus propagate themfelves,
but which feem to a£l like flow poifons. Of this kind was the con-
tagious matter, which produced the jail-fever at the affizes at Oxford
about a century ago. Which, though fatal to fo many, was not
communicated to their nurfes or attendants. In theie cafes, the imi-
tations of the fine veflels, as above defcribed, appear to be imperfect,
and do not therefore produce a matter fimilar to that, which Simulates
them ; in this circumftance refembling the venereal matter in ulcers
of the throat or fkin, according to the curious difcovery of Mr. Hun-
ter above related, who found, by repeated inoculations, that it would
not infecl. Hunter on Venereal Difeafe, Part vi. ch. i.

Another example of morbid imitation is in the produftion of a great
quantity of contagious matter, as in the inoculated fmall-pox, from a
fmall quantity of it inferted into the arm, and probably ditFufed in the
blood. Thefe particles of contagious matter flimulate the extremities
of the fine arteries of the fkin, and caufe them to imitate fome pro-
perties of thofe particles of contagious matter, fo as to produce a thou-
fandfold of a fimilar material. See Se£l. XXXIII. 2. 6. Other in-
flances are mentioned in the Se(ftion on Generation, which fliew the
probability that the extremities of the feminal glands may imitate cer-
tain ideas of the mind, or actions of the organs of fenfe, and thus oc-
cafion the male or female fex of the embryon. See Sedl. XXXIX. 6.

4. We come now to thofe imitations, which are not attended with,
fenfation. Of thefe are all the irritative ideas already explained, as
when the retina of the eye imitates by its adion or configuration the
tree or the bench, which I fhun in walking pait without attending
to them. Other examples of thefe irritative imitations are daily ob-

L 1 fervable

258 REPETITION AND IMITATION. Sect. XXII. 5,

fervable in common life : thus one yawning perfon (hall fet a whole
company a yawning ; and fome have acquired winking of the eyes or
impediments of fpeech by imitating their companions without being
confcious of it.

5. Befides the three fpecies of imitations above defcribed there may
be fome affociate motions, which may imitate each other in the kind
as well as in the quantity of their a6tion ; but it is difficult to dif-
tinguifli them from the aflbciations of motions treated of in Sedlioa
XXXV. Where the a£lions of other perfons are imitated there can be
no doubt, or where we imitate a preconceived idea by exertion of our
locomotive mufcles, as in painting a dragon ; all thefe imitations may
aptly be referred to the fources above defcribed of the propenfity to
activity, and the facility of repetition ; at the fame time I do not af-
firm, that all thofe other apparent fenfitive and irritative imitations
may not be refolvable into aflbciations of a peculiar kind, in which
certain diftant parts of fimilar irritability or fenfibility, and which have
habitually afled together, may affedl each other exadly with the fame
kinds of motion ; as many parts are known to fympathife in the quan-
tity of their motions. And that therefore they may be ultimately re-
folvable into aflbciations of a£lion, as defcribed in Sedt. XXXV.

SECT.

Sect. XXIII. i. OF THE CIRCULATORY SYSTEM. 259

SECT. XXIII.

OF THE CIRCULATORY SYSTEM.

I. 'The heart and arteries have no antagonift mujcles. Veins ahforh the Mood, pro-
pel it forwards, and diftend the heart; contraSiion of the heart diflends the ar-
teries. Vena portarmn. II. Glands which take their fluids from the blood.
With long necks, with fhort necks. III. Abjorhent Jyflem. IV. Heat given
out from glandular fecretions. Blood changes colour in the lungs and in the
glands and capillaries. V. Blood is abforbed by veins, as chyle by laSeal vef-

fels, otherwife they could not join their fir earns. VI. Two kinds of flimidus,
agreeable and difagreeable. Glandular appetency. Glands originally pojfejjed

fenjation.

I. WE now flep forwards to illuftrate feme of the phzenomena of
difeafes, and to trace out their moft efficacious methods of cure ; and
fhall commence this fubje£l with a fhort defcription of the circulatorj
fyftem.

As the nerves, whofe extremities form our various organs of fenfe
and mufcles, are all joined, or communicate, by means of the brain,
for the convenience perhaps of the diftribution of a fubtile ethereal
fluid for the purpofe of motion; fo all thofe veffels of the bodj,
■which carry the groffer fluids for the purpofes of nutrition, communi-
cate with each other by the heart.

The heart and arteries are hollow mufcles, and are therefore in-
dued with power of contraction in confequence of ftimulus, like all
other mufcular fibres ; but, as they have no antagonifl mufcles," the
cavities of the veflels, which they form, would remain for e\-er

L 1 2 clofed.

26o OF THE CIRCULATORY SYSTEM. Sect. XXIII. i,

clofed, after they have contradled themfelves, unlefs fome extraneous
power be applied to again diftend them. This extraneous power in
refpeft to the heart is the current of blood, which is perpetually ab-
forbed by the veins from the various glands and capillaries, and
pufhed into the heart by a power probably very fimilar to that, which
raifes the fap in vegetables in the fpring, which, according to Dr.
Hale's experiment on the ftump of a vine, exerted a force equal to a
column of water above twenty feet high. This force of the current
of blood in the veins is partly produced by their abforbent power, ex-
erted at the beginning of every fine ramification ; which may be con-
ceived to be a mouth abforbing blood, as the mouths of the lafteals
and lymphatics abforb chyle and lymph. And partly by their inter-
mitted compreffion by the pulfations of their generally concomitant ar-
teries ; by which the blood is perpetually propelled towards the heart,
as the valves in many veins, and the abforbent mouths in them all,
will not fuffer it to return.

The blood, thus forcibly injected into the chambers of the heart,
diftends this combination of hollow mufcles; till by the ftimulus of
diftention they contrail themfelves; and, pufhing forwards the blood
into the arteries, exert fufficient force to overcome in lefs than a
fecond of time the vis inertias, and perhaps fome elafticity, of the very
extenfive ramifications of the two great fyftemsof the aortal and pul-
monary arteries. The power neceffary to do this in fo Ihort a time
mull: be confiderable, and has been varioufly eftimated by different
phyfiologifts.

The mufcular coats of the arterial fvftem are then brought into ac-
tion by the ftimulus of diftention, and propel the blood to the mouths,
or through the convolutions, which precede the fecretory apertures of
the various glands and capillaries. ,

In the veffels of the liver there is no intervention of the heart; but
the vena poitariun, which does the office of an artery, is diftended by
the blood poured into it from the mefenteric veins, and is by this

diftention

Sect.XXIII. 2. OF THE CIRCULATORY SYSTEM. 261

diftention Simulated to contraft itfelf, and propel the blood to the
mouths of the numerous glands, which compofe that vifcus.

II. The glandular fyftem of veffels may be divided into thofe,
which take fome fluid from the circulation ; and thofe, which give
fomething to it. Thofe, which take their fluid from the circulation,
are the various glands, by which the tears, bile, urine, perfpiration,
and many other fecretions are produced; thefe glands probably confifh
of a mouth to fele£l, a belly to digeft, and an excretory aperture to
emit their appropriated fluids ; the blood is conveyed by the power of
the heart and arteries to the mouths of thefe glands, it is there taken
up by the living power of the gland, and carried forwards to its belly,
and excretory aperture, where a part is feparated, and the remainder
abforbed by the veins for further purpofes.

Some of thefe glands are furnifhed with long convoluted necks or
tubes, as the feminal ones, which are curioufly feen when injedled
with quickfilver. Others feem to confift of fhorter tubes, as that
great congeries of glands, which conftitute the liver, and thofe of the
kidneys. Some have their excretory apertures opening into refervoirs,
as the urinary and gall-bladders. And others on the external body, as
thofe which fecret the tears, and perfpirable matter.

Another great fyftem of glands, which have very fhort necks, are
the capillary veflels ; by which the infenlible perfpiration is fecreted
on the Ikin ; and the mucus of various confidences, which lubricates
the interftices of the cellular membrane, of the mufcular fibres, and
of all the larger cavities of the body. From the want of a long con-
volution of veffels fome have doubted, whether thefe capillaries lliould
be confidered as glands, and have been led to conclude, that the per-
fpirable matter rather exuded than was fecreted. But the fluid of
perfpiration is not fimple water, though that part of it which exhales
into the air may be fuch ; for there is another part of it, which in a
ftate of health is abforbed again ; but which, when the abfcrbents are

^ difeafed.

262 OF THE CIRCULATORY SYSTEM. Sect. XXIII. 3. 4,

dlfeafed, remains on the furface of the fkin, in the form of fcurf, or
indurated mucus. Another thing, which fhews their fimiUtude to
other glands, is their fenfibility to certain afFeftions of the mind ; as
is feen in the deeper colour of the Ikin in the blufti of fhame, or the
greater palenefs of it from fear.

III. Another feries of glandular velTels is called the abforbent
fyftem ; thefe open their mouths into all the cavities, and upon all
thofe furfaces of the body, where the excretory apertures of the
other glands pour out their fluids. The mouths of the abforbent
fyftem drink up a part or the whole of thefe fluids, and carry them,
forwards by their living power to their refpective glands, which are
called conglobate glands. There thefe fluids undergo fome change,
before they pafs on into the circulation ; but if they are very acrid,
the conglobate gland fwells, and fometimes fuppurates, as in inocu-
lation of the fmall-pox, in the plague, and in venereal abforptions ;
at other times the fluid may perhaps continue there, till it undergoes
fome chemical change, that renders it lefs noxious ; or, what is more
likely, till it is regurgitated by the retrograde motion of the gland in
fpontaneous fweats or diarrhoeas, as difagreeing food is vomited from
the ftomach.

IV. As all the fluids, that pafs through thefe glands, and capillary
veiTels, undergo a chemical change, acquiring new combinations,
the matter of heat is at the fame time given out ; this is apparent,
fince whatever increafes infenfible perfpiration, increafes the heat of
the flcin ; and when the aftion of thefe veflels is much increafed but
for a moment, as in blulhing, a vivid heat on the Ikin is the immedi-
ate confequence. So when great bilious fecretions, or thofe of any
other o-land, are produced, heat is generated in the part in proportion
to the quantity of the fecretion.

The heat produced on the flcin by blufliing may be thought by
fome too fudden to be pronouaced a chemical efFed, as the fermenta-
tions

Sect. XXIII. 5. OF THE CIRCULATORY SYSTEM. 263

tions or new combinations taking place in a fluid is in general a flower
procefs. Yet are there many chemical mixtures in which heat is
given out as infl:antaneoufly ; as in folutions of metals in acids, or in
mixtures of eflential oils and acids, as of oil of cloves and acid of
nitre. So the bruifed parts of an unripe apple become almoft inflan-
taneoufly fweet ; and if the chemico-animal procefs of digeftion be
flopped for but a moment, as by fear, or even by voluntary eruda-
tion, a great quantity of air is generated, by the fermentation, which
infl:antly fucceeds the fl:op of digeftion. By the experiments of Dr.
Hales it appears, that an apple during fermentation gave up above fix
hundred times its bulk of air ; and the materials in the ftomach are
fuch, and in fuch a lituation, as immediately to run into fermenta-
tion, when digeftion is impeded.

As the blood pafles through the fmall vefl™els of the lungs, which
conne£l the pulmonary artery and vein, it undergoes a change of co-
lour from a dark to a light red ; which may be termed a chemical
change, as it is known to be efFefted by an admixture of oxygene,
or vital air; which, according to a difcovery 'of Dr. Prieftley, pafles
through the moift membranes, which conftitute the fides of thefe
veflels. As the blood pafles through the capillary veflels, and glands,
which connedl the aorta and its various branches with their corre-
fpondent veins in the extremities of the body, it again lofes the bright
red colour, and undergoes fome new combinations in the glands or
capillaries, in which the matter of heat is given out from the fecreted
fluids. This procefs therefore, as well as the procefs of refpiration,
has fome analogy to combuftion, as the vital air or oxygene feems to
become united to fome inflammable bafe, and the matter of heat
efcapes from the new acid, which is thus produced.

V. After the blood has pafled thefe glands and capillaries, and
parted with whatever they chofe to take from it, the remainder is re-
ceived by the veins, which are a fet of blood-abforbiiig veflels in ge-
neral

264 OF THE CIRCULATORY SYSTEM. Sect.XXIIL 6.

neral correfponding with the ramifications of the arterial fyftem. At
the extremity of the fine convolutions of the glands the arterial force
ceafcs ; this in refpe^l to the capillary veffels, which unite the extre-
mities of the arteries with the commencement of the veins, is evident
to the eye, on viewing the tail of a tadpole by means of a folar, or
even by a common microfcope, for globules of blood are feen to en-
deavour to pafs, and to return again and again, before they become
abforbed by the mouths of the veins ; which returning of thefe glo-
bules evinces, that the arterial force behind them has ceafed. The
veins are furnifhed with valves Ijike the lymphatic abforbents ; and
the great trunks of the veins, and of the ladleals and lymphatic, join
together before the ingrefs of their fluids into the left chamber of the
heart J both which evince, that the blood in the veins, and the lymph
and chyle in the lafleals and lymphatics, are carried on by a fimilar
force; otherwife the flream, which was propelled with a lefs power,
could not enter the veffels, which contained the ftream propelled with
a greater power. From whence it appears, that the veins are a fyftem
of veffels abforbing blood, as the ladteals and lymphatics are a fyftem
of veffels abforbing chyle and lymph. See Setfl. XXVII. i.

VI. The movements of their adapted fluids in the various veffels of
the body are carried forwards by the adlions of thofe veffels in confe-
quence of two kinds of ftimulus, one of which may be compared to a
pleafureabie fenfation or defire inducing the veffel to feize, and, as it
were, to fwallovv the particles thus felefted from the blood; as is
done by the mouths of the various glands, veins, and other abforbents,
which may be called glandular appetency. The other kind of ftimu-
lus rriay be compared to difagreeable fenfation, or averfion, as when
the heart has received the blood, and is ftimulated by it to pufh it for-
wards into the arteries ; the fame again ftimulates the arteries to con-
tract, and carry forwards the blood to their extremities, the glands
and tapillaries. Thus the mefenteric veins abforb the blood from the

jnteftines

Sect.XXIIL 6. OF THE CIRCULATORY SYSTEM. i^{

inteftines by glandular appetency, and carry it forward to the vena por-
tarum ; which adling as an artery contrails itfelf by difagreeable fti-
naulus, and puflies it to its ramified extremities, the various glands,
which conftitute the liver.

It feems probable, that at the beginning of the formation of thefe
veflels in the embryon, an agreeable fenfation was in reality felt by
the glands during fecretion, as is now felt in the a<3: of fwallowing
palatable food; and that a difagreeable fenfation was originally felt by
the heart from the diftention occafioned by the blood, or by its che-
mical ftimulus; but that by habit thefe are all become irritative mo-
tions; that is, fuch motions as do not afFedl the whole fyflem^ except
wiien the veflels are difeafed by inflammation.

Mm SECT.

M OF THE SALIVA AND TEARS. Sect. XXI V.x,

SECT. XXIV.

OF THE SECRET 10 N-S OF SALIVA^ AND OF TEARS, ANU OF
THE LACRYMAL SACK,.

1^ Secretion ofjaliva increqfed by mercury in the blood', i.. By the food in the mouth,
Drynefs of the mouth not from a deficiency of f diva.. 2. Byfenfitive ideas. 3..
By volition.^ 4. By dijiafteful fubftances. Itisfecreted in a dilute and /aline-
fiate. It then becomes more vifcid. 5. By ideas of difi:aftefuljubfiances. 6. By
natifea. 7. By averfton. 8. By catenation, 'with ftimulating fubftances in the-.
ear. II. i. Secretion, of tears lefs in Jleep. From Jlimulation of their excretory
du^. 1. Lacrymal fack is a gland.. 3. J/j «/&j. 4. 'T!ears are fecreted^,
when the nafal du5l is Jiimulated. 5. Or when it is excited by fenfation. 6,.
Or by volition, j. "The lacrymal fack can regurgitate its contents into the eye..
8. More tears are fecreted by affociation with the irritation of the nafal duSl of
the lacrymal fack., than, the punSfa lacrymalia can imbibe. Of the gout in the:
liver and ftomachi

I. THE falival glands drink up a certain fluid from the circumflu-
ent bloo'd,. and pour it into the mouth. They are fometimes ftimulatedi
into a£lion by the blood, that furrounds their origin,- or by fome part:
of that heterogeneous fluid : for when mercurial falts, or oxydes, are
mixed with the blood, they ftimulate thefe glands into unnatural ext-
ertions ; and then an unufual quantity of faliva is feparated.

As the faliva fecreted by thefe glands is moft wanted during the
maftication of our food, it happens, when the terminations of their
dufts in the mouth, are ftimulated into adion, the falival glands them-

3 felves

Sect. XXIV. I. OF THE SALIVA AND TEARS. 267

felves arc brought into increafed aftion at the fame time by aflbciation,
and feparate a greater quantity of their juices from the blood ; in the
iame manner as tears are produced in greater abundance during the
flimulus of the vapour of onions, or of any other acrid material in the
eye.

The faliva is thus naturally poured into the mouth only during the
flimulus of our food in maftication ; for when there is too great an ex-
halation of the mucilaginous fecretion from the membranes, which
line the mouth, or too great an abforption of it, the mouth becomes
dry, though there is no deficiency in the quantity of faliva ; as in thofc
who deep with their mouths open, and in fome fevers.

2. Though during the maftication of our natural food the falival
glands are excited into action by the ftimulus on their excretory du£lSj
and a due quantity of faliva is feparated from the blood, and poured
into the mouth ; yet as this maftication of our food is always attended
with a degree of pleafure; and that pleafureable fenfation is alfb con-
iie<9;ed with our ideas of certain kinds of aliment ; it follows, that
when thefe ideas are reproduced, the pleafureable fenfation arifes
along with them, and the falival glands are excited into aftion, and
fill the mouth with faliva from this fenfitive aftbciation, as is frequent-
ly feen in dogs, who flaver at the fight of food.

3. We have alfo a voluntary power over the adibri of d\efc falival^
glands, for we can at any time produce a flow of faliva intoour mouth,'
and fpit out, or fwallow it at will.

4^ If any very acrid material be held in the mouth, as the root of
py^-ethrum, or the leaves of tobacco, the falival glands are ftimulated"*
into ftronger action than is natural, and thence fecrete a much larger
quantity of faliva; which is at the fame tirtie more vifcid than in its
natural ftate J becaufe the lymphatics, that open their mouths into
the dufts of the falival glands, and on the membranes, which line the
iaioBth, are likewifeftimulated into ftronger adion, and abforb the-

. M m 2 more

268 OF THE SALIVA AND TEARS. Sect. XXIV. r^

more liquid parts of the faliva with greater avidity j and the remainder
is left both, in greater quantity and more vifcidv

The increafed abforption in the mouth- by fome ftimuiating fub»
fiances, which are called aftringents, as crab juice, is evident from^
the inftant drynefs produced in the mouth by a fmall quantity of
them..

As the extremities of the glands are of exquifite tenuity, as appears-
by their difficulty of injedlion, it was neceffary for them to fecrete
their fluids in a very dilute ftate ; and, probabdy for the purpofe of
ftimuiating them into a£tion, a quantity of neutral fait is like wife fe*
Greted or formed by the gland. This aqueous and faline part of all
fecreted fluids is again reabforbed into the habit.. More than half of
fome fecreted fluids is thus imbibed from the refervoirs, into which,
they are poured ; as in the urinary bladder much more than half of
what is fecreted by the kidneys becomes reabforbed by the lymphaticsy.
which are thickly difperled around the neck- of the bladder. This,
feems to be the purpofe of the urinary bladders of fifh, as otherwife:
fuch a receptacle for the urine could have been of no ufe to an- animal-,
immerfed in water.

,5. The idea of fubffances difagreeably acrid will alfo produce as.
quantity of faliva in the mouth ; as when we fmell very putrid va-
pours,, we. are induced to fpit out our faliva, as if fomething difagree---
able was actually upon our palates.

6. When difagreeable food in the ftomach produces naufea^ a flow-'
of faliva is excited in the mouth by affociation ;, as efforts to vomit are
frequently produced by difagreeable drugs in the mouth by the fame
kind of alfociation.

7. A preternatural flow of faliva is likewife fometimes occafioned?
by a difeafe of the voluntary power; for if we think about our faliva* ,
and determine not to fwallow it, or not to fpit it out, an exertion is
produced by the will, and more faliva; is fecreted againft our wifh ;=

that-

Sect. XXIV. 2. OF THE SALIVA AND TEARS. 2^9

that is, by our averfion, which bears the fame analogy to defire, as
pain does to pleafure ; as they are only modifications of the fame dif-
pofition of the fenforium. See Clafs- IV. 3. 2. r.

8. The quantity of faliva may alfo be increafed beyond what is na-
tural, by the catenation of the motions of thefe glands with other mo-
tions, or fenfations, as by an extraneous body in the ear j of which I
have known an inftance ; or by the application of flizolobium, fdiqua-
h-irfuta, cowhage, to the feat of the parotis, as fome writers have af^
firmed .-

II. I. The lacrymal gland drinks up a certain fluid from the cir-
cumfluent blood, and pours it on the ball of the eye, on the upper
part of the external corner of the eyelids. Though it may perhaps
be ftimulated into the performance of its natural adion by the blood,,
which furrounds its origin, or by fome part of that heterogeneous
fluid ;■ yet as the tears fecreted by this gland are more wanted at fome^
times than at others, its fecretion is variable, like that of the faliva:
above mentioned, and is chiefly produced when it's excretory du(5l is-
ftiraulated'; for in our common fleep there feems to be little or no fe-
cretion of tears ; though they are occafionally produced by our fenia—
tions in dreams.

Thus when any extraneous material on the eye-ball, or thedrynefs
of the external covering of it, or the coldnefs of the air, or the acri-
mony of fome vapours, as of onions, Simulates the excretory dudl of
the lacrymal gland, it difcharges its contents upon the ball ; a quicker
fecretion takes place in the gland, and abundant tears fucceed; to
moiften, clean, and lubricate the eye. Thefe by frequent nidlitation
are difFufed over the whole baD, and as the external angle of the eye
in winking is clofed fooner than the internal angle, the tears are gra-
dually driven forwards, and downwards from the lacrymal gland to the
punda lacrymalia-.

2. The lacrymal fack, Avith its punfta lacrymalia, and its nafal
dud, is a complete gland; and is Angular in this refped, that it nei-
ther

27® OF THE SALIVA AND TEARS. Sect. XXIV. 2.

ther derives its fluid from, nor difgorges it into the circulation. The
iimplicity of the ftrudure of this gland, and both the extremities of it
tbeing on the furface of the body, makes it well worthy our minuter
obfervation ; as the aftions of more intricate and concealed glands may
'be better underftood from their analogy to this.

3. This fimple gland confifts of two abforbing mouths, a belly, and
an excretory dud. As the tears are brought to the internal angle of
the eye, thefe two mouths drink them up, being ftimuiated into ac-
tion by this fluid, which they abforb. The belly of the gland, or
lacrymal fack, is thus filled, in which the faline part of the tears is
abforbed, and when the other end of the gland, or nafal du<St, is fti-
mulated by the diynefs, or pained by the coldnefs of the air, or af-
fedted by any acrimonious duft or vapour in the noftrils, it is excited
into a€lion together with the fack, and the tears are difgorged upon
the membrane, which lines the noflrils ; where they ferve a fecond
purpofe to moiflen, clean, and lubricate, the organ of fmell.

4^. When the nafal du6l of this gland is Simulated by any very
acrid material, as the powder of tobacco, or volatile fpirits, it not
only difgorges the contents of its belly or receptacle (the lacrymai:
fack), and abforbs haftily all the fluid, that is ready for it in the cor-
ner of the eye ; but by the aflTociation of its motions with thofe of the
lacrymal gland, it excites that alfo into increafed a(5lion, and a large
flpw of tears is poured into the eye,

5. This ri^fal duft is likewife excited into ftrong adion by fenfitive
ideas, as iii grief, or joy, and then alfo by its affociations with the la-
crymal gland.it produces a great flow of tears without any external ftifi
mulus ; as is more fully explained in Se£l. XVI. 8. on Inftind.

6. There are fome, famous in the arts of exciting compa/lion^

who are faid to have acquired a voluntary power of producing a flowi

of tears in the eye ; which, from what has been faid in the fe£lion,on<;

Iqftinfl: abqve.-meritioned, I fliould fufped, is -performed by acqpiring

a voluntary power oyer the adipn of this nafal dwd. .

7. Tliere

S-ECT. XXIV. 2. OF THE SALIVA AND TEARS-. 2 yr

7. There is another circumftance well: worthy our attention, that
when by any accident this nafal du£l is obfl:ru£led, the lacrymal fack,
which is the beliy or receptacle of this gland, by flight preffure of the
finger is enabled to difgorge its contents again into the eye ; perhaps
the bile in the lame manner,, when the biliary dufts are obflrufted, is^
returned- into the blood by the veflels which fecrete it }-

8. A very important though minute occurrence mufl: here be ob-
ferved, that though the lacrymal gland is only excited into a6tion,.
when we weep at a diftrefsful- tale,, by its aflbciation with this nafaL
du£l, as is more fully explained in Sedl. XVI. 8 ; yet the Quantity of"
tears fecreted at once is more than the punfta lacrymalia can readily
abforb; which fhews that the motions occajioned by ajfoeiations are fre-
quently more energetic than the original motions., by which they were oc^
cajioned. Which we fhall have occafion to mention^ hereafter, to il-
luftrate, why pains frequently exift in. a part diftant from the caufe of
them, as in the other end of the urethra, when a ftone ftimulates the
Heck of the bladder. And why inflammations frequently ariie in parts--
diftant from their caufe, as the gutta rofea of drinking people, fram an-,
inflamed liver.

The inflammation of a part is generally preceded by a. torpor or"
quiefcence of it ; if this exifts in any large congeries of glands, as in;
the liver, or any membranous part, as the flomach, pain, is produced,,
and chillinefs in confequence of the torpor of the veflels. In this fitu-
ation fometimes an inflammation of the parts fucceeds the torpor; at:
other times a diflant more fenfible part becomes inflamed ; whofe ac-
tions have previoufly been aflbciated with it; and the torpor of the firft.
part, ceaies. This I apprehend happens,, when the gout of the foot
fucceeds a pain of the biliary duft, or of the flomach. Laflly, it fome-
times happens, that the pain of torpor exifts without any confequent
inflammation of the afFe£led part, or of any diftant part aflbciated with:
it, as in the membranes about the temple and eye-brows in hemicra—
nia,, and in thofe pains, which occafion convulfioas ; if this happens

372 -OF THE SALIVA AND TEARS. Sect. XXIV. z.

to gouty people, when it afFe£ls the liver, I fuppofe epileptic fits are
•produced ; and, when it afFedts the ftomach, death is the confequence.
In thefe cafes the pulfe is weak, and the extremities cold, and fuch
medicines as ftirciulate the quiefcent parts into action, or which induce
inflamnnation in them, or in -any diftant part, which is affociated with
them, cures the prefent pain of torpor, and faves the patient.

I have twice feen a gouty inflammation of the liver, attended with
jaundice ; the patients after a few days were both of them affeded
with cold fits, like ague-fits, and their feet became afFe£ted with gout,
^nd the inflammation of their livers ceafed. It is probable, that the
uueafy fenfations about the ftomach, and indigeftion, which precedes
gouty paroxyfms, are generally owing to torpor or flight inflammation
of the liver, and biliary, du£l:s; but where great pain with continued
iicknefs, with feeble pulfe, and fenfation of cold, affedt the ftomach in
•patients debilitat-ed by the gout, that it is a torpor of the ftomach itfelf,
and deftroys the patient from the great connexion of that vifcus with
ihe vital organs. See Se£l. XXV. ly.

SECT.

Sect.XXV. r. STOMACH AND INTESTINES, 273

SECT. XXV,

OF THE STOMACH AND INTESTINESc

X. Ofjwallowing our food. Ruminating animals. 2. Aciion of the flomach. 3,
ASfion of the intejiines. Irritative motions connected with theje. 4. EffeSis of
repletion. 5. Stronger aSfion of the flomach and intefiines from more flimulating
food. 6. Their aSlion inverted by flill greater Jlimuli. Or by dijgtiftfid ideas.
Or by volition, 7. Other glands flrengthen or invert their motions by fympathy.
8. Vomiting performed by intervals. 9. Inverfton of the cutaneous ahforbents.
10. Increafedjecretion of bile a.nd pancreatic juice. 11. Inverfionofthe laSfeals.
12. And of the bile-du£ls. 13. Cafe of a cholera. 14. Further account of
the inverfton of la£feals. 15. Iliac paffion. Valve of the colon. .16. Cure of
the iliac paffion. 17. Tain of gall-fione diftinguifhed from pain of the flomach.
Gout of the flomach from torpor, from inflammation. Intermitting pvJfe owing to
indigefion. To overdofe of foxglove. Weakpulfe from emetics. Death from a
hlotx) m thejlomach. From gout of the Jiomach,

I. THE throat, flomach and inteilincs, may be confidered as
one great gland; which, like the lacrymal fack above mentioned, nei-
ther begins nor ends in the circulation. Though the ztk. of mafticat-
ing our aliment belongs to the fenfitive clafs of motions, for the plea-
ilire of its tafte induces the mufcles of the jaw into adlion; yet the
deglutition of it when mafticated is generally, if not always, an irrita-
tive motion, occalioned by the application of the food already mafti-
cated to the origin of the pharix ; in the fame manner as we often,
fwallow our fpittle without attending to it.

N a The

274 STOMACH AND INTESTINES. Sect. XXV. 2.3- 4<.

The ruminating clafs of animals have the power to invert the mo-
tion of their gullet, and of their firft ftomach, from the ftimulus of
this aliment, when it is a little further prepared ; as is their dailjr
pradice in chewing the cud ; and appears to the eye of any one, wha.
attends to them, whilfl they are employed in this fecond maftication,
of their food,

2. When our natural aliment arrives into the ftomach, this organ is-
ftimulated into its proper vermicular aftion ; which beginning at the
upper orifice of it, and terminating at the lower one, gradually mixes^
together and pufhes forwards the digefting materials into the inteftinc
beneath it.

At the fame time the glands, that fupply the gaftric juices, whicb
are neceflary to promote the chemical part of the procefs of digeflion^
are ftimulated to difcharge their contained fluids, and to feparate a
further fupply from the blood-veflels i and the lafteals or lymphatics,^
which open their mouths into the ftomach, are ftimulated into adtion,,
and take up fome part of the digefting materials.

3. The remainder of thefe digefting materials is carried forwards-
into the upper inteftines, and ftimulates them into their periftaltic-
motion iimilar to that of the ftomach ; which continues gradually to
mix the changing materials, and pafs them along through the valve-
of the colon to the excretory end of this great gland, the fphiuder-

ani.

The digefting materials produce a flow of bile, and of pancreatic
juice, as they pafs along the duodenum, by ftimulating the excretory
du6ls of the liver and pancreas, which terminate in that inteftine : and
other branches of the abforbent or lymphatic fyftem, called ladeals^
are excited to drink up, as it paffes, thofe parts of the digefting me-
terials, that are proper for their purpofe, by its ftimulus on their
mouths.

4. When the ftomach and inteftines are thus filled with their pro-
per food, not only the motions of the gaftric glands> the pancreas,.

liver,

Sect. XXV. 5- 6. STOMACH AND INTESTINES. 275

liver, and ladleal veffels, are excited into aftion ; but at the fame time
the whole tribe of irritative motions are exerted with greater energy,
a greater degree of warmth, colour, plumpnefs, and moifture, is given
to the Ikin from the increafed a£lion of thofe glands called capillary
veffels ; pleafureable fenfation is excited, the voluntary motions are
lefs eafily exerted, and at length fufpended; and fleep fucceeds, un-
lefs it be prevented by the ftimulus of furrounding objects, or by vo-
luntary exertion, or by an acquired habit, which was originally pro-
duced by one or other of thefe circumftances, as is explained in Sed:.
XXI. on Drunkennefs.

At this time alfo, as the blood-veflels become replete with chyle,
more urine is feparated into the bladder, and lefs of it is reabforbed ;
more mucus poured into the cellular membranes, and lefs of it re-
abforbed ; the pulfe becomes fuller, and fofter, and in general quicker.
The reafon why lefs urine and cellular mucus is abforbed after a full
meal with fufficient drink is owing to the blood-veffels being fuller :
hence one means to promote abforption is to decreafe the refiftance by
emptying the veffels by venefe£lion. From this decreafed abforption
the urine becomes pale as well as copious, and the Ikin appears plump
as well as florid.

By daily repetition of thefe movements they all become conneded
together, and make a diurnal circle of irritative adlion, and if one of
this chain be difturbed, the whole is liable to be put into diforder. See
Sea. XX. on Vertigo.

5. When the flomach and inteftines receive a quantity of food,
•whofe ftimulus is greater than ufual, all their motions, and thofe of
the glands and lymphatics, are ftimulated into ftronger action than
ufual, and perform their offices with greater vigour and in lefs time :
fuch are the effe6ts of certain quantities of fpice or of vinous fpirit.

6. But if the quantity or duration of thtfe ftlmuli are flill further
increafed, the ftomach and throat are Simulated into a motion, whofe
■^ireftion is contrary to the natural one above defcribed ; and they re-

N n 2 gurgitate

276' STOMACH AND INTESTINES. SECT.XXV.7;

gurgitate the materials, which they contain^ inftead of carrying them
forwards. This retrograde motion of the ftomach may be compared
to the ftretchings of wearied limbs the contrary way, and is well elu-
cidated by the following experiment.. Look earneftly for a minute or
two on an area an inch fquare of pink filk, placed in a ftrong light,
the eye becomes fatigued, the colour becomes faint, and at length
vanifhes, for the fatigued eye can no longer be ftimulated into dired!
motions -^ then on clofing the eye a green fpeilrum will appear in it^
which is a colour direftly contrary to pink, and which will appear
and difappear repeatedly, like the efforts in vomitings See Se<flioa
XXIX. II.

Hence all thofe drugs, which by their bitter or aftringent ftimurus
increafe the a6lion of the ftomach, as camomile and white vitriol, tf
their quantity is iucreafed above a certain dofe become emetics*

Thefe inverted motions of the ftomach and throat are generally
produced from the ftimulus of unnatural food, and are attended with
the fenfation of naufea or ficknefs : but as this fenfation is again con*-
ne6;ed with an idea of the diftafteful food, which induced it ; fo an:
idea of naufeous food will alfo fometimes excite the a6tion of naufea r
and that give rife by aflbciation to the inverfion of the motions of the
ftomach and throat. As fome, who have had horfe-flefti or dogs-
flefli given them for beef or mutton, are faid to have vomited many-
hours afterwards, when they have been told' of the impofition.

I have been told of a perfbn, who had gained- a voluntary command'
over thefe inverted motions of the ftomach- and throat, and fupported
himfelf by exhibiting this curiofity to the public. Atthefe exhibitions
he fw allowed a pint of red rough goofeberries, and a pint of white
fmooth ones, brought them up in fmall parcels into his mouth, and
reftored them feparately to the fpedators, who called for red or white
as they pleafed, till the whole were redelivered.

y. At the fame time that thefe motions of the ftomach and throat
are ftimulated int-o inverlionj fome of the other irritative motions,

that

Sect. XXV. 8.9. 10. STOMACH AND INTESTINES. 27;

that had acquired more immediate connexions with the flomach, as
thofe of the gaftric glands, are excited into ftronger aftion by this
aflbciation ; and fome other of thefe motions, which are more eafily
excited, as thofe of the gaftric lymphatics, are inverted by their aflb-
ciation with the retrograde motions of the flomach, and regurgitate
their contents, and thus a greater quantity of mucus, and of lymph,
or chyle, is poured into the flomach^ and thrown up along with its
contents.

8. Thefe inverlions of the motion of the ftomach in vomiting are
performed by intervals, for the fame reafon that many other motions
are reciprocally exerted and relaxed ; for during the time of exertioa
the ftimulus, or fenfation, which caufed this exertion, is not per-
ceived ; but begins to be perceived again, as foon as the exertioa
ceafes, and is fome time in again producing its efFecfl. As explained.
in Seel. XXXIV. on Volition, where it is fhewn,. that the contrac-
tions of the fibres, and the fenfation of pain, which occafioned that
exertion, cannot exift at the fame time. The exertion ceafes froin
another caufe alfo, which is the exhauftion of the fenforial power of
the part, and thefe two caufes frequently operate together.

9. At the times of thefe inverted efforts of the flomach not only
the lymphatics, which open their mouths into the flomach,^ but thofe
of the fkin alfo, are for a time inverted ; for fweats are fometimes.
pufhed out during the efforts of vomiting without an increafe o£
heat.

10. But if by a greater fflmulus the motions of the flomach are in-
verted ftill more violently or more permanently, the duodenum has.
its periflaltic motions inverted at the fame time by their affociation.
with thofe of the flomach ; and the bile and pancreatic juice, which
it contains, are by the inverted motions brought up into the flomach,
and difcharged along with its contents ; while a greater quantity
of bile and pancreatic juice is poured into this intefline ; as the

glands,.-

37B STOMACH AND INTESTINES. Sect.XXV. i i. 12. 13.

glands, that fecrete them, are by their affociation with the motions of
the inteftine excited into Wronger aftion than ufual.

11. The other inteftines are by affociation excited into more power-
fial adlion, while the lymphatics, that open their mouths into them,
fuffer an inverfion of their motions correfponding with the lymphatics
of the ftomach, and duodenum ; which with a part of the abundant
lecretion of bile is carried downwards, and contributes both to ffimu-
late the bowels, and to increafe the quantity of the evacuations.
This inverfion of the motion of the lymphatics appears from the
quantity of chyle, which comes away by ftools ; which is otherwifc
abforbed as foon as produced, and by the immenfe quantity of thin
fluid, which is evacuated along with it.

12. But if the ftimulus, which inverts the ftomach, be ftill more
powerful, or more permanent, it fometimes happens, that the motions
of the biliary glands, and of their excretory duds, are at the fame
time inverted, and regurgitate their contained bile into the blood-vef-
fels, as appears by the yellow colour of the Ikin, and of the urine;
and it is probable the pancreatic fecretion may fuffer an inverfion at
the fame time, though we have yet no mark by which this can be
afcertained.

13. Mr. eat two putrid pigeons out of a cold pigeon-pye,

and drank about a pint of beer and ale along with them, and immedi-
ately rode about five miles. He was then feized with vomiting,
which was after a few periods fucceeded by purging ; thefe con-
tinued alternately for two hours ; and the purging continued by
intervals for fix or eight hours longer. During this time he
could not force himfeif to drink more than one pint in the
whole, this great inability to drink was owing to the naufea, or
inverted motions of the flomach, which the voluntary exertion
of fwallowing could feldom and with difficulty overcome ; yet
he difcharged in the whole at leafl fix quarts ; whence came this

3 quantity

Sect.XXV. 14. r^. STOMACH AND INTESTINES. ay?.

quantity of liquid ? Firft, the contents of the flonnach were emitted,,
then of the duodenum, gall-bladder, and pancreas, by vomitings
After this the contents of the lower bowels, then the chyle, that was.
in the lacteal veffels, and in the receptacle of chyle, was regurgitated
into the inteftines by a retrograde motion of thefe veffels. And after-
wards the mucus depofited in tiie cellular membrane,, and on the fur-
face of all the other membranes, feems to have been abforbed ; and
■with the fluid abforbed from the air to have been carried up their re-
fpedlive lymphatic branches by the increafed energy of their natural
motions, and down the vifceral lymphatics, or lafteals, by the inver-
fion of their motions.

14. It may be difficult to invent experiments to demonffrate the
truth of this inverfion of fome branches of the abforbent fyftem, and
increafed abforption of others, but the analogy of thefe veffels to the
inteftinal canal, and the fymptoms of many difeafes, render this opi-
nion more probable than many other received 'opinions of the animal
ceconomy.

In the above Inftance, after the yellow excrement was voided, the
fluid ceafed to have any fmell, and appeared like curdled milk, and
then a thinner fluid, and fome mucus, were evacuated : did not
thefe feem to partake of the chyle, of the mucus fluid from all the
cells of the body, and laftly, of the atmofpheric moifture ? All
thefe fadls may be eafily obferved by any one, who takes a brific
purge.

15. Where the ftimulus on the ftomach, or on fome other part of
the inteffinal canal, is ffill more permanent, not only the ladleal vef-
fels, but the whole canal itfelf, becomes inverted from its affocia-
tious : this is the iliac paffion, in which all the fluids mentioned
above are thrown up by the mouth. At this time the valve in the
colon, from the inverted motions of that bowel, and the inverted ac-
tion of this living valve, does not prevent the regurgitation of its
contents.

The

28o STOMACH AND INTESTINES. Sect. XXV. 15.

The {l:ru6ture of this valve may be reprefented by a flexile leathern
pipe {landing up from the bottom of a veffel of water : its fides col-
lapfe by the preffure of the ambient fluid, as a fmall part of that fluid
paffes through it ; but if it has a living power, and by its inverted ac-
tion keeps itfelf open, it becomes like a rigid pipe, and will admit the
whole liquid to pafs. See Se£l. XXIX. 2. 5.

In this cafe the patient is averfe to drink, from the conflant inver-
fion of the motions of the flomach, and yet many quarts are daily
ejefted from the ftomach, which at length fmell of excrement, and
at lafl feem to be only a thin mucilaginous or aqueous liquor.

From whence is it pofllble, that this great quantity of fluid for
many fuccefllve days can be fupplied, after the cells of the body have
given up their fluids, but from the atmofphere ? When the cutaneous
branch of abforbents a6ls with unnatural ftrength, it is probable the
inteftinal branch has its motions inverted, and thus a fluid is fupplied .
without entering the arterial fyftem. Could oiling or painting the
Ikin give a check to this difeafe ?

So when the ftomach has its motions inverted, the lymphatics of
the ftomach, which are moft ftridly affociated with it, invert their
motions at the fame time. But the more diftant branches of lympha-
tics, which are lefs ftriftly affociated with it, a£t.with increafed ener-
o-y ; as the cutaneous lymphatics in the cholera, or iliac paflion, above
defcribed. And other irritative motions become decreafed, as the
pulfatlons of the arteries, from the extra-derivation or exhauftion of
the fenforial power.

Sometimes when ftronger vomiting takes place the more diftant
branches of the lymphatic fyftem invert their motions with thofe of
the ftomach, and loofe ftools are produced, and cold fweats.

So when the ladteals have their motions inverted, as during the,
operation of ftrong purges, the urinary and cutajieous abforbents have
their motions increafed to fupply the want of fluid in the blood, as in
great thirftj but after a meal with fufficient potation the urine is pale,

that

Sect. XXV. i 6. 1 7. STOMACH AND INTESTINES. 28 1

that is, the urinary abforbents a6l weakly, no fupply of water being
wanted for the blood. And when the inteftinal. abforbents zGt too
violently, as when too great quantities of fluid have been drank, the
iirinary abforbents invert their motions to carry off the fuperfluity,
which is a new circumftance of affociation, and a .temporary diabetes
fupervenes.

16. I have h^d the opportunity of feeing four patients in the iliac
paflion, where the ejefted material fmelled and looked like excrement.
Twoof thefe were fo exhaufted at the time I faw them, that more
blood could not be taken from them, and as their pain had ceafed, and
they continued to vomit up every thing which they drank, I fufpeded
that a mortification of the bowel had already taken place, and as they
were both women advanced in life, and a mortification is produced
with lefs preceding pain in old and weak people, thefe both died.
The other two, who were both young men, had ftill pain and
iftrength fufficient for further venefedion, and they neither of them
had any appearance of hernia, both recovered by repeated bleeding,
and a fcruple of calomel given to one, and half a dram to the other,
in very fmall pills: the ufual means of clyfters, and purges joined
with opiates, had been in vain attempted. I have thought an ounce
or two of crude mercury in lefs violent difeafes of this kind has been
of ufe, by contributing to reftore its natural motion to fome part of
the inteftinal canal, either by its weight or ftimulus ; and that hence
the whole tube recovered its ufual affociations of progreffive periftaltic
motion. I have in three cafes feen crude mercury given in fmall
dofes, as one or two ounces twice a day, have great efFe£tin flopping
pertinaceous vomitings.

1 7. Befides the aff'edions above defcribed, the ftomach is liable,
like many other membranes of the body, to torpor without confequent
inflammation : as happens to the membranes about the head in fome
cafes of hemicrania, or in general head-ach. This torpor of the fto-

O o mach

282 STOMACH AND INTESTINES. ' Sect. XXV. 17,.

mach is attended with indigeftion, and confequent flatulency, and
with pain, which is ufually called the cramp of the- ftomach, and is
relievable by aromatics, eflential oils, alcohol^ ot opium.

The intrufion of a gall-ftone into the common bile-du£t from
the gall-bladder is fometimes miftaken for a pain of the ftomach,.
as neither of them are attended with fever ;. but in the paflage of a
gall-ftone, the pain is confined to a lefs fpace,^ which is exaftly,/
where the common bile-dudl enters the duodenum, as explained. ia.
Seftion XXX. 3. Whereas in this gaftrodynia the pain is
difFufed over the whole ftomach ; and, lik€ other difeafes fronst
torpor, the pulfe is weaker,, and the extremities colder, and the ge-
neral debility greater, than in the paflage of a gall-ftone; for in the
former the debility is the confequence of the pain, in the latter it is
the caufe of it.

Though the firft fits of the gout, I believe, commence with a.
torpor of the liver ; and the ball of the toe becomes inflamed inftead
of the membranes of the liver in confequence of this torpor, as a,
coryza or catarrh frequently fucceeds a long expofure of the feet to
cold, as in fnoW, oi" on a moift brick-floor ;.. yet in old or exliaufted
conftitutioHS, which have been long habituated to its attacks, it fome»
times commences with a torpor of the ftomach, and is transferable
to every membrane of the body. When the gout begins with torpor
of the ftomach, a painful fenfation of cold occurs, which the patient
compares to ice, with weak pulfe, cold extremities, and licknefs ;
this in its flighter degree is relievable by fpiee, wine, or opium ;
in its greater degree it is fucceeded by fudden death, which is owing
to the fympathy of the ftomach with the heart, as explained
below.

If the ftomach becomes inflamed in confequence of this gouty
torpor of it, or in confequence of its fympathy with fome other
part, the danger is lefs. A ficknefs and vomiting continues many

3 «3^7s,

Sect.XXV.I7. stomach and intestines. 2S3

•days, or even weeks, the ftomach rejeding every thing ftimulant,
€ven cpiutn or alcohol, together with much vifcid mucus ; till
the inflammation at length ceafes, as happens when other membranes,
as thofe of the joints, are the feat of gouty inflammatioa ; as obferved
in Sed. XXIV. 2.8.

The fympathy, or affociation of motions, between thofe of the
ilomach and thofe of the heart, are evinced in many difeafes. Firft,
many people are occafionally affedled with an intermiffion of their
pulfe for a few days, which then ceafes again. In this cafe there
is a flop of the motion of the heart, and at the fame time a
■tendency to eruiftation from the ftomach. As foon as the patient
feels a tendency to the intermiffion of the motion of his heart, if
lie voluntarily brings up wind from his flomach, the flop of the
heart does not occur. From hence I conclude that the flop of
digeflion is the primary difeafe ; and that air is inftantly generated
from the aliment, which begins to ferment, if the digeflive pro-
cefs is impeded for a moment, (fee Seft. XXIII. 4.) ; and that the
flop of the heart is in confequence of the aflbciation of the motions
of thefe vifcera, as explained in Seft. XXXV. 1.4.; but if the little
air, which is inflantly generated during the temporary torpor of the
flomach, be evacuated, the digeflion recommences, and the tempo-
rary torpor of the heart does not follow. One patient, whom I lately
faw, and who had been five or fix days much troubled with this in-
termiffion of a pulfation of his heart, and who had hemicrania with
fome fever, was immediately relieved from them all by lofing ten
ounces of blood, which had what is termed an inflammatory crufl
on it.

Another inflance of this affociation between the motions of the
ilomach and heart is evinced by the exhibition of an over dofe of
foxglove, which induces an incefTant vomiting, which is attended
with very flow, and fometimes intermitting pulfe. — Which continues

O o 2 in

284 STOMACH AND INTESTINES. Sbct. XXV. 17-.

in fpite of the exhibition of wine and opium for two or three days^
To the fame affociation mufl be afcribed the weak pulfe, which con-
ftantly attends the exhibition of emetics during their operation. And
alfo the fudden deaths, which have been occafioned in boxing by a
blow on the ftomachj and laftly, the fudden death of thofe, wha
have been long debilitated by the gout, from the torpor of the ftomacho.
See Sedt, XXV. i, 4.

SECT.

Sect. XXVI. i. OF GLANDS AND MEMBRANES.. 285

SECT, xxvn

OF THE CAPILLARY GLANDS AND MEMBRANES*

I. I. 'The. capillary vejjels are glands. 2. Their excretory du^s. Experiments on
the mucus of the intejiines, abdomen, cellular membrane, and on the humours of
the eye. 3. Scurf on the head, cough, catarrh, diarrhoea, gonorrhoea. 4.
Rheumatifin. Gout. Leprojy. II. i. The moft minute membranes are un~
organized. 0.. Larger membranes are cor,ipofed of the duSls of the capillaries,
and the mouths of the abf or bents. 3. Mucilaginous fadd is fecreted on their-
furfaces. Ill, Three kinds of rheumatifm.

1. I. THE capillary veffek are like all the. other glands except
the abforbent fyflem, inafmuch as they receive blood from the ar-
teries,, feparate. a fluid from it, and return the remainder by the
veins.

2. This feriesof glands is of the moft extenlive ufe, as their ex-
cretory dufts open on the whole external Ikin forming its perfpirative
pores,, and on the internal furfaces of every cavity of the body. Their
fecretion on the fkia is termed infenfible perfpiration, which in health
is in part reabforbed by the mouths of the lymphatics, and in part
evaporated in the air ; the fecretion on the membranes, which line the
larger cavities of the body, which have external openings, as the
mouth and inteftinal.caual, is termed mucus, but is not however co-
agulable by heat ; and the fecretion on the membranes of thofe cavi-
ties of the body, which have no external openings, is called lymph or

water,

286 GF GLANDS AND MEMBRANES. Sect. XXVI. 2.

water, as in the cavities of the cellular membrane, and of the abdo-
men ; this lymph however is coagulable by the heat of boiling wa-
ter. Some, mucus nearly as vifcid as the white of egg, which was
difcharged by ftool, did not coagulate, though I evaporated it to one
fourth of the quantity, nor did the aqueous and vitreous humours of a
fheep's eye coagulate by the like experiment : but the feroiity from
an anafarcous leg, and that from the abdomen of a dropfical perfon,
and the cryftalline humour of a fheep's eye, coagulated in the fame
heat.

3. When any of thiefe capillary glands are flimulated into greater
irritative anions, than is natural, they fecrete a more copious mate-
rial; and as the mouths of the abforbent fyftem, which open in their
vicinity, are at the fame time flimulated into greater aftion, the
thinner and more faline part of the fecreted fluid is taken up again;
and the remainder is not only more copious but alfo more vifcid thaa
natural. This is more or lefs troublefome or noxious according to the
importance of the functions of the part afFefted: on the Ikin and
bronchiae, where this fecretion ought naturally ,to evaporate, it be-
comes fo vifcid as to adhere to the membrane; on the tongue it forms
a pellicle, which can with difficulty be fcraped off; produces the fcurf
on the heads of many people; and the mucus, which is fpit up by
others in coughing. On the noftrils and fauces, when the fecretion
of thefe capillary glands is increafed, it is termed finaple catarrh.;
when in the inteftines, a mucous diarrhoea,; and in ;the urethra, or
vagina, it has the name of gonorrhoea, or fluor albus.

4. When thefe capillary glands become inflamed, a ftill more vifcid
or even cretaceous humour is produced upon the furfaces of the mem-^
branes, which is the caufe orthe efFe6l of rheumatifm, gout, leprofy,
and of hard tumours of the legs, which are generally termed fcorbutic;
all which will be treated of hereafter.

H. I . The whole furface of the body, with all its cavities and con-

.tentSc,

Sect. XXVI. 2. OF GLANDS AND MEMBRANES. 287

tents, are covered with membrane. It lines every veffel, forms every
cell, and binds together all the mufcular and perhaps the ofTeous fibres
of the bodyi and is itfelf therefore probably a fimpler fubftance than
thofe fibres. And as the containing veflels of the body from the
krgeft to the leaft are thus lined and connefted with membrnines, it
follows that thefe membranes themfelves confided of unorganized
materials.

For however fmall we may conceive the diameters of the minuteft
veflels of the body, which efcape our eyes and glafles, yet thefe vef-
fels muft confift of coats or fides, which are made up of an unorga-
nized material, and which are probably produced from a gluten,
which hardens after its produdlion, like the filk or web of caterpillars
and fpiders. Of this material confift the membranes, which line the
Ihells of eggs, and the fliell itfelf, both which are unorganized, and
are formed from mucus, which hardens after it is formed, either by the
abforption of its more fluid part, or by its uniting with fome part of
the atmofphere. Such is alfo the produ£lion of the fhells of fnails,
and of fliell-fifh, and I fuppofe of the enamel of the teeth.

2. But though the membranes, that compofe the fides of the mofl:
minute veflTels, are in truth unorganized materials, yet the larger
membranes, which are perceptible to the eye, feern to be com-
pofed of an intertexture of the mouths of the abforbent fyftem,
and of the excretory du£ls of the capillaries, with their concomitant
arteries, veins, and nerves : and from this conftruftion it is evident,
that thefe membranes muft poflefs great irritability to peculiar fl:i-
muli,. though they are incapable of any motions, that are vifible to
the naked eye : and daily experience fliews us, that in their inflamed
ftate they have the greatefl: fenfibillty to pain, as in the pleurify and
paronychia.

3. On all thefe membranes a mucilaginous or aqueous fluid is
fecreted, which moiftens and lubricates their furfaces, as was ex-
plained

i88 OF GLANDS AND MEMBRANES. Sect. XXVL 3.

-plained in Sedtion XXIII. 3. Some have doubted, whether this
mucus is feparated from the blood by an appropriated fet of glands,
•or exudes through the membranes, or is an abrafion or deftruc-
tion of the furface of the membrane itfelf, which is continually
repaired on the other fide of it, but the great analogy between
■the capillary veflfels, and the other glands, countenances the former
opinion ; and evinces, that thefe capillaries are the glands, that
fecrete it; to which we muft add, that the blood in paffing
thefe capillary veffels undergoes a change in its colour from
florid to purple, and gives out a quantity of heat ; from whence,
as in other glands, we muft conclude that fomething is fecreted
from it.

III. The feat of rheumatifm is in the mem'branes, or upon them ;
but there are three very diflindl difeafes, which commonly are
confounded under this name. Pirft, when a membrane becomes
affeded with torpor, or inactivity of the veffels which compofe it,
pain and coldnefs fucceed, as in the hemicrania, and other head-
achs, which are generally termed nervous rheumatifm i they exift
whether the part be at reft or in motion, and are generally attended
witli other marks of debility.

Another rheumatifm is faid to exift, wlien inflammation and
fwelling, as well as pain, aiFedt fome of the membranes of the
joints, as of the ancles, wrifts, knees, elbows, and fometimes of
the ribs- This -is accompanied with fever, is analogous to pleu-
rify, and other inflammations, and is termed the acute rheuma-
tifm.

A third difeafe is called chronic rheumatifm, which is diftin-
guiflied from that firft mentioned, as in this the pain only affeds
ihe patient during the motion of .the part, and from the fecond kind
of rheumatifm above defcribed, as it is not attended with quick pulfe
or infl?.mmation. It is generally believed to fucceed the acute rheu-
matifm

Sect. XXVI. 3. OF GLANDS AND MEMBRANES. 289

matifm of the fame part, and that fome coagulable lymph, or creta-
ceous, or calculous material, has been left on the membrane ; which
gives pain, when the mufcles move over it, as fome extraneous body
would do, which was too infoluble to be abforbed. Hence there is
an analogy between this chronic rheumatifm and the difeafes which
produce gravel or gout-ftones ; and it may perhaps receive relief from
the fame remedies, fuch as aerated fal fpda.

SECT,

290 OF HAEMORRHAGES. Sect. XXVII. i.

SECT. XXVII.

OF HEMORRHAGES.

I. The veins are abjorhent vejfels. i. Hemorrhages from inflammation. Cafe of
hemorrhage from the kidney cured by cold bathing. Cafe of hamorrhage from
the nofe cured by cold immerjion. II. Hemorrhage from venous paralyjts. Of
Piles. Black fl:ools. Petechia. Confumption. Scurvy of the lungs. Black-
nefs of the face and eyes in epileptic fits. Cure of hemorrhages from venous
inability.

I. A S the Imbibing mouths of the abforbent fyftem already de-
fcribed open on the furface, and into the larger cavities of the body,
fo there is another fyftem of abforbent veffels, which are not com-
monly efteemed fuch, I mean the veins, which take up the blood
from the various glands and capillaries, after their proper fluids or fe-
cretions have been feparated from it.

The veins refemble the other abforbent veffels j as the progreffion
of their contents is carried on in the fame manner in both, they alike
abforb their appropriated fluids, and have valves to prevent its regur-
gitation by the accidents of mechanical violence. This appears firft,
becaufe there is no pulfation in the very beginnings of the veins, as is
feen by microfcopes ; which muft happen, if the blood was carried
into them by the a£lion of the arteries. For though the concurrence
of various venous ftreams of blood from difl^erent diftances mufl: pre-
vent any pulfation in the larger branches, yet in the very beginnings
of all thefe branches a pulfation mufl unavoidably exift, if the circu-
lation

Sect. XXVII. 1. OF HAEMORRHAGES. 291

lation in them was owins; to the intermitted force of the arteries.
Secondly, the venous abforption of blood from the penis, and from
the teats of female animals after their eredlion, is flill more fimilar to
the lymphatic abforption, as it is previoufly poured into cells, where
all arterial impulfe muft ceafe.

There is an experiment, which feems to evince this venous abforp-
tion, which confifts in the external application of a ftimulus to the
lips, as of vinegar, by which they become iuftantly pale ; that is, the
bibulous mouths of the veins by this ftimulus are excited to abforb the
blood fafter, than it can be fupplied by the ufual arterial exertion. See
Sea. XXIII. 5.

There are two kinds of hemorrhages frequent in difeafes, one is
where the glandular or capillary adlion is too powerfully exerted, and
propels the blood forwards more haftily, than the veins can abforb it ;
and the other is, where the abforbent power of the veins is diminiflied,
or a branch of them is become totally paralytic.

The former of thefe cafes is known by the heat of the part, and
the general fever or inflammation that accompanies the haemorrhage.
An haemorrhage from the nofe or from the lungs is fometimes a crifis
of inflammatory difeafes, as of the hepatitis and gout, and generally
ceafes fpontaneoufly, when the velTels are confiderably emptied.
Sometimes the haemorrhage recurs by daily periods accompanying the
hot fits of fever, and ceafing in the cold fits, or in the intermiffions j
this is to be cured by removing the febrile paroxyfms, which will be
treated of in their place. Otherwife it is cured by venefeftion, by
the internal or external preparations of lead, or by the application of
cold, with an abftemious diet, and diluting liquids, like other inflam-
mations. Which by inducing a quiefcence on thofe glandular parts,
that are affedleJ, prevents a greater quantity of blood from being pro-
truded forwards, than the veins are capable of abforbing.

Mr. B had an hemorrhage from his kidney, and parted with

not lefs than a pint of blood a day (by conjedture) along with his

P p 2 urine

292 OF HiEMORRHAGES. Sect. XXVII. 2.

urine for above a fortnight : venefedtions, mucilages, balfams, pre-
parations of lead, the bark, alum, and dragon's blood, opiates, with a
large blifter on his loins, were feparately tried, in large dofes, to no
purpofe. He was then directed to bathe in a cold fpring up to the
middle of his body only, the upper part being covered, and the
haemorrhage diminifhed at the firft, and ceafed at the fecond im-
merfion.

In this cafe the external capillaries were rendered quiefcent by the
coldnefs of the water, and thence a lefs quantity of blood was cir-
culated through them ; and the internal capillaries, or other glands,
became quiefcent from their irritative affociations with the external
ones ; and the haemorrhage was flopped a fufficient time for the rup-
tured veffels to contraft their apertures, or for the blood in thofe aper-
tures to coagulate.

Mrs. K • had a continued haemorrhage from her nofe for

fome days ; the ruptured veflel was not to be reached by plugs up the
noftrils, and the fenfibility of her fauces was fuch that nothing
could be borne behind the uvula. After repeated venefeftion, and
other common applications, fhe was dire£led to immerfe her whole
head into a pail of water, which was made colder by the addi-
tion of feveral handfuls of fait, and the hemorrhage immediately
ceafed, and returned no more ; but her pulfe continued hard,
and fhe was neceffitated to lofe blood from the arm on the fucceed-
ing day.

Query, might not the cold bath inftantly flop haemorrhages from
the lungs in inflammatory cafes ? — for the fhortnefs of breath of
thofe, who go fuddenly into cold water, is not owing to the
accumulation of blood in the lungs, but to the quiefcence of the
pulmonary capillaries from alTociation, as explained in Section XXXII.

3. 2.

II. The other kind of haemorrhage is known from its being at-
tended with a weak pulfe, and other fymptoms of general debility,

.>> and

Sect. XXVII. 2. OF HEMORRHAGES. 293

and very frequently occurs in thofe, who have difeafed livers, owing
to intemperance in the lafe of fermented liquors. Thefe conftitutions
are fliewn to be liable to paralyfis of the lymphatic abforbents, pro-
ducing the various kinds of dropfies in Seftion XXIX. 5. Now if
any branch of the venous fyftem lofes its power of abforption, the part
fwells, and at length burfls and difcharges the blood, which the ca-
pillaries or other glands circulate through them.

It fometimes happens that the large external veins of the legs
burfl, and effufe their blood ; but this occurs moft frequently in the
veins of the inteflines, as the vena portarum is liable to fuffer from a
fchirrus of the liver oppofing the progreffion of the blood, which is
abforbed from the inteftines. Hence the piles are a fymptom of he-
patic obftruction, and hence the copious difcharges downwards or
upwards of a black material, which has been called melancholia, or
black bile; but is no other than the blood, which is probably difcharged
from the veins of the inteftines.

J. F. Meckel, in his Experimenta de Finibus Vaforum, publifhed
at Berlin, 1772, mentions his difcovery of a communication of a
lymphatic veffel with the gaftric branch of the vena portarum. It
is poffible, that when the motion of the lymphatic becomes retro-
grade in fbme difeafes, that blood may obtain a paflage into it, where
it anaftomofes with the vein, and thus be poured into the inteftines.
A difcharge of blood with the urine fometimes attends diabetes, and
may have its fource in the fame manner.

Mr. A • , who had been a hard drinker, and had the ^utta

rofacea on his face and breaft, after a ftroke of the palfy voided near
a quart of a black vifcid material by ftool : on diluting it with water
it did not become yellow, as it muft have done if it had been inlpiflated
bile, but continued black like the grounds of coffee.

But any other part of the venous fyftem may become quiefcent

or totally paralytic as well as the veins of the inteftines : all which

5 occur

294 OF HEMORRHAGES. Sect. XXVII. 2.

occur more frequently in thofe who have difeafed livers, than in any
others. Hence troublefome bleedings of the nofe, or from the lungs
with a weak pulfe ; hence haemorrhages from the kidneys, too great
menflruation; and hence the oozing of blood from every part of the
body, and the petechias in thofe fevers, which are termed putrid,
and which is erroneoufly afcribed to the thinnefs of the blood : for
the blood in inflammatory difeafes is equally fluid before it coagulates
in the cold air.

Is not that hereditary confumption, which occurs chiefly in dark-
eyed people about the age of twenty, and commences with flight pul-
monary hemorrhages without fever, a difeafe of this kind ? — Thefe
hzemorrhages frequently begin during fleep, when the irritability of
the lungs is not fufficient in thefe patients to carry on the circula-
tion without the afliftance of volition ; for in our waking hours,
the motions of the lungs are in part voluntary, efpecially if any
difficulty of breathing renders the efforts of volition neceflary. See
Clafs I. 2. I. 2. and Clafs III. 2. i. 10. Another fpecies of pulmo-
nary confumption which feems more certainly of fcrophulous origin
is defcribed in the next Sedion, No. 2.

I have feen two cafes of women, of about forty years of age,
both of whom were feized with quick weak pulfe, with difficult
refpiration, and who fpit up by coughing much vifcid mucus mixed
with dark coloured blood. They had both large vibices on their
limbs, and petechia; in one the feet were in danger of mortifica-
tion, in the other the legs were oedematous. To relieve the diffi-
cult refpiration, about fix ounces of blood were taken from one of
them, which to my furprife was fizy, like inflamed blood : they
had both palpitations or unequal pulfations of the heart. They con-
tinued four or five weeks with pale and bloated countenances, and
did not ceafe fpitting phlegm mixed with black blood, and the pulfe
feldom flower than 130 or 135 in a minute. This blood, from its

dark

Sect. XXVII. 2. OF HEMORRHAGES. 295

dark colour, and from the many vibices and petechia, feems to have
been venous blood ; the quicknefs of the pulfe, and the irregularity
of the motion of the heart, are to be afcribed to debility of that part
of the lyftem ; as the extra vafation of blood originated from the de-
fect of venous abforption. The approximation of thefe two cafes to
fea-fcurvy is peculiar, and may allow them to be called fcorbutus pul-
monaUs. Had thefe been younger fubjedls, and the paralyfis of the
veins had only aftefted the lungs, it is probable the difeafe would have
been a pulmonary confumptlon.

Lafl week I faw a gentleman of Birmingham, who had for ten
days laboured under great palpitation of his heart, which was fo dif-
tindlly felt by the hand, as to difcountenance the idea of there being
a fluid in the pericardium. He frequently fpit up mucus ftained with
dark coloured blood, his pulfe very unequal and very weak, with
cold hands and nofe. He could not lie down at all, and for about
ten days paft could not flcep a minute together, but waked perpetually
with great uneafinefs. Could thofe fymptoms be owing to very ex-
tenfive adheiions of the lungs ? or is this a fcorbutus pulmonalis ?
After a few days he fuddenly got fo much better as to be able to fleep
many hours at a time by the ufe of one grain of powder of foxglove
twice a day, and a grain of opium at night. After a few days longer,
the bark was exhibited, and the opium continued with fome wine ;
and the palpitations of his heart became much relieved, and he reco-
vered his ufual degree of health.

In epileptic fits the patients frequently become black in the face,
from the temporary paralyfis of the venous lyftem of this part. I have
known two inftances where the blacknefs has continued many days.

M. P , who had drank intemperately, was feized with the epi-

lepfy when he was in his fortieth year ; in one of thefe fits the white
part of his eyes was left totally black with effufed blood ; which was
attended with no pain or heat, and was in a few weeks gradually ab-
forbed, changing colour as is ufual with vibices from bruifes.

The

296 OF HAEMORRHAGES. Sect.XXVII. 2.

The haemorrhages produced from the inability of the veins to ab-
forb the refluent blood, is cured by opium, the preparations of fteel,
lead, the bark, vitriolic acid, and blifters ; but thefe have the effedb
with much more certainty, if a venefedtion to a few ounces, and a
moderate cathartic with four or fix grains of calomel be premifed>
where the patient is not already too much debilitated ; as one great
means of promoting the abforption of any fluid confifts in previoufly
emptying the veffels, which are to receive it.

SECT.

^ECT. XXVIIl, r. PARALYSIS OP ABSORBENTS. 297

SECT. XXVIII.

OF THE PARALYSIS OF THE ABSORBENT SYSTEM.

I. Parahfis of the laSfeals, atrophy. Dijiajle to animal food. II. Canfe of
dropfy. Caufe of herpes. Mefenteric confimption. Pulmonary conjumption.
Why idcers in the lungs arefo difficult to heal.

THE term paralyfis has generally been ufed to exprefs the
■lofs of voluntary motion, as in the hemiplagia, but may with equal
propriety be applied to exprefs the difobediency of the mufcular
iibres to the other kinds of ftimulus ; as to thofe of irritation or fen-
fation.

I. There is a fpecies of atrophy, which has not been well under-
flood ; when the abforbent vefleis of the ftomach and inteftines have
been long inured to the flimulus of too much fpirituous liquor, they
at length, either by the too fudden omiffion of fermented or fpirituous
potation, or from the gradual decay of nature, become in a certain
degree paralytic ; now it is obferved in the larger mufcles of the body,
■when one fide is paralytic, the other is more frequently in motion,
owing to the lefs expenditure of fenforial power in the paralytic
limbs ; fo in this cafe the other part of the abforbent fy flem afts with
greater force, or with greater perfeverance, in confequence of the
paralyfis of the lafbeals ; and the body becomes greatly emaciated in a
fmall time.

Q^q I have

298 PARALYSIS Off ABSORBENTS. Sect. XXVIII. 2.

I have feen feveral patients iti this difeafe, of v/hich the following
are the circumftances, i. They were men about fifty years of age,
and had lived freely in refpeift to fermented hquors. 2. They loft
their appetite to animal food» 3. They became kiddenty emaciated;
to a great degree. 4. Their flcins were dry and rough. 5. They
coughed and expeftorated with' difficulty a vifcid phlegm. 6. The
membrane of the tongue was dry and red, and liable to become ul-
cerous.

The inability to digeft animal food, and the confequent diftafte to
it, generally precedes the dropfy, and other difeafes, which originate
from fpirituous potation. I fuppofe when the fiomach becomes in-
irritable, that there is at the fame time a deficiency of gaftric acid ;
hence milk feldom agrees with thefe patients> unlefs it be previoufly
curdled,^ as they have not fufficient gaflric acid to curdle it ; and^
hence vegetable food, which is itfelf acefcent, will agree with theic
flomachs longer than animal food, which requires more of the gaftric
acid for its digeftion.

In this difeafe the Ikin is dry from the increafed abforption of the
cutaneous lymphatics, the fat is abforbed from the increafed abforption.
of the cellular lymphatics, the mucus of the lungs is too vifcid to be
eafily fpit up by the increafed- abforption of the thinner parts of it, the.
membrana fneideriana becomes dry, covered with hardened mucus,
and at length becomes inflamed and full of apthae, and either thefe
floughs, or pulmonary ulcers, terminate the fcene.

II. The immediate caufe of dropfy is the paralyfis of fome other
branches of the abforbent fyftem, which are called lymphatics, and'
which open into the larger cavities of the body, or into the cells of
the cellular membrane ; whence thofe cavities or cells become diftend-
ed with the fluid, which is hourly fecreted into them for the purpofe
of lubricating their furfaces. As is more fully explained in No. 5. of
the next Seiliono

Sect. XXVIII. 2. PARALYSIS OF ABSORBENTS. 299

As thofe lymphatic veflels confift generally of a long neck or mouth,
which drinks up its appropriated fluid, and of a conglobate gland, in
which this fluid undergoes fome change, it happens, that fometimes
the mouth of the lymphatic, and fometimes the belly or glandular
part of it, becom-es totally or partially paralytic. In the former cafe,
where the mouths of the cutaneous lymphatics become torpid or qui-
efcent, the fluid fecreted on the flcin ceafes to be abforbed, and
erodes the fkia by its faline acrimony, and produces eruptions termed
herpes, the difcharge from which is as fait, as the tears, which are
fecreted too fafl: to be reabforbed, as in grief, or when the punfta la-
crymalia are obftrudled, and which running down the cheek redden
and inflame the fkin.

When the mouths of the lymphatics, which open on the mucous
membrane of the noftrils, become torpid, as on walking into the
air in a frofty morning ; the mucus, which continues to be fecreted,
has not its aqueous and faline part reabforbed, which runninty over
the upper lip inflames it, and has a fait tafte, if it falls on the
tongue.

When the belly, or glandular part of thefe lymphatics, becomes
torpid, the fluid abforbed by its mouth Magnates, and forms a
tumour in the gland. This difeafe is called the fcrophula. If
thefe glands fuppurate externally, they gradually heal, as tliofe of
the neck; if they fuppurate without an gpening on the external
habit, as the mefenteric glands, a hedlic fever enfues, which de-
ftroys the patient ; if they fuppurate in the lungs, a pulmonary
confumption enfues, which is believed thus to differ from that
defcribed in the preceding SeftLon, in refpeft to its feat or proximate
caufe.

It is remarkable, that matter produced by fuppuration will lie
concealed in the body many weeks, or even months, without pro-
ducing hedic fever ; but as foon as the wound is opened, fo as to

Q^q 2 admit

300 PARALYSIS OF ABSORBENTS; Sect. XXVIII. 2-.

admit air to the furface of the ulcer, a hedtic fever fupervenes, even.
in very few hours, which is probably owing to the azotic part
of the atmofphere rather than to the oxygene ; becaufe thofe me-
dicines, which contain much oxygene, as the calces or oxydes o£
metals, externally applied, greatly contribute to heal ulcers, of thefe
are the folutions of lead and mercury, and copper in acids, or their-
precipitates.

Hence when ulcers are to be healed by the firfl intention, as it is-
called, it is neceflary carefully to exclude the air from them. Hence
we have one caufe, which prevents pulmonary ulcers from healing,,
which is their being perpetually expofed to the air.

Both the dark-eyed patients, which are afFefted with pulmonary
ulcers fi'om deficient venous abforption, as defcribed in SedioiB
XXVII. 2. and the light-eyed patients from deficient lymphatic ab-
forption, which we are now treating of, have generally large aper-
tures of the iris ; thefe large pupils of the eyes are a common mark
of want of irritability ; and it generally happens, that an increafe oi
fenfibility, that is, of motions in confequence of fenfation, attends
thefe conflitutions. See Sedc. XXXI. z. Whence inflammations
may occur in thefe from ftagnated fluids more frequently than ia
thofe conflitutions, which pofTefs more irritability and lefs feii:-

fibility.

Great expectations in refpe6t to the cure of confumptions, as well;
as of many other difeafes, are produced by the very ingenious exer-
tions of Dr. Beddoes ; who has eftablilhed an apparatus for breathing
various mixtures of aii's or gaffes, at the hot-wells near Briflol, which*
well defervcs the attention of the public.

Dr. Beddoes very ingenioufly concludes, from the florid colour of
the blood of confumptive patients, that it abounds in oxygene ; and-
that the rednefs of their tongues, and lips, and the fine biufh of their
cheeks fhew the prefence of the fame principle, like flefh reddened

7 ^^

Sect. XXVIII. 2. PARALYSIS OF ABSORBENTS. 301

by nitre. And adds, that the circumftance of the confumptlons of
pregnant women being flopped in their progrefs during pregnancy,
at which time their blood may be fuppofed to be in part deprived of
its oxygene, by oxygenating the blood of the foetus, is a forceable ar-
gument in favour of this theory ; which muft foon be confirmed or
confuted by his experiments. See Effay on Scurvy, Confumption,
&c. by Dr. Beddoes. Murray. London. Alfo Letter to Dr. Darwin,
by the fame. Murray. London.

SECT,

J02 RETROGRADE ABSORBENTS. Sect. XXIX. u

SECT. XXIX.

fON THE RETROGRADE MOTIONS OP THE ABSORBENT SYSTEM.

I. jiaount of the ahjorhent fyfiem. II. 'the valves of the abjorhent veffels mayfuf-
fer their fluids to regurgitate in fame difeafes. III. Communication from the
alimentary canal to the bladder by means of the abforbent vejfels. IV. The pha~
.nomena of diabetes explained, V. i. "The phenomena of dropfies explained.
2. Cafes of the life of foxglove. VI. Of cold fweats. VII. Tranjlations of
matter, of chyle, of milk, of urine, operation of purging drugs applied external^
ly. VIII. Circumftances by which the fluids, that are effufed by the retrograde
motions of the abforbent vejfels, are dijlinguifjed. IX. Retrograde motions of
vegetable juices. X. Objections anfwered. XL The caufes, which induce the
retrograde motions of animal vejfels, and the medicines by which the natural
motions are rejlored.

N. B. 'The following SeSiion is a tranjlation of a part of a Latin thefts written
by the late Mr. Charles "Darwin, which was printed with his prize-dijferta-

tion on a criterion between matter and mucus in I'-jio. Sold by Cadell,
London.

I. Account of the Abforbent Syflem.

I. THE abforbent fyftem of veffels in animal bodies confifts of fe-
veral branches, differing in refpefl: to their fituations, and to the fluids,
■which they abforb.

The inteftinal abforbents open their mouths on the internal fur-
faces of the inteftines; their office is to drink up the chyle and the

3 other

S-ECT.XXIX. I. RETROGRADE ABSORBENTS. 303

other fluids from the alimentary canal ; and they are termed ladleals,
to diftinguifh them from the other abforbent veflel-s,. which have been
termed lymphatics.

Thofe,. whofe mouths are difperfed on the external' fkin, imbibe a
great quantity of water from the atmofphere, and a part of the per-
fpirable matter, which does- not evaporate, and are termed cutaneous
abforbents.

Thofe, which arife from the internal furface of the bronchia, and
which imbibe moiflure from the atmofphere, and a part of the bron-
chial mucus, are called pulmonary abforbents.

Thofe, which open their innumerable mouths into the cells of the
whole cellular membrane;- and whofe ufe is to take up the fluid,
which is poured into thofe cells,, after it hasdbne its office there; may^
be called cellular abforbents.

Thofe, which arife from the internal furfaces of the membranes,,
which line the larger cavities of the body, as the thorax, abdomen^,
fcrotum, pericardium, take up the mucus poured into thofe ca-
vities ; and are diftinguifhed by the names of their reipe<Slive
cavities..

Whilfl thofe, which arife from the internal furfaces of the urinary-
bladder, gall-bladder, falivary dufts, or other receptacles of fecreted
fluids, may take their names from thofe fluids ; the thinner parts of
which it is their office to abforb : as urinary, bilious, or falivary ab--
forbents.

2. Many of thefe abforbent veffels, both ladleals and lymphatics^,^
like fome of the veins, are replete with valves: which feem defigned^
toaflifl: the progrefs of their fluids, or atleaft to prevent their regur-
gitation;, where- they are fubjedled to the intermitted preflure of the-
mufcular, or arterial ailions in. their neighbourhood.

Thefe valves do not however appear to be neceflary to all the ab--
forbents, any more than to all the veins; fince they are not found to
exift in theabforbent fyflem of fifh ; according to the difcoveries of th&-

ingenious,.

304 RETROGRADE ABSORBENTS. Sect. XXIX. i.

ingenious, and much lamented Mr. Hewfon. Philof. Tranf. v. 59,
Enquiries into the Lymph. Syll. p. 94.

3. Thefe abforbent veffels are alfo furnifhed with glands, which
are called conglobate glands ; whofe ufe is not at prefent fufficiently
invefligated ; but it is probable that they refemble the conglomerate
glands both in ftruflure and in ufe, except that their abforbent
mouths are for the conveniency of lituation placed at a greater dif-
tance from the body of the gland. The conglomerate glands open
their mouths immediately into the fanguiferous veffels, which bring
the blood, from whence they abforb their refpeftive fluids, quite up
to the gland: but thefe conglobate glands collefl their adapted fluids
from very diftant membranes, or cyfls, by means of mouths furnifh-
ed with long necks for this purpofe; and which are called ladeals, or
lymphatics.

4. The fluids, thus collefled from various parts of the body, pafs
by means of the thoracic du£t into the left fubclavian near the ju-
gular vein ; except indeed that thofe coUedled from the right fide of
the head and neck, and from the right arm, are carried into the right
fubclavian vein : and fometimes even the lymphatics from the right
fide of the lungs are inferted into the right fubclavian vein j whilfl
thofe of the left fide of the head open but juft into the fummit of the
thoracic du£l.

5. In the abforbent fyftem there are many anaflomofes of the vef-
fels, which feem of great confequence to the prefervation of health.
Thefe anaftomofes are difcovered by diffeftion to be very frequent
between the inteftinal and urinary lymphatics, as mentioned by Mr.
Hewfon, (Phil. Tranf. v. 58).

6. Nor do all the inteftinal abforbents feem to terminate in the

thoracic d\i£l, as appears from fome curious experiments of D. Monro,

who gave madder to fome animals, having previoufly put a ligature on

the thoracic du6t, and found their bones, and the ferum of their blood,

coloured red.

II. The

Sect. XXIX. 2. RETROGRADE ABSORBENTS. 305

II. ^he Valves of the Abforbent Syjiem may fuffer their Fluids to
regurgitate in fame Difeafes.

I. The many valves, which occur In the progrefs of the lymphatic
and ladteal veflels, would feem infuperable obflacles to the regurgita-
tion of their contents. But as thefe valves are placed in veffels,
which are indued with life, and are themfelves indued with life alfo ;
and are very irritable into thofe natural motions, which abforb, or
propel the fluids they contain ; it is poflible, in fome difeafes, where
thefe valves or vefTels are ftimulated into unnatural exertions, or are
become paralytic, that during the diaflole of the part of the veffel to
which the valve is attached, the valve may not fo completely clofe,
as to prevent the relapfe of the lymph or chyle. This is rendered
more probable, by the experiments of injedting mercury, or water, or
fuet, or by blowing air down thefe veffels ; all which pafs the valves
very eafily, contrary to the natural courfe of their fluids, when the
veffels are thus a little forcibly dilated, as mentioned by Dr. Haller,
Elem. Phyfiol. t. iii. f. 4.

*' The valves of the thoracic du(3: are few, fome affert they are not
more than twelve, and that they do not very accurately perform their
office, as they do not clofe the whole area of the du£l, and thence
may permit chyle to repafs them downwards. In living animals,
however, though not always, yet more frequently than in the dead,
they prevent the chyle from returning. The principal of thefe valves
is that, which prefides over the infertion of the thoracic du£t, into
the fubclavian vein ; many have believed this alfo to perform the of-
fice of a valve, both to admit the chyle into the vein, and to preclude
the blood from entering the dudl ; but in my opinion it is fcarcely
fufficient for this purpofe." Haller, Elem. Phyf. t. vii. p. 226.

R r 2. The

3o6 RETROGRADE ABSORBENTS. Sect. XXIX. 2,

2. The mouths of the lymphatics feem to admit water to pafs
through them after death, the inverted way, eafier than the natural
one ; fince an inverted bladder readily lets out the water with which
it is filled ; whence it may be inferred, that there is ao obftacle at
the mouths of thefe veflels to prevent the regurgitation of their con-
tained fluids.

I w,as induced to repeat this experiment, and having accurately tied
the ureters and neck of a frefli ox's bladder, I made an opening at the
fundus of it ; and then, having turned it infide outwards, filled it
half full with water, and was furprifed to fee it empty itfelf fo haftily.
I thought the experiment rhore appofite to my purpofe by fufpending
the bladder with its neck downwards, as the lymphatics are chiefly
fpread upon this part of it ; as fliewn by Dr. Watfon, Philof. Tranf.
V. 59. p. 392.

3. In fome difeafes, as in the diabetes and fcrophula, it is probable
the valves themfelves are difeafed, and are thence incapable of pre-
venting the return of the fluids they fhould fupport. Thus the valves
of the aorta itfelf have frequently been found fchirrous, according ta
the diflTedlions of Monf. Lieutaud, and have given rife to an inter-
rupted pulfe, and laborious palpitations, by fufFering a return of part
of the blood into the heart. Nor are any parts of the body.fo liable;
to fchirrofity as the lymphatic glands and veflels, infomuch that
their fchirrofities have acquired a difl:inct name, and been termed
fchrophula.

4. There are valves in other parts of the body, analogous to thofe
of the abforbent fyfliem, and which are liable, when difeafed, to re-
gurgitate their contents : thus the upper and lower orifices of the
llomach are clofed by valves, which, when too great quantities of
warm water have been drank with a defign to promote vomiting,
have fometimes refifl:ed the utmoft effbrts of the abdominal mufcles,
and diaphragm : yet, at other times, the upper valve, or cardia,
eafily permits, the evacuation of the contents of the ftomach ; whilfb

4 the

Sect. XXIX, 2. RETROGRADE ABSORBENTS. 307

the inferior valve, or pylorus, permits the bile,' and other contents of
the duodenum, to regurgitate into the ftomach.

5. The valve of the colon is well adapted to prevent the retrograde
motion of the excrements ; yet, as this valve is poffefled of a living
power, in the iliac pafiion, either from fpafm, or other unnatural ex-
ertions, it keeps itfelf open, and either fuffers or promotes the retro-
grade movements of the contents of the inteftines b'slow ; as in rumi-
natine animals the mouth of the firft flomach feems to be fo con-
flruded, as to facilitate or uflifi: the regurgitation of the food ; the
rings of the oefophagus afterwards contracting themfelves in inverted
order. De Haen, by means of a fyringe, forced fo much water into
the rectum inteftinum of a dog, that he vomited it in a full ftream
from his mouth ; and in the iliac paflion above mentioned, excre-
ments and clyiler are often evacuated by the mouth. See Section
XXV. 15.

6. The pun£ta lacrymalia, with the lacrymal fack and nafal du£t,
compofe a complete gland, and much refemble the inteflinal canal *
the punifta lacrymalia are abforbent mouths, that take up the tears
from the eye, when they have done their office there, and convey
them into the noftrils ; but when the nafal du(ft is obftru6ted, and
the lacrymal fack diflended with its fluid, on preflure with the finger
the mouths of this gland (puncta lacrymalia) will readily difgorge the
fluid, they had previouily abforbed, back into the eye.

7. As the capillary veflels receive blood from the arteries, and fe-
parating the mucus, or perfpirable matter from it, convey the re-
mainder back by the veins ; thefe capillary veflels are a fet of glands,
in every refpedt fimilar to the fecretory veflTels of the liver, or other
large congeries of glands. The beginnings of thefe capillary veflTels
have frequent anafl:omofes into each other, in which circumftance
they are refembled by the ladteals ; and like the mouths or beginnings
of other glands, they are a fet of abforbent veflTels, which drink up the
blood which is brought to them by the arteries, as the chyle is drank

R r 3 up

3o8 RETROGRADE ABSORBENTS. Sect. XXIX. 3.

■up by the ladeals: fo|- the circulation of the blood through the capil-
laries is proved to be independent of arterial impulfe ; fince in the blufli
of (hanae, and in partial inflammations, their aftionis increafed, with-
out any increafe of the motion of the heart.

8. Yet not only the mouths, or beginnings of thefe anaftomoling
capillaries are frequently feen by microfcopes, to regurgitate fome par-
ticles of blood, during the ftruggles of the animal ; but retrograde
motion of the blood, in the veins of thofe animals, from the very
heart to the extremity of the limbs, is obfervable, by intervals, during
the diftreffes of the dying creature. Haller, Elem. Phyfiol. t. i.
p. 216. Now, as the veins have perhaps all of them a valve fome-
where between their extremities and the heart, here is ocular de-
monftration of the fluids in this difeafed condition of the animal, rc-
paffing through venous valves : and it is hence highly probable, from
the llriftcft analogy, that if the courfe of the fluids, in the lymphatic
veffels, could be fubjefted to microfcopic obfervation, they would alfo,
in the difeafed ftate of the animal, be feen to repafs the valves, and the
mouths of thofe veffels, which had previoufly abforbed them, or pro--
moted their progreflion.

III. Communication from the Alimentary Canal to the Bladder ^ By
means of the Abforbent Vejfeh.

Many medical philofophers, both ancient and modern, have fuf-
peded that there was a nearer communication between the ftomach
and the urinary bladder, than that of the circulation : they were led
into this opinion from the great expedition with which cold water,
when drank to excefs, paffes off by the bladder ; and from the iimila-
rity of the urine, when produced in this hafty mamierj with the ma-
terial that was drank.

The

Sect. XXIX. 3. RETROGRADE ABSORBENTS. 309

The former of thefe circumftances happens perpetually to thofc
who drink abundance of cold water, when they are much heated by
exercife, and to many at the beginning of intoxication.

Of the latter, many inftances are recorded by Etmuller, t. xi.
p. 716. where fimple water, wine, and wine with fugar, and emul-
fions, were returned by urine unchanged.

There are other experiments, that feem to demonftrate the exiftence
of another paffage to the bladder, befides that through the kidneys.
Thus Dr. Kratzenftein put ligatures on the ureters of a dog, and then
emptied the bladder by a catheter ; yet in a little time the dog drank
greedily, and made a quantity of water, (Difputat. Morbor. Halleri.
t. iv. p. 63.) A fimilar experiment is related in the Philofophical
Tranfaftions, with the fame events (No. 6^, 6'j^ for the year
1670.)

Add to this, that in fome morbid cafes the urine has continued to
pafs, after the fuppuration or total deftruftion of the kidneys ; of
which many inftances are referred to iii the Elem. Phyiiol. t. vii,
p. 379. of Dr. Haller.

From all which it muft be concluded, that fome fluids have paffed
from the ftomach or abdomen, without havins: sone through the
fanguiterous circulation: and as the bladder is fupplied with many
lymphatics, as defcribed by Dr. Watfon, m the Philof. Tranf. v. 59.
p. 392. and as no other veliels open into it befides thefe and the ure-
ters, it feems evident, that the unnatural urine, produced as above de-
fcribed, when the ureters were tied, or the kidneys obliterated, was
carried into the bladder by the retrograde motions of the urinarj
branch of the lymphatic fyftem.

The more certainly to afcertain the exiftence of another communi-
cation between the ftomach and bladder, befides that of the circula-
tion, the following experiment was made, to which I muft beg your
patient attention: — A friend of mine (June 14, 1772) on drinking re-
peatedly of cold fmall punch, till he began to be intoxicated, made a

q^uantity

3IQ- RETROGRADE ABSORBENTS. Sect. XXIX. 3;

quantity of colourlefs urine. He then drank about two drams of nitre
diflblved in feme of the punch, and eat about twenty ftalks of boiled
afparagus : on continuing to drink more of the punch, the next urine
that he made was quite clear, and without fmell; but in a little time
another quantity was made, which was not quite fo colourlefs, and
had a ftrong fmell of the afparagus : he then loft about four ounces of
blood from the arm.

The fmell of afparagus was not at all perceptible in the blood, nei*'
ther when frefti taken, nor the next morning, as myfelf and two,
others accurately attended to; yet this fmell was ftrongly perceived in
the urine, which was made juft before the blood was taken from his
arm.

Some bibulous paper, moiftened in the lerum of this blood, and
fuffered to dry, fhewed no figns of nitre by its manner of burning.
But fome of the fame paper, moiftened in the urine, and dried, on
being ignited, evidently ftiewed the prefence of nitre. This blood
and the urine ftood fome days expofed to the fun in the open air, till
they were evaporated to about a fourth of their original quantity, and
began to ftink : the paper, which was then moiftened with the con-
centrated urine, fliewed the prefence of much nitre by its manner of
burning ; whilft that moiftened with the blood fhewed no fuch ap-
pearance at all.

Hence it appears, that certain fluids at the beginning of intoxica-
tion, find another paffage to the bladder belides the long courfe of the
arterial circulation ; and as the inteftinal abforbents are joined with the
■urinary lymphatics by frequent anaftomofes, as Hewfon has deraon-
ftrated ; and as there is no other road, we may juftly conclude,- that
thefe fluids pafs into the bladder by the urinary branch of the lym-
phatics, which has its motions inverted during the difeafed ftate of the
animal.

A gentleman, who had been fome weeks affeded with jaundice,
and whofe urine was in confequence of a very deep yellow, took fome

cold

Sect. XXIX. 4. RETROGRADE ABSORBENTS. 311

cold fmall punch, in which was diffolved about a dram of nitre ; he
then took repeated draughts of the punch, and kept himfelf in a cool
room, till on the approach of flight intoxication he made a large
quantity of water ; this water had a flight yellow tinge, as might be
expefted from a fmall admixture of bile fecreted from the kidneys ;
but if the whole of it had paffed through the fanguiferous veflels,
which were now replete with bile {his whole Ikin being as yellow as
gold) would not this urine alfo, as well as that he had made for weeks
before, have been of a deep yellow ? Paper dipped in this water, and
dryed, and ignited, ihewed evident marks of the prefence of nitre^.
when the flarne, wAS, b|9,\y,Q,Qut.,

IV. The Phcenomena of the Diabetes explained, and of fame

Diarrhoeas..

The phsenomenaof many dlfeafes are only explicable from ■ the re? -
trograde motions of feme of the branches of the lymphatic fyftem ; as-
the great and immediate flow of pale urine in. the beginning of drunk'-
cnnefs ; in hyfteric paroxyfms ;, from being expofed to cold air j. or to
the influence of fear or anxiety..

Before we endeavour to illuftrate this doctrine, by defcribing the
phsenomena of thefe difeafes, we mufl: premife. one circumftance ;
that all the branches of the lymphatic fyftem have a certain fympathy.
with each other, infomuch that when one branch is ftimulated intO'
unufual kinds or quantities of motion, fome other branch has its mo-
tions either increafed, or decreafed, or inverted at the fame time..
This kind, of fympathy can only be proved by the concurrent tefti-
ipony of numerous fads, which will be related in the courfe of the
work. I fliall only add here, that it is probable, that this fympathy
does., not depend on any communication of nervous filaments, but on;

habit I ;

312 RETROGRADE ABSORBENTS. Sect. XXIX. 4.

habit ; owing to the various branches of this fyftem having frequently
been {Simulated into a6lion at the fame time.

There are a thoufand inflances of involuntary motions aflbciated in
this manner ; as in the a£t of vomiting, w^hile the motions of the fto-
mach and oefophagus are inverted, the pulfations of the arterial fyftem
by a certain fympathy become vi^eaker ; and when the bowels or kid-
neys are ftimulated by poifon, a ftone, or inflammation, into more
violent a£lion ; the ftomach and oefophagus by ' fympathy invert their
motions. .i. , j

1. When any one drinks a moderate quantity of vinous fpirit, the
whole fyftem a<3:s with more energy by confent with the ftomach and
inteftines, as is feen from the glow on the Ikin, and the increafe of
ftrength and a£livity; but when a greater quantity of this inebriating
material is drank, at the fame time that the ladteals are excited into
greater action to abforb it ; it frequently happens, that the urinary
branch of abforbents, which is conne£ted w^ith the la£leals by many
anaftomofes, inverts its motions, and a great quantity of pale unani-
malized urine is difcharged. By this wife contrivance too much of
an unneceffary fluid is prevented from entering the circulation — This
may be called the drunken diabetes, to diftinguifh it from the other
temporary diabetes, which occur in hyfteric difeafes, and from con-
tinued fear or anxiety.

2. If this idle ingurgitation of too much vinous fpirit be daily prac-
tifed, the urinary branch of abforbents at length gains an habit of in-
verting its motions, whenever the ladeals are much ftimulated ; and
the whole or a great part of the chyle is thus daily carried to the blad-
der without entering the circulation, and the body becomes emaci-
ated. This is one kind of chronic diabetes, and may be diftinguiftied
from the others by the tafte and appearance of the urine ; which is
fweet, and the colour of whey, and may be termed the chyliferous
diabetes.

3. Ma^iy

Sect.XXIX.4. retrograde absorbents. 313

3. .Many children have a fimilar depofition of chyle in their urine,
from the irritation of worms in their inteftines, which ftimulating the
mouths of the lacleals into unnatural a6tion, the urinary branch of
the abforbents becomes inverted, and carries part of the chyle to the
bladder : part of the chyle alfo has been carried to the iliac and lumbar
glands, of which inftances are recorded by Haller, t. vii, 235. and
which can be explained on no other theory: but the diffedlions of the
lymphatic fyftem of the human body, which have yet been publiflied,
are not fufficiently extenfive for our purpofe ; yet if we may reafon
from comparative anatomy, this tranflation of chyle to the bladder is
much illuftrated by the account given of this fyftem of veffels in a
turtle, by Mr. Hewfon, who obferved, " That the ladeals near the
root of the mefentery anaftomofe, fo as to form a net-work, from
which feveral large branches go into fome coniiderable lymphatics ly-
ing near the fpine ; and which can be traced almoft to the anus, and
particularly to the kidneys. Philof. Tranf. v. 59. p. 199 — Enquiries,
p. 74.

4. At the fame time that the urinary branch of abforbents, in the
beginning of diabetes, is excited into inverted action, the cellular
branch is excited by the fympathy above mentioned, into more ener-
getic action ; and the fat, that was before depofited, is reabforbed and
thrown into the blood veffels ; where it floats, and was miftaken for
chyle, till the late experiments of the ingenious Mr. Hewfon demon-
ftrated it to be fat.

This appearance of what was m.iftaken for chyle in the blood,
which was drawn from thefe patients, and the obftrucled liver,
which very frequently accompanies this difeafe, feems to have led
Dr. Mead to fufpe£l the diabetes was owing to a defect of fanguifica-
tion ; and that the fchirrofity of the liver was the original caufe of it :
but as the fchirrhusof the liver is moft frequently owing to the fame
caufes, that produce the diabetes and dropfies ; namely, the great ufe

Sf . of

31-4 RETROGRADE ABSORBENTS. Sect. XXIX. 4..

of fermented liquors ; there is no wander they fliould exifl together,
without being the confequence of each other.

- 5. If the cutaneous branch of abforbents gains a habit of being ex-
cited into ftronger aflion, and imbibes greater quantities of moiilure.
from the atmofphere, at the fame time th^t the urinary branch has
its motions inverted, another kind of diabetes is formed, which may
be termed the aqueous diabetes. In this diabetes the cutaneous ab-
forbents frequently imbibe an amazing quantity of atmofpheric moif-
ture ; infomuch that there are authentic hiftories, where many gallons,
a day, for many weeks together, above the quantity that has beea
drank, have been difcharged by urine..

Dr. Keil, in his Medicina Statica, found that he gained eighteeoi
ounces from the moift air of one night ; and Dr. Percival affirms,,
that one of his hands imbibed, after being well chafed, near an ounce-
and half of water, in a quarter of an hour. (Tranfa£t. of the College,.
London, vol. ii. p. 102). Home's Medic. Fa£ts, p. 2. fecft. 3.

The pale urine in hyfterical women, or which is produced by fear
or anxiety, is a temporary complaint of this kind; and it would ia re-
ality be the fame difeafe, if it was confirmed by habit.

6. The purging ftools, and pale urine, occafioned by expofing the-
naked hody to cold air, or fprinkling it with cold water, originate
from a" fimilar caufe; for the mouths of the cutaneous lymphatics,
being fuddenly expofed to cold become torpid, and ceafe, or nearly
ceafe, to a£l ; whilft, by the fympathy above defcribed, not only the
lymphatics of the bladder and inteftines ceafe alfo to abforb the more
aqueous and faline^part of the fluids fecrcted into them;, but it is
probable that thefe lymphatics invert their motions, and return the
fluids, which were previoufly abforbed, into the inteftines and bladder.
At the very infliant that the body is expofed naked to the cold air, an
unufual movement is felt in the bowels ; as is experienced by boys
going into the cold bath : this could not occur from an obflrudion of

the

Sect.XXIX.4. retrograde absorbents. 315

the perfplrable matter, fince there is not time for that to be returned
to the bowels bv the courfe of the circulation.

There is alfo a chronic aqueous diarrhoea, in which the atmofpheric
moifture, drank up by the cutaneous and pulmonary lymphatics, is
poured into the inteftines, by the retrograde motions of the lacleals.
This difeafe is moft limilar to the aqueous diabetes, and is frequently
exchanged for it: a diflinct injftance of this is recorded by Benninge-
rus, Cent, v. Obf. 98. in which an aqueous diarrhcea fucceeded an
aqueous diabetes, and deflroyed the patient. There is a curious ex-
ample of this, defcribed by Sympfon (De Re Medica) — '* A young man
(fays he) was feized with a fever, upon which a diarrhoea came on,
with great ftupor ; and he refufed to drink any thing, though he was
parched up with exceffive heat : the better to fupply him with moif-
ture, I diredled his feet to be immerfed in cold water; immediately I
obferved a wonderful decreafe of water in the veffel, and then an im-
petuous ftream of a fluid, fcarcely coloured, was dlfcharged by ftool,
like a cataraft."

7. There is another kind of diarrhoea, which has been called c£e-
liaca ; in this difeafe the chyle, drank up by the lacteals of the fmall
inteftines, is probably poured into the large inteftines, by the retro-
grade motions of their lafteals : as in the chyliferous diabetes, the
chyle is poured into the bladder, by the retrograde motions of the
urinary branch of abforbents.

The chyliferous diabetes, like this chyliferous diarrhoea, produces
fudden atrophy ; fince the nourifhment, which ought to fupply the
hourly wafte of the body, is expelled by the bladder, or redlum :
"whilft the aqueous diabetes, and the aqueous diarrhoea produce excef-
five thirft ; hecaufe the moifture, which is obtained from the atmo-
fphere, is not conveyed to the thoracic receptacle, as it ought to be,
but to the bladder, or lower inteftines ; whence the chyle, blood,
and whole fyftem of glands, are robbed of their proportion of hu-
midity.

S f 2 8. There

31 6 RETROGRADE ABSORBENTS. Sect. XXIX. 4,

8. There is a third fpecies of diabetes, in which the urine is mu-
cilaginous, and appears ropy in pouring it from one veflel into another ;
and will fometimes coagulate over the fire. This difeafe appears by
intervals, and eeafes again, and feems to be occafioned by a previous
dropfy in fome part of the body. When fuch a colledlion is reab-
forbed, it is not always returned into the circulation ; but the fame
irritation that ftimulates one lymphatic branch to reabforb the depo-
fited fluid, inverts the urinary branch, and pours it into the bladder.
Hence this mucilaginous diabetes is a cure, or the confequence of a.
cure, of a warfe difeafe, rather than a difeafe it felf.

Dr. Cotunnius gave half an ounce of cream of tartar, every
morning, to a patient, who had the anafarca ; and he voided a great
quantity of urine ; a part of which, put over the fire, coagulated, on;
the evaporation of half of it, fo as to look like the white of an egg..
De Ifchiade Nervos.

This kind of diabetes frequently precedes a dropfy ; and has this.
remarkable circumflance attending it, that it generally happens in the.
night ; as during the recumbent flate of the body,, the fluid, that waj.
accumulated in the cellular membrane, or in the lungs,, is more rea.-
dily abforbed, as it is lefs impeded by its gravity. I have feen more
thaa one inflance of this difeafe. Mr. D; a man in the decline of life^.
who had long accuflomed himfelf to fpirituOus liquor, had fvvelled
legs, and other fymptoms of approaching anafarca ; about once in a,
week, or ten days, for feveral months, he was feized, on gpingto bed,,
with great general uneafinefs, which his attendants refembled to aini
" hyfteric fit ; and which terminated in a great difcharge of vifcid urine j,
ibis legs "became lefs fwelled, and he continued in better health for,
fome days afterwards. I had not the opportunity to try if this urine-
would coagulate over the fire, when part of it was evaporated, whidh;
I imagine would be the criterion of this kind of diabetes ; as the mu-
cllaginous fluid depofited in the cells and cyfls of the body, which have
no communication with the external air, feems to acquire,, by flagna-

tionj

Sect. XXIX. 4. RETROGRADE ABSORBENTS. 51 7

tion, this property of coagulation by heat, which the fecreted mucus
of the inteftines and bladder do not appear to poffefs ; as I have found'
by experiment : and if any one fhould fuppofe this coagulable urine
was feparated from the blood by the kidneys, he may recoUedl, that
in the moffc inflammatory difcafes, in which the blood is moft replete^
or moft ready to part with the coagulable lymph, none of this appears
in the urine*

9. Different kinds of diabetes require different methods of cure..
For the firft kind, or chyliferous diabetes, after clearing the ftomacb
and inteflines, by ipecacuanha and rhubarb, to evacuate any acid ma-
terial,, which may too powerfully ftimulate the mouths of the ladeals,.
repeated and large dofes of tinfture of cantharides have been much re-
commended^ The fpecific ftimulus of this medicine,, on the neck of
the bladder, is likely to excite the numerous abforbent vefTels, which;
are fpread on that part, into ftronger natural adions, and by that
jaieans prevent their retrograde ones ; till, by perfifting in the ufe of
the medicine, their natural habits of motions might again be eftablifh-
ed. Another indication of cure, requires fuch medicines, as^ by lin-
ing the inteftines with mucilaginous fubftances, or with fiich as con-
lift of fmooth particles, or which chemically deftroy the acrimony of
their contents, may prevent the too great aftion of the inteftinal ab-
fbrbents. For this purpofe, I have found the earth precipitated froran .
a. folution of alum, by means of fixed alcali, given in the dofe of half
a dram every fix hours, of great advantage, with a. few grains of rhu-
barb, fo as to procure a daily evacuation.

The food fhould confift of materials that have the leaft ftimulus,
with calcareous water, as of Briftol and Matlock ; that the mouths of
the lafteals may be as little fHrnulated as is necefTary for their proper
abforption ; left with their greater exertions, fliould be conneded by
fympathy, the inverted motions of the urinary lymphatics.

The fame method may be employed with equal advantage in. the-
aqueous diabetes, fo great is. the fympathy between the Ikin and the

ftomach..

3i8 RETROGRADE ABSORBENTS. Sect. XXIX. 4.

ftomach. To which, however, fome application to the fkin might
be ufefully added ; as rubbing the patient all over with oil, to prevent
the too great aftion of the cutaneous abforbents. I knew an ex- '
periraent of this kind made upon one patient with apparent ad-
vantage.

The mucilaginous diabetes will require the fame treatment, which
is moft efficacious in the dropfy, and will be defcribed below. I muft
add, that the diet and medicines above mentioned, are ft r on gly re-
commended by various authors, as by Morgan, Willis, Harris, and
Etmuller ; but more hiflories of the fuccefsful treatment of thefe
difeafes are wanting to fully afcertain the moft efficacious methods of
cure.

■ In a letter from Mr. Charles Darwin, dated April 24, 1778, Edin-
burgh, is the fubfequent paflage: — " A man who had long laboured
under a diabetes died yefterday in the clinical ward. He had for fome
time drank four, and paffed twelve pounds of fluid daily ; each pound

■ of urine contained an ounce of fugar. He took, without confiderable
relief, o-um kino, fanguis draconis melted with alum, tindture of can-
tharides, ifinglafs, gum arable, crabs eyes, fpirit of hartfliorn, and eat
ten or fifteen oyfters thrice a day. Dr. Home, having read my thefts,
bled him, and found that neither the frefli blood nor the ferum tafted
fweet. His body was opened this morning — every vifcus appeared in
a ft)und and natural ftate, except that the left kidney had a very fmall
pelvis, and that there was a confiderable enlargement of moft of the ,
mefenteric lymphatic glands. I intend to infert this in my thefis, as
it coincides with the experiment, v^'here fome afparagus was;eaten'_at •,
the beginning of intoxication, and its ftnell perceived in the urine,
though rxot in the blood."

The following cafe of chyliferous diabetes is extradled from fome
letters of Mr. Hughs, to whofe unremitted care the infirmary at Staf-
ford for many years was much indebted. Dated Odober 10,

1778.
'-' Richard

Sect.XXIX.4. retrograde absorbents. 315,

Richard Davis, aged 33J a whitefmith by trade, had drank hard
by intervals ; was much troubled with fweating of his hands, which
incommoded him in his occupation, but which ceafed on his frequent-
ly dipping them in lime. About feven months ago he began to make
large quantities of water; his legs are oedematous, his belly tenfe, and
he complains of a rifing in his throat, like the globus hyftericus : he
eats twice as much as other people, drinks about fourteen pints of fmall
beer a day, befides a pint of ale, fome milk-porridge, and a bafon of
broth, and he makes about eighteen pints of water a day.

He tried alum, dragon's blood, fteel, blue vitriol, and cantharides
in large quantities, and duly repeated, under the care of Dr. Under-
bill, but without any efFed ; except that on the day after he omitted
the cantharides, he made but twelve pints of water, but on the next
day this good efFedt ceafed again.

November 21. — He made eighteen pints of water, and he now, at
Dr. Darwin's requeft, took a grain of opium every four hours, and
five grains of aloes at night j. and had a flannel ibirt given him.

22. — Made fixteen pints. 23. — Thirteen pints : drinka lefs.

24. — Increafed the opium to a grain and quarter every four hours t
he made twelve pints.

25. — Increafed the opium to a grain and half: he now makes ten
pints ; and drinks eight pints in a day.

The opium was gradually increafed during the next fortnight, till
he took three grains every four hours, but without any further dimu-
nition of his water. During the ute of the opium he fweat much in
the nights, fo as to have large drops ftand on his face and all over him.
The quantity of opium was then gradually decreafed, but not to-
tally omitted, as he continued to take about a grain morning and

evening.

January 17. — He makes fourteen pints of water a day. Dr. Un-
derbill now direded him two fcruples of common rofln triturated

with

|2o RETROGRADE ABSORBENTS. Sect. XXIX. 4.

with as much fu gar, every fix hours; and three grains of opium
every night.

19. — Makes fifteen pints of water: fweats at night.

21. — Makes feventeen pints of water; has twitchings of his hmbs
in a morning, and pains of his legs: he now takes a dram of rofin for
a dofe, and continues the opium.

33. — Water more coloured, and reduced to fixteen pints, and he
thinks has a brackifh tafte.

26. — Water reduced to fourteen pints.

28. — Water thireen pints: he continues the opium, and takes four
fcruples of the rofin for a dofe.

February i. — ■ Water twelve pints.

4.-^ Water eleven pints : twitchings lefs : takes five fcruples for
a dofe.

8. — Water ten pints : has had many flools.

12. — Appetite lefs : purges very much.

After this the rofin either purged him, or would not ftay on his
flomach ; and he gradually relapfed nearly to his former condition, and
in a few months funk under the difeafe.

Oftober 3, Mr. Hughs evaporated two quarts of the water, and
obtained from it four ounces and half of a hard and brittle faccharine
mafs, like treacle which had been fome time boiled. Four ounces of
blood, which he took from his arm with defign to examine it, had
the common appearances, except that the ferum refembled cheefe-
whey; and that on the eviderice of four perfons, two of whom did
not know what it was they tafted, the ferum had afaltijh tajie.

From hence it appears, that the faccharine matter, with which the
urine of thefe patients fo much abounds, does not enter the blood-
veffels like the nitre and afparagus mentioned above ; but that thc'
procefs of digeftion refembles the procefs of the germination of ve-
getables, or of making barley into malt ; as the- vaft quantity of fugar

■2 found

Sect. XXIX. 4. RETROGRADE ABSORBENTS. 321

found in the urine muil be made from the food which he took (which
was double that taken by others), and from the fourteen pints of
fmall beer which he drank. And, fecondly, as the ferum of the
blood was not fvveet, the chyle appears to have been conveyed to the
bladder without entering the circulation of the blood, fince fo large a
quantity of fugar, as was found in the urine, namely, twenty ounces
a day, could not have previoufly exifted in the blood without being
perceptible to the tafte.

November i. Mr. Hughes diffolved two drams of nitre in a pint of
a deco£lion of the roots of afparagus, and added to it two ounces of
tinfture of rhubarb: the patient took a fourth part of this mixture
every five minutes, till he had taken the whole. — In about half an
hour he made eighteen ounces of water, which was very manifeftly
tinged with the rhubarb ; the fmell of afparagus was doubtful.

He then loft four ounces of blood, the ferum of which was not fb
opake as that drawn before, but of a yellowifli caft, as the ferum of
the blood ufually appears.

Paper, dipped three or four times in the tinged urine and dried
again, did not fcintillate when it was fet on fire ; but when the flame
was blown out, the fire ran along the paper for half an inch; which,
when the fame paper was unimpregnated, it would not do ; nor when,
the fame paper was dipped in urine made before he took the nitre, and
dried in the fame manner.

Paper, dipped in the ferum of the blood and dried in the iame'
manner as in the urine, did not fcintillate when the flame was blown
out, but burnt exadlly in the fame manner as the fame paper dipped in
the ferum of blood drawn from another perfon.

This experiment, which is copied from a letter of Mr. Hughes, as
well as the former, feems to evince the exiftence of another pafiage
from the inteftines to the bladder, in this difeafe, befides that of the
fanguiferous fyftem j and coincides with the curious experiment re-
lated in fedion the third, except that the fmell of the afparagus was

T t not

322 RETROGRADE ABSORBENTS. Sect. XXIX. 5

not here perceived, owing perhaps to the roots having been made ufe
of inftead of the heads.

The rifing in the throat of this patient, and the twitchings of hh
limbs, feem to indicate fome fimilarity between the diabetes and the
hyfteric difeafe, befides the great flow of pale urine, which is common
to them both.

Perhaps if the mefenteric glands were nicely infpefted in the dif-

. fe£lions of thefe patients ; and if the thoracic dudt, and the larger

branches of the lafteals, and if the lymphatics, which arife from the

bladder, were well examined by injection, or by the knife, the caufe

of diabetes might be more certainly underftood.

The opium alone, and the opium with the rofin, feem much to
have ferved this patient, and might probably have effected a cure, if
the difeafe had been {lighter, or the medicine had been exhibited, be-
fore it had been confirmed by habit during the feven months it had
continued. The increafe of the quantity of water on beginning the
large dofes of rofin was probably owing to his omitting the morning
dofes of opium.

V. T'/je Phixnomma of Dropjies explained.

I. Some inebriates have their paroxyfms of inebriety terminated by
much pale urine, or profufe fweats, or vomiting, or ftools ; others
have their paroxyfms terminated by ftupor, or fleep, without the
above evacuations.

The former kind of thefe inebriates have been obferved to be more
liable to diabetes and dropfy; and the latter to gout, gravel, and le-
profy. Evoe ! attend ye bacchanalians ! flart at this dark train of evils,
and, amid your immodeft jefls, and idiot laughter, recoiled,

Quern Deus vnlt peidere, prius dementat.

Sect. XXIX. 5- RETIIOGRADE ABSORBENTS, 323

In thofe who are fubjedl to diabetes and dropfy, the abforbent vef-
fels are naturally more irritable than in the latter ; and by being fre-
quently difturbed or inverted by violent flimulus, and by their too
great lympathy with each other, they become at length either entire-
ly paralytic, or are only fufceptible of motion from the ftimulus of
very acrid materials ; as every part of the body, after having been ufed
to great irritations, becomes lefs affefted by fmaller ones. Thus we
cannot diftinguifli objefts in the night, for fome time after we come
out of a ftrong light, though the iris is prefently dilated ; and the air
of a fummer evening appears cold, after we have been expofed to the
heat of the day.

There are no cells in the body, where dropfy may not be produced,
if the lymphatics ceafe to abforb that mucilaginous fluid, which is
perpetually depofited in them, for the purpofe of lubricating their
furfaces.

If the lymphatic branch, which opens into the cellular membrane,
either does its office imperfe6lly, or not at all ; thefe cells become re-
plete with a mucilaginous fluid, which, after it has ftagnated fome
time in the cells, will coagulate over the fire 3 and is erroneoufly called
water. Wherever the feat of this difeafe is, (unlefs in the lungs or
other pendent vifcera) the mucilaginous liquid above mentioned will
fubfide to the moft depending parts of the body, as the feet and legs,
when thofe are lower than the head and trunk; for all thefe cells have
communications with each other.

When the cellular abforbents are become inlenfible to their ufual
irritations, it moft frequently happens, but not always, that the cuta-
neous branch of abforbents, which is flridlly alTociated with them,
fuffers the like inability. And then, as no water is abforbed from the
atmofphere, the \irine i^ not only lefs diluted at the time of its fecre-
tion, and confequently in lefs quantity and higher coloured : but great
thirfl: is at the fame time induced, for as no water is abforbed from the
atmofphere to dilute the chyle and blood, the la(3:eals and other ab-

T t 2 ' forbent

324 RETROGRADE ABSORBENTS. Sect. XXIX. 5.

forbent veffels, which have not loft their powers, are excited into
more conftant or more violent a£lion, to fupply this deficiency;
whence the urine becomes ftill lefs in quantity,, and of a deeper colour,
and turbid like the yolk of an egg, owing to a greater abforption of
its thinner parts. From this ftronger adlion of thofe abforbents,
which ftill retain their irritability, the fat is alfo abforbed, and the
whole body becomes emaciated. This increafed exertion of fome
branches of the lymphatics, while others are totally or partially pa-
ralytic, is refembled by what conftantly occurs in the hemiplagia ;
when the patient has loft the ufe of the limbs on one fide, he is in-
ceflantly moving thofe of the other ; for the moving power, not hav-
ing accefs to the paralytic limbs, becomes redundant in thofe which
are not difeafed.

The paucity of urine and thirft cannot be explained from a greater
quantity of mucilaginous fluid being depofited in the cellular mem-
brane : for though thefe fymptoms have continued many weeks, or
even months, this colleilion frequently does not amount to more
than very few pints. Hence alfo the difficulty of promoting copious
fweats in anafarca is accounted for, as well as the great thirft, paucity
of urine, and lofs of fat ; fince, when the cutaneous branch of abfor-
bents is paralytic, or nearly fo, there is already too fmall a quantity
of aqueous fluid in the blood : nor can thefe torpid cutaneous lympha-
tics be readily excited into retrograde motions.

Hence likewife we underftand, why in the afeites,. and fome other
dropfies, there is often no thirft, and no paucity of urine ; in thefe
cafes the cutaneous abforbents continue to do their office.

Some have believed, that dropfies were occafioned by the inability
of the kidneys, from having only obferved the paucity of urine ; and
have thence laboured much to obtain diuretic medicines ; but it is daily
obfervable, that thofe who die of a total inability to make water, do
not become dropfical in confequence of it : Fernelius mentions one,
who laboured under a perfed fuppreffioii of urine during twenty days

before

Sect. XXIX. 5:. RETROGRADE ABSORBENTS. 325

before his death, and yet had no fymptoms of dropfy. Pathol. 1. vL
c. 8. From the fame idea many phyficians have reftrained their pa-
tients from drinking, though their thirft .has been very urgent ; and
fome cafes have been publifhed^ where this cruel regimen has been
thought advantageous : but others of nicer obfervation are of opinion,
that it has always aggravated the diftrelTes of the patient ; and though,
it has abated his fwelllngs, yet by inducing a fever it has haftened his
diflblution. See Tranfadions of the College, London,, vol. ii. p. 235.
Cafes of Dropfy by Dr. G. Baker.

The cure of anafarca, fo far as refpefts the evacuation of the accu'-
mulated fluid, coincides with the idea of the retrograde adlion of the
lymphatic fyflem. It is well known that vomits, and other drugs,,
which induce ficknefs or naufea ; at the fame time that they evacuate
the ftomach, produce a great abforption of the lymph accumulated in
the cellular membrane. In the operation of a vomit, not only the
motions of the ftomach and duodenuhi become inverted, but alfo thofe
of the lymphatics and la£leals, which belong to them; whence a
great q,uantity of chyle and lymph is perpetually poured into the fto-
mach and inteftines, during the operation, and evacuated by the
mouth. Now at the fame time, other branches of the lymphatic
fyftem, viz. thofe which, open on the cellular membrane, are brought
into more energetic action, by the fympathy above mentioned, and an
increafe of their abforption is produced.

Hence repeated vomits, and cupreous falts, and fmall dofes of fquill
or foxglove, are fo efficacious in this difeafe. And as draftic purges
a£l alfo by inverting the motions of the lacteals ; and thence the other
branches of lymphatics are induced into more powerful natural action,
by fympathy, and drink up the fluids from all the cells of the body ;
and by their anaftomofes, pour them into the lafteal branches ; which,
by their inverted a£lions, return them into the inteftines ; and they are
thus evacuated from the body : — thefe purges alfo are ufed with fuccefs

in difcharging the accumulated fiuid.in anafarca.

II. The

326 "RETROGRADE ABSORBENTS. SECT.XXlX.5.

II. The following cafes are related with defiga to afcertain the par-
ticular kinds of dropfy in which the digitalis purpurea, or common
foxglove, is preferable to ^fquill, or other evacuants, and were firfl
publifhed in 1780, in a pamphlet entitled Experiments on mucila-
ginous and purulent Matter, &c. Cadell. London. Other cafes of
dropfy, treated with digitalis, were afterwards publifhed by Dr. Darwin
in the Medical Tranfadllons, vol. iii. in which there is a miftake in
refpe6lto the dofe of the powder of foxglove, which fhould have
been froni £ve sirains to one, inilead of from five grains to ten^

Anafarca of the Lungs,

1 . A lady, between forty and fifty years of age, had been indif-
pofed fome time, was then feized with cough and fever, and after-
wards expeftorated much digefted mucus. This expectoration fud-
denly ceafed, and a confiderable difficulty of breathing fupervened,
with a pulfe very irregular both in velocity and ftrength ; Ihe was
much diftreffed at firft lying down, and at firft rifing ; but after a
minute or two bore either of thofe attitudes with eafe. She had no
pain or numbnefs in her arms ; fhe had no hedtic fever, nor any
cold Ihlverings, and the urine was in due quantity, and of the natu-
ral colour.

The difficulty of breathing was twice confiderably relieved by fmall
dofes of ipecacuanha, which operated upwards and downwards, but
recurred in a few days : Ihe was then diredled a deco£tion of foxglove,
(digitalis purpurea) prepared by boiling four ounces of the frefli leaves
from two pints of water to one pint ; to which was added two ounces
of vinous fpirit : ffie took three large fpoonfuls of this mixture every
two hours, till fhe had taken it four times ; a continued ficknefs fu-
pervened, with frequent vomiting, and a copious flow of urine :
thefe evacuations continued at intervals for two or three days, and

relieved

Sect. XXIX. 5- RETROGRADE ABSORBENTS. 327

relieved the difficulty of breathing — She had fome relapfes after-
wards, which were again relieved by the repetition of the decodlion
of foxglove.

2. A gentleman, about fixty years of age, who had been addi£ted
to an immoderate ufe of fermented liquors, and had been very cor-
pulent, gradually loft his ftrength and flefh, had great difficulty of
breathing, with legs fomewhat fwelled, and a very irregular pulfe.
He was very much diftreffed at firfl lying down, and at firil rifing
from his bed,, yet in a minute or two was eafy in both thofe attitudes.
He made ftraw-coloured urine in due quantity, and had no pain or
numbnefs of his arms.'

He took a large fpoonful of the decoflion of foxglove, as above,
every hour, for ten or twelve fucceffive hours, had inceffant ficknefs
for about two days, and pafied a large quantity of urine ; upon which
his breath became quite eafy, and the fwelling of his legs fubfided ;
but as his whole conftitution was already finking from the previous
intemperance of his life, he did not furvive more than three or four
months.

Hydrops Pericardii.

3. A gentleman of temperate life and fedulous application to bufi-
nefs, between thirty and forty years of age, had long been fubjeft, at
intervals, to an irregular pulfe : a few months ago he became weak,
with difficulty of breathing, and dry cough. In this fituation a phy-
fician of eminence diredled him to abftain from all animal food and
fermented liquor, during which regimen all his complaints increafed ;
he now became emaciated, and totally loft his appetite ; his pulfe
very irregular both in velocity and ftrength; with great difficulty of
breathing, and fome fwelling of his legs ; yet he could lie down ho-
rizontally in his bed, though he got little fleep, and pafled a due

8 quantity

328 RETROGRADE ABSORBENTS. Sect. XXIX. 5-.

quantity of uriae, and of the natural colour: no fullnefs or hardnefs
could be perceived about the region of the livei' ; and he had no pain
or numbnefs in his arms.

One night he had a moft profufe fweat all over his body and limbs,
which quite deluged his bed, and for a day or two fomewhat relieved
his difficulty of breathing, and his pulfe became lefs irregular : this
copious fweat recurred three or four times at the intervals of five or fix
days, and repeatedly alleviated his fymptoms.

He was directed one large fpoonful of the above decodlion of fox-
glove every hour, till it procured fome confiderable evacuation : after
he had taken it eleven fucceffive hours he had a few liquid flools, at-
tended with a great flow of urine, which laft had a dark tinge, as if
■mixed with a few drops of blood: he continued fick at intervals for
two days, but his breath became quite eafy, and his pulfe quite regu-
lar, the fwelling of his legs difappeared, and his appetite and fleep
returned.

He then took three grains of white vitriol twice a day, with fome
bitter medicines, and a grain of opium with five grains of rhubarb
every night ; was advifed to eat flefh meat, and fpice, as his ftomach
would bear it, with fmall beer, and a few glaffes of wine; and had
iffues made in his thighs ; and has fuffered no relapfe.

4. A lady, about fifty years of age, had for fome weeks great dif-
ficulty of breathing, with very irregular pulfe, and confiderable ge-
neral debility : fhe could lie down in bed, and the urine was in <iue
quantity and of the natural colour, and fhe had no pain or numbnefs
of her arms.

She took one large fpoonful of the above deco£tion of foxglove
every hour, for ten or twelve fucceflive hours ; was fick, and made
a quantity of pale urine for about two days, and was quite relieved
both of the difficulty of breathing, and the irregularity of her pulfe.
She then took a grain of opium, and five grains of rhubarb, every

night,

Sect. XXIX. 5. RETROGRADE ABSORBENTS. 329

night, for many weeks; with fome flight chalybeate and bitter medi-
cines, and has fufFered no relapfe.

Hydrops Thoracis.

5. A tradefman, about fifty years of age, became weak and fhort
-of breath, efpecially on increafe of motion, with pain in one arm,
about the infertion of the biceps mufcle. Ke obferved he fbmetimes
in the night made an unufual quantity of pale water. He took calo-
mel, alum, and peruvian bark, and all his fymptoms increafed : his
legs began to fwell confiderably ; his breath became more difficult,
and he could not lie down in bed ; but all this time he made a due
quantity of ftraw-coloured water.

The decodlion of foxglove was given as in the preceding cafes,
which operated chiefly by purging, and feemed to relieve his breath
for a day or two ; but alfo feemed to contribute to weaken him. — He
became after fome weeks univerfally dropfical, and died comatous.

6. A young lady of delicate conftitution, with light eyes and hair,
and who had perhaps lived too abftemioufly both in refpedt to the
q'uantity and quality of what fhe eat and drank, was feized with great
difficulty of breathing, fo as to threaten immediate death. Her ex-
tremities were quite cold, and her breath felt cold to the back of one's
hand. She had no fweat, nor could lie down for a fingle moment;
and had previoufly, atid at prefent, complained of great weaknefs and
pain and numbnels of both her arms j had no fwelling of her legs, no
thlrft, water in due quantity and colour. Her fifter, about a year
before, was affli6led with limiiar fymptoms, was repeatedly blooded,
and died univerfally dropfical.

A grain of opium was given immediately, and repeated everv fix
hours with evident and amazing advantage ; afterwards a blifter, with
chalybeates, bitters, and eflential oils, were exhibited, but nothing

U u had

330 RETROGRADE ABSORBENTS. Sect. XXIX. 5.,

had fuch eminent effeft in relieving the difficulty of breathing and
coldnefs of her extremities as opium, by the ufe of which in a few
weeks Ihe perfeftly regained her health, and has fufFered no relapfe..

^Afcitei.

7. A young lady of delicate conflitution having been expofed to
great fear, cold, and fatigue, by the overturn of a chaife in the night,,
began with pain and tumour in the right hypochondrium : in a few
months a flu£tuation was felt throughout the whole abdomen, more
diftindly perceptible indeed about the region of the flomach ; fince
the integuments of the lower part of the abdomen- generally become:
thickened in this difeafe by a degree of anafarca. Her legs were not
fwelled, no thirft, water in due quantity and colour.— She took the
foxglove fo as to induce ficknefs and ftools, but without abating;
the fwelling, and was obliged at length to fubmit to the operation of
tapping.

8. A man about fixty-feven, who had long been accuftomed to^
fpirituous potation, had fome time laboured under afcites ; his legs-^
fomewhat fwelled ; his breath eafy in all attitudes j no appetite; great
thirft ; urine in exceedingly fmall quantity, very deep colotu-ed, and;
turbid ; pulfe equal. He took the foxglove in fuch quantity as vo-
mited him, and induced (icknefs for two days ; but procured no flow
of urine, or diminution of his fwelling ; but was thought to leave him.
confiderably weaker.

9. A corpulent man, accuftomed to large potation of fermented
liquors, had vehement cough, difficult breathing,- anafarca of his legs,,
thighs, and hands, and conliderable tumour, with evident flinSuatioa
of his abdomen ; his pulfe was equal ; his urine in fmall quantity, of
deep colour, and turbid. Thefe fwellings had been twice confider-
ably

Sect. XXIX. 5. RETROGRADE ABSORBENTS. 331

ably abated by draftic cathartics. He took three ounces of a deco£tioa
of foxglove (made by boiling one ounce of the frefh leaves in a pint of
water) every three hours, for two whole days; it then began to vo-
mit and purge him violently, and promoted a great flow of urine ; he
was by thefe evacuations completely emptied in twelve hours. After
two or three months all thefe fymptoms returned, and were again
relieved by the ufe of the foxglove ; and thus in the fpace of about
three years he was about ten times evacuated, and continued all that
time his ufual potations : excepting at firft, the medicine operated
only by urine, and did not appear confiderably to weaken him — The
laft time he took it, it had no efFed ; and a few weeks afterwards he
vomited a great quantity of blood, and expired.

q^JJERIES.

1. As the firft fix of thefe patients had a due difcharge of urine,
and of the natural colour, was not the feat of the difeafe confined to
fome part of the thorax, and the fwelling of the legs rather a fymp-
tom of the obftrudled circulation of the blood, than of a paralyfis of
the cellular lymphatics of thofe parts ?

2. When the original difeafe is a general anafarca, do not the cu-
taneous lymphatics always become paralytic at the fame time with the
cfillular ones, by their greater fympathy with each other ? and hence
the paucity of urine, and the great thirft, diftinguifh this kind of
dropfy ?

3. In the anafarca of the lungs, when the difeafe is not very great,
though the patients have confiderable difficulty of breathing at their
firfl lying down, yet after a minute or two their breath becomes eafy
again ; and the fame occurs at their firft rifing. Is not this owing
to the time iiecelTary for the fluid in the cells of the lungs to change

U u 3 its

352 ~ RETROGRADE ABSORBENTS. Sfxt.XXIX. 5.

its' place, &> as the lead to incommode refpiratlon ia the new -at>
titude ?

4. In the dropfy of the pericardium does not the patient bear the
horizontal or perpendicular attitude with equal eafe ? Does this cir.-
curaftance diftinguifh the dropfy of the pericardium from that of the
lungs and of the thorax ?

5. Do the univerfal fweats dlftinguifli the dropfy of the pericardium,
or of the thorax ? and thofe, which cover the upper parts of the body
only, the anafarca of the lungs ?

6. When in the dropfy of the thorax,, the patient endeavours to lie-
down., does not the extravafated fluid comprefs the upper parts, of the
bronchia, and totally preclude the accefs of air to every part, of the
lungs ; whilft in the perpendicular attitude the inferior parts of the
lungs only are compreffed ? Does not fomething fimilar to this occur
in the anafarca of the lungs, _ when the. difeafe is very great, and thus,
prevent thofe patients alfo from lying down ?

7. As a principal branch of the fourth cervical nerve of the left
fide, after having joined a branch of the third and of the fecond cer-
vical nerves, defcending between the fubclavian vein and artery, is
I'eceived in a groove formed for it in the pericardium, and is obliged
to make a confiderable turn outwards to go over the prominent part
of it, where the point of the head is liDdged, in its courfe to the dia-
phragm ; and as the other phrenic nerve of the right fide has a fi:raight
courfe to the diaphragm ; and as many other confiderable branchesof
this fourth pair of cervical nerves are fpread on the arms ; does ncft z
pain in the left arm dlftinguifli a difeafe of the pericardium, as in the
angina pectoris, or in the dropfy of the pericardium ? and does not a
pain or weaknefs in both arms diftinguifh the dropfy of the thorax ?

8. Do not the dropfies of the thorax and pericardium frequently
exift together, and thus ad'd to the uncertainty and fatality of the
difeafe ?

9. Might

Sect. XXIX. 6. RETROGRADE ABSORBENTS, 3,35:

9. Might not the foxglove be ferviceable in hydrocephalus internus,-
m hydrocele, and in white fwellings of the joints i

VI. Of cold Sweat's.

There have been hiftories given of chronical immoderate fvs^eat-
ings, which bear feme analogy to the diabetes. Dr. Willis mentions ar
lady then living, whofe fweats were for many years fo profufe, that
all her bed-clothes were not only moiftened, but deluged with them
every night ;. and that many ounces, and fometimes pints, of this
fweat, were received in veffels properly placed, as it trickled down her
body. He adds, that flie had great thirft, had taken many medicines,
and fubmitted to various rules of life, and changes of climate, but
flill continued to have thefe immoderate fweats. Pharmac. ration,
de fudore anglico.

Dr. Willis has alfo' obferved, that the fudor anglicanus which ap-
peared in England, in 1483, and continued till 1551, was in fome
refpefts fimilar to the diabetes ; and as Dr. Caius, who faw this dif-
eafe, mentions the vifeidity, as well as the quantity of thefe fweats,
and adds, that the extremities were often cold, when the internal parts
were burnt up with heat and thirft, with great and fpeedy emaciatioa
and' debility : there is great reafon to believe, that the fluids vt'cre ab-
forbed from the cells of the body by the cellular and cyftic branches
of the lymphatics,, and poured on the fkjn by the retrograde motions
of the cutaneous ones.

Sydenham has recorded, in the ftationary fever of the year 1685,
the vifcid fweats flowing from the head, which were probably from
the fame fource as thofe in the fweating plague above mentioned.
■ It is very common in dropfles of the cheft or lungs to have the
difficulty of breathing relieved by copious fweats, flowing from the
bead and neck. Mr. P. about 50 years of age, had for many weeks

beea

334 RETROGRADE ABSORBENTS. Sect.XX1X.6;

been affli6led with anafarca of his legs and thighs, attended with dif-
ficulty of breathing ; and had repeatedly been relieved by fquill, other
bitters, and chalybeates. — One night the difficulty of breathing became
fo great, that it was thought he muft have expired; but fo copious a
fweatcame out of his head and neck, that in a few hours fome pints,
by eflimation, were wiped off from thofe parts, and his breath was for
a time relieved. This dyfpnoea and thefe fweats recurred at intervals,
and after fome weeks he ceafed to exifl. The Ikin of his head and neck
felt cold to the hand, and appeared pale at the time thefe fweats flowed
fo abundantly ; which is a proof, that they were produced by an inverted
motion of the abforbeats of thofe parts : for fweats, which are the con-
fequence of an increafed a£tion of the fanguiferous fyftem, are always at-
tended with a warmth of the Ikin, greater than is natural, and a more
florid colour ; as the fweats from exercife, or thofe that fucceed the cold
fits of agues. Can anyone explain how thefe partial fweats (hould relieve
the difficulty of breathing in anafarca, but by fuppofing that the pul-
monary branch of abforbents drank up the fluid in the cavity of the tho-
rax, or in the cells of the lungs, and threw it on the Ikin, by the retro-
grade motions of the cutaneous branch ? for, if we could fuppofe, that
the increafed adion of the cutaneous glands or capillaries poured upon
the Ikin this fluid, previoufly abforbed from the lungs ; why is not the
whole furface of the body covered with fweat ? why is not the Ikia
warm ? Add to this, that the fweats above mentioned were clammy
or glutinous, which the condenfed perfpirable matter is not ; whence
it would feem to have been a different fluid from that of common
perfpiration.

Dr. Dobfon, of Liverpool, has given a very ingenious explanation of
the acid fweats, which he obferved in a diabetic patient — he thinks part
of the chyle is fecreted by the flcin, and afterwards undergoes an ace-
-tous fermentation. — Can the chyle get thither, but by an inverted
motion of the cutaneous lymphatics I in the fame manner as it is car-

2 ried

Sect. XXIX. 7- RETROGRADE ABSORBENTS. 355

ried to the bladder, by the inverted motions of the urinary lymphatics.
Medic. Obfervat. and Enq. London, vol. v.

Are not the cold fweats in fome fainting fits, and in dying people^
owing to an inverted motion of the cutaneous lymphatics I for in
thefe there can be no increafed arterial or glandular a6Vion.

Is the difficulty of breathing, arifing from anarfaca of the lungs,
relieved by fweats from the head and neck ; whilfl that difficulty of
breathing, which arifes from a dropfy of the thorax, or pericardium^
is never attended with thefe fweats of the head ? and thence can thefe
difeafes be diftinguifhed from each other ? Do the periodic returns of
no£lurnal afthma rife from a temporary dropfy of the lungs, colle6led
during their more torpid flate in found, fleep, and then re-abforbed by
the vehement efforts of the difordered organs of refpiration, and car-
ried off by the copious fweats about the head and neck ?

More extenfive and accurate diffedlions of the lymphatic fyftent
are wanting to enable us to unravel thefe knots of fcience.

VII. Tranjlations »f Matter, of Chyle, of Milk., of Urine. Operatloit:
of purging Drugs applied externally.

1. The tranflations of matter from one part of the body to another,
can only receive an explanation from the do£lrine of the occafional re-
trograde motions of fome branches of the lymphatic fyflem : for how
can matter, abforbed and mixed with the whole mafs of blood, be fo
haftily collected again in any one part ? and is it not an immutable
law, in animal bodies, that each gland can fecrete no other, but its
own proper fluid ? whicL is, in part, fabricated in the very gland by
an animal procefs, which it there undergoes : of thefe purulent tranf--
lations innumerable and very remarkable inftances are recorded.

2. The chyle, which is feen among the materials thrown up by vio-

lent

23^ RETROGRADE ABSORBENTS. Sect. XXIX. 7.

lent vomiting, or in purging flools, can only conae thither by its
having been poured into the bowels by the inverted motions of the
.la£leals: for our aliment is not converted into chyle in the ftomach or
inteftines by a chemical proce'fs, but is made in the very mouths of
the lafteals; or in the mefenteric glands; in the fame manner as other
fecrcted fluids are made by an animal procefsin their adapted glands.

Here a curious phaenomenon in the exhibition of mercury is worth
explaining : — If a moderate dofe of calomel, as fix or ten grains, be
fwallowed, and within one or two days a cathartic is given, a laliva-
tion is prevented : but after three or four days, a falivation having
come on, repeated purges every day, for a week or two, are required
to eliminate the mercury from the conftitution. For this acrid me-
tallic preparation, hei.ng abforbed by the mouths of the ladleals, con-
tinues, for a time arrefted by the mefenteric glands, (as the variolous
,or venereal poifons fwell the fubaxillar or inguinal glands) : which,
durinty the operation of a cathartic, is returned into the inteftines by
the inverted a6lion of the ladeals, and thus carried out of the fyftem.

Hence we underftand the ule of vomits or purges, to thofe who
have fwallowed -either .contagious or poifonous materials, even though
exhibited a day or even two days after fuch accidents ; namely, that
by the retrograde motions of the ladteals and lymphatics, the material
ftill arrefted in the mefenteric, or other glands, may be eliminated
from the body.

3. Many inftances of mlllc and chyle found in uicers are given by
Haller, El. Phyfiol. t. vii. p. 12, 23, which admit of no other expla-
nation than by fuppofing, that the chyle, imbibed by one branch of the
-abforbent fyflem, was carried to the ulcer, by the inverted motions of
■another branch of the fame fyflem.

4. Mrs. P. on the fecond day after delivery, wasfelzcd with a vio-
lent purging, in which, though ^opiates, mucilages, the bark, and
•teftacea were profufely ufed, continued many days, till at length (ho
jecovercd. During the time of ithis purging, no milk could be drawn

from

Sect. XXIX. 7- RETROGRADE ABSORBENTS. 33;

from her breafts ; but the ftools appeared like the curd of milk broken
into fmall pieces. In this cafe, was not the milk taken up from the
follicles of the perioral glands, and thrown on the inteftines, by a re-
trogreffion of the inteftinal abforbcnts ? for how can we for a moment
fufpeft that the mucous glands of the inteftines could feparate pure
milk from the blood ? Dodlor Smelly has obferved, that loofe flools,
mixed with milk, which is curdled in the inteftines, frequently re-
lieves the turgefcency of the breafts of thofe who ftudioufly repel
their milk. Cafes in Midwifery, 43, No. 2. i.

5. J. F. Meckel obferved in a patient, whofe urine was in. fmall
quantity and high coloured, that a copious fweat under the arm-pits,
of a perfedly urinous fmell, flained the linen; which ceafed again
when the ufual quantity of urine was difcharged by the urethra. Here
we muft believe from analogy, that the urine was firft fecreted in the
kidneys, then re-abforbed by the increafed aftion of the urinary lym-
phatics, and laftly carried to the axillae by the retrograde motions of
the lymphatic branches of thofe parts. As in the jaundice it is ne-
ceffary, that the bile (hould firft be fecreted by the liver, and re-ab-
forbed into the circulation, to produce the yellownefs of the (kin; as
was formerly demonftrated by the late Dr. Monro, (Edin. Medical
Effays) and if in this patient the urine had been re-abforbed into the -
mafs of blood, as the bile in the jaundice, why was it not detedled in
other parts of the body, as well as in the arm-pits ?

6. Cathartic and vermifuge medicines applied externally to the ab-
domen, feem to be taken up by the cutaneous branch of lymphatics,
and poured on the inteftines by the retrograde motions of the ladleals,
without having pafled the circulation.

For when the draftic purges are taken by the mouth, they excite
the lafteals of the inteftines into retrograde motions, as appears from
the chyle, which is found coagulated among the fffices, as was fhewn
above, (fe£l 2 and 4.) And as the cutaneous lymphatics are joined
with the ladeals of the inteftines, by frequent anaftomofes ; it would

Xx be

338 RETROGRADE ABSORBENTS. Sect. XXIX. g,

be more extraordinary, when a ftrong purging drug, abforbed by the
Ikin, is carried to the anaflomofing branches of the la£leals unchanged^
if it fbould not excite them into retrograde aftion as efficacioufly, as
if it was taken by the mouth, and mixed with the food of the fto-
mach.

VIII. C'lrcumjiances by which the Fluids, that are effiifedhy the retrOf
■grade Motions of the abforbent Fejfels, are dijiingwjhed.

I . We frequently obferve an unufual quantity of mucus or othe?
fluids in fome difeafes, although the aftion of the glands, by which
thofe fluids are feparated from the blood, is not unufually increafed ;
but when the power of abforption alone is diminished. Thus the ca-
tarrhal humour from the noftrils of fome, who ride in frofty weather;
and the tears, which run down the cheeks of thofe, who have an ob-
flru£tion of the pundla lacrymalia ; and the ichor of thofe phagedenic
tslcers, which are not attended with inflammation, are all inftances of
this circvimftance.

Thefe fluids however are eafily diftinguiflied from others by their
abounding in ammoniacal or muriatic falts; whence they inflame the
circumjacent Ikin: thus in the catarrh the upper lip l)ecomes red and
fwelled from the acrimony of the mucus, and patients complain of
the faltnefs of its tafte. The eyes and cheeks are red with the corro-
fivc tears, and the ichor of fome herpetic eruptions erodes far and wide
the contiguous parts, and is pungently fait to the tafte, as fome pa-
tients have informed me.

Whilfl, on the contrary, thofe fluids, which are eiFufed by the re-
trograde adion of the lymphatics, arc for the moft part mild and in-
nocent; as water, chyle, and the natural mucus: or they take their
properties from the materials previoufly abforbed, as in the coloured

Sect. XXIX. 8. RETROGRADE ABSORBENTS, 339

or vinous urine, or that fcented with afparagus, defcribed be-
fore.

2. Whenever the fecretion of any fluid Is increafed, there Is at the
fame time an increafed heat in the part; for the fecreted fluid, as the-
bile, did not previoufly exifl: in the mafs of blood, but a new combi-
nation is produced in the gland. Now as folutions are attended with,
cold, fo combinations are attended with heat ; and it is probable the
fum of the heat given out by all the fecreted fluids of animal bodies
may be the caufe of their general heat above. that of the atmolphere.

Hence the fluids derived from increafed fecretions are readily diftin-
guiflied from thofe originating from the retrograde motions of the
lymphatics: thus an increafe of heat either in the difeafed parts, or
difFufed over the whole body, is perceptible, when copious bilious
ftoolsare confequent to an inflamed liver ; or a copious mucous faliva-
tion from the inflammatory angina.

3. When any fecreted fluid is produced In an unufual quantity,
and at the fame time the power of abforption is increafed in equal pro-
portion, not only the heat of the gland becomes more intenfe, but the
fecreted fluid becomes thicker and milder, its thinner and faline parts
being re-abforbed : and thele are diflinguifliable both by their greater
confiftence, and by their heat, from the fluids, which are efFufed by
the retrograde motions of the lymphatics ; as is obfervable towards the
termination of gonorrhoea, catarrh, chincough, and in thofe ulcers,
which are faid to abound with laudable pus.

4. When chyle is obferved in ftools, or among the materials ejefl:-
ed by vomit, we may be confident it muft have been brought thither
by the retrograde motions of the ladeals ; for chyle does not previoufly
exifl amid the contents of the inteflines, but is made in the very
mouths of the lafteals, as was before explained.

5. When chyle, milk, or other extraneous fluids are found ia
the urinary bladder, or in any other excretory receptacle of a gland ;
no one can for a moment believe, that thefe have been coUedled from

X X 2 the

340 RETROGRADE ABSORBENTS. Sect. XXIX. 9.

the mafs of blood bj a morbid fecretion, as it contradidls all ana-«
logy.

■Aurea durs

Mala ferant quercus ? Narcifco floreat alnus ?
Pinguia corticibus fudent eledra myrics ?

Virgil,

IX. Retrograde Motions of Vegetable Juices,

There are befides fome motions of the fap in vegetables, which
bear analogy to our prefent fubjedl j and as the vegetable tribes are by
many phiiofophers held to be inferior animals, it may be a matter of
curiofity at lead to obferve, that their abforbent veffels feem evidently,
at times, to be capable of a retrograde motion. Mr. Perault cut off
a forked branch of a tree, with the leaves on ; and inverting one of
the forks into a velTel of water, obferved, that the leaves on the other
branch continued green much longer than thofe of a fimilar branch,
cut off from the fame tree; which fhews, that the water from the
veffel was carried up one part of the forked branch, by the retrograde
motion of its veflels. and fupplied nutriment fome time to the other
part of the branch, which was out of the water. And the celebrated
Dr. Hales found, by numerous very accurate experiments, that the
fap of trees rofe upwards during the warmer hours of the day, and in
part defcended again during the cooler ones. Vegetable Statics.

It is well known that the branches of willows, and of many other
trees, will either take root in the earth or engraft on other trees,
fo as to have their natural diredlion inverted, and yet flourifh with
vigour.

Dr. Hope has alfo made this pleafing experiment, after the manner
of Hales — he has placed a forked branch, cut from one tree, ere£l be-
tween two others ; then cutting off a part of the bark from one fork
4 applied

Sect. XXIX. 10. RETROGRADE ABSORBENTS. 341

applied it to a fimilar branch of one of the trees in its vicinity ; and
the fame of the other fork ; fo that a tree is {een to grow fufpended in
the air, between two other trees; which fupplj their fofler friend
with due nourifhment.

Miranturque novas frondes, et non fua poma»

All thefe experiments clearly evince, that the juices of vegetables
can occafionally pafs either upwards or downwards in their abforbent
fyftem of veflels.

X. Objetilons anjwered.

The following experiment, at firlT: view, would feem to invalidate
this opinion of the retrograde motions of the lymphatic veflels, in
fome difeafes.

About a gallon of milk having been given to an hungry fwine, he
was fuffered to live about an hour, and was then killed by a ftroke or
two on his head with an axe. — On opening his belly the ladteals were
well feen filled with chyle; on irritating many of the branches of
them with a knife, they did not appear to empty themfelves haftily ;
but they did however carry forwards their contents in a little time.

I then pafled a ligature round feveral branches of la£leals, and irri-
tated them much with a knife beneath the ligature, but could not
make them regurgitate their contained fluid into the bowels,

I am not indeed certain, that the nerve was not at the fame time
included in the ligature, and thus the lymphatic rendered unirritable
or lifelefs ; but this however is certain, that it is not any quantity of
any flimulus, which induces the veflels of animal bodies to revert
their motions ; but a certain quantity of a certain flimulus, as appears
from wounds in the flomach, which do not produce vomitings and
wounds of the inteftines, which do not produce the cholera morbus.

342 RETROGRADE ABSORBENTS. Sect. XXIX. u.

At Nottingham, a few years ago, two flioemakers quarrelled, and
one of them with a knife, which they ufe in their occupation, {tabbed
his companion about the region of the ftomach. On opening the ab-
domen of the wounded man after his death the food and medicines
he had taken were in part found in the cavity of the belly, on the
otitfide of the bowels; and there was a wound about half an inchlonsr
at the bottom of the flomach ; which I fuppofe was difteiided with
liquor and food at the time of the accident ; and thence was more li-
able to be injured at its bottom : but during the whole time he lived,
which was about ten days, he had no efforts to vomit, nor ever even
complained of being lick at the ftomach i Other cafes fimilar to this
; are mentioned in the philofophical tranfa£lions.

Thus, if you vellicate the throat with a feather, naufea is produced;
if you wound it with a penknife, pain is induced, but not ficknefs.
So if the foles of the feet of children or their armpits are tickled,
convulfive laughter is excited, which ceafes the moment the hand is
applied, fo as to rub them more forcibly.

The experiment therefore above related upon the la£teals of a
-dead pig, which were included in a flridl ligature, proves nothing ; as
it is not the quantity, but the kind of flimulus, which excites the
lymphatic veffels into retrograde motion.

XL ^he Caufes which induce the Retrograde Motions of animal Vejfsls ;
4and the Medicines by which the natural Motions are refiored,

1. Such is the conftruflion of animal bodies, that all their parts,
which are fubjeded to lefs flimuli than nature defigned, perform their
fundions with lefs accuracy: thus, when too watery or too acefcent
food is taken into the ftomach, indigeftion, and flatulency, and heart-
burn fucceed.

2. Another law of irritation, connate with our exiftence, is, that

all

Sect. XXIX. II. RETROGRADE ABSORBENTS. 343

all thofe parts of the body, which have previoufly been expofed to too
great a quantity of fuch ftlmuli, as flrongly afFe£l them, become for
feme time afterwards difobedient to the natural quantity of their adapt-
ed ftimuli. — Thus the eye is incapable of feeing obje6ls in an obfcure
room, though the iris is quite dilated, after having been expofed to
the meridian fun.

3. There is a third law of irritation, that all the parts of our bodies,
which have been lately fubjefted to lefs flimulus, than they have been
accuftomed to, when they are expofed to their ufual quantity of fli-
mulus, are excited into more energetic motions : thus when we come
from a duiky cavern into the glare of daylight, our eyes are dazzled i
and after emerging from the cold bath, the fkin becomes warm and-
red.

4. There is a fourth law of irritation, that all the parts of our
bodies, which are fubjefted to flill ftronger ftimuli for a length of time,
become torpid, and refufe to obey even thefe flronger flimuli; and
thence do their offices very imperfeftly. — Thus, if any one looks
earneftly for fome minutes on an area, an inch diaineter,. of red filk,
placed on a ftieet of white paper, the image of the lilk will gradually
become pale, and at length totally vanilh.

5. Nor is it the nerves of fenfe alone, as the optic and auditory
nerves, that thus become torpid, when the flimulus is withdrawn or
their irritability decreafed; but the motive mufcles, when they are
deprived of their natural ftimuli, or of their irritability, become torpid
and paralytic ; as is feen in the tremulous hand of the drunkard in a
morning; and in the awkward ftep of age.

The hollow mufcles alfo, of which the various velTels of the body
are confl:ru£ted, when they are deprived of their natural ftimuli, or of
their due degree of irritability, not only become tremulous, as the ar-
terial, pulfations of dying people j but alfo frequently invert their
motions, as in vomiting, in hyfteric fufFocations, and diabetes above
defcribed.

Imuit

344 RETROGRADE ABSORBENTS. Sect. XXIX. 1 1,

I tnuft beg your patient attention, for a few moments whilft I en-
deavour to explain, how the retrograde a£lions of our hollow mufcles
are the confequence of their debility ; as the tremulous actions of the
folid mufcles are the confequence of their debility. When, through
fatigue, a mufcle can aft no longer ; the antagonift mufcles, either by
their inanimate elafticity, or by their animal aftion, draw the limb
into a contrary diredion : in the folid mufcles, as thofe of locomotion,
their a£lions are affociated in tribes, which have been accuflomed to
lynchronous aftion only; hence when they are fatigued, only a fingle
contrary effort takes place ; which is either tremulous, when the fa-
tigued mufcles are again immediately brought into adlion ; or it is a
pandiculation, or flretching, where they are not immediately again
brought into aftion.

Now the motions of the hollow mufcles, as they in general pro-
pel a fluid along their cavities, are aflbciated in trains, which have
been accuftomed to fucceflive actions : hence when one ring of fuch
a mufcle is fatigued from its too great debility, and is brought into
retrograde aftion, the next ring from its affociation falls fucceffively
into retrograde aftion ; and fo on throughout tl;ie whole canal. See
Sea. XXV. 6.

6. But as the retrograde motions of the ftomach, cefophagus, and
fauces in vomiting are, as it were, apparent to the eye; we fhall
confider this operation more minutely, that the limilar operations
in the more recondite parts of our fyflem may be eafier underftood.

From certain naufeous ideas of the mind, from an ungrateful tafte
in the mouth, or from foetid fmells, vomiting is fometimes inftantly
excited ; or even from a ftroke on the head, or from the vibratory
motions of a fhip; all which originate from affociation, or fy mpathy.
See Sea. XX. on Vertigo.

But when the flomach is fubjeded to a lefs ftimulus than is na-
tural, according to the firft law of irritation mentioned above,
its motions become diflurbed, as in hunger; firft pain is produced,

then

Sect. XXIX. II. RETROGRADE ABSORBENTS. 345

then ficknefs, and at length vain efforts to vomit, as many authors
inform us.

But when a great quantity of wine, or of opium, is fvYallowed,
the retro2:rade motions of the ftomach do not occur till after feveral
minutes, or even hours ; for when the power of fo ftrong a ftimulus
ceafes, according to the fecdnd law of irritation, mentioned above,
the periflaltic motions become tremulous, and at length retrograde ;
as is well known to the drunkard, who on the next morning has
licknefs and vomitings.

When a flill greater quantity of wine, or of opium, or when nau-
feous vegetables, or ftrong bitters, or metallic falts, are taken into the
ftomach, they quickly induce vomiting ; though all thefe in lefs
dofes excite the ftomach into more energetic adtiou, and ftrengthen
the digeftion ; as the flowers of chamomile, and the vitriol of zinc :
for, according to the fourth law of irritation, the flomach will not
long be obedient to a ftimulus fo much greater than is natural; but
its aftion becomes firfl tremulous and then retrograde.

7. When the motions of any veffels become retrograde, lefs heat
of the body is produced ; for in paroxyfms of vomiting, of hyfteric
affeftions, of diabetes, of afthma, the extremities of the body are cold :
hence we may conclude, that thefe fymptoms arife from the debility
of the parts in a£tion ; for an increafe of mufcular a6lion is always
attended with increafe of heat.

8. But as animal debility is owing to defect of ftimulus, or to defect
of irritability, as (hewn above, the method of cure is eafily deduced :
when the vafcular mufcles are not excited into their due adion by
the natural ftimuli, we fhould exhibit thofe medicines, which poffefs a
Hill greater degree of flimulus ; amongft thefe are the foetids, the vo-
latiles, aromatics, bitters, metallic falts, opiates, wine, which indeed
fhould be given in fmall dofes, and frequently repeated. To thefe
ihould be added conftant, but moderate exercife, cheerfulnefs of mind,
and change of country to a warmer climate ; and perhaps occalionally
the external ftimulus of bliflers.

Y y I|

34^ RETROGRADE ABSORBENTS. Sect. XXIX. ii.

It is alfo frequently ufeful to dimiiiifli the quantity of natural
ftimulus for a lliort time, by which afterwards the irritability of
the fyftem becomes increafed; according to the third law of irritation
above-mentioned, hence the ufe of baths fomewhat colder than ani-
mal heat, and of equitation in the open air.

'The catalogue of difeafes ozving to the retrograde motions of lymphatics
is here omitted, as it will appear in the fecond volume of this work.
The following is the conclufion to this thefts of Mr. Charles
Darwin.

Thus have I endeavoured in a concife manner to explain the nu-
merous difeafes, which deduce their origin from the inverted motions
of the hollow mufcles of our bodies : and it is probable, that Saint
Vitus's dance, and the ftammering of fpeech, originate from a fimiiar
inverted order of the affociated motions of fome of the folid mufcles ;
which, as it is foreign to my prefent purpofe, I (hall not here difcufs.

I beg, illuftrious profeflbrs, and ingenious fellow-ftudents, that
you will recolledt how difficult a talk I have attempted, to evince the
retrograde motions of the lymphatic veffels, when the veffels them-
felves for fo many ages efcaped the eyes and glaffes of philofophers :
and if you are not yet convinced of the truth of this theory, hold, I
entreat you, your minds in fufpenfe, till Anatomy draws her fword
with happier omens, cuts afunder the knots, which entangle Phy^
siOLOGY ; and, like an augur infpefting the immolated vidlim, an-
nounces to mankind the wifdom of HEAVEN.

SECT,

Sect. XXX. i. PARALYSIS OF THE LIVER. 347

SECT. XXX.

PARALYSIS OF THE LIVER AND KIDNEYS.

Bile-duSls lejs irritable after having been ftimulated much. 1. Jaundice from
faralyfis of the bile du£is cured by ek5iric Jhocks. 3. From bile-ftones. Expe-
riments on bile-Jiones. Oil vomit. 4. Palfy of the liver, two cafes, 5. Schir-
rofity of the liver. 6. Large livers of geefe. II. Paralyfis of the kidneys^
III. Story of Protnetheus.

I. FROM the ingurgltatioii of fpirituous liquors into the ftomach
and duodenum, the ternaination of the common bile-dudl in that
bowel becomes ftimulated into unnatural a£tion, and a greater quan-
tity of bile is produced from all the fecretory veflels of the liver, by
the aflbciation of their motions with thofe of their excretory duds;
as has been explained in Seftion XXIV. and XXV. but as all parts
of the body, that have been afFeded with ftronger ftimuli for any
length of time, become lefs fufceptible of motion, from their natural
weaker ftimuli, it follows, that the motions of the fecretory veflels,
and in confequence the fecretion of bile, is lefs than is natural durino-
the intervals of fobriety. 2. If this ingurgitation of fpirituous liquors
has been daily continued in coniiderable quantity, and is then fud-
denly intermitted, a languor or paralyfis of the common bile-dud is
induced ; the bile is prevented from being poured into the inteftines;
and as the bilious abforbents are ftimulated into ftronger adion by its
accunaulation, and by the acrimony or vifcidity, which it acquires by

Y y 2 delay.

34S PARALYSIS OF THE LIVER. Sect. XXX. r.

delay, it is abforbed, and carried to the receptacle of the chyle ; or
otherwile the fecretory velTels of the liver, by the above-mentioned
flimulus, invert their motions, and regurgitate their contents into
the blood, as fometimes happens to the tears in the lachrymal fack,
fee Se6t. XXIV. 2. 7. and one kind of jaundice is brought on.

There is reafon to believe, that the bile is moft frequently returned
into the circulation by the inverted motions of thefe hepatic glands,
for the bile does not feem liable to be abforbed by the lymphatics,
for it foaks through the gall-du6ls, and is frequently found in the
cellular membrane. This kind of jaundice is not generally attended
with pain, neither at the extremity of the bile-du6l, where it enters
the duodenum, nor on the region of the gall-bladder.

Mr. S. a gentleman between 40 and 50 years of age, had had the
jaundice about fix weeks, without pain, ficknefs, or fever; and had
taken emetics, cathartics, mercurials, bitters, chalybeates, effential
oil, and ether, without apparent advantage. On a fuppofition that
the obflruftion of the bile might be owing to the paralyiis, or torpid
action of the common bile-du<fl, and the frimulants taken into the
ftomach feeming to have no efFedl, I direfted half a fcore fmart
eleflric fhocks from a coated bottle, which held about a quart, to
be pafl'ed through the liver, and along the courfe of the common gall-
du£l> as near as could be guefled, and on that very day the ftools
became yellow ; he continued the eledric Ihocks a few days more,
and his fkin gradually became clear.

3. The bilious vomiting and purging, that affects fome people by
intervals of a few weeks, is a lefs degree of this difeafe ; the bile-duft
is lefs Irritable than natural, and hence the bile becomes accumulated
in the gall-bladder, and hepatic dudls, till by its quantity, acrimony or
vifcidity, a greater degree of irritation is produced, and it is fuddenly
evacuated, or laftly from the abforption of the more liquid parts of
the bile, the remainder becomes infpiflated, and chryftallizes into
4 mafles

Sect. XXX. i. PARALYSIS OF THE LIVER. 349

maiTes too large to pafs, and forms another kind of jaundice, where
the bile-duct is not quite paralytic, or has regained its irritability.

This difeafe is attended with much pain, which at firft is felt at the
pit of the ftomach, exactly in the centre of the body, where the bile-
du(£l enters the duodenum ; afterwards, when the fize of the bile-
ftones increafe, it is alfo felt on the right fide, where the gall-bladder
is fituated. The forrtier pain at the pit of the ftomach recurs by in-
tervals, as the bile-ftone is pufhed againft the neck of the du6t ; like
the paroxyfms of the flone in the urinary bladder, the other is a more
dull and conftant pain.

Where thefe bile-ftones are too large to pafs, and the bile-dufls
poffefs their fenfibility, this becomes a very painful and hopelefs
difeafe. I made the following experiments with a view to their
chemical folution.

Some fragments of the fame bile-ftone were put into the weak
fpirit of marine fait, which is fold in the fhops, and into folution of
mild alcalij and into a folution of cauftic alcali ; and into oil of tur-
pentine ; without their being diflblved. All thefe mixtures were
after fome time put into a heat of boiling water, and then the oil of
turpentine diffolved its fragments of bile-ftone, but no alteration
was produced upon thofe in the other liquids except fome change of
their colour.

Some fragments of the fame bile-ftone were put into vitriolic
aether, and were quickly diffolved without additional heat. Might
not aether mixed with yolk of egg or with honey be given advan-
tageoufly in bilious concretions ?

I have in two inftances feen from 30 to 50 bile-ftones come
away by ftool, about the fize of large peafe, after having given fix
grains of calomel in the evening, and four ounces of oil of almonds
or olives on the fucceeding morning. I have alfb given half a pint of
good olive or almond oil as an emetic during the painful fit, and

repeated

350 ^ PARALYSIS OF THE LIVER. Sect. XXX. i.

repeated it in half an hour, if the firft did not operate, with frequent
good effed.

4. Another difeafe of the Uver, which I have feveral times ob-
ferved, confifts in the inabihty or paralyfis of the fecretory veflels.
This difeafe has generally the fame caufe as the preceding one, the
too frequent potation of fpirituous liquors, or the too fudden omiffion
of them, after the habit is confined; and is greater or lefs in propor-
tion, as the whole or a part of the liver is affedled, and as the inability
or paralyfis is more or lefs complete.

This palfy of the liver is knowu from thefe fymptoms, the pa-
tients have generally paffed the meridian of life, have drank fer-
mented liquors daily, but perhaps not been opprobrious drunkards;
they lofe their appetite, then their flefh and ftrength diminifh in con-
fequence, there appears no bile in their ftools, nor in their urine, nor
is any hardnefs or fwelling perceptible on the region of the liver.
But what is peculiar to this difeafe, and diftinguifhes it from all others
at the firft glance of the eye, is the bombycinous colour of the fkin,
which, like that of full-grown filk worms, has a degree of tranf-
parency with a yellow tint not greater than is natural to the ferum of
the blood.

Mr. C. and Mr. B. both very ftrong men, between 50 and 60
years of age, who had drank ale at their meals inflead of fmall beer,
but were not reputed hard-drinkers, fuddenly became weak, loft
their appetite, flefli, and ftrength, with all the fymptoms above enu-
merated, and died in about two months from the beginning of their
malady. Mr- C. became anafarcous a few days before his death, and
Mr. B. had frequent and great haemorrhages from an iffiie, and fome
parts of his mouth, a few days before his death. In both thefe cafes
calomel, bitters and chalybeates were repeatedly ufed without effedl.

One of the patients defcribed above, Mr. C, was by trade a
plumber ; both of them could digeft no food, and died apparently for

want

Sect. XXX. I. PARALYSIS OF THE LIVER. ss^

want of blood. Might not the transfufion of blood be ufed in thefe
cafes with advantage ?

5. When the paralyfis of the hepatic glands is lefs complete, or lefs
univerfal, a fchirrofity of fome part of the liver is induced ; for the
fecretory veflels retaining fome of their living power take up a fluid
from the circulation, without being fufficiently irritable to carry it
forwards to their excretory dufts; hence the body, or receptacle of
each gland, becomes inflated, and this diftenfion increafes, till by its
very great ftimulus inflammation is produced, or till thofe parts of
the vifcus become totally paralytic. This difeafe is diflinguifliable
from the foregoing by the palpable hardnefs or largenefs of the liver ;
and as the hepatic glands are not totally paralytic, or the whole liver
not afFedled, fome bile continues to be made. The inflammations of
this vifcus, confequent to the fchirrofity of it, belong to the difeafes
of the fenlitive motions, and will be treated of hereafter.

6. The ancients are faid to have poflTefled an art of increafing the
livers of geefe to a fize greater than the remainder of the goofe.
Martial. 1. 13. epig. 58. — .This is faid to have been done by fat and
figs. Horace, 1. 2. fat. 8. — Juvenal fets thefe large livers before an
epicure as a great rarity. Sat. 5. 1. 114; and Perlius, fat. 6. 1. 71.
Pliny fays thefe large goofe-livers were foaked in mulled milk, that
is, I fuppofe, milk mixed with honey and wine; and adds, " that it
is uncertain whether Scipio Metellus, of confular dignity, or M.
Seftius, a Roman knight, was the great difcoverer of this excellent
difh." A modern traveller, I believe Mr. Brydone, aflerts that the
art of enlarging the livers of geefe ftill exifl:s in Sicily; and it is to
be lamented that he did not import it into his native country, as fome
method of affecting the human liver might perhaps have been col-
ledted from it ; befides the honour he might have acquired in improv-
ing our giblet pies.

Our wifer caupones, I am told, know how to fatten their fowls,
as well as their geefe, for the London markets, by mixing gin inftead

35a PARALYSIS OF THE LIVER. SECT.XXX.2.3.

of figs and fat with their food ; by which they are faid to become
fleepy, and to fatten apace, and probably acquire enlarged livers ; as
the fwine are aflerted to do, which are fed on the fediments of barrels >
in the diftilleries ; and which fo frequently obtains in thofe, who in-.
Efursitate much ale, or wine, or drams.

II. The irritative difeafes of the kidneys, pancreas, fpleen, and
other glands, are analogous to thofe of the liver above defcribed,
differing only in the confequences attending their inability to a<£tion.
For inftance, when the fecretory veffels of the kidneys become dif-
obedient to the ftimulus of the paffing current of blood, no urine is
feparated or produced by then) ; their excretory mouths become filled
with concreted mucus, or calculus matter, and in eight or tea days
ftupor and death fupervenes in confequence of the retention of the
feculent part of the blood.

This difeafe in a (lighter degree, or when only a part of the kidney
is affefted, is fucceeded by partial inflammation of the kidney in con-
fequence of previous torpor. In that cafe greater adlions of the
fecretory veffels occur, and the nucleus of gravel is formed by the in-
flamed mucous membranes of the tubuli uriniferi, as farther explained
in its place.

" This torpor, or paralyfis of the fecretory veffels of the kidneys,
like that of the liver, owes its origin to their being previoufly habi-
bituated to too great flimulus ; which in this country is generally
owino" to the alcohol contained in ale or wine; and hence muft be
reo"iftered amongft the difeafes owing to inebriety; though it may be
caufed bv whatever occafionally inflames the kidney; as too violent
ridino' on horfeback, or the cold from a damp bed, or by fleeping
on the cold ground; or perhaps by drinking in general too little
aqueous fluids.

III. I fliall conclude this fedion on the difeafes of the liver induced
by fpirituous liquors, with the well-known ffory of Prometheus,
which feems indeed to have been invented by phyficians in thofe

ancient

Sect. XXX. 3. PARALYSIS OF THE LIVER. 35-

ancient times, when all things were clothed in hieroglyphic, or in
fable. Prometheus was painted as flealing fire from heaven, which
might well reprefent the inflammable fpirit produced by fermentation ;
which may be faid to animate or enliven the man of clay : whence
the conquefts of Bacchus, as well as the temporary mirth and noife of
his devotees. But the after puniflTment of thofc, who fteal this ac-
curfed fire, is a vulture gnawing the liver; and well allegorifes
the poor inebriate lingering for years under painful hepatic dif-
eafes. When the expediency of laying a further tax on the diftilla-
tion of fpirituous liquors 'from grain was canvaffed before the Houfe
of Commons fome years ago, it was faid of the diftillers, with great
truth, " They take the bread from the people^ and convert it hito poifonV
Yet is this manufactory of difeafe permitted to continue, as appears by
its paying into the treafury above 920,000/. near a million of money
annually. And thus, under the names of rum, brandy, gin, whiiky,
ufquebaugh, wine, cyder, beer, and porter, alcohol is become the
baae of the Chriftian world, as opium of the Mahometan.

Evoe ! parce, liber?
Farce, gravi metuende thirfo !

HOR.

7. 7. SECT.

354' OF TEMPERAMENTS. Sect. XXXI. lo

SECT. XXXI.

OF TEMPERAMENTS.

'The temperament of decreajed irritahiltty known by weak ■pulje, targe pupils of the
eyes, cold extremities. Are generally Juppofed to be too irritable. Bear pain
better than labour. Natives of North-America contrafled with thofe upon the ■
coaji of Africa. Narrow and broad-fhouldered people. Irritable confiitutions
bear labour better than pain. II. Temperament of increafed fenftbility. Liable
to intoxication, to inflammation, hamontoe, gutta ferena, enthuftafm, delirium^
reverie. Thefe confiitutions are indolent to voluntary exertions, and dull to irri-
tations. The natives of South-America, and brute animals of this temperament,
III. Of increafed voluntarily ; thefe arefubjeSi to locked jaw, convulfions, epilepfy,
mania. Are very active, bear cold, hunger, fatigue. Arefuited to great exer-
tions. This temperament dijlinguifhes mankind from other animals. FV. Of
increafed affociation. Thefe have great memories, are liable to quartan agues,
and flronger fympathies of parts with each other. V. Change of temperaments
into one another.

ANTIENT writers have fpoken much of temperaments, but

without fufEcient precifioii. By temperament of the fyftem fhould

be meant a permanent predifpofition to certain clafles of difeafes :

without this definition a temporary predifpofition to every diftindl

malady might be termed a temperament. There are four kinds of

conftitution, which permanently deviate from good health, and are

perhaps fufficiently marked to be diftinguiflied from each other, and

conftitute the temperaments or predifpofitions to the irritative, fenii-

tive, voluntary, and aflbciate clafles of difeafes.

I. "the

Sect. XXXT. i. OF TEMPERAMENTS. ^^^

I. 77je Temper ameni of dea-eafed Irritability,

The difeafes, which are caufed by irritation, mofl frequently ori-
ginate from the defe6l of it ; for thofe, which are immediatelv owincr
to the excefs of it, as the hot fits of fever, are generally occafioned
by an accumulation of fenforial power in confequence of a previous
defedl of irritation, as in the preceding cold fits of fever. Whereas
the difeafes, which are caufed by fenfation and volition, moft fre-
quently originate from the excefs of thofe fenforial powers, as will
be explained below.

The temperament of decreafed irritability appears from the follow-
ing circumftances, which fliew that the mufcular fibres or organs of
{ei\(e. are liable to become torpid of quiefcent from lefs defeft of ili-
mulation than is produ6live of torpor or quiefcence in other con-
ftitutions.

I. The firfl is the weak pulfe, which in fome conftitutions is at
the fame time quick. 2. The next moft marked criterion of this tem-
perament is the largenefs of the aperture of the iris, or pupil of the
eye, which has been reckoned by fome a beautiful feature in the fe-
male countenance, as an indication of delicacy, but to an experienced
obferver it is an indication of debility, and is therefore a defe(fl, not
an excellence. The third moft marked circumftance in this confti-
tution is, that the extremities, as the hands and feet, or nofe and
ears, are liable to become cold and pale in fituations in refpe£l to
warmth, where thofe of greater flrength are not affefted. Thofe
of this temperament are fubjed to hyfteric affeilions, nervous ievers
hydrocephalus, fcrophula, and confumption, and to all other difeafes
of debility.

Thofe, who poffefs this kind of conflitution, are popularly fup-
pofed to be more irritable than is natural, but are in reality lefs fo.

Z z 2 ' This

356 OF TEMPERAMENTS. Sect. XXXI. i.

This miftake has arifen from their generally having a greater quick-
nefs of pulfe, as explained in Sedl. XII. i. 4. XII. 3. 3. ; but this fre-
quency of pulfe is not neceffary to the temperament, like the debility
of it.

Perfons of this temperament are frequently found amongft the
fofter fex, and amongft narrow-fliouldered men; who are faid to bear
labour worfe, and pain better than others. This laft circumftance is
fuppofed to have prevented the natives of North America from hav-
ing been made flaves of by the Europeans. They are a narrow-
fhouldered race of people, and will rather expire under the la(h, than
be made to labour. Some nations of Afia have fmall hands, as may
be feen by the handles of their fcymetars ; which with their narrow
fhoulders fhew, that they have not been accuftomed to fo great la-
bour with their hands and arms, as the European nations in agricul-
ture, and thofe on the coafts of Africa in fvvimming and rowing.
Dr. Maningham, a popular accoucheur in the beginning of this
century, obferves in his aphorlfms, that broad -Ihouldered men pro-
create broad-fhouldered children. Now as labour ftrengthens the
mufcles employed, and increafes their bulk, it would feem that a few
generations of labour or of indolence may in this refpedxhange the
form and temperament of the bod/.

■ On the contrary, thofe who are happily poffeffed of a great degree
of irritability, bear labour better than pain ; and are ftrong, active,
and ingenious. But there is not properly a temperament of in-
creafed irritability tending to difeafe, becaufe an increafed quantity
of irritative motions generally induces an increaie of pleafur.e or pain,
as in intoxication, or inflammation; and then the new motions are
the immediate confequences of increafed fen fation, not of increafed
irritation; which have hence been fo perpetually confounded with
each other.

11. 'Temperament

Sect. XXXI. 2. OF TEMPERAMENTS. -^^-j

II. 'Temperament of Senjibllity.

There is not properly a temperament, or predifpofition to difeafe,
from decreaied leniibility, (ince irritability and not fenlibility is im-
mediately neceffary to bodily health. Hence it is the excefs of fen-
fation alone, as it is the defe£l of irritation, that mofl frequently pro-
duces difeafe. This temperament of increafed fenfibility is known
from the increafed activity of all thofe motions of the organs of fenfe
and mufcles, which are exerted in confequence of pleafure or pain,
as in the beginning of drunkennefs, and in inflammatory fever. Hence
thofe of this conftitution are liable to inflammatory dileafes, as hepa-
titis ; and to that kind of confumption which is hereditary, and com-
mences with flight repeated hoemoptoe. They have high-coloured
lips, frequently dark hair and dark eyes with large pupils, and are in
that cale fubje£l to gutta ferena. They are liable to enthufiafm, de-
lirium, and reverie. In this lail circumftance they are liable to f!:art
at the clapping of a door; becaufe the more intent any one is on the
pafling current of his ideas, the greater furprife he experiences on
their being diflevered by fome external violence,, as explained in
Sedt. XIX. on reverie.

As in thefe conflitutions more than the natural quantities of fen-
fitive motions are produced by the increafed quantity of fenfation
exifting in the habit, it follows, that the irritative motions will be
performed in fome degree with lefs energv, owing to the great ex-
penditure of fenforial power on the fenfitive ones. Hence thofe of
this temperament do not attend to flight Emulations, as explained in
Se£l. XIX. But when a ftimulus is fo great as to excite fenfation, it
produces greater fenfitive aftions of the fyftem than in others ; fuch
as delirium or inflammation. Hence they are liable to be abfent in
company ; fit or lie long in one pofture ; and in winter have the Ikin

35S OF TEMPERAMENTS. Sect. XXXI. 3.

of their legs burnt into various colours by the fire. Hence alfo they
are fearful of pain ; covet mufic and fleep ; and delight in poetry and
romance.

♦As the motions in confequence of fenfation are more than natural,
it alfo happens from the greater expenditure of fenforial power oix
them, that the voluntary motions are lefs eafilj exerted. Hence the
I'ubjefts of this temperament are indolent in refpe6l to all voluntary
exertions, M'hether of mind or body.

A race of people of this defcription feems to have been found by
the Spaniards in the iflands of America, where they firft landed, ten
of whom are faid not to have confumed more food than one Spaniard,
nor to have been capable of more than one tenth of the exertion of a
Spaniard. Robertfon's Hiftory. — In a ftate fimilar to this the greateft
part of the animal world pafs their lives, between fleep or inadive
reverie, except when they are excited by the call of hunger.

III. 'The 'Temperament of increafed Vduntarity.

Those of this conftitution differ from both the lafl: mentioned ia
this, that the pain, which gradually fubfides in the firft, and is pro-
dudive of inflammation or delirium in the fecond, is in this fucceded
by the exertion of the mufcles or ideas, which are moft frequently
conneded with volition ; and they are thence fubjefl to locked jaw,
convulfions, epilepfy, and mania, as explained inSedt.XXXIV. Thofe
of this temperament attend to the flighteft irritations or fenfations,
and immediately exert themfelves to obtain or avoid the objeds of
them ; they can at the fame time bear cold and hunger better than
others, of which Charles the Twelfth of Sweden was an inftance.
They are fuited and generally prompted to all great exertions of ge-
nius or labour, as their defires are more extenfive and more vehement,
and their powers of attention and of labour greater. . It is this facility
8 of

Sect. XXXI. 4. OF TEMPERAMENTS. 359

of voluntary exertion, which diftinguiihes men firom brutes, and which
has made them lords of the creation.

IV. Tie 'temperament ofincreafed ^Jfociation,

This conftitution confifts in the too great facility, with which the
fibrous motions acquire habits of affociation, and by which thefe af-
fociations become proportionably ftronger than in thofe of the other
temperaments. Thofe of this temperament are flow in voluntary
exertions, or in thofe dependent on fenfation, or on irritation. Hence
great memories have been faid to be attended with lefs fenfe and lefs-
imagination from Ariftotle down to the prefent time ; for by the word
memory thefe writers only underftood the unmeaning repetition of
words or numbers in the order they were received, without any vo-
luntary efforts of the mind.

In this temperament thofe aflbciations of motions, which are com-
monly termed fympathies, a£l with greater certainty and energy, as
thofe between difturbed vifion and the inverfion of the motion of the
ftomach, as in fea-ficknefs ; and the pains in the ftioulder from hepatic
inflammation. Add to this, that the catenated circles of anions are of
g;reater extent than in the other conftitutions. Thus if a flrons; vo-
mit or cathartic be exhibited in this temperament, a fmaller quantity
will produce as great an efFeft, if it be given feme weeks afterwards ;
whereas in other temperaments this is only to be expefted, if it be
exhibited in a ftw days after the firfl: dofe. Hence quartan agues are
formed in thofe of this temperament, as explained in Sedlion XXXII.
on dileafes from irritation, and other intermittents are liable to recur
from flight caufes many weeks after they have been cured by the
bark.

V. The

360 OF TEMPERAMENTS. Sect. XXXI. 5.

V. The firft of thefe temperaments differs from the ftandard of
health from defedl, and the others from excefs of fenforial power;
but it fometimes happens that the fame individual, from the changes
introduced into his habit by the different feafons of the year, modes
or periods of Ufe, or by accidental difeafes, palTes from one of thefe
temperaments to another. Thus a long ufe of too much fermented
liquor produces the temperament of increafed fenfibility ; great indo-
lence and folitude that of decreafed irritability ; and want of the ne»
ceflaries of life that of increafed voluntarity.

SECT.

Sect .XXXII. r. DISEASES OF IRRITATION. q6i

SECT. XXXII.

DISEASES OF IRRITATION.

I, Irritative fevers ivith ftrong p'ulfe. With weak pul/e. Symptoms of fever.
Their fource. II. I. ^ick pulfe is owing to decreafed irritability. 2. Not in
jleep or in apoplexy. 3. From inanition. Owing to deficiency of fenforial power.
III. I. Caufes of fever. From defe£i of heat. Heat fromfecretions. Fain
of cold in the loins and forehead, 1. Great expenje of fenforial power in the vital
motions. Immerfton in cold water. Succeeding glow of heat. Difficult refpi-
ration in cold bathing explained. Why the cold bath invigorates. Bracing and
relaxation are mechanical terms. 3. Ufes of cold bathing. Ufes of coid air in
fevers. 4. Ague fits froin cold air. Whence their periodical returns. IV. De-
feat of diftention a caufe of fever. Deficiency of blood. Transfufion of Mood.
V. I. DefeSl of momentum of the blood from mechanic ftimuli. 2. jiir injeoied
into the blood-veffels. 3. Exercife increafes the momentum of the blood, j^. Some-
times bleeding increafes the momentum of it. VI. Influence cf the fun and moon
on difeafes. The chemical ftimulus of the blood. Menftruation obeys the luna-
tions, juries, VII. ^iefcence of large glands a caufe of fever. Swelling of
the pracordM. VIII. Other caufes cf quiefce-nce, as hunger, bad air, feary
anxiety. IX. i. Symptoms of the cold fit. 2. Of the hot fit. 3. Second cold
fit why. 4. Inflammation introduced, or delirium, crftupor. X. Recapitulation.
Fever not an effort ofjtatiire to relieve herfelf, Do£frine offpafm.

I. WHEN the contractile fides of the heart and arteries perform
a greater number of pulfations in a given time, and move through a
orreater area at each pulfation, whether thefe motions are occafioned
by the ftimulus of the acrimony or quantity of the blood, or by their
affociation with other irritative motions, or by the increafed irritability

3 A ' of

362 t)ISEASES OF IRRITATION. Sect. XXXII. r.

of the arterial fyftem, that is, by an increafed quantity of fenforial
power, one kind of fever is produced ; which may be called Synocha
irritativa, or Febris irritativa pulfu forti, or irritative fever with ftrong
pulfe.

When the contra<5lile fides of the heart and arteries perform s).
greater number of pulfations in a given time, but move through a.
much lefs area at each pulfation, whether thefe motions are occafioned:
by defeat of their natural ftimuli, or by the defeft of other irritative
motions with which they are alTociated, or from the inirritability o£
the arterial fyftem, that is, from a decreafed quantity of fenforial
power, another kind of fever arifes ; which may be termed, Typhus
irritativus, or Febris irritativa pulfu debili, or irritative fever with weak
pulfe. The former of thefe fevers is the fynocha of nofologifts, and'
the latter the typhus mitior, or nervous fever. In the former there
appears to be an increafe of fenforial power, in the latter a deficiency
of it ; which is fliewn to be the immediate caufe of ftrength and
weaknefs, as defined in Se£l. XII. i. 3;^

It ftiould be added, that a temporary quantity of ftrength or debility^
may be induced by the defedl or excefs of ftimulus above what is.
natural; and that in the fame fever debility always exijls during the-
cold jit, though Jirength does not always exijl during the hot Jit,

Thefe fevers are always connedled with,, and generally induced by,,
the difordered irritative motions of the organs of fenfe, or of the in-
teftinal canal, or of the glaiidular fyftem, or- of the abforbent fyftem ; '-
and hence are always complicated with fome or many of thefe dif-
ordered motions, which are termed the fymptoms of the fever, and;
which compofe the great variety in thefe difeafes.

Th-e irritative fevers both with ftrong and with weak pulfe, as well
as the fenfitive fevers with ftrong and with weak pulfe, which are to-
be defcribed in the next feftion, are liable to periodical remiflions, and.
then they take the name of intermittent fevers, and are diftinguiflied:
fey the periodical times of their accefs,^

XL For

Sect. XXXII. 2. DISEASES OF IRRITATION. 363

II, For the better illuftration of the phenomena of irritative
fevers we muft refer the reader to the circunnftances of irritation ex-
plained in Se6t. XII. and {hall commence this intricate fubjedt by
fpeaking of the quick pulfe, and proceed by confidering many of the
caufes, which either feparately or in combination moft frequently
produce the cold fits of fevers.

I. If the arteries are dilated but to half their ufual diameters,
though they contract twice as frequently in a given time, they will
circulate only half their ufual quantity of blood ; for as they are cy-
linders, the blood which they contain muft be as the fquares of their
diameters. Hence when the pulfe becomes quicker and fmaller in
the fame proportion, the heart and arteries acl with lefs energy than
in their natural ftate. See Sedl. XII. i. 4.

That this quick fmall pulfe is owing to want of irritability, ap-
pears, firfl:, becaufe it attends other fymptoms of want of irritability ;
and, fecondly, becaufe on the application of a fcimulus greater than
ufual, it becomes flower and larger. Thus in cold fits of agues, in
hyfleric palpitations of the heart, and when the body is much ex-
haufted by haemorrhages, or by fatigue, as well as in nervous fevers,
the pulfe becomes quick and fmall ; and fecondly, in all thofe cafes if
an increafe of ftimulus be added, by giving a httle wine cr opium ;
the quick fmall pulfe becomes flower and larger, as any one may
eafily experience on himfelf, by counting his pulfe after drink in o- one
or two glafles of wine, when he is faint from hunger or fatigue.

Now nothing can fo ftrongly evince that this quick fmall pulfe is
owing to defeft of irritability, than that an additional ftimulus, above
what is natural, makes it become flower and larger immediately : for
what is meant by a defeft of irritability, but that the arteries and
heart are not excited into their ufual exertions by their ufual quantity
of ftimulus ? but if you increafe the quantity of ftimulus, and they
immediately ad with their ufual energy, this proves their previous
want of their natural degree of irritabihty. Thus the tremblino-

3 A 2 hands

364 DISEASES OF IRRITATION. Sect. XXXIL 2.

hands of drunkards in a morning become fteady, and acquire ftrength
to perform their ufual offices, by the accuflomed ftimulus of a glafs
or two of brand V.

1. In fleep and in apoplexy the pulfe becomes flower, which is not
owing to defe6l of irritability, for it is at the fame time larger ; and
thence the quantity of the circulation is rather increafed than diminiihed.
In thefe cafes the organs of fenfe are clofed, and the voluntary power
is fufpended, while the motions dependent on internal irritations, as
thofe of digeftion and fecretion, are carried on with more than their
ufiial vigour ; which has led fuperficial obfervers to confound thefe
cafes with thofe arifing from want of irritability. Thus if you lift
up the eyelid of an apoplectic patient, who is not actually dying, the
iris will, as ufual, contradl itfelf, as this motion is aflbciated with
the ftimulus of light ; but it is not fo in the laft ftages of nervous
fevers, where the pupil of the eye continues expanded in the broad
day-light : in the former cafe there is a want of voluntary power, in
the latter a want of irritability.

Hence alfo thofe conftitutions which are deficient in quantity of
irritability, and which poflefs too great fenfibility, as during the pain
of hunger, of hyfteric fpafms, or nervous headachs, are generally
fuppofed to have too much irritability; and opium, which in its due
dofe is a moft powerful ftimulant, is erroneoufly called a fedative ;
becaufe by increafing the irritative motions it decreafes the pains
arifing from defedl of them.

Why the pulfe fliould become quicker both from an increafe of
irritation, as in the fynocha irritativa, or irritative fever with ftrong
pulfe ; and from the decreafe of it, as in the typhus irritativus, or irri-
tative fever with weak pulfe ; feems paradoxical. The former cir-
cumftance needs no illuftration ; fince if the ftimulus of the blood, or
the irritability of the fanguiferous fyftem be increafed, and the ftrength
of the patient not diminiihed, it is plain that the motions muft be
performed quicker and ftronger.

Sect. XXXII. 2. DISEASES OF IRRITATION. 365

In the latter circumftance the weaknefs of the mufcular power of
the heart is foon over-balanced by the elafticity of the coats of the ar-
teries, which they poffefs befides a mufcular power of contraftion ;
and hence the arteries are diftended to lefs than their ufual diameters.
The heart being thus flopped when it is but half emptied, begins
fooner to dilate again ; and the arteries being dilated to lefs than their
•ufual diameters, begin fo much fooner to contract: themfelves ; info-
much, that in the lad ftages of fevers with weaknefs the frequency of
pulfation of the heart and arteries becomes doubled ; which, however,
is never the cafe in fevers with ftrength, in which they feldom ex-
ceed 118 or 120 pulfations in a minute. It muft be added, that in
thefe cafes, while the pulfe is very fmall and very quick, the heart
often feels large, and labouring to one's hand ; which coincides with,
the above explanation, fliewing that it does not completely empty
itfelf. ' ,

3. In cafes however of debility from paucity of blood, as in ani-
mals which are bleeding to death in the flaughter-houfe, the quick
pulfations of the heart and arteries may be owing to their not being
diftended to more than half their ufual diaftole ; and in confequence
they muft contra£l fooner, or more frequently, in a given time. As
weak people are liable to a deficient quantity of blood, this caufe may
occafionally contribute to quicken the pulfe in fevers with debility,
which may be known by applying one's hand upon the heart as
above ; but the principal caufe 1 fuppofe to confift in the diminution
of fenforial power. When a mufcle contains, or is fupplied with
but little fenforial power, its contraftion foon ceafes, and in confe-
quence may foon recur, as is feen in the trembling hands of people
weakened by age or by drunkennefs. See Se£t. XII. i . 4. XII. 3. 4.

It may neverthelefs frequently happen, that both the deficiency

of fllmulus, as where the quantity of blood is leffened (as defcribed

in No. 4. of this fedion), and the deficiency of fenforial power, as in

5 thofe

366 DISEASES OF IRRITATION. Sect. XXXII. 3.

thofe of the temperament of inirritability, defcrlbed in Seft. XXXI.
occur at the fame time j which will thus add to the quicknefs of the
pulfe and to the danger of the difeafe.

III. I. A certain degree of heat is neceflary to mufcular motion,
and is, in confequence, effential to hfe. This is obferved in thofe ani-
mals and infefts which pafs the cold feafon in a torpid ftate, and which
revive on being warmed by the fire. This neceffary ftimulus of heat
has two fources ; one from the fluid atmofphere of heat, in which all
things are immerfed, and the other from the internal combinations of
the particles, which form the various fluids, which are produced in
the extenfive fyftems of the glands. When either the external heat,
which furrounds us, or the internal production of it, becomes leffened
to a certain degree, the pain of cold is perceived.

This pain of cold is experienced moll: fenfibly by our teeth, when,
ice is held in the mouth ; or by our whole fyflem after having been
previoufly accuftomed to much warmth. It is probable, that this
pain does not arife from the mechanical or chemical efFefts of a defi-
ciency of heat ; but that, like the organs of fenfe by which we per-
ceive hunger and thirft, this fenfe of heat fufi"ers pain, when the ftimu-
lus of its objeft is wanting to excite the irritative motions of the or-
gan; that is, when the fenforial power becomes too much accumu-
lated in the quiefcent fibres. See Sedt. XII. 5. 3. Fer as the pe-
riftaltic motions of the ftomach are leffeued, when the pain of hunger
is great, fo the a£lion of the cutaneous capillaries are leflened during
the pain of cold ; as appears by the palenefs of the Ikin, as explained
in Seft. XIV. 6. on the production of ideas.

The pain in the fmall of the back and forehead in the cold fits of
the ague, in nervous hemicrania, and in hyfteric paroxyfms, when all
the irritative motions are much impaired, feems to arife from this
caufe ; the vefTels of thefe membranes or mufcles become torpid by
their irritative affociations with other parts of the body, and thence'

7 ^ produce

Sect.XXXII.3. diseases OF IRRITATION. 367

produce lefs of their accuftomed fecretioiis, and in confequence lefs
heat is evolved, and they experience the pain of cold ; which eold-
nefs may often be felt by the hand applied upon the affefted part.

2. The importance of a greater or lefs dediiilion of heat from the
fyftem M'ill be more eafy to comprehend, if we firft confider the great
expenfe of fenforial power ufed in carrying on the vital motions ;
that is, which circulates, abforbs, fecretes, aerates, and elaborates the
whole mafs of fluids with unceafing affiduity. The fenfcwial power,
or fpirit of animation, ufed in giving perpetual and ftrong motion to
the heart, which overcomes the elaflicity and vis inertise of the whole
arterial fyftem j next the expenfe of fenforial power in moving with
great force and velocity the innumerable trunks and ramifications of
the arterial fyftem ; the expenfe of fenforial power in- circulating the
whole mafs of blood through the long and intricate intortions of the
very fine vefTels, which compofe the glands and capillaries ; then the
expenfe of fenforial power in the exertions of the abforbent extremi-
ties of all the la£teals, and of all the lymphatics, which open their
mouths on the external furface of the Ikin, and on the internal fur-
faces of every celt or interftice of the body ; then the expenfe of fen-
forial power in the venous abforption, by which the blood is received
from the capillary veffels, or glands, where the arterial power ceafeSy
and is drank up, and returned to the heart ; next the expenfe of fen-
forial power ufed by the mufcles of refpiration in their office of perpetu-
ally expanding the bronchia, or air-vefiels, of the lungs ; and laftly in
the unceafing periflaltic motions of the ftomach and whole fyftem of
inteftines, and in all the fecretions of bile, gaftric juice, mucus, per-
ipirable matter, and the various excretions from the fyftem. If we
confider the ceafelefs expenfe of fenforial power thus perpetually em-
ployed, it will appear to be much greater in a day than all the volun-
tary exertions of our mufcles and organs of fenfe confume in a week ;;
and all this without any fenfible fatigue ! Now, if but a part of thefe
vital motions are impeded, or totally flopped for but a Ihort time, we:

gain

368 DISEASES OF IRRITATION. Sect. XXXII. 3.

gain ail idea, that there muft be a great accumulation of fen ferial
power ; as its produ£tion in thefe organs, which are fubjedt to perpe-
tual adivity, is continued during their quiefcence, and is in confe-
quence accumulated.

While, on the contrary, where thofe vital organs a£t too forcibly
by increafe of ftimulus without a proportionally-increafed produdion
of fenforial power in the bi^ain, it is evident, that a great deficiency of
action, that is torpor, muft foon follow, as in fevers ; whereas the
locomotive mufcles, which a£t only by intervals, are neither liable to
fo great accumulation of fenforial power during their times of inadi-
vity, nor to fo great an exhauftion of it during their times of adion.

Thus, on going into a very cold bath, fuppofe at ^^ degrees of
heat on Fahrenheit's fcale, the aftion of the fubcutaneous capillaries, -or
o-lands, and of the mouths of the cutaneous abforbents is diminifhed,
or ceafes for a time. Hence lefs or no blood paflfes thefe capillaries,
and palenefs fucceeds. But foon after emerging from the bath, a
more florid colour and a greater degree of heat is generated on the
fkin than was poffefied before immerfion ; for the capillary glands,
after this quiefcent ftate, occafioned by the want of ftimulus, become
more irritable than ufual to their natural ftimuh, owing to the accu-
mulation of fenforial power, and hence a greater quantity of blood is
tranfmitted through them, and a greater fecretion of perfpirable mat-
ter; and, in confequence, a greater degree of heat fucceeds. During
the continuance in cold water the breath is cold, and the ad of re-
fpiration quick and laborious ; which have generally been afcribed to
the obftrudion of the circulating fluid by a fpafm of the cutaneous
veflels, and by a confequent accumulation of blood in the lungs, oc-
cafioned by the preflure as well as by the coldnefs of the water. This
is not a fatisfadory account of this curious phsenomenon, fince at this
time the whole circulation is lefs, as appears from the fmallnefs of the
pulfe and coldnefs of the breath ; which fliew that lefs blood pafles
through the lungs in a given time; the fame laborious breathing

imme-

Sect. XXXII. 3- DISEASES OF IRRITATION. 3^9

immediately occurs when the palenefs of the ikhi 15 produced by fear,
■where no external cold or prefiure are applied.

The minute veffels of the bronchia, through which the blood pafles
from the arterial to the venal fyflem, and which correfpond with the
cutaneous capillaries, have frequently been expofed to cold air, and
become quiefcent along with thofe of the Ikin ; and hence their mo-
tions are fo affociated together, that when one is affected either with
quiefcencc or exertion, the other fympathizes with it, according to
the laws of irritative aflbciation. See Seft. XXVII. i. on hsemor-
rhages.

Befides the quiefcence of the minute veffels of the lungs, there are
many other fyftems of veffels which become torpid from their irrita-
tive affociations with thofe of the (kin, as the abforbents of the blad-
der and inteftines ; whence an evacuation of pale urine occurs, when
the naked Ikin is expofed only to the coldnefs of the atmofphere ; and
fprinkling the naked body with cold water is known to remove even
pertinacious conflipation of the bowels. From the quiefcence of
fuch extenfive fyftems of veffels as the glands and capillaries of the
Ikin, and the minute veffels of the lungs, with their various ablbrb-
ent feries of veffels, a great accumulation of fenforial powers is occa-
lioned ; part of which is again expended in the increafed exertion of
all thefe veffels, with an univerfal glow of heat in confequence of
this exertion, and the remainder of it adds vigour to both the vital and
voluntary exertions of the whole day.

If the aclivity of the fubcutaneous veffels, and of thofe with which
their aftions are affociated, was too great before cold immerfion, as in the
hot days of fummer, and by that means the fenforial power was previ-
eufly diminifhed, we fee the caufe why the cold bath gives fuch prefent
ftrength ; namely, by flopping the unneceffary activity of the fubcu-
taneous veffels, and thus preventing the too great exhauftion pf fen-
forial power ; which, in metaphorical language, has been called ^•<7^/;^g•
tJie fylliem : which is, however, a mechanical term, only applicable

5 B to

370 DISEASES OF IRRITATION. S^ct. XXXII. 3,.

to drums, or mufical firings : as oa the ceritrary the word relaxa-
tion, when applied to living animal bodies, can only mean too fmall;
a quantity of flimulus, or too fmall a quantity of lenforial power ; as
explained in Se<^. XII. i.

3.. This experiment of cold bathing prefents us with a fimple fe-
v.er-fit ; for the pulfe is weak, fmall, and quick during the cold im-
merfion.; and becomes flrong, full, and quick during the fubfequent
glow of heat ; till in a few minutes thefe fymptoms fubfide, and the:
temporary fever ceafes.

In thofe conftitutions where the degree of inirritability, or of debi-
lity, is greater than natural, the coldnefs and palenefs of the Ikinwith
the quick and weak pulfe continue a long time after the patient leaves
the bath ; and the fubfequent heat approaches by unequal flufhings,
and he feels himfelf difordered for many hours. Hence the bathing;
in a cold fpringof water, where the heat is but forty-eight degrees orij
Fahrenheit's thermometer, much difagrees with thofe of weak or inirri--
table habits of body ; who poffefs fo little fenforial power, that they,
cannot without injury bear to have it diminifhed even for a (hort
time; but who can neverthelefs bear the more temperate coldnefs.
of Buxton bath, which is about eighty degrees of. heat, and which;:,
ftreno-thens them, and makes them by habit lefs liable to great quief-
cence from fmall variations of cold, and thence lefs liable to be difor--
dered by the unavoidable accidents of life. Hence it appears, why.-
people of thefe inirritable conftitutions, which is another expreflioii,
for fenforial deficiency,. are often much injured by bathing in a cold;
fpring of water ; and why they fhould continue but a very fhort time
in baths.v which are colder than their bodies ; and fliouid gradually in-
creafe both the degree of coldnefs of the water, and the time of their-
continuance in it, if they would obtain falutary effedls from cold im-?
merfions. See Sed. XII. 2. i.

On the other hand in all cafes where the heat of the external fur-
face of the body, or of the internal furface of the lungs, is greater than :
7 natural,,

Sect. XXXII. 3. DISEASES OF IRRITATION. 371

natural, the ufe of expofure to cool air may be deduced. In fever-
fits attended with ftrength, that is with great quantity of'fenforial
power, it removes the additional ftimulus of heat from the furfaces
above mentioned, and thus prevents their excefs of ufelefs motion ;
and in fever- fits attended with debility, that is with a deficiency of
the quantity of fenforial power, it prevents the great and dangerous
wafte of fenforial power expended in the unnecefTary increafe of the
adlions of the glands and capillaries of the fkin and lungs.

4. In the fame manner, when any one is long expofed to very cold
air, a quiefcence is produced of the cutaneous and pulmonary ca-
pillaries and abforbents, owing to the deficiency of their ufual flimu-
lus of heat ; and this quiefcence of fo great a quantity of veiTels af-
fefts, by irritative afTociation, the whole abforbent and glandular {yf-
tem, which becomes in a greater or lefs degree quiefcent, and a cold
fit of fever is produced.

If the deficiency of the flimulus of heat is very great, the quief-
cence becomes fo general as to extinguifh life, as in thofe who are fro-

zen to death.

If the deficiency of heat be in lefs degree, but yet fo great as in

fome meafure to diforder the fyflem, and fhould occur the lucceeding
day, it will induce a greater degree of quiefcence than before, from
its acling in concurrence with the period of the diurnal cnxle of ac-
tions, explained in Sedl. XXXVI. Hence from a fmall beginning a
greater and greater degree qf quiefcence may be induced, till a com-
" plete fever-fit is formed ; and which will continue to recur at the pe-
riods by which it was produced. See Se£t. XVII. 3. 6.

If'the degree of quiefcence occafioned hy defeft of the ftimulus of
heat be very great, it will recur a fecondtime by a {lighter caufe, than
that which firfl: induced it. If the caufe, which induces the fecond
fit of quiefcence, recurs the facceeding day, the quotidian fever is pro-
duced ; if not till the alternate day, the tertian fever ; and if not till
;after feventy-two hours from the firft fit of quiefcence, the quartan

3 B 5 fever

373 DISEASES OF IRRITATION. Sect. XXXII. 4,

fever is formed. This laft kind of fever recurs lefs frequently thaa
the other, as it is a difeafe only of thofe of the temperament of affoci-
ability, as mentioned in Seft. XXXI. ; for in other conftitutions the
eapability of forming a habit ceafes, before the new caufe of quiefcence.
is again applied, if that does not occur fooner than in feventy-two
hours.

And heace thofe fevers, whofe caufe is from col-d air of the night or-
morning, are more liable to obferve the folar day in their periods ;.
while thofe from other ca,ufes frequently obferve the lunar day in
their periods, their paroxyfms returning near an hour later every day,
as explained in Sedl. XXXVI.

IV. Another frequent caufe of the cold fits of fever is the defe£l of
the flimulus of diftention. The whole arterial fyftem would appear^
by the experiments of Haller, to be irritable by no other ftimulus, and.
the motions of the heart and alimentary canal are certainly in fome
meafure dependant on the fame caufe. See Sedl. XIV. 7. Hence
there can be no wonder, that the diminution of diftention fhould fre-^
quently induce the quiefcence, which conftitutes the beginning of fe-
ver-fits. ~ •

Monfieur Leiutaud has judicioufly mentioned the deficiency of the-
quantity of blood amongft the caufes of difeafes, which he fays is fre-
quently evident in difleftions : fevers are hence brought on by great
haemorrhages, diarrhoeas, or other evacuations; or from the continued;
-ufe of diet, which contains but little nourifhraent ; or from the exhauf-
tion occafioned by violent fatigue, or by thofe chronic difeafes irt
which the digeftion is much impaired ; as where the ftomach has
been long affeded with the gout or fchirrus; or in the paralyfis of
the liver, as defcribed in Sed. XXX. Hence a paroxyfm of gout is.
liable to recur on bleeding or purging ; as the torpor of fome vifcus,.
which precedes the inflammation of the foot, is thus induced by the
want of the ftimulus of diftention. And hence the extremities of
the body, as the nofe and fingers, are more liable to become cold,.

when

Sect. XXXII. 5. DISEASES OF IRRITATION. ^-js

when we have long abftained from food ; and hence the pulfe is in-
creafed both in ftrength and velocity above the natural ftandard after
a full meal by the flimulus of diftention^

However, this ftimulus of diftention, like the flimulus of heat
above defcribed, though it contributes much to the due adtion not only
of the heart, arteries, and alimentary canal, but feems neceflary to the
proper fecretion of all the various glands ; yet perhaps it is not the
fole caufe of any of thefe numerous motions : for as the la6leals, cu-
taneous abforbents, and the various glands appear to be Simulated into
action by the peculiar pungency of the fluids they abforb, fo in the
inteftinal canal the pungency of the digefting aliment, or the acri-
mony of the faeces, feem to contribute, as well as their bulk, to pro-
mote the periflaltic motions ; and in the arterial fyflem, the mo-
' mentum of the particles of the circulating blood, and their acrimony,
ftimulate the arteries, as well as the diftention occafioned by it.
Where the pulfe is fmall this defedl of diftention is prefent, and con-
tributes much to produce the febris irritativa pu'lfu debili, or irritative
fever with weak pulfe, called by modern writers nervous fever, as a
predifponent caufe. See Sedl. XII. i. 4. Might not the transfufioa
of blood, fuppofe of four ounces daily from a ftrong man, or other
healthful animal, as a fheep or an afs, be ufed in the early ftate of ner--
vous or putrid fevers with great profpeft of fuccefs ?

V. The defedl of the momentum of the particles of the circu-
lating blood is another caufe of the quiefcence, vvith which the cold
fits of fever commence. This ftimulus of the momentum of the
progreffive particles of the blood does not ad over the whole body
like thofe of heat and diftention above defcribed, but is confined to the
arterial fyflem j and differs from the ftimulus of the diftention of the
blood, as much as the vibration of the air does from the currents of
it. Thus are the different organs of our bodies ftimulated by four
different mechanic properties of the external world : the fenfe of
touch by the preffure of folid bodies fo as to diftinguifh their figure %.

the- .

374 DISEASES OF IRRITATION. Sect. XXXII. 5,

the mufcular fyftem by the diftentioa, which they occafion ; the in-
ternal furface of the arteries, by the momentum of their moving par-
ticles ; and the auditory nerves, by the vibration of them : and thefe
four mechanic properties are as different from -each other as the vari-
ous chemical ones, which are adapted to the numerous glands, and to
the other organs of fenfe.

2. The momentum of the progreffive particles of blood is com-
pounded of their velocity and their quantity of matter : hence what-
ever circumftances diminifh either of thefe without proportionally in-
creafing the other, and without fuperadding either of the general fti-
muli of heat or diftention, will tend to produce a quiefcence of the ar-
terial fyilem, and from thence of all the other irritative motions, which
are conne£ted with it.

Hence in all thofe conftitutions or difeafes where the blood con-
tains a greater /proportion of ferum, which is the lighteft part of its
compofition, the pulfations of the arteries are weaker, as in nervous -
fevers, chlorofis, and hyfteric complaints ; for in thefe cafes the mo-
mentum ofthe progreffive particles of blood is lefs : and hence, where
the denfer parts of its compofition abound, as the red part of it, or the
coagulable lymph, the arterial pulfations are frronger ; as in thofe of
Toblift health, and in inflammatory difeafes.

That this ftimulus of the momentum ofthe particles ofthe circu-
lating fluid is of the greateft confequence to the arterial aftion, appears
from the experiment of injecting air into theblood veffels, which feems
to deftroy animal life from the want of this ftimulus of momentum ;
•for the diftention ofthe arteries is not diminiflied by it, it pofleffes no
corroiive acrimony, and is lefs liable to repafs the valves than the blood
itfelf; iince air-valves in all machinery require much lefs accuracy of
conftrudlion than thofe which are oppofed to water.

3. One method of increafing the velocity of the blood, and in^con-
■fequence the momentum of its particles, is by the exerciie of the
rbody, or by the fri£tion of its furface: fo, on the contrary, too great

indolence

S^EGT. XXXII. 6. DISEASES OF IRRITATION. o^-js

indolence contributes to decreafe this flinaulus of the monientum of
the particles of the circulating blood, and thus tends to induce quief-
cence ; as is feeu in hyfteric cafes, and chlorofis, and the other difeafes
of fedentary people.

4. The velocity of the particles of the blood iu certain circum-
dftances is increafed by venefe£lion, which, by removing a part of it,
diminifties the refiftance to the motion of the other part, andhence the
momentum of the particles of it is increafed. This may be eafily un-
derftood by conlidering it in the extreme, fince, if ttie refiftance was
greatly increafed, lo as to overcome the propelling power, there could
be no velocity, and in confequence no momentum at all.. From this
eircumftance arifes that curious phenomenon, the truth of which I
have been more than once witnefs to, that venefe6tion will often in-
ilantaneoufly relieve thofe nervous pains, which attend the cold pe-
riods of hyfteric, afthmatic, or epileptic difeafes; and that even where
large dofes of opium have been in vain exhibited. In thefe cafes the
pulfe becomes ftronger after the bleeding, and the extremities regain
their natural v/armth ; and an opiate then given a6ls with much more_
certain eifeft.

VI. There is another caufe, which feems occafionally to induce
quiefcence into fome part of our fyftem, I mean the influence of the.
fun and moonj the attradion of thefe luminaries, by decreaftng the
gravity of the particles of the blood, cannot afFe£t their momentum,,,
as their vis inertias remains the famej but it may neverthelefs pro-
duce fome chemical change in them, bscaufe whatever afFeds the ge-
neral attraftions of the particles of matter may be fuppofed from ana--
logy to affed their fpecific attradions or affinities : and thus the ftimu-
lus of the particles of blood may be diminiftied, though not their mo-
mentum. As the tides of the fea obey the fouthing and northing of
the moon (allowing for the time neceflary for- their motion, and the;-
obftruclions of the fliores), it is probable, that there are alfo atmofphe-
ric tides on. both fides of the earth, which to the inhabitants of ano-
ther.-

376 DISEASES OF IRRITATION. Sect. XXXII. 6.

ther planet might fo defledl the light as to refemble the ring of Sa-
turn. Now as thefe tides of water, -or of air, are raifed by the dimi-
nution of their gravity, it follows, that their preffbre on the furface
of the earth is no greater than the preflure of the other parts of the
ocean, or of the atmofphere, wh-ere no fuch tides exift ; and there-
fore that they cannot affect the mercury in the barometer. In the
fame manner, the gravity of all other terreftrial bodies is dimini(hed
at the times of the fouthing and northing of the moon, and that in a
greater degree when this coincided with the fouthing and northing of
the fun, and this in a flill greater degree about the times of the equi-
noxes. This decreafe of the gravity of all bodies during the time the
moon pafles our zenith or nadir might poffibly be (hewn by the
flower vibrations o^f a pendulum, compared with a fpring clock, or
with aflronomical obfervation. Since a pendulum of a certain length
moves flower at the line than near the poles, becaufe the gravity be-
ing diminiflied and the vis inerti^e continuing the fame, the motive
pov/er is lefs, but the refiftance to be overcome continues the fame.
The combined powers of the lunar and folar attraction is eftimated by
Sirlfaac Newton not to exceed one 7,868,850th part of the power of
gravitation, which feems indeed but a fmall circumftance to produce
any confiderable effeft on the weight of fublunary bodies, and yet this
is fufficient to raife the tides at the equator above ten feet high ; and
if it be confidered, what fmall impulfes of other bodies produce their
effefts on the organs of fenfe adapted to the perception of them, as of
vibration on the auditory nerves, we fhall ceafe to be furprifed, that
fo minute a diminution in the gravity of the particles of blood fhould
fo far affetS: their chemical changes, or their ftimulating quality, as,
joined with other caufes, fometimes to produce the beginnings of
difeafes.

Add to this, that if the lunar influence produces a very fmall degree
of quiefcence at firft, and if that recurs at certain periods even with
lefs power to produce quiefcence than at firft, yet the quiefcence will

daily

Sect. XXXir. 6. DISEASES OF IRRITATION. 377

daily increafe by the acquired habit afting at the fame time, till at
length fo great a degree of quiefcence is induced as to produce
phrenfy, canine madnefs, epilepfy, hyfteric pains, or cold fits of fever,
inftances of many of which are to be found in Dr. Mead's work on
this fubjetfl. The folar influence alfo appears daily in feveral dif-
eafes ; but as darknefs, filence, fleep, and our periodical meals mark
the parts of the folar circle of a6lions, it is fometimes dubious to which
of thefe the periodical returns jof thefe difeafes are to be afcribed.

As far as 1 have been able to obferve, the periods of inflammatory
difeafes obferve the folar day j as the gout and rheumatifm have their
greateil: quiefcence about noon and midnight, and their exacerbations
ibme hours after ; as they have more frequently their immediate caufe
from cold air, inanition, or fatigue, than from the effects of lunations :
whilfl; the cold fits of hyfteric patients, and thofc in nervous fevers,
more frequently occur twice a day, later by near half an hour each
time, according to the lunar day; whilfl fome fits of intermittents,
which are undiflurbed by medicines, return at regular folar periods,
and others at lunar ones ; which may, probably, be owing .to the dif-
ference of the periods of thofe external circumftances of cold, inani-
tion, or lunation, which immediately caufed them.

We muft, however, obferve, that the periods of quiefcence and ex-
acerbation in difeafes do not always commence at the times of the fy-
zygies or quadratures of the moon and fun, or at the times of their
pafiing the zenith or nadir ; but as it is probable, that the flimulus of
the particles of the circumfluent blood is gradually dim/mifhed from
the time of the quadratures to that of the fyzygies, the quiefcence
may commence at any hour, when, co-operating with other caufes of
quiefcence, it becomes great enough to produce a difeafe : afterwards
it will continue to recur at the fame period of the lunar or folar influ-
ence ; the fame caufe operating conjointly with the acquired habit,
that is with the catenation of this new motion with the difievered
links of the lunar or folar circles of animal action.

qC la

378 DISEASES OF IRRITATION. Sect.XXXIL6.

la this manner the periods of menflruation obey the lunar month
with great exaftnefs in healthy patients (and perhaps the vene-
real orgafm in brute animals does the fame), yet thefe periods do not
commence either at the fyzygies or quadratures of the lunations, but
at whatever time of the lunar periods they begin, they obferve the
, fame in their returns till fome greater caufe diflurbs them.

Hence, though the befl way to calculate the time of the expefted
returns of the paroxyfms of periodical difeafes is to count the number
of hours between the commencement of the two preceding fits, yet
the following obfervations may be worth attending to, when we en-
deavour to prevent the returns of maniacal or epileptic difeafes ; whole
periods (at the beginning of them efpecially) frequently obferve the
fyzygies of the moon and fun, and particularly about the equinox.

The greateft of the two tides happening in every revolution of the
moon, is that when the moon approaches neareft to the zenith or na-
dir ; for this reafon, while the fun is in the northern figns, that is during
the vernal and fummer months, the greater of the two diurnal tides
in our latitude is that, when the moon is above the horizon ; and when
the fun is in the fouthern figns, or during the autumnal and winter
months, the greater tide is that, which arifes when the moon is below
the horizon : and as the fun approaches fomewhat nearer the earth in
winter than in fummer, the greateft equinodial tides are obferved to be
a little before the vernal equinox, and a little after the autumnal one.

Do not the cold periods of lunar difeafes commence a few hours be-
fore the fouthiug of the moon during the vernal and fummer months,
and before the northing of the moon during the autumnal and winter
months ? Do not palfies and apoplexies. Which occur about the equi-
noxes, happen a few days before the vernal equinoftial lunation, and
after the autumnal one ? Are not the periods of thofe diurnal dif.
eafes more obftinate, that commence many hours before the fouthing,
or northing of the moon, than of thofe which commence at thofe-
times ? Are not thofe palfies and apoplexies more dangerous which
3 commence.

Sect.XXXII.7-S. diseases of irritation. 379

commence many days before the fyzygies of the moon, than thofe
which happen at thofe times ? See Se(5t. XXXVI. on the periods of
difeafes.

VII. Another very frequent caufe of the cold fit of fever is the
quiefcence of fome of thofe large congeries of glands, which compofe
the liver, fpleen, or pancreas j one or more of which are frequently
fo enlarged in the autumnal intermittents as to be perceptible to the
touch externally, and are called by the vulgar ague-cakes. As thefe
glands are ftimulated into adlion by the fpecific pungency of the
fluids, which they abforb, the general caufe of their quiefcence feems
to be the too great infipidity of the fluids of the body, co-operating
perhaps at the fame time with other general caufes of quiefcence.

Hence, in marfhy countries at cold feafons, which have fucceeded
hot ones, and amongfl thole, who have lived on innutritious and un-
ftimulating diet, thefe agues are mofl frequent. The enlargement of
thefe quiefcent vifcera, and the fwelling of the prtecordia in many
other fevers, is, moll: probably, owing to the fame caufe ; which may
confifl in a general deficiency of the produdlion of feuforial power, as
well as in the diminifhed ftimulation of the fluids; and when the
quiefcence of lb great a number of glands, as conftitute one of thofe
large vifcera, commences, all the other irritative motions are affefted
by their connection with it, and the cold fit of fever is produced.

VIII. There are many other caufes, which produce quiefcence of
fome part of the animal fyftem, as fatigue, hunger, thirfl, bad diet,
difappointed love, unwholefome air, exhauftion from evacuations, and
many others ; but the lafl: caufe, that we fhall mention, as frequently
productive of cold fits of fever, is fear or anxiety of mind. The pains,
which we are firft and moft generally acquainted with, have been pro-
duced by defeat of fome fl:imulus ; thus, foon after our nativity we
become acquainted with the pain from the coldnefs of the air, from
the want of refpiration, and from the want of food. Now all thefe
pains occalioned by defed of ftimulus are attended with quiefcence

3 C 2 of

380 DISEASES OF IRRITATION. . Sect. XXXII. 9.

of the organ, and at the fame time with a greater or lefs degree of
quiefcence of other parts of the fyftem : thus, if we even endure the
pain of hunger fo as to mifs one meal inftead of our daily habit of re-
pletion, not only the periftaltic motions of the ftomach and bowels are
diminiftied, but we are more liable to coldnefs of our extremities, as
of our nofes, and ears, and feet, than at other times.

Now, as fear is originally excited by our having experienced pain,
and is itfelf a painful afFedtion, the fame quiefcence of other fibrous
motions accompany it, as have been moft frequently conneded with
this kind of pain, as explained in Sed:. XVI. 8. i. as the coldnefs
and palenefs of the ikin, trembling, difficult refpiration, indigeftion,
and other fymptoms, which contribute to form the cold fit of fevers.
Anxiety is fear continued through a longer time, and, by producing
chronical torpor of the fyftem, extinguiflies life flowly, by what is
commonly termed a broken heart.

IX. I. We now flep forwards to confider the other fymptoms
in confequence of the quiefcence which begins the fits of fever. If
by any of the circumftances before defcribed, or by two or more
of them adling at the fame time, a great degree of quiefcence is in-
duced on any confiderable part of the circle of Irritative motions, the
whole clafs of them is more or lefs difturbed by their irritative aflbcia-
tions. If this torpor be occafioned by a deficient fupply of fenforial
power, and happens to any of thofe parts of the fyflem, which- are ac-
cuftomed to perpetual a£livity, as the vital motions, the torpor in-
creafes rapidly, becaufe of the great expenditure of fenforial power by
the inceffant adivity of thofe parts of the fyftein, as fhewn in No. 3. ti
of this Seftion. Hence a deficiency of all the-fecretions fuceeeds, and
as animal heat is produced in proportion to the quantity of thofe fecre-
tions, the coldnefs of the Ikin is. the firft circumftance, which isat-
tended to. Dr. Martin afierts, that fome parts of his body were-
warmer than natural in the cold fit of fever; but it is certain, that
thofe, which are uncovered,, as the fingers, and nofe, and ears,. are

much*

Sect. XXXII. 9- DISEASES OF IRRITATION, 3^1

much colder to the touch, and paler in appearance. It is poffible,,
that his experiments were made at the beginning of the fubfequent
hot hts ; which commence with partial diftributions of heat, owing
to fome parts of the body regaining their natural irritability fooner
than others.

From the quiefcence of the anaftomofing capillaries a palenefs of
the Ikin fucceeds, and a lefs fecretion of the perfpirable matter ; from
the quiefcence of the pulmonary capillaries a difficulty of refpiration
arifes ; and from the quiefcence of the other glands lels bile, lefs gaf-
trie and pancreatic juice, are fecreted into the ftomach and inteftines,
and lefs mucus and faliva are poured into the mouth ; whence arifes
the dry tongue, coftivenefs, dry ulcerSy and paucity of urine. From
the quiefcence of the abforbent fy flem arifes the great thirft, as
lefs moifture is abforbed from the atmofphere. The abforption from
the atmofphere was obferved by Dr. Lyfter to amount to eighteen
ounces in one night, above what he had at the fame time infenfibly
perfpired. See Langrifh. On the fame account the urine is pale,
though in fmall quantity, for the thinner part is not abforbed from it ;
and when repeated ague-fits continue long,, the legs fwell from the
diminifhed abforption of the cellular abforbents.

From the quiefcence of the- inteftinal canal a lofs of appetite and
flatulencies proceed. From the partial quiefcence of the glandular
vifcera a fwelling and tenfion about the prscordia becomes fenfible to
the touch ; which is occafioned by the delay of the fluids from the
defedt of venous or lymphatic abforption. The pain of the forehead,
and of the limbs, and of the fmall of the back, arifes from the q^uief-
cence of the membranous fafcia, or mufcles of thofe parts, in the
fame manner as the Ikin becomes painful, when the veflels, of which it
is compofed, become quiefcent from- cold. The trembling in confer
quence of the pain of coldnefs, the reftleflhefs, and the yawning, and
ijretching of the. limbs, together with the Ihuddering, or rigours, are

convulfive.

383 , DISEASES OF IRRITATION. Sect. XXXII. 9.

convulfive motions ; and will be explained amongft the difeafes of vo-
lition, Sea. XXXIV.

Sicknefs and vonaiting is a frequent fympton:i in the beginnings of
fever-fits, the mufciilar fibres of the ilomach fhare the general torpor
and debility of the fyftem ; their motions become firft leflened, and
then flop, and then become retrograde ; for the a£t of vomiting, like
the globus hyftericus and the borborigmi of hypocondriafis, is always
a fymptom of debility, either from want of ftimulus, as in hunger ;
or from want of fenforial power, as after intoxication ; or from fym-
pathy with fome other torpid irritative motions, as in the cold fits of
ague. See Sect. XII. 5. 5. XXIX. 11. and XXXV. i. 3. where this
a£t of vomiting is further explained.

The fmall pulfe, which is faid by fome writers to be flow at the
commencement of ague-fits, and which is frequently trembling and
intermittent, is owing to the qulefcence of the heart and arterial fyf-
tem, and to the refinance oppofed to the circulating fluid from the
inadtivity of all the glands and capillaries. The great weaknefs and
inability to voluntary motions, with the infenfibility of the extremi-
ties, are owing to the general quiefcence of the whole moving fyftem ;
or, perhaps, fimply to the deficient produftion of fenforial power.

If all thefe fymptoms are further increafed, the quiefcence of all the
rnufcles, including the heart and arteries, becomes complete, and death
enfues. This is, moft probably, the cafe of thofe who are flarved to
death with cold, and of thofe who are faid to die in Holland from long
fkaiting on their frozen canals. .

a. As foon as this general quiefcence of the fyflem ceafes, either by
the diminution of the caufe, or by the accumulation of fenforial power,
(as in fyncope, Se£l. XII. 7. i .) which is the natural confequence of
previous quiefcence, the hot fit commences. Every gland of the
body is now ftimulated into ftronger adlion than is natural, as its irri-
tability is increafed by accumulation of fenforial power during its late

quiefcence.

Sect.XXXII. 9- DISEASES OF IRRITATION. 3$^

quiefcence, a fiiperabundance of all the fecretions is produced, and an
increafe of heat in confequence of the increafe of thefe fecretions.
The fkin becomes red, and the perfpiration great, owing to the in-
creafed action of the capillaries during the hot part of the paroxyfna.
The fecretion of perfpirable matter is perhaps greater during the hot
fit than in the fweating fit which follows ; but as the abforption of it
alfb is greater, it does not fland on the fkin in vifible drops : add to
this, that the evaporation of it alfo is greater, from the increafed heat
of the fkin.. But at the decline of the hot fit, as the mouths of the ab-
forbents of the fkin are expofed to the cooler air, or bed-clothes, thefe
vefiels fooner lofe their increafed adlivity, and ceafe to ablorb more than
their natural quantity : but the fecerning vefTels for fome time longer,,
being kept warm by. the circulating blood, continue to pour out an in-
creafed quantity of perfpirable matter, which now flands on the fkin
in large vifible drops ; the exhalation of it alfo being leffened by the
greater coolnefs of the fkin, as well as its abforption by the diminifLed
a6lion of the lymphatics. See Clafs I. i. 2. 3.

The increafed fecretion of bile and of other fluids poured into the
inteflines frequently induce a purging at the decline of the hot fit;;
for as the external abforbent veflels have their mouths expofed to the
cold air, as above mentioned, they ceafe to be excited into unnatural-
adivity fooner than the fecretory vefTels, whofe mouths are expofed
to the warmth of the blood : now, as the internal abforbents fympa-
thize v/ith the external ones, thefe alfo, which during the hot fit
drank up the thinner part of the bile, or of other fecreted fluids, lofe
their increafed adivity before the gland lofes its increafed activity, at
the decline of the hot fit ; and the loofe dejections are produced from
the fame caufe, that the increafed perfpiration flands on the fur-
face of the fkin, from the increafed abforption ceafing fooner than the
increafed fecretion.

The urine during the cold fit is in fmall quantity and pale, both-
Irom a deficiency of the fecretion and a deficiency of the abforption,. .

During

384 DISEASES OF IRRITATION. SECT.XXXn.9.

During the hot fit it is in its ufual quantity, but very high coloured
and turbid, becaufe a greater quantity had been fecreted by the in-
creafed aftion of the kidnies, and alfo a greater quantity of its more
aqueous part had been abforbed from it in the bladder by the increafed
aftion of the abforbents ; and laftly, at the dedine of the hot fit it is
in laro-e quantity and lefs coloured, or turbid, becaufe the abforbent
velTels of the bladder, as obferved above, lofe their increafed adion by
fympathy with the cutaneous ones fooner than the fecretory veffels
of the kidnies lofe their increafed aftivity. Hence the quantity of
the fediment, and the colour of the urine, in fevers, depend much
on the quantity fecreted by the kidnies, and the quantity abforbed
from it again in the bladder : the kinds of fediment, as the lateri-
tious, purulent, mucous, or bloody fediments, depend on other
caufes. It fhould be obferved, that if the fweating be increafed by
the heat of the room, or of the bed-clothes, that a paucity of turbid
urine vi^ill continue to be produced, as the abforbents of the bladder
will have their activity increafed by their fympathy with the veffels
of the Ikin, for the purpofe of fupplying the fluid expended in per-
fpiration.

The pulfe becomes ftrong and full owing to the increafed irritabi-
lity of the heart and arteries, from the accumulation of fenforial
power during their quiefcence, and to the quicknefs of the return of
the blood from the various glands and capillaries. This increafed ac-
tion of all the fecretory veflels does not occur very fuddenly, nor uni-
verfally at the fame time. The heat feems to begin about the center,
and to be difFufed from thence irregularly to the other parts of the
fyftem. This imay be owing to the fituation of the parts which firft
became quiefcent and caufed the fever-fit, efpecially when a hardnefs
or tumour about the praecordia can be felt by the hand ; and hence
this part, in whatever vifcus it is feated, might be the firft to regain its
natural or increafed irritability.

Sect. XXXII. 9. DISEASES OF IRRITATION. 385

3. It muft be here noted, that, by the increafed quantity of heat,
and of the impulfe of the blood at the conamencement of the hot fit,
a great increafe of flimulus is induced, and is now added to the in-
creafed irritabihty of the fyftem, which -was occafioned by its previ-
ous quiefcence. This additional ftimulus of heat and momentum of
the blood augments the violence of the movements of the arterial and
glandular fyftem in an increafing ratio. Thefe violent exertions ftill
producing more heat and greater momentum of the moving fluids,
till at length the fenforial power becomes wafted by this great ftimu-
lus beneath its natural quantity, and predifpofes the fyftem to a fe-
cond cold fit.

At length all thefe unnatural exertions fpontaneoufly fubfide with
the increafed irritability that produced them ; and which was itfelf
produced by the preceding quiefcence, in the fame manner as the eye,
on coming from darknefs into day-light, in a little time ceafes to be
<lazzled and pained, and gradually recovers its natural degree of irri-
tability.

4. But if the increafe of irritability, and the confequent increafe
of the ftimulus of heat and momentum, produce more violent exer-
tions than thofe above defcribed ; great pain arifes in feme part of the
moving fyftem, as in the membranes of the brain, pleura, or joints;
and new motions of the veflels are produced in confequence of this
■pain, which are called inflammation; or delirium or ftupor arifes;
as explained in Se£l. XXI. and XXXIII. : for the immediate efFe6l is
the fame, whether the great energy of the moving organs arifes from
an increafe of ftimulus or an increafe of irritability ; though in the
former cafe the wafte of fenforial power leads to debility, and in the
latter to health.

3 D Recafitulation.

386 DISEASES OF IRRITATION. Sect. XXXII. lo.

Recapitulation.

X. Thofe mufcles, which are lefs frequently exerted, and whofe
acStioas are interrupted by fleep, acquire lefs accumulation of fenfo-
rial power during their quiefcent flate, as the nnufcles of locomotion.
In thefe mufcles after great exertion, that is, after great exhauftion of
fenforial power, the pain of fatigue enfues ; and during reft there is a
renovation of the natural quantity of fenforial power; but where the
reft, or quiefcence of the mufcle, is long continued, a quantity of fen-
forial power becomes accumulated beyond what is neceffary ; as ap-
pears by the uneafinefs occafioned by want of exercife; and which in
young animals is one caufe exciting them into aftion, as is feen in the
play of puppies and kittens.

But when thofe mufcles, which are habituated to perpetual adion,
as thofe of the ftomach by the ftimulus of food, thofe of the veffels
of the Ikin by the ftimulus of heat, and thofe which conftitute the
arteries and glands by the ftimulus of the blood, become for a time
quiefcent, from the want of their appropriated ftimuli, or by their af-
lociations with other quiefcent parts of the fyftem ; a greater accu-
mulation of fenforial power is acquired during their quiefcence, and a
greater or quicker exhauftion of it is produced during their increafed

a£lion.

This accumulation of fenforial power from deficient adion, if it
happens to the ftomach from want of food, occafions the pain of hun-
ger ; if it happens to the veflels of the Ikin from want of heat, it oc-
cafions the pain of cold; and if to the arterial fyftem from the want
of its adapted ftimuli, many difagreeable fenfations are occafioned,
fuch as are experienced in the cold fits of intermittent fevers, and are

Sect. XXXII. 10. DISEASES OF IRRITATION. 3S7

as various, as there are glands or membranes in the fyfl:em, and are
generally termed univerfal uneafmefs.

When the quiefcence of the arterial fyfteni is not owing to defed:
of ftimulus as above, but to the defedlive quantity of lenforial power,
as in the commencement of nervous fever, or irritative fever with weak
pulfe, a great torpor of this fyftem is quickly induced ; becaufe both
the irritation from the Aimulus of the blood, and the affociation of the
vafcular motions with each other, continue to excite the arteries into
a£lion, and thence quickly exhaufl the ii!-fupplied vafcular mufcles ;
for to reft is death ; and therefore thofe vafcular mufcles continue to
proceed, though with feebler action, to the extreme of wearinefs or
faintnefs : while nothing limilar to this afFeils the locomotive mufcles,
whofe adlions are generally caufed by volition, and not much fubje<Sl
cither to irritation or to other kinds of aflbciations belides the vo-
luntary ones, except indeed when they are excited by the la/h of
flavery.

In thcfe vafcular mufcles, which are fubje£t to perpetual adiort,
and thence liable to great accumulation of fenforial power during their
quiefcence from want of ftimulus, a great increafe of a£livity occurs,
either from the renewal of their accuftomed ftimulus, or even from
much lefs quantities of ftimulus than ufual. This increafe of aftion
conftitutes the hot fit of fever, which is attended with various in-
creafed fecretions, with great concomitant heat, and general uneafi-
nefs. The uneafinefs attending this hot paroxyfm of fever, or fit
of exertion, is very different from that, which attends the previous
cold fit, or fit of quielcence, and is frequently the caufe of inflamma-
tion, as in pleurify, which is treated of in the next fedion.

A fimilar effedl occurs after the quiefcence of our organs of fenfe ;
thofe which are not fubjeft to perpetual a£lion, as the tafte and fmell,
are lefs liable to an exuberant accumulation of fenforial power after
their having for a time been inactive ; but the eye, which is in per-

3 D 2 petual

388 DISEASES OF IRRITATION. Sect. XXXII. lo.

petual acStioii during the day, becomes dazzled, and liable to inflam-
ixiation after a temporary quiefcence.

Where the previous quiefcence has been owing to a defed: of fen-
forial power, and not to a defedt of ftimulus, as in the irritative fever
with weak pulfe, a fimilar increafe of adliivity of the arterial fyftem
fucceeds, either from the ufual fl:imulus of the blood, or from a fti-
mulus lefs than iifual ; but as there is in general in thefe cafes of fe-
ver with weak pulfe a deficiency of the quantity of the blood, the pulfe
in the hot fit is weaker than in health, though it is ftronger than in
the cold fit, as explained in No. 2. of this feftion. But at the fame
time in thofe fevers, where the defe£l of irritation is owing to the
defefl: of the quantity of fenforial power, as well as to the defe£t of
ftimulus, another circumflance occurs ; which confifts in the partial
diftribution of it, as appears in partial flulhings, as of the face or bo-
fom, while the extremities are cold ; and in the increafe of particular
fecretions, as of bile, faliva, infenfible perfpiration, with great heat of
the Ikin, or with partial fweats, or diarrhoea.

There are alfo many uneafy fenfations attending thefe increafed ac-
tions, which, hke thofe belonging to the hot fit of fever with ftrong
pulfe, are frequently followed by inflammation, as in fcarlet fever;
which inflammation is neverthelefs accompanied with a pulfe weaker,
though quicker, than the pulfe during the remiflion or intermiffion
of the paroxyfms, though ftronger than that of the previous cold fit.

From hence I conclude, that both the cold and hot fits of fever are
neceffary confequences of the perpetual and inceflant a£tion of the ar-
terial and glandular fyftem ; fince thofe mufcular fibres and thofe or-
gans of fenfe, which are moft frequently exerted, become neceflarily
moft afFeiled both with defe<9: and accumulation of fenforial power :-
and that htnce fever -Jits are not an effort of nature to relieve herfelf
and that therefore they fhould always be prevented or diminifhed as
much as poflible, by any means which decreafe the general or partial
2 v.afc.ular

Sea. XXXII. 10. DISEASES OF IRRITATION. 3S9

vafcular aftions, when they are greater, or by increafing them whea
they are lefs than in health, as defcribed in Se£l. XII. 6. i.

Thus have I endeavoured to explain, and I hope to the fatisfadion
of the candid and patient reader, the principal lymptoms or circum-
flances of fever without the introduftion of the fupernatural power of
fpafm. To the arguments in favour of the doftrine of fpafm it may
be fufficient to reply, that in the evolutioa of medical as well as of
dramatic cataftrophe.

Nee Deus interlit, nili dignus vindice nodus incident.

HOR;

SECT.

390 DISEASES OF SENSATION. Sect. XXXIII. i.

SECT. XXXIII.

DISEASES OF SENSATION.

I. Motions excited by fenfation. Digejiiou. Generation. Pleafure of exijience.
Hypocbondriacijm. 2. Pain introduced. Senfttive fevers of two kinds. ^.Two
Jenforial -powers exerted in Jenfitive fevers. Size of the blood. I\/ervous fevers
diflinguifhed from putrid ones. The feptic and antifeptic theory. 4. Two kindf
cf delirium. 5. Other animals are lefs liable to delirium^ cannot receive our con-
tagious difeajes, and are lefs liable to madne/s. II. 1. Senfitive motions generated.
2. Inflammation explained. 3. Its remote caufes from excefs of irritation, or of
irritability, not from thofe pains which are owing to defeSl of irritation. New
vejfels produced, and much heat. 4. Purulent matter fecreted. 5. Contagion
explained. 6. Received but once. ^ . If common matter be contagious ? Z. Why
Jome contagions are received but once. 9. Why others may be received frequently.
Contagions of fmall-pox and meafles do not a£l at the fame times. Two cafes of
Juch patients. 10. The blood from patients in the fmall-pox will mtinfeSl others.
Cafes of children thus inoculated. The variolous contagioh is not received into
the blood. It alls byfenfitive ajfociation between thefiomach andjkin. III. i . Ab"
forption of folids and fluids. 2. Art of healing ulcers, 3. Mortification at~
tended with lefs pain in weak people.

I. I. AS many motions of the body are excited and continued by
irritations, fo others require, either conjun£lly with thefe, or fepa-
rately, the pleafurable or painful fenfations, for the purpofe of pro-
ducing them with due energy. Araongft thefe the bufinefs of di-
geftion fupplies us with an inftance : if the food, which we fwallow,
is not attended with agreeable fenfation, it digefts lefs perfeftty ; and
if very difagreeable fenfation accompanies it, fuch as a naufeous idea,

Sect. XXXIII. 1. DISEASES OF SENSATION. 391

or very difguftful tafte, the digeftion becomes impeded ; or retrograde
motions of the ftomach and oefophagus fucceed, and the food is
ejefled.

The bufinefs of generation depends fo much on agreeable fenfation,
that, where the objeft is dlfguftful, neither voluntary exertion nor irri-
tation can effeft the purpofe ; which is alio liable to be interrupted by
the pain of fear or bafhfulnefs.

Befides the pleafure, which attends the irritations produced by the
objefts of luft and hunger, there feems to be a fum of pleafurable af-
fedlion accompanying the various fecretions of the numerous glands,
which conftitutes the pleafure of life, in contradiftinttion to the te-
dium vit£c. This quantity or fum of pleafurable affection feems to
contribute to the due or energetic performance of the whole move-
able fyftem, as well that of the heart and arteries, as of digeftion
and of abforption ; fince without the due quantity of pleafurable fenfa-
tion, flatulency and hypochondriacifm affedt the inteftines, and a lan-
guor feizes the arterial pulfations and fecretions ; as occurs in great
and continued anxiety of the mind.

2. Befides the febrile motions occafioned by irritation, defcribed in
Sedl. XXXII. and termed irritative fever, it frequently happens that
pain is excited by the violence of the fibrous contra£tions ; and other
new motions are then fuperadded, in confequence of fenfation, which
we fhall term febris fenfitiva, or fenfitive fever. It muft be obferved,
that mofl irritative fevers begin with a decreafed exertion of irritation,
owing to defedl of flimulus ; but that on the contrary the fenfitive
fevers, or inflammations, generally begin with the increafed exertion
of fenfation, as mentioned in Se6t. XXXI. on temperaments : for
though the cold fit, which introduces inflammation, commences with
decreafed irritation, yet the inflammation itfelf commences in the hot
fit during the increafe of fenfation. Thus a common puftule, or
phlegmon, in a part of little fenfibility does not excite an inflamma-
tory fever; but if the ftomach, inteftines, or the tender fubftance
5 beneath

392 DISEASES OF SENSATION. Sect. XXXIII. i.

beneath the nails, be injured, great fenfatiou is produced, and the
whole fyftenn is thrown into that kind of exertion, which confiitutes
inflammation.

Thefe fenfitive fevers, like the Irritative ones, refolve themfelves
into thofe with arterial ftrength, and thofe with arterial debility, that
is with excefs or defeat of fenforlal power ; thefe may be termed the
febris fenfitiva pulfu forti, fenfitive fever with ftrong pulfe, which is
the fynocha, or inflammatory fever ; and the febris fenfitiva pulfu de-
bili, fenfitive fever with weak pulfe, which is the typhus gravior, or
putrid fever of fome writers.

3. The inflammatory fevers, which are here termed fenfitive fe-
vers with ftrong pulfe, are generally attended with fome topical in-
flammation, as pleurify, peripneumony, or rheumatifm, which dif-
tinguifhes them from irritative fevers v/ith ftrong pulfe. The
pulfe is ftrong, quick, and full ; for in this fever there is great irri-
tation, as well as great fenfation, employed in moving the arterial
fyftem. The fize,.or coagulable lymph, which appears on the blood,
is probably an increafed fecretion from the inflamed internal lining of
the whole arterial fyftem, the thinner part being taken away by the
increafed abforption of the inflamed lymphatics.

The fenfitive fevers with weak pulfe, which are termed putrid or
malignant fevers, are diftinguiflied from irritative fevers with weak
pulfe, called nervous fevers, defcribed in the laft feflion, as the for-
mer confift of inflammation joined with debility, and the latter of de-
bility alone. Hence there is greater heat and more florid colour of
the Ikin in the former, with petechias, or purple fpots, and aphtha,
or floughs in the throat, and generally with previous contagion.

When animal matter dies, as a flough in the throat, or the morti-
fied part of a carbuncle, if it be kept moift and warm, as during its
adhefion to a living body, it will foon putrify. This, and the origin
of contagion from putrid animal fubftances, feem to have given rife
to the feptic and antifeptic theory of thefe fevers.

The

Sect. XXXIII. I. DISEx^SES OF SENSATION. 393

The matter in puftules and ulcers is thus liable to become putrid,
and to produce microfcopic animalcula ; the urine, if too long re-
tained, may alfo gain a putrefcent fmell, as well as the alvine feces ;
but fome writers have gone fo far as to believe, that the blood itfelf
in thcfe fevers has fmelt putrid, when drawn from the arm of the pa-
tient : but this feems not well founded ; fince a fnigle particle of putrid
matter taken into the blood can produce fever, how can we conceive
that the whole mafs could continue a minute in a putrid flate without
deftroying life ? Add to this, that putrid animal fubftances give up
air, as in gangrenes ; and that hence if the blood was putrid, air
fhould be given out, which in the blood-veffels is known to occaficn
immediate death.

In thefe fenfitive fevers with flrong pulfe (or inflammations) there
are two fenforial faculties concerned in producing the difeafe, viz. ir-
ritation and fenfation ; and hence, as their combined aftion is more
violent, the general quantity of fenforial power becomes further ex-
haufled during the exacerbation, and the fyftem more rapidly weak-
ened than in irritative fever with flrong pulfe; where the fpirit of
animation is weakened by but one mode of its exertion : fo that this
febris fenfitiva pulfu forti (or inflammatory fever,) may be confidered
as the febris irritativa pulfu forti, with the addition of inflammation ;
and the febris fenfitiva pulfu debili (or malignant fever) may be con-
fidered as the febris irritativa pulfu debili (or nervous fever), with the
addition of inflammation.

4. In thefe putrid or malignant fevers a deficiency of irritability ac-
companies the increafe of fenlibility ; and by this wafte of fenforial
power by the excefs of fenfation, which was already too fmall, arifes
the delirium and flupor which fo perpetually attend thefe inflamma-
tory fevers with arterial debility. In thefe cafes the voluntary power
firfl ceafes to acl from deficiency of fenforial fpirit; and the iiimuli
from external bodies have no etFect on the exhaufted fenforial power,
and a delirium hke a dream is the confequence. At length the in-

3 E ternal

394- DISEASES OF SENSATION. Sect.XXXIIL i,

teriial fllmuli ceafe to excite fufficient irritation, and the fecretions are
either not produced at all, or too parfimonious in quantity. Amongft
thefe the fecretion of the brain, or produdlion of the fenforial power,
becomes deficient, till at laft all fenforial power ceafes, except what
is juft neceffary to perform the vital motions, and a ftupor fucceeds ;
which is thus owing to the fame caufe as the preceding delirium ex-
erted in a greater degree.

This kind of delirium is owing to a fufpenfion of volition, and to
the difobedience of the fenfes to external flimuli, and is always occa-
fioned by great debility, or paucity of fenforial power ; it is therefore
a bad fign at the end of inflammatory fevers, which had previous ar-
terial ftrength, as rheumatifm, or pleurify, as it fhews the prefeace
of great exhauftion of fenforial power in a fyflem, which having lately
been expofed to great excitement, is not fo liable to be ftimulated into
its healthy adion, either by additional ftimulus of food and medicines,
or by the accumulation of fenforial power during its prefent torpor.
]n inflammatory fevers with debility, as thofe termed putrid fevers,
delirium is fometimes, as well as ftupor, rather a favourable fign ; as
lefs fenforial power is wafted during its. continuance (fee Clafs II.
1. 6. 8.), and the conftitution not having been previoufly expofed to
excefs of ftimulation, is more liable to be excited after previous
quiefcence.

When the fum of general pleafurable fenfation becomes too great,
another kind of delirium fupervenes, and the ideas thus excited are
miftaken for the irritations of external objefts : fuch a delirium is pro-
duced for a time by intoxicating drugs, as fermented liquors, or
opium : a permanent delirium of this kind is fometimes induced by
the pleaiufes of inordinate vanity, or by the enthufiaftic hopes of
heaven. In thefe cales the power of volition is incapable of exertion,
and in a great degree the external fenfes become incapable of perceiv-
ing their adapted ftimuli, becaufe the whole ienforial power is em-
ployed or expended on the ideas excited by pleafurable fenfation.

This

Sect .XXXIII. 2. DISEASES OF SENSATION. 395

This kind of delirium is diftinguinied from that which attends the
fevers above mentioned from its not being accompanied with general
debilitv, but fimply with excefs of pleafureable fenfation ; and is
therefore in fome mealure allied to madnels or to reverie ; it ditFers
from the delirium of dreams, as ia this the power of volition is not
totally lufpended, nor are the fenfes precluded from external ftimula-
tion ; there is therefore a degree of confiftency, in this kind of deli-
rium, and a degree of attention to external objeds, neither of which
exift in the delirium of fevers or in dreams.

5. It would appear, that the vafcular fyftem of other animals are
lefs liable to be put into action by their general fum of pleafureable or
painful ienlation ; and that the trains of their ideas, and the mufcular
motions ufually aflbciated with them, are lefs powerfully connedled
than in the human fyftem. For other animals neither weep, nor
fmlle, nor laugh ; and are hence feldom fubjeifl to delirium, as treated
of in Se£t. XVI. on InftincEl. Now as our epidemic and contagious
difeafes are probably produced by difagreeabie fenfation, and not fimply
by irritation ; there appears a reafon, why brute animals are lefs liable
to epidemic or contagious difeafes ; and fecondly, why none of our
contagions, as the fmall-pox or meafles, can be communicated to
them, though one of theirs, viz. the hydrophobia, as well as many
of their poifons, as thofe of fnakes and of infedls, communicate their
deleterious or painful effedls to mankind.

Where the quantity of general painful fenfation is too great in the
fyftem, inordinate voluntary exertions are produced either of our
ideas, as in melancholy and madnefs, or of our mufcles, as in con-
vulfion. From thefe maladies alfo brute animals are much more ex-
empt than mankind, owing to their greater inaptitude to voluntary
exertion, as mentioned in Seft. XVI. on Inftinft.

II. I. When any moving organ is excited into fuch violent mo-
tions, that a quantity of pleafureable or painful fenfation is produced,
it frequently happens (but not always) that new motions of the af-

3 E 2 fcaed

396 DISEASES OF SENSATION. Sect.XXXIII. 2.

fedled organ are generated in coafequence of the pain or pleafure,
which are termed inflammation.

Thefe new motions are of a peculiar kind, tending to diftend the
old, and to produce new fibres, and thence to elongate the ftraight
mufcles, which ferve locomotion, and to form new veflels at the ex-
tremities or fides of the vafcular mufcles.

2. Thus the pleafureable fenfations produce an enlargement of the
nipples of nurfes, of the papillae of the tongue, of the penis, and
probably produce the growth of the body from its embryori flate to its
maturity ; whilft the new motions in confeqilence of painful fenfa-
tion, with the growth of the fibres or veflels, which they occafion,
are termed inflammation.

Hence when the ftraight mufcles are inflamed, part of their ten-
dons at each extremity gain new life and fenfibility, and thus the
mufcle is for a time elongated ; and inflamed bones become foft, vaf-
cular, and fenfible. Thus new veflels flioot over the cornea of in-
flamed eyes, and into fchirrous tumours, when they become inflamed;
and hence all inflamed parts grow together by intermixture, and in-
ofculation of the new and old veflels.

The heat is occalioned from the increafed fecretions either of mu-
cus, or of the fibres, which produce or elongate the veflels. The red
colour is owing to the pellucidity of the newly formed veflels, and as
the arterial parts of them are probably formed before their corre-
Ipondent venous parts.

3. Thefe new motions are excited either from the increafed quan-
tity of fenfation in confequence of greater fibrous contradlions, or
from increafed fenfibility, that is, from the increafed quantity of fen-
forial power in the moving organ. Hence they are induced by great
external ftimuli, as by wounds, broken bones ; and by acrid or in-
fectious materials ; or by -common ftimuli on thofe organs, which
have been fome time quiefcent ; as the ufual light of the day inflames
the eyes of thofe, who have been confined in dungeons ; and the

warmth

Sect. XXXIII. 2. DISEASES OF SENSATION. 39y

warmth of a common fire inflames thofe, who have been previoufly
expofed to much cold.

But thefe new motions are never generated by that pain, which
arifes from defedl of (limulus, as from hunger, thirft, cold, or in-
anition, with all thofe pains, which are termed nervous. Where
thefe pains exift, the motions of the afFefted part are leflened ; and if
inflammation fucceeds, it is in fome difl:ant parts ; as coughs are
caufed by coldnefs and moifture being long applied to the feet ; or it
is in confequedce of the renewal of the ftimulus, as of heat or food,
which excites our organs into ftronger aftion after their temporary
quiefcence ; as kibed heels after walking in fnow.

4. But when thefe new motions of the vafcular mufcles are ex-
erted with greater violence, and thefe veffels are either elongated too
much or too haftily, a new material is fecreted from their extremi-
ties, which is of various kinds according to the peculiar animal mo-
tions of this new kind of gland, which lecretes it ; fuch is the pus
laudabile or common matter, the variolous matter, venereal matter,
catarrhous matter, and many others.

5. Thefe matters are the produd of an animal procefs ; they are
fecreted or produced from the blood by certain difeafed motions of the
extremities of the blood-veflTels, and are on that account all of them
contagious ; for if a portion of any of thefe matters is tranfmitted into
the circulation, or perhaps only inferted into the Ikin, or beneath the
cuticle of an healthy perfon, its ftimulus in a certain time produces
the fame kind of morbid motions, by which itfelf was produced ; and
hence a fimilar matter is generated. See Seft. XXXIX. 6. i.

6. It is remarkable, that many of thefe contagious matters are
capable of producing a fimilar difeafe but once ; as the fmall-pox and
meafles ; and I fuppofe this is true of all thofe contagious difeafes,
which are fpontaneoufly cured by nature in a certain time ; for if the
body was capable of receiving the difeafe a fecond time, the patient
mufl perpetually infedl himfelf by the very matter, which he has

himfelf

39§ DISEASES OF SENSATION. Sect. XXXIII. 2.

hirafelf produced, and is lodged about him ; and hence he could
never become free from the dileafe. Something fimilar to this is
feen in the fecondary fever of the confluent fmall-pox; there is a
great abforption of variolous matter, a very minute part of which
would give the genuine fmall-pox to another perfon ; but here it
only ftimulates the fyftem into common fever ; like that which
common pus, or any other acrid material might occafion.

7. In the pulmonary confumption, where common matter is
daily abforbed, an irritative fever only, not an inflammatory one, is
produced ; which is terminated like other irritative fevers by fweats,
or loofe ftools. Hence it does not appear, that this abforbed matter
always aidls as a contagious material producing frefh inflammation or
new abfcefles. Though there is reafon to believe, that thefirft time
any common matter is abforbed, it has this efFefl:, but not the fecond
time, like the variolous matter above mentioned.

This accounts for the opinion, that the pulmonary confumption is
fometimes infedlious, which opinion was held by the ancients, and
continues in Italy at prefent ; and I have myfelf feen three or four
inftances, where a hulband and wife, who have flept together, and
have thus much received each other's breath, who have infe£ted each
other, and both died in confequence of the original taint of only one
of them. This alfo accounts for the abfcefles in various parts of the
body, that are fometimes produced after the inoculated Imall-pox is
terminated ; for this fecond abforption of variolous matter afts like
common matter, and produces only irritative fever in thofe children,
whofe conftitutions have already experienced the abforption of com-
mon matter ; and inflammation with a tendency to produce new ab-
fcefles in thofe, whofe confl:itutions have not experienced the abforp-
tions of common matter.

It is probable, that more certain proofs might have been found to
fliew, that common matter is infedious the firfl; time it is abforbed,

tending

Sect. XXXIII. 2. DISEASES OF SENSATION. 399

tending to produce fimilar abfcefles, but not the fecond time of its
abforption, if this fubjeft had been attended to.

8. Thefe contagious difeafes are very numerous, as the plague,
fmall-pox, chicken-pox, meafles, fcarlet-fever, pemphigus, catarrh,
chincough, venereal difeafe, itch, trichoma, tinea. The infe6lious
material does not feem to bediflblved by the air, but only mixed with
it perhaps in tine powder, which foon fubfides ; fince many of thefe
contagions can only be received by adual contact ; and others of
them only at Imall diftances from the infedted perfon ; as is evident
from many perfons having been near patients of the fmall-pox with-
out acquiring the difeafe.

The reafon, why many of thefe difeafes are received but once,
and others repeatedly, is not well underflood ; it appears to me, that
the conftitution becomes fo accuflomed to the flimuli of thefe infec-
tious materials, by having once experienced them, that though irri-
tative motions, as hedic fevers, may again be produced by them, yet
no fenfation, and in confequence no general inflammation fucceeds ;
as difagreeable fmells or taftes by habit ceafe to be perceived ; they
continue indeed to excite irritative ideas on the organs of fenfe, but
thefe are not fucceeded by fenfation.

There are many irritative motions, which were at firft fucceeded
by fenfation, but which by frequent repetition ceafe to excite fenfa-
tion, as explained in Seft. XX. on Vertigo. And, that this circum-
ftance exifts in refpeft to infectious matter appears from a known
faft ; that nurfes, who have had the fmall-pox, are liable to experi-
ence fmall ulcers on their arms by the conta6l of variolous matter iu
lifting their patients ; and that when patients, who have formerly
had the fmall-pox have been inoculated in the arm, a phlegmon, or
inflamed fore, has fucceeded, but no fubfequent fever. Which
fhews, that the contagious matter of the fmall-pox has not loft its
power of ftimulating the part it is applied to, but that the general

fjftcm

400 DISEASES OF SENSATION. Sect.XXXUT. 2.

fyftem Is not afFe6led in confequence. See Seftioii XII. 7. 6.
XIX. 10.

9. From the accounts of the plague, virulent catarrh, and putrid
dyfentery, it feems uncertain, whether thefe difeafes are experienced
more than once ; but the venereal difeafe and itch are doubtlefs re-
peatedly infectious ; and as thefe difeafes are never cured fpontaneoufly,
but require medicines, which ail without apparent operation, fome
have fufpefted, that the contagious material produces fimilar matter
rather by a chemical change of the fluids, than by an animal procefs ;
and that the fpecific medicines deftroy their virus by chemically com-
bining with it. This opinion is fuccefsfully combated by Mr. Hun-
ter, in his Treatife on Venereal Difeafe, Parti, c. i..

But this opinion wants the fupport of analogy, as there is no
known procefs in animal bodies, which is purely chemical, not even
digeflion ; nor can any of thefe matters be produced by chemical pro-
cefles. Add to this, that it is probable, that the infefts, obferved in
the puflules of the itch, and in the ftools of dyfenteric patients, are
the confequences, and not the caufes of thefe difeafes. And that the
fpecific medicines, which cure the itch and lues venerea, as brimftone
and mercury, ail only by increafing the abforption of the matter in
the ulcufcles of thofe difeafes, and thence difpofmg them to heal ;
which would otherwife continue to fpread.

Why the venereal difeafe, and itch, and tenia, or fcald head, are
repeatedly contagious, while thofe contagions attended with fever can
be received but once, feems to depend on their being rather local dif-
eafes than univerfal ones, and are hence not attended with fever, ex-
cept the purulent fever in their laft ftages, when the patient is deftroy-
ed by them. On this account the whole of the fyftem does not be-
come habituated to thefe morbid adions, fo as to ceafe to be afFeded
with fenfation by a repetition of the contagion. Thus the contagious
inatter of the venereal difeafe, and of the tenia, affeils the lymphatic
5 glands,

SECT.XXXIir.2. DISEASES OF SENSATION. 401

glands, as the iuquhnl glands, and thofe about the roots- of the iiair
and neck, where it is arrefted, but does not feeoi to aife^l the blood-
veflels, fince no lever enlues.

Hence it would appear, that thefe kinds of contagion are propa-
gated not by ncieans of the circulation, but by fvmpathy of diftanC
-parts with each other ; fmce if. a diftant part, as the palate, Ihould
be excited by feniitive aflbciation into the fame kind of motions, as
the parts originally affe£led by the contadl of infedious matter ; that
diftant part will produce the fame kind of infedlious matter ; for every
fecretion from the blood is formed from it by the peculiar motions of
the fine extremities of the gland, which fecretes it; the various fe-
creted fluids, as the bile, faliva, gaftric juice, not previoufly exiftin"-,
as fuch, in the blood-veflels.

And this peculiar fympathy between the genitals and the throat,
owing to fenfitive aflbciation, appears not only in the produ6lion of
venereal ulcers in the throat, but in variety of other inftances, as in
the mumps, in the hydrophobia, fome coughs, ftrangulation, the
produ£lion of the beard, change of voice at puberty. Which are fur-
ther defcribed in Clafs IV. z. 1.7.

To evince that the produ6lion of fuch large quantities of contagi-
ous matter, as are feen in fome variolous patients, fo as to cover the
whole Ikin almoft with puftules, does not arife from any chemical fer-
mentation in the blood, but that it is owing to morbid motions of the
fine extremities of the capillaries, or glands, whether thefe be rup-
tured or not, appears from the quantity of this matter always cor-
refponding with the quantity of the fever ; that is, with the violent
exertions of thofe glands and capillaries, which are the terminations
of the arterial fyftem.

The truth of this theory is evinced further by a circumftance ob-
ferved by Mr. J. Hunter, in his Treatife on Venereal Difeafe ; that
in a patient, who was inoculated for the fmall-pox, and who appear-
jgd afterwards to have been previoufly infected with the meafles,

3 F the

402 DISEASES OF SENSATION. Sect. XXXIII. 2.

the progrefs of the fmall-pox was delayed till the meafles had run
their courfe, and that then the fmall-pox went through its ufual
periods.

Two fimilar cafes fell under my care, which I fliall here relate, as
it confirms that of Mr. Hunter, and contributes to illuftrate this part
of the theory of contagious difeafes. I have tranfcribed the particu-
lars from a letter of Mr. Lightwood of Yoxal, the furgeon who
daily attended them, and at my requeft, after I had (sen them, kept
a kind of journal of their cafes.

Mifs H. and Mifs L. two fifters, the one about four and the other
about three years old, were inoculated Feb. 7, 1791. On the loth
there was a rednefs on both arms difcernible by a glafs. On the
Jith their arms were fo much inflamed as to leave no doubt of the
infedlion having taken place. On the 12th lefs appearance of in-
flammation on their arms. In the evening Mifs L, had an eruption,
which refembled the meafles. On the 13th the eruption on Mifs L.
"was very full on the face and breaft, like the meafles, with confider-
able fever. It was now known, that the meafles were in a farm houfe
in the neighbourhood. Mifs H.'s arm lefs inflamed than yefl:erday.
On the 14th Mifs L.*s fever great, and the eruption univerfal. The
arm appears to be healed. Mifs H.'s arm fomewhat redder. They
were nov/ put into feparate rooms. On the 15th Mifs L.'s arms as
yefl:erday. Eruption continues. Mifs H.'s arms have varied but little.
16th, the eruptions on Mifs L. are dying away, her fever gone. Be-
o-ltis to have a little rednefs in one arm at the place of inoculation.
Mifs H.'s arms get redder, but fhe has no appearance of complaint.
20th, "Mifs L.'s arms bav^e advanced flowly till this day, and now a
few puflules appear. Mifs H.'s arm has made little progrefs from the
16th to this day, and now fhe has fome fever, aift, Mifs L. as
yeflerday. Mifs H. has much inflammation, and an iiicreafe of the
red circle on one arm to the fize of half a crown, and had much fever
at ni<^ht, with fetid breath.. 22d, Mifs L.'s puflules continue advanc-

ing.

SiiCT.XXXril. 2. DISEASES OF SENSATION. 403

ing. I\/i(s H.'s infiammstioii of he; arm ar.cl red ciicle inci'cafcs. A
few red (pots appear ii! dilH;rent parts with loaie deorcc of fever this
moroing. 23d Mifs L. has a larger crop of puftules. rslifs H. has
Imall pufiults and great inflammation of her arms, with but one
puftule likely to fuppurate. After this day they gradually got v\-eli,
and the puflules difappeared.

In one of thefe cafes the meafles went throii2;h their common courfe
with milder fymptoms than ufual, and in the other the meafly conta-
gion feemed juft fuificient to flop the progrefs of variolous contagion,
but without itfelf throwing the conflitutiou into any diforder. At the
fame time both the meafles and fmall-pox feem to have been rendered
milder. Does not this s;ive an idea, that if they were both inoculated
at the fame time, that neither of them might afFeft the patient ?

From thefe cafes I contend, that the contagious matter of thefe dif-
eafes does not affc6l the conflitution by a fermentation, or chemical
change of the blood, becaufe then they muft have proceeded together,
and have produced a third fomething, not exactly fimilar to cither of
them : but that they, produce new motions of the cutaneous termina-
tions of the blood-vefleis, which for a time proceed daily with increaf-
ing activity, like fome paroxyfms of fever, till they at length fecrete
or form a fimilar poifon by thefe unnatural aclions.
. Now as in the meafles one kind of unnatural motion takes place,
and in the fmall-pox another kind, it is ealy to conceive, that thefe
different kinds of morbid motions cannot exift together ; and there-
fore, that that which has firft begun will continue till the fyflem be-
comes habituated to the ftimulus which occafions it, and has ceafed to
be thrown into ailion by it ; and then the other kind of ftunulus will
in its turn produce fever, and new kinds of motions peculiar to itfelf.

10. On further confidering the aftion of contagious matter, fince

' the former part of this work was fent to the prefs ; where 1 haveaf-

ferted, in Sedt. XII. 3. 6. that it is probable, that the variolous matter

is dittufed through the blood ; I prevailed on my friend Mr. Power,

3 F 2 furgeon

404 DISEASES OF SENSATION. Sect. XXXIII. z,

furgeon at Bofworth in Leicefterfhire to try, whether the fmall-pox
could be inoculated by ufing the blood of a variolous patient inftead
of the matter from the puftules ; as I thought fuch an experiment
migh throw fome light at leaft on this interefting fubjedl. The fol-
lowing is an extradl from his letter : — •

" March ii, 1793. 1 inoculated two children, who had not had
the fmall-pox, with blood ; which was taken from a patient on the
fecond day after the eruption commenced, and before it was com-
pleted. And at the fame time I inoculated myfelf with blood from
the fame perfon, in order to compare the appearances, which might
arife in a perfon liable to receive the infection , and in one not liable to
receive it. On the fame day I inoculated four other children liable
to receive the infeftion with blood taken from another perfon on the
fourth day after the commencement of the eruption. The patients
from whom the blood was taken had the difeafc mildly, but had the
moft puftules of any I could fele£t from twenty inoculated patients ;
and as much of the blood was infinuated under the cuticle as I could
introduce by elevating the Ikin without drawing blood ; and three or
four fuch punftures were made in each of their arms, and the blood
was ufed in its fluid ftate.

*' As the appearances in all thefe patients, as well as in myfelf,,
were fimilar, I fliall only mention them in general terms. March 13.
A flight fubcuticular difcoloration, with rather a livid appearance,
without forenefs or pain, was viiible in them all, as well as in my
own hand. 15. The difcoloration fbmewhat lefs, witkout pain or
forenefs. Some patients inoculated on the fame day with variolous
matter have confiderable inflammation. 17. The difcoloration is
quite gone in them all, and from my own hand, a dry mark only re-
maining. And they were all inoculated on the i8th, with variolous
matter, which produced the difeafe in them all."

Mr. Power afterwards obferves, that, as the patients from whom
the blood was taken had the difeafe mildly, it may be fuppofed, that

though

Sect. XXXIII. 2. DISEASES OF SENSATION, 405

though the contagious matter might be mixed with the blood, it
might ftill be in too dilute a flate to convey the infedion ; but adds at
the fame time, that he has diluted recent matter with at leaft five
times its quantity of watery and which has ftill given the infedion ;:
though he has fometimes diluted it fo far as to fail.

The following experiments were inftituted at my requeft by my
friend Mr. Hadley, furgeon in Derby, to afcertain whether the blood,
of a perfon in the fmall-pox be capable of communicating the difeafe.
"Experiment ifl. .October i8th, 1793. I took fome blood from a
vein in the arm of a perfon, who had the fmall-pox on the fecond
day of the eruption, and introduced a fmall quantity of it immedi-
ately with the point of a lancet between the fcarf and true Ikin of the;
right arm of a boy nine years old in two or three different places ; the
other arm was inoculated with variolous matter at the fame time.

** 19th. The pundlured parts of the right arm were furrounded
with Ibme degree of fubcuticular inflammation. 20th. The inflam-
mation more conliderable, with a flight degree of itching, but no pairt
tipon preflTure. 21 ft. Upon examining the arm this day with a lens
I found the inflamniation lefs extenfive, and the rednefs chansine to
a deep yellow or orange- colour. 22d, Inflammation nearly gone.
23d. Nothing remained, except a flight difcoloration and a little fcurfv
appearance on the pun£tures. At the fame time the inflammation of
the arm inoculated with variolous matter was increafing faft, and he
had the difeafe mildly at the ufual time.

" Experiment 2d. I inoculated another child at the fame time and.
in the fame manner, with blood taken on the firfl; day of the erup-
tion ; but as the appearance and eftefts were fimilar to thofe in the
preceding experiment, 1 fliall not relate them minutely..

Experiment 3d. October 20th. Blood was taken from a perfon
who had the fmall-pox, on the third day of the eruption, and on-
the fixth from the commencement of the eruptive fever. I introduced
fome of it in its fluid fl:ate into both arms of a boy feven years old.

2-1 ft..

4c5 \ - DISEASES OF SENSATION. Sect. XXXiil. 2.

2,i!l. There apoeared to be fome inflammation under the cuticle,
M-here the puuilures were made. 22J. Inflammation more coa-
fiderable. a^cl. Ou this day the iiifiammatioa was fomewhat greater,
and the cuticle ratlier elevated.

24th. Inflammation much lefs, and only a brown or orange-colour
remained. 25th. Scarcely any difcoloration left. On this day he
was inoculated with variolous matter, the progrels of the infediou
went on ia the ufual v-av, and he had the fmall-pox very favour-

ablv.

" At this time I was requeued to inoculate a young perfon, who
was thought to have had the Imall-pox, but his parents were not quite
certain ; in one arm I introduced variolous matter, and in the other
blood, taken as in experiment 3d. On the fecond day after the ope-
ration, the pA^inclured parts were inflamed, though I think the arm in
which i had inferted variolous matter was rather more fo than the
other. On the third the inflammation was increafed, and looked
much the fame as in the preceding experiment. 4th. The inflam-
mation was much diminiflied, and on the 5th almoft gone. He was
ex poled at the fame time to the natural infedlion, but has continued

perfe6lly well.

" I have frequently obferved (and believe moft ' praftitioners have
done the fame), that if variolous matter be inferted in the arm of a
perfon who has previoufly had the fmall-pox, that the inflammation
on the fecond or third days is much greater, than if they had not had
the difeafe, but on the fourth or fifth it difappears.

" On the 23d I introduced blood into the arms of three more chil-
dren, taken on the third and fourth days of the eruption. The ap-
pearances v/ere much the fame as mentioned in experiments firft and
third. They were afterwards inoculated with variolous matter, and
had the difeafe in the regular way.

" The above experiments were made with blood taken from a
fmall vein in the hand or foot of three or four different patients,

whom

SEcr.XXXIir. 2. DISEASES OF SENSATION. 407

whom I had at that time under inoculation. They were feledled
from 160, as having the greateft number of puftules. The part was
wafhed with warm water before the blood was taken, to prevent the
poffibility of any matter being mixed with it from the furface.'*

Shall we conclude from hence, that the variolous matter never en-
ters the blood- veflels ? but that the morbid motions of the veflels of
the fkin around the infertion of it continue to increafe in a larger and
larger circle for fix or feven days ; that then their quantity of morbid
aftion becomes great enough to produce a fever-fit, and to afFedt the
ftomach by affociation of motions ? and finally, that a fecond affocia-
tion of motions is produced between the ftomach and the other parts
of the fkin, inducing them into morbid adlions fimilar to thofe of the
circle round the infertion of the variolous matter ? Alany more ex-
periments and obfervations are req^uired before this important queftion
can be fatisfacftorily anfwered.

It may be adduced, that as the matter inferted into the flcin of the
arm frequently fwells the lymphatic in the axilla, that in that cir-
cumftance it feems to be there arrefted in its progrefs, and cannot be
imagined to enter the blood by that lymphatic gland till the fwelling
of it fubfides. Some other phasnomena of the dil'eafe are more eafilv
reconcileable to this theory of fyrapathetic motions than to that of
abforption ; as the time taken up between the infertion of the matter,
and the operation of it on the fyftem, as mentioned above. For the
circle around the infertion is {een to increafe, and to inflame ; and I
believe, undergoes a kind of diurnal paroxyfm of torpor and palenefs
with a lucceeding increafe of aclion and colour, like a topical fever-
fit. Whereas if the matter is conceived to circulate for fix or {tveix
days with the blood, without producing diforder, it ought to be ren-
dered milder, or the blood-veflels more familiarized to its acrimony.

It is much eafier to conceive from this doctrine of allbciated or
fympathetic motions of diftant parts of the fyftem, how it happens,,
that the variolous infedtion can be received but once, as before ex-
plained ;;

4:1 DISEASES OF SENSATION. Sect.XXXIII. 2.

plained ; tlian by fiippofing, that a change is efFecled in the m;tfs of
iblood by any kind of fermentative procefs.

. ' The curious circumftance of the two contagions of fmall-pox and
meafles not afting at the fame time, but one of them refting or fuf-
pending its aclion till that of the other ceafes, may be much eafier
explained from fympathetic or affociated adtions of the infedted part
with other parts of the fyftem, than it can from fuppofing the two
contagions to enter the circulation.

The fkin of the face is fubjeft to more frequent viciffitudes of heat
and cold, from its expofure to the open air, and is in confequence more
liable to fenfitive aflbciation with the ilomach than any other part of
the furface of the body, becaufe their adions have been more fre-
quently thus aflbciated. Thus in a furfeit from drinking cold water,
when a perfon is very hot and fatigued, an eruption is liable to appear
on the face in confequence of this fympathy. In the fame manner
the rofy eruption on the faces of drunkards more probably arifes from
the fympathy of the face with the flomach, rather than between the
face and the liver, as is generally fuppofed.

This fympathy between the ftomach and the Ikln of the face is ap-
parent in the eruption of the fmall-pox ; lince, where the difeafe is in
confiderable quantity, the eruption on the face firft fucceeds the lick-
nefs of the ftomach. In the natural difeafe the ftomach feems to be
frequently primarily affected, either alone or along with the tonfils, as
the matter feems to be only difFufed in the air, and by being mixed
with the faliva, or mucus of the tonfils, to be fwallowed into the
ftomach.

After fome days the irritative circles of motions become difordered
by this new ftimulus, which a£ls upon the mucous lining of the fto-
mach ; and ficknefs, vertigo, and a diurnal fever fucceed. Thefe
jdifordered irritative motions become daily increafed for two or three
days, and then by their increafed adion certain fenfitive motions, or
inflammation, is produced^ and at the next cold fit of fever, when

the

Sect. XXXIII. 3. DISEASES OF SENSATION. 409

the ftomach recovers from its torpor, an inflammatiou of the exter-
nal Ikin is formed in points (which afterwards fuppurate), by fenfitive
aflbciation, in the fame manner as a cough is produced in confequence
of expofing the feet to cold, as defcribed in Sedl. XXV. i. i. a-nd
Clafs IV. 2. 2. 4. If the inoculated fkin of the arm, as far as it ap-
pears inflamed, was to be cut out, or deftroyed by cauftic, before the
fever commenced, as fuppofe on the fourth day after inoculation,
would this prevent the difeafe ? as it is fuppofed to prevent the hy-
drophobia.

III. I. Where the new veffels, and enlarged old ones, which
conflitute inflammation, are not fo haftily diftended as to burft, and
form a new kind of gland for the fecretion of matter, as above men-
tioned ; if fuch circumftances happen as diminiih the painful fenfa-
tion, the tendency to growth ceafes, and by and by an abforption
commences, not only of the fuperabundant quantity of fluids depo-
fited in the inflamed part, but of the folids likewife, and this even
of the hardeft kind.

Thus during the growth of the fecond fet of teeth in children,
the roots of the firft fet are totally abforbed, till at length nothing of
them remains but the crown ; though a few weeks before, if they are
drawn immaturely, their roots are found complete. Similar to this
Mr. Hunter has obferved, that where a dead piece of bone is to exfo-
liate, or to feparate from a living one, that the dead part does not pu-
trify, but remains perfedly found, while the furface of the living
part of the bone, which is in contail with the dead part, becomes
abforbed, and thus effefts its feparation. Med. Comment. Edinb. V.
I. 425. In the fame manner the calcareous matter of gouty concre-
tions, the coagulable lymph depofited on inflamed membranes in rheu*
matifm and extravafated blood become abforbed ; which are all as fo-
lid and as indilToluble materials as the new veflels produced in inflam-
mation.

This abforption of the new veffels and depofited fluids of inflamed

3 G parts

4IO DISEASES OF SENSATION. Sect. XXXIII. 3.

parts is called refolution : it is produced by firfi: uiing fuch internal
means as decreafe the pain of the part, and in confequence its new
motions, as repeated bleeding, cathartics, diluent potations, and warm
bath.

After the veffels are thus emptied, and the abforption of the new
veffels and depofited fluids is evidently begun, it is much promoted
by flimulating the part externally by folutions of lead, or other me-
tals, and internally by the bark, and fmall dofes of opium. Hence
when an ophthalmy begins to become paler, any acrid eye- water, as
a folution of fix grains of white vitriol in an ounce of water, haftens
the abforption, and clears the eye in a very Ihort time. But the lame
application ufed a few^ days fooner would have increafed the inflam-
mation. Hence after evacuation opium in Imall dofes may contri-
bute to promote the abforption of fluids depofited on the brain, as ob-
ferved by Mr. Bromfield in his treatife of furgery.

2. Where an abfcefs is formed by the rupture of thefe new veflels,,
the violence of inflammation ceafes, and a new gland feparates a ma-
terial called pus : at the fame time a lefs degree of inflammation pro-
duces new veflels called vulgarly proud flefh ; which, if no bandage
confines its growth, nor any other circumflance promotes abforption.
in the wound, would rife to a great height above the ufual fize of the
part.

Hence the art of healing ulcers confifts in producing a tendency to
abforption in the wound greater than the depofition. Thus when an.
ill-conditioned ulcer feparates a copious and thin difcharge, by the ufe
of any ftimulus, as of falts of lead, or mercury, or copper exter-
nally applied, the difcharge becomes diminiChed in quantity, and be-
comes thicker, as the thinner parts are firft abforbed.

But nothing fo much contributes to increafe the abforption in a

•wound as covering the whole limb above the fore with a bandage,,

which fhould be fpread with fome plafter, as with emplaftrum

de minio, to prevent it from flipping. By this artificial tight-

7 uefa

Sect. XXXIII. 3. DISEASES OF SENSATION. 411

nefs of the fkin, the arterial pulfations a£l with double their ufual
power in promoting the afcending current of the fluid in the val-
vular lymphatics.

Internally the abforption from ulcers fhould be promoted firft by
evacuation, then by opium, bark, mercury, fteel.

3. Where the inflammation proceeds with greater violence or ra-
pidity, that is, when by the painful fenfation a more inordinate ac-
tivity of the organ is produced, and by this great aitivity an additional
quantity of painful fenfation follows in an increafing ratio, till the
whole of the fenforial power, or fpirit of animation, in the part be-
comes exhaufted, a. mortification enfues, as in a carbuncle, in in-
flammations of the bowels, in the extremities of old people, or in
the limbs of thofe who are brou2;ht near a fire after having been much
benumbed with cold. And from hence it appears, why weak people
are more fubje£t to mortification than ftrong ones, and why in weak
perfons lefs pain will produce mortification, namely, becaufe the fen-
forial power is fooner exhaufted by any excefs of adivity. I remem-
ber feeing a gentleman who had the preceding day travelled two ftages
in a chaife with what he termed a bearable pain in his bowels ; which
when I faw him had ceafed rather fuddenly, and without a paflage
through him ; his pulfe was then weak, though not very quick ; but
as nothing which he fwallowed would continue in his ftomach many
minutes, I concluded that the bowel was mortified ; he died on the
next day. It is ufual for patients finking under the fmall-pox with
mortified puftules, and with purple fpots intermixed, to complain of
no pain, but to fay they are pretty well to the lad moment.

G 2 Rccapiiu-

4 1 3 DISEASES OF SENSATION. Sect. XXXIII. 4,

Recapitulation.

IV. When the motions of any part of the fyftem, in confequence
of previous torpor, are performed with more energy than in the irri-
tative fevers, a difagreeable fenfation is produced, and new adions of
fome part of the fyftem commence in confequence of this fenfation
conjointly with the irritation ; which motions conftitute inflamma-
tion. If the fever be attended with a ftrong pulfe, as in pleurify, or
rheumatifm, it is termed fynocha fenfitiva, or fenfitive fever with
flrong pulfe ; which is ufually termed inflammatory fever. If it be
attended with weak pulfe, it is termed typhus fenfitivus, or fenfitive
fever with weak pulfe, or typhus gravior, or putrid malignant fever.

The fynocha fenfitiva, or fenfitive fever with ftrong pulfe, is ge-
nerally attended with fome topical inflammation, as in peripneumony,'
hepatitis, and is accompanied with much coagulable lymph, or fize;
■which rifes to the furface of the blood, when taken into a bafon, as
it cools ; and which is believed to be the increafed mucous fecretion
from the coats of the arteries, infpiffated by a greater abforption of
its aqueous and faline part, and perhaps changed by its delay in the
circulation. ,

The typhus fenfitivus, or fenfitive fever with weak pulfe, is fre-
quently attended with delirium, which is caufed by the deficiency
of the quantity of fenforial power, and with variety of cutaneous
eruptions.

Inflammation, is caufed by the pains occafioned by excefs of aftion,
and not by thofe pains which are occafioned by defe6l of aftion.
Thefe morbid anions, which are thus produced by two fenforial
powers, viz. by irritation and fenfation, fecrete new Hving fibres,

which

Sect. XXXIII. 4- DISEASES OF SENSATION. 413

which elongate the old vefTels, or form new ones, and at the fame
time much heat is evolved from thefe combinations. By the rupture
of thefe veffels, or bj a new conftruclion of their apertures, purulent
matters are fecreted of various kinds ; which are infeflious the firfl
time thej are applied to the fkin beneath the cuticle, or fwallowed
with the faliva into the ftomach. This contagion adls not by its be-
ing abforbed into the circulation, but by the fympathies, or aflbciated
a£lions, between the part firfl: flimulated by the contagious matter
and the other parts of the fyfl:em. Thus in the natural fmall-pox the
contagion is fwallowed with the faliva, and by its flimulus inflames
the flomach ; this variolous inflammation of the fl:omach increafes every
day, like the circle round the punfture of an inoculated arm, till it
becomes great enough to diforder the circles of irritative and fenfitive
motions, and thus produces fever- fits, with ficknefs and vo^niting.
Laftly, after the cold paroxyfm, or fit of torpor, of the flomach has
increafed for two or three fucceflive days, an inflammation of the ikin
commences in points ; which generally firfl appear upon the face, as
the aflbciated aclions between the fl^:in of the face and that of the flo-
mach have been more frequently exerted together than thofe of any
other parts of the external furface.

Contagious matters, as thofe of the meafles and fmall-pox, do not
a£l upon the fyfl:em at the fame time ; but the progrefs of that which
was laft received is delayed, till the adlion of the former infedion
ccafes. All kinds of matter, even that from common ulcers, are pro-
bably contagious the firfl time they are inferted beneath the cuticle or
fwallowed into the flomach ; that is, as they were formed by certain
morbid aftions of the extremities of the veflels, they have the power
to excite fimilar morbid adlions in the extremities of other veflTels, to
which they are applied ; and thefe by fympathy, or aflxDciations of
motion, excite fimilar morbid aftions in diflant parts of the fyflrem,
without entering the circulation ; and hence the blood of a patient in
the fmall-pox will not give that difeafe by inoculation to others.

When

414 DISEASES OF SENSATION. Sect. XXXIII. 4.

When the new fibres or veflels become again abforbed into the cir-
culation, the inflammation ceafes ; which is promoted, after fufficient
evacuations, by external ftimulants and bandages : but where the ac-
tion of the veflels is very great, a mortification of the part is liable to
enfue, owing to the exhauftion of fenforial power ; which however
occurs in weak people without much pain, and without very violent
previous inflammation ; and, like partial paralyfis, may be efleemed one
mode of natural death of old people, a part dying before the whole.

SECT.

Sect. XXXIV. DISEASES OF VOLITION. 415

SECT. XXXIV.

DISEASES OF VOLITION.

I. I. Volition defined. Motions termed involuntary are caufed hy volition. Dejires
oppofed to each other. Deliberation. AJs between two hay -cocks. Saliva Jwal-
lozved againjl one's defire. Voluntary ^notions diftinguijhed from thoje ajfociated
with Jenfitive motions. 2. Fains from excefs, and from defeat of motion. No
pain is felt during vehement voluntary exertion ; as in cold fits of ague, labour-
pains, ftrangury, tenefmus, vomiting, reftlejfnefs in fevers, convulfion of a
wounded mufcle. 3. Of holding the breath and Jcreaming in pain; why /wine
and dogs cry out in pain, and not fheep and horjes. Of grinning and biting in
pain; why mad animals bite others. 4. Epileptic convidfions explained, why
the fits begin with quivering of the under jaw, biting the tongue, and Jetting the
teeth ; why the convulfive motions are alternately relaxed. The phenomenon of
laughter explained. Why children cannot tickle themjelves. How fame have died,
from immode}' ate laughter. 5. Of cataleptic fpafms , of the locked jaw, of pain-
ful cramps. 6. Syncope explained. Why no external objects are perceived in
Jyneope. 7. Of pal/y and apoplexy from violent exertions. Cafe of Mrs. Scot.
From dancing, /eating, /wimming. Ca/e of Mr. Nairn. Why pal/ies are not
fdways immediately preceded by violent exertions. Pal/y and epilep/y from
di/ea/ed livers. Why the right arm more frequently paralytic than the left.
How paralytic iimbs regain their ^notions. II. Difeafes of the /en/ual
motions from exce/s or defe£i of voluntary exertion, i. Madne/s. 1. Di/-
tiyiguijhed from delirium. 3. Why mankind more liable to in/anity than
brutes. 4. Si/picion. Want of fljame, and of cleanline/s. 5. They bear cold,
hunger, and fatigue. Charles 'KW. of Sweden. 6. Plea/ureable delirium, and
in/anity. Child riding on a ftick. Tains of martyrdom not felt. 7, Dropfy._
8. Inflammation cured by h/anity. III. i. Pain relieved by reverie. Reveiie

4i6 DISEASES OF VOLITION. Sect. XXXIV. i.

is an exertion of voluntary and fenfitive motions. i. Cafe of reverie. 3. Lactf
fuppojed to have two fouls. 4. Methods of relieving fain.

I. I. BEFORE we commence this Seftion on Difeafed Voluntary
Motions, it may be neceflary to premife, that the word volition is
not ufed in this work exa£tly in its common acceptation. Volition is
faid in Sedlion V. to bear the fame analogy to defire and averfioii,
which fenfation does to pleafure and pain. And hence that, when
defire or averfioa produces any aftion of the mufcular fibres, or of the
organs of fenfe, they are termed volition ; and the adlions produced
in confequence are termed voluntary a<Slions. Whence it appears,
that motions of our mufcles or ideas may be produced m confequence
of defire or averfion without our having the power to prevent them,
and yet thefe motions may be termed voluntary, according to our
definition of the word; though in common language they would be
called involuntary.

The objedrs of defire and averfion are generally at a diftance, where-
as thofe of pleafure and pain are immediately afting upon our organs.
Hence, before defire or averfion are exerted, fo as to caufe any ac-
tions, there is generally time for deliberation ; which confifiis in dif-
covering the means to obtain the obje£l of defire, or to avoid the ob-
je6l of averfion ; or in examining the good or bad confequences, which
may refuit from them. In this cafe it is evident, that we have a
power to delay the propofed aftion, or to perform it ; and this power
of choofing, whether we fhall ad or not, is in common language ex-
preffed by the word volition, or will. Whereas in this work the
word volition means fimply the aftive ftate of the .fenforial faculty in
producing motion in confequence of defire or averfion ; whether we
have the power of reftraining that adion, or not ; that is, whether
we exert any anions in confequence of oppofite defires or averfions,
or not.

5 For

Sect. XXXIV. i. DISEASES OF VOLITION. 4^7

For if the obje£ts of defire or averfion are prefent, there is no ne-
ceffity to inveftigate or compare the means of obtaining them, nor do
we always dehberate about their confequences ; that is, no delibera-
tion neceflkrily intervenes, and in confequence the power of choofing
to a£l or not is not exerted. It is probable, that this twofold ufe of
the word volition in all languages has confounded the metaphyficians,
who have difputed about free will and neceffity. Whereas from the
above analyfis it would appear, that during our fleep, we ufe no vo-
luntary exertions at all ; and in our waking hours, that they are the
confequence of defire or averfion.

To will is to ail in confequence of defire ; but to defire means to
defire fomething, even if that lomething be only to become free from
the pain, which caufes the defire ; for to defire nothing is not to de-
fire; the word defire, therefore, includes both the a£lion and the ob-
jeiS: or motive ; for the obje6t and motive of defire are the fame thing.
Hence to defire without an obje6l, that is, without a motive, is a
folecifm in language. As if one Ihould afk, if you could eat without
food, or breathe without air.

From this account of- volition it appears, that convulfions of the-
raulcles, as in epileptic fits, may in the common fenfe of that word
be termed involuntary ; becaufe no dehberation is interpofed between,
the defire or averfion and the coniequent a6lion ; but in the fenfe of
the word, as above defined, they belong to the clafs of voluntary mo-
tions, as delivered in Vol. II. Clafs III. If this ufe of the word be
difcordant to the ear of the reader, the term morbid voluntary mo-
tions, or motions in confequence of averfioa, may be fubfl:ituted in its
ftead.

If a perfon has a defire to be cured of the ague, and has at the fame
time an averfion (or contrary defire) to fwallowing an ounce of Pe-
ruvian bark ; he balances defire againfl: defire, or averfion againfi:
averfion; and thus he acquires the power of choofing, which is the
common acceptation of the word zvi/ling. But in the cold fit of ague,';

3 H after

41 8 DISEASES OF VOLITION. S>gcr.XXXW,x^i

after having difcovered that the ad of (huddering, or exerting the fub-
eutaneous mufcles, relieves the pain of cold ; he immediately exerts
this a£l of volition, and (hudders, as foon as the pain and confequent
averfion return, without any deliberation intervening ; yet is this a(3:,
as well as that of fwallowing an ounce of the bark, cauled by voli--
tion ; and that even though he endeavours in vain to prevent it by a
weaker contrary volition. This recalls to our minds the flory of the
"hungry afs between two hay-ftacks, where the two defires are fup-
pofed fo exa£lly to countera6b each other, that he goes to neither of
the ftacts, but pcrifhes by want. Now as two equal and oppofite de-
fires are thus fuppofed to balance each other, and prevent all a£lion,
it follows, that if one of thefe hayflacks was fuddenly removed, that
the afs would irrefiflibly be hurried to the other, which in the com-
mon ufe of the word might be called an involuntary a£t ; but which,
in our acceptation of it, would be claffed amongft voluntary actions,
as above explained.

Hence to deliberate is to compare oppofmg defires or ayerfions, and
that which is the moft intereftingat length prevails, and produces ac-
tion. Similar to this, where two pains oppofe each other, the ftronger
or more interefting one produces action ; as in pleurify the pain from
fuffocation would produce expanfion of the lungs, but the pain occa-^
fioned by- extending the inflamed membrane, which lines the cheft,
oppofes this€xpanfion, and one or the other alternately prevails.

When any one moves his hand quickly near another perfon's eyes,
the eye-lids inftantly clofe ; this aft in common language is termed
involuntary, as we have not time to deliberate or to exert any con-
trary defire or averfion, but in this work it would be termed a volun-
tary aO:, becaule -it is caufed by the faculty of volition, and after a
few trials the niiSlvtation can be prevented by a contrary or oppofing

volition.

The power of oppofing volitions is beft exemplified in the ftory of
Mutius ScKVola, who is laid to have thruft his hand into the fire be-
fore

Sbct.xxxiv. I. DISEASES OF Volition. 41^

fore Porcenna, and to have fuffered it to be confumcd for having
failed him ia his attempt on the life of that general. Here the aver-
fion for the lofs of fame, or the unfatisfied defire to ferve his country,
the" two prevalent enthufiafms at that time, were more powerful than,
the defire of withdrawing his hand, which muft be occafioned by the
pain of combuftion ; of thefe oppofiiig volitions

Vincit amor pjitrise, laudumijuc immenfa cnpiJo.

If any one is told not to fwallow his faliva for a minute, he foon
fwallows it contrary to his will, in the common fenfe of that word ;
but this alfo is a voluntary a<flion, as it is performed by the faculty of
volition, and is thus to be underflood. When the power of volitiori
is exerted on any of our fenfes, they become more acute, as in our
attempts to hear fmall noifes in the night. As explained in Setflioii
XIX. 6. Hence by our attention to the fauces from our defire not to
fwallow our faliva ; the fauces become more fenfible ; and the stimu-
lus of the faliva is followed by greater fenfation, and confequent de-
sire of fwallowing it. So that the defire of volition. in confequence of
the increafed fenfation of the faliva is more powerful, than the previ-
ous defire not to fwallow it. See Vol. II. Deglutitio invita. In the"
fame manner if a modeft man wilhes not to want to make water,
when he is confined with ladies in a coach or an affembly-room ; that
very acl of volition induces the circumftanc«, which he wiflies tcr
avoid, as above explained ; infomuch that I once faw a partial infa-
nity, which might be called a voluntary diabetes, which was occa-
fioned by the fear (and confequent averfion) of not being able to raaks
water at all.

It is further neceflary to obferve here, to prevent any confufion of
voluntary, with fenfitive, or alTociate motions, that in all the inftance^
of violent efforts to relieve pain, thofe efforts are at firft voluntary
exertions ; but after they have been frequfently repeated far the pur-

3 H 2 j)oie

420 DISEASES OF VOLITION. Sect.XXXIV. i;

pofe of relieving certain pains, they become affociated with thofe
pains, and ceafe at thofe times to be fubfervient to the will; as in
coughing, fneezing, and ftrangury. Of thefe motions thofe which
contribute to remove or diflodge the offending caufe, as the a£lions of
the abdominal mufcles in parturition or in vomiting, though they
were originally excited by volition, are in this work termed fenfitive
motions ; but thofe anions of the mufcles or organs of fenfe, which
do not contribute fo remove the offending caufe, as in general convul-
lions or in madnefs, are in this work termed voluntary motions, or
motions in confequence of averfion, though in common language they
are called involuntary ones. Thofe fenfitive -unreflrainable adlions,
which contribute to remove the caufe of pain are uniformly and inva-
riably exerted, as i^i coughing or fneezing ; but thofe motions which
are exerted in confequence of averfion without contributing to remove
the painful caufe, but only to prevent the fenfation of it, as in epi-
leptic, or cataleptic fits, are not uniformly and invariably exerted,
but change from one fet of mufcles to another, as will be further ex-
plained ; and may. by this criterion alfo be diflinguifhed from the
former.

, At the fame time thofe motions, which are excited by perpetual
flimulus, or by aflbciation, with each other, or immediately by plea-
fureable or painful fenfation, may properly be. termed involuntary mo-
tions, as thofe of the heart and arteries ; as the faculty of volition fel-
dom afFtds thofe, except when it exifls in unnatural quantity, as iu
maniacal people.

2. It. was obferved in Sedlion XIV. on the Produftion of Ideas,
that thofe parts of the fyflem, which are ufually termed the organs
of fenfe, are liable to be excited into pain by the excefs of the flimu-
lus of thofe objects, which are by .nature adapted to affeft them ; as of
too great light, found, or prefiure. But that thefe organs receive no
pain from the defect or abfence of thefe flimuli,_ as in darknefs or
filence. But that our other organs of perception, which have gene-
rally

Sect. XXXIV. i . DISEASES OF VOLITION. 42 1

rally been called appetites, as of hunger, thirfl, want of heat, want
of frefh air, are liable to be afFe£led with pain by the defeft, as well
as by the excefs of their appropriated ftimuli.

This excefs or defeft of ftimulus is however to be confidered only
as the remote caufe of the pain, the immediate caufe being the excefs
or defedl of the natural a£lion of the afFedled part, according to Se£t.
IV. 5. Hence all the pains of the body may be divided into thofe from
excefs of motion, and thofe from defe£l of motion ; which diflinftion
is of great importance in the knowledge and the cure of many difeafes.
For as the pains from excefs of motion either gradually fubfide, or are
in general fucceeded by inflammation ; fo thofe from defe6l of motion
either gradually fubfide, or are in general fucceeded by convulfion,
or madnefs. Thefe pains are eafily diflinguifhable from each other by
this circumflance, that the former are attended with heat of the pain-
ed part, or of the whole body ; whereas the latter exifls without in-
creafe of heat in the pained part, and is generally attended with cold-
nefs of the extremities of the body ; which is the true criterion of
"what have been called nervous pains.

Thus when any acrid material, as fnufFor lime, falls into the eye,
pain and inflammation and heat are produced from the excefs of fti-
mulus ; but violent hunger, hemicrania, or the clavus hyftericus,
are attended with coldnefs of the extremities, and defeat of circula-
tion. When we are expofed to great cold, the pain we experience
from the deficiency of heat is attended with a quiefcence of the mo-
tions of the vafcular fyftem ; fo that no inflammation is produced,
but a great defire of heat, and a tremulous motionof the fubcutaneous
mufcles, which is properly a convulfion in confequence of this pain
from defe£l of the ftimulus of heat.

It was before mentioned, that as fenlation confifts in certain move-
ments of the fenforium, beginning at fome of the extremities of it,.
and propagated to the central parts of it; fo volition confifts of cer-
tain other movements of the fenforium, commencing in the central

parts

■42^ DISEASES OF VOLITION. Seer. XXXIV. r.

^parts of it, and propagate;] to fome of its-extremities. This idea of
^ihefe two great -powers of rnotion in the animal machine is confirmed
from obferviiig, that they never exifl: in a great degree or univerfally
at tiie fame time; for while we ftrongly exert our voluntary motions,
we ceafetofeel the pains or uneafmefles, which occafioned us to exert
them.

Flence during the time of fighting M'ith fifts or fvvords no pain is
felt by the combatants, till they ceafe to exert themfelves. Thus in
the beginning of ague-fits the painful fenfation of cold is diminifhed,
while the patient exerts himfelf in the fhivering and gnafhing of his
teeth. He then ceafes to exert himfelf, and the pain of cold returns;
and he is thus perpetually induced to reiterate thefe exertions, from
■which he experiences a temporary relief. The fame. occurs in labour-
pains, the exertion of the parturient woman relieves the violence of
the pains for a time, which recur again foon after fhe has ceafed to
'ufe thofe exertions. The fame is true in many other painful difeafes,
as in the llrangury, tenefmus, and the efforts of vomiting ; all thefe
difagreeable fenfations are diminifhed or removed for a time by the
various exertions they occafion, and recur alternately with thofe.ex-
ertions.

The reftlefihefs in fome fevers is an almofl perpetual exertion of
this kind, excited to relieve fome difagreeable fenfations ; the recipro-
cal oppofite exertions of a wounded worm, the alternate emproftlio-
tonos and opiflhotonos of fome fpafmodic difeafes, and the intervals of
all convulfions, from whatever caufe, feem to be owing to this cir-
cumflance of the laws of animation ; that great or univerfal exertion
cannot exift at the fame time with great or univerfal fenfation, though
they can exift reciprocally ; which is probably refolvable into the
more general law, that the whole fenforial power being expanded in
one mode of exertion, there is none to fpare for any other. Whence
fyncope, or temporary apoplexy, fucceeds to epileptic convul-
fions.
' 6 ' 2' Hence

Sect. XXXIV. I. DISEASES OF VOLITION. 423.

3. Hence when any violent pain affjids us, of which we can nei-
ther avoid nor remove the caufc, we foon learn to endeavour to alle-
viate it, by exerting fome violent voluntary effort, as mentioned
above; and are naturally induced to ufe thofe mufcles for this pur-
pofe, which have been in the early periods of our lives mofl frequent-
ly or moil powerfully exerted.

Now the firft mufcles, which infants ufe moft frequently, f.re
thofe of refpiration ; and on this account we gain a habit of holding
our breath, at the fame time that we ufe great efforts to exclude it,
for this purpofe of alleviating unavoidable pain ; or we prefs out our
breath through a fmaU aperture of the larinx, and Icream violently,
when the pain is greater than is relievable by the former mode of ex-
ertion. Thus children fcrcam to relieve any pain either of body or
mind, as from anger, or fear of being beaten.

Hence it is curious to obferve, that thofe animals, who have more
frequently exerted their mufcles of refpiration violently, as in talking,
barking, or grunting, as children, dogs, hogs, fcream much more,
when they are in pain, than thofe other animals, who ufe little or
no language in their common modes of life; as horfes, fheep, and
cows.

The next mofl: frequent or mofl: powerful efforts, which infants are
firfl: tempted to produce, are thofe with the mufcles in biting hard
fubftances ; indeed the exertion of thefe mufcles is vcrv powerful in
common maftication, as appears from the pain we receive, if a bit of
bone is unexpecledly found amongft our fofter food ; and further ap-
pears from their afting to fo great mechanical diladvantage, particu-
larly when we bite with the incifores, or canine teeth ; which are
firft formed, and thence are tirfl: uled to violent exertion.

Hence when a perion is in great pain, the caufe of ^vhich he can-
Hot remove, he fets his teeth firmly together, or bites fome fubftance
between them v/ith great vehemence, as another mode of violent ex-
ertion to produce a temporary relief. Thus we have a proverb vvhere

424 DISEASES OF VOLITION. Sect.XXXIV, r.

no help can be had in pain, *' to grin and abide ;" and the tortures of
hell are faid to be attended with " gnashing of teeth."

Hence in violent fpafmodic pains I have feen people bite not only
their tongues, but their arms or fingers, or thofe of the attendants',
or any objeft which was near them ; and alfo ftrike, pinch, or tear,
others or themfelves, particularly the part of their own body, which
is painful at the time. Soldiers, who die of painful wounds in battle,
are faid by Homer to bite the ground. Thus alfo in the bellon, or
colica faturnina, the patients are faid to bite their own flefh, and
dogs in this difeafe to bite up the ground they lie upon. It is pro-
bable that the great endeavours to bite in mad dogs, and the violence
of other mad animals, is owing to the fame caufe.

4. If the efforts of our voluntary motions are exerted with flill
greater energy for the relief of fome difagreeable fenfation, convul-
sions are produced ; as the various kinds of epilepfy, and in fome hyf-
teric paroxifms. In all thefc difeafes a pain or difagreeable fenfation
is produced, frequently by worms, or acidity in the bowels, or by
a difeafed nerve in the fide, or head, or by the pain of a difeafed
liver.

In fome conftitutions a more intolerable degree of pain is produced
in fome part at a diftance from the caufe by fenfitive affociation, as
before explained i thefe pains in fuch conftitutions arife to fo great a
degree, that I verily believe no artificial tortures could equal fome,
which I have witneiled ; and am confident life would not have long
been preferved, unlefs they had been foon diminifhed or removed by
the univerfal couvulfion of the voluntary motions, or by temporary
madnefs.

In fome of the unfortunate patients I have obferved, the pain has
rifen to an inexpreliible degree, as above defcribed, before the con-
vulfions have fupervened ; and which were preceded by fcreaming,
and grinning ; in others, as in the common epilepfy, the convulfion
has immediately fucceeded the commencement of the difagreeable

5 fenfations ;

Sect. XXXIV. I. DISEASES OF VOLITION. 425

fenfations ; and as a ftupor frequently fucceeds the convulfions, they
only feemed to remember that a pain at the ftomach preceded the fit,
or fome other unealy feel ; or more frequently retained no memory at
all of the immediate caufe of the paroxyfm. But even in this kind of
epilepfy, where the patient does not recolleft any preceding pain, the
paroxifms generally are preceded by a quivering motion of the under
jaw, with a biting of the tongue ; the teeth afterwards become
preffed together with vehemence, and the eyes are then convulfed,
before the commencement of the univerfal convullion ; which are all
efforts to relieve pain.

The reafon why thefe convulfive motions are alternately exerted
and remitted was mentioned above, and in Sedt. XII. i. 3. when the
exertions are fuch as give a temporary relief to the pain, which ex-
cites them, they ceafe for a time, till the pain is again perceived ; and
then new exertions are produced for its relief. We fee daily examples
of this in the loud reiterated laughter of fome people ; the pleafure-
able fenfation, which excites this laughter, arifes for a time fo high
as to change its name and become painful : the convulfive motions of
the refpiratory mufcles relieve the pain for a time ; we are, however,
unwilling to lofe the pleafure, and prefently put a flop to this ex-
ertion, and immediately the pleafure recurs, and again as infcantly
rifes into pain. All of us have felt the pain of immoderate laughter ;
children have been tickled into convulfions of the whole body ; and
others have died in the z€t of laughing ; probably from a paralyfis
fucceeding the long continued adions of the mufcles of refpira-
tion.

Hence we learn the reafon, why children, who are fo eafily ex-
cited to laugh by the tickling of other people's fingers, cannot tickle
themfelves into laughter. The exertion of their hands in the en-
deavour to tickle themfelves prevents the neceffity of any exertion of
the refpiratory mufcles to relieve the excefs of pleafureable affecdon.
See Se6l. XVII. 3. 5.

3 1 Chryfippus

426 DISEASES OF VOLITION. Sect. XXXIV. i.

Chryfippus is recorded to have died laughing, when an afs was in-
vited to fup with him. The fame is related of one of the popes,
who, when he was ill, faw a tame monkey at his bedfide put on the
holy thiara. Hall. Phyf. T. III. p. 306.

There are inftances of epilepfy being produced by laughing recorded
by Van Swieton, T. III. 402 and 308. And it is well known, that
many people have died inftantaneoufly from the painful excefs of joy,
which probably might have been prevented by the exertions of
laughter.

Every combination of ideas, which we attend to, occafions pain or
pleafure ; thofe which occafion pleafure, furnifli either focial or felfifh
pleafure, either malicious or friendly, or lafcivious, or fublime plea-
fure ; that is, they give us pleafure mixed with other emotions, or
they give us unmixed pleafure, without occalioning any other emo-
tions or exertions at the fame time. This unmixed pleafure, if it
be great, becomes painful, like all other animal motions from flimuli
of every kind; and if no other exertions are occafioned at the fame
time, we ufe the exertion of laughter to relieve this pain. Hence
laughter is occafioned by fuch wit as excites fimple pleafure without
any other emotion, fuch as pity, love, reverence. For fublime ideas
are mixed with admiration, beautiful ones with love, new ones with
furprife ; and thefe exertions of our ideas prevent the a£lion of laugh-
ter from being necelTary to relieve the painful pleafure above defcribed.
Whence laughable wit confifts of frivolous ideas, without connexions
of any confequence, fuch as. puns on words, or on phrafes, incon-
gruous junftions of ideas; on which account laughter is fo frequent
in children.

Unmixed pleafure lefs than that, which caufes laughter, caufes
fleep, as in finging children to fleep, or in flight intoxication from
wine or food. See Sedl. XVIII. 12.

5. If the pains, or difagreeable fenfations, above defcribed do not
obtain a temporary relief from thefe convulfive exertions of the muf-

5 cles.

Sect.XXXIV. I. DISEASES OF VOLITION. 427

cles, thofe convulfive exertions continue without remiflion, and one
kind of cataleply is produced. Thus when a nerve or tendon pro-
duces gre^t pain by its being inflamed or wounded, the patient lets
his teeth firmly together, and grins violently, to diminifli the pain ;
and if the pain is not relieved by this exertion, no relaxation of the
maxillary mufcles takes place, as m the convulfions above defcribed,
but the jaws ren.aln firmly fixed together. This locked jaw is the
moft frequent inftance of cataleptic Ipalm, becaule we are more in-
clined to exert the mufcles fubfervient to maftication from their early
obedience to violent efforts of volition.

But in the cafe related in Seel. XIX. on Reverie, the cataleptic
lady had pain in her upper teeth ; and preffing one of her hands ve-
hemently againft her cheek-bone to dlminifh this pain, it remained in
that attitude for about half an hour twice a day, till the painful pa-
roxyfm was over.

I have this very day feen a young lady in this difeafe, (with which
file has frequently been affli6led,) fhe began to-day with violent pain
fliooting from one fide of the forehead to the occiput, and after various
flruggles lay on the bed with her fingers and wrifts bent and ftiff for
about two hours ; in other refpefts fhe feemed in a fyncope with a
natural pulfe. She then had intervals of pain and of ipafm, and took
three grains of opium every hour till flie had taken nine grains, before
the pains and fpafm ceafed.

There is, however, another fpecies of fixed fpafm, which differs
from the former, as the pain exifls in the contracted mufcle, and
would feem rather to be the coniequence than the caufe of the con-
tradlion, as in the cramp in the calf of the leg, and in many other
parts of the body.

In thefe fpafms it fhould feem, that the mufcle itfelf is firfl thrown
into contrailion by fome dilagreeable fenfation, as of cold ; and that
then the violent pain is produced by the great contradtion of the muf-

2 I 2 cular

428 DISEASES OF VOLITION. Sect. XXXIV. r.

cular fibres extending its own tendons, which are faid to be fenfible
to extenfion only ; and is further explained in Se£t. XVIII. 1 5.

6. Many inftances have been given in this work, where after vio-
lent motions excited by irritation, the organ has become quiefcent to
lefs, and even to the great irritation, which induced it into violent
motion ; as after looking long at the fun or any bright colour, they
ceafe to be feen ; and after removing from bright day-light into a
o-loomy room, the eye cannot at firft perceive the objefts, which Si-
mulate it lefs. Similar to this is the fyncope, which fucceeds after
the violent exertions of our voluntary motions, as after epileptic fits,
for the power of volition a£ls in this cafe as the ftimulus in the other.
This fyncope is a temporary palfy, or apoplexy, which ceafes after a
time, the mufclcs recovering their power of being excited into adioii
by the efforts of volition ; as the eye in the circumftance above m.en-
tioned recovers in a little time its power of feeing objects in a gloomy
room ; which were inviiible immediately after coming out of a flronger
lio-ht. This is owing to an accumulation of fenforial power during
the ina6lion of thofe fibres, which were before accuftomed to per-
petual exertions, as explained in Se£t. XII. 7. i. A {lighter degree
of this difeafe is experienced by every one after great fatigue, when
the mufcles gain fuch inability to further adlion, that we are obliged
to reft them for a while, or to fummon a greater power of volition to.
continue their motions.

In all the fyncopes, which I have feen induced after convulfive fits,-
the pulfe has continued natural, though the organs of fenfe as well as
the locomotive mufcles, have ceafed to perform their funftions ; for
it is neceffary for the perception of objeds, that the external organs
of fenfe fhould be properly excited by the voluntary power, as the
eye-lids muft be open, and perhaps the mufcles of the eye put into
aftion to diftend, and thence give greater pellucidity to the cornea,
wliich in fyncope^ as in death, appears flat and lefs tranfparent.

The

Sect.XXXIV.i. diseases of volition. 429

The tympanum of the ear alfo feems to require a voluntary exertion
of its mufcles, to gain its due tenfion, and it is probable the other
external organs of fenfe require a fimilar voluntary exertion to adapt
them to the diftinft perception of objefts. Hence in fyncope as in
deep, as the power of volition is fufpended, no external obje6ls are
perceived. See Se£l. XVIII. 5. During the time which the patient
lies in a fainting fit, the fpirit of animation becomes accumulated ;
and hence the mufcles in a while become irritable by their ufual fti-
mulation, and the fainting fit ceafes. See Seel. XII. 7. i.

7. If the exertion of the voluntary motions has been ftill more
energetic, the quiefcence, which fucceeds, is fo complete, that they
cannot again be excited into a6lion by the efforts of the will. In this
manner the palfy, and apoplexy (which is an univerfal palfy) are fre-
quently produced after convulfions, or other violent exertions ; of this
i fhall add a few inftances.

Platernus mentions feme, who have died apoplectic from violent
exertions in dancing ; and Dr. Mead, in his EfTay on Poifons, records
a patient in the hydrophobia, who at one effort broke the cords
which bound him, and at the fame inftant expired. And it is pro-
bable, that thofe, who have expired from immoderate laughter, have
died from this paralyfis confequent to violent exertion. Mrs. Scott of
Stafford was walking in her garden in perfedt health with her neigh-
bour Mrs. ; the latter accidentally fell into a muddy rivulet,

and tried in vain to difengage herfelf by the afliftance of Mrs. Scott's
hand. Mrs. Scott exerted her utmofl power for many minutes, firfl
to affift her friend, and next to prevent herfelf from being pulled into
the moraf's, as her dittreffed companion would not difengage her hand.
After other affiftance was procured by their united fcreams, Mrs.
Scott walked to a chair about twenty yards from the brook, and was
feized with an apoplectic ftroke ; which continued many days, and
terminated in a total lofs of her right arm, and her fpeech ; neither of
which fhe ever after perfedlly recovered.

430 . DISEASES OF VOLITION. Sect. XXXIV. i.

It is faid, that many people in Holland have died after fkating too
long or too violently on their frozen canals ; it is probable the death
of thefe, and of others, who have died fuddenly in fwimming, has
been owing to this great quiefcence or paralyfis ; which has fucceeded
very violent exertions, added to the concomitant cold, which has had
greater efFeft after the fufFerers had been heated and exhaufted by pre-
vious exercife.

I remember a young man of the name of Nairne at Cambridge,
who walking on the edge of a barge fell into the river. His coufin
and fellow-ftudent of the fame name, knowing the other could not
fvvim, plunged into the water after him, caught him by his clothes,
and approaching the bank by a vehement exertion propelled him fafe
to the land, but that inftant, feized, as was fuppofed, by the cramp^
or paralyfis, funk to rife no more. The reafon why the cramp of
the mufcles, which compofe the calf of the leg, is fo liable to affect
fwimmers, is, becaufe thefe mufcles have very weak antagonifts, and
are in walking generally elongated again after their contraction by the
weight of the body on the ball of the toe, which is very much greater
than the refiftance of the water in fwimming. See Sedion
XVIII. 15.

It does not follow that every apople£lic or paralytic attack is im-
mediately preceded by vehement exertion ; the quiefcence, which
fucceeds exertion, and which is not {a great as to be termed paralyfis,
frequently recurs afterwards at certain periods ; and by other caufes
of quiefcence, occurring with thofe periods, as was explained in treat-
ing of the paroxyfms of intermitting fevers ; the quiefcence at length
becomes fo great as to be incapable of again being removed by the
efforts of volition, and complete paralyfis is formed. See Sedion
XXXII. 3. 2.

Many of the paralytic patients, vvhom Ihive feen, have evidently
had dileafed livers from the too frequent potation of fpirituous liquors ;
fome of them have had the gutta rofea on their faces and breafts ;

which

Sect. XXXIV. I. DISEASES OF VIOLITION. 431

which has in fome degree receded either fpontaneoufly, or by the ufe
of external remedies, and the paralytic flroke has fucceeded ; and as
in fcveral perfons, who have drank much vinous fpirits, I have ob-
ferved epileptic fits to commence at about forty or fifty years of age,
without any hereditary taint, from the flimulus, as I believed, of a
difeafed liver ; I was induced to afcribe many paralytic cafes to the
fame fource ; which were not evidently the effe£fc of age, or of un-
acquired debility. And the account given before of dropfies, which
very frequently are owing to a paralyfis of the abforbent fyftem, and
are generally attendant on free drinkers of fpirituous liquors, con-
firmed me in this opinion.

The difagreeable irritation of a difeafed liver produces exertions and
confequent quiefcence ; thefe by the accidental concurrence of other
caufes of quiefcence, as cold, folar or lunar periods, inanition, the
want of their ufual portion of fpirit of wine, at length produces pa-
ralyfis.

This is further confirmed by obferving, that the mufcles, we mofl
frequently, or moft powerfully exert, are moft liable to palfy ; as
thofe of the voice and of articulation, and of thofe paralytics which I
have feen, a much greater proportion have loft the ufe of their right
arm ; which is fo much more generally exerted than the left.

I cannot difmifs this fubjedl without obferving, that after a para-
lytic ftroke, if the vital powers are not much injured, that the pa-
tient has all the movements of the affedled limb to learn over aeain,
jufl as in early infancy ; the limb is firft moved by the irritation of
its mufcles, as in ftretching, (of which a cafe was related in Se6lion
VII. I. 3.) or by the eledlric concuffion j afterwards it becomes
obedient to fenfation, as in violent danger or fear ; and laftly, the
mufcles become again alTociated with volition, and_ gradually acquire
their ufual habits of aftins: tog-ether.

Another phacnomenon in palfies is, that when the limbs of one fide

are

432 DISEASES OF VOLITION, Sect. XXXIV. 2.

are difabled, thofe of the other are in perpetual motion. This can
only be explained from conceiving that the power of motion, what-
ever it is, or wherever it refides, and which is capable of being ex-
haufted by fatigue, and accumulated in reft, is now lefs expended,
whilft one half of the body is incapable of receiving its ulual propor-
tion of it, and is hence derived with greater eafe or in greater abundance
into the limbs, which remain unaffefted.

11. I. The" excefs or defe6t of voluntary exertion produces fimilar
efFedls upon the fenfual motions, or ideas of the mind, as thofe al-
ready mentioned upon the mufcular fibres. Thus when any violent
pain, arifing from the defedl of fome peculiar ftimulus, exifts either
in the mufcular or fenfual fyftems of fibres, and which cannot be
removed by acquiring the defedlive ftimulus ; as in fome conftitutions
convulfions of the mufcles are produced to procure a temporary relief,
fo in other conftitutions vehement voluntary exertions of the ideas of
the mind are produced for the fame purpofe ; for during this exertion,
like that of the mufcles, the pain either vanifhes or is diminifhed :
this violent exertion conftitutes madnefs ; and in many cafes I have
feen the madnefs take place, and the convulfions ceafe, and recipro-
cally the madnefs ceafe, and the convulfions fupervene. See Se£tion
III. 5. 8.

2. Madnefs is diftingulftiable from delirium, as in the latter the
patient knows not the place where he refides, nor the perfons of his
friends or attendants, nor is confcious of any external obje£ls, except
when fpoken to with a louder voice, or ftimulated with unufual force,
and even then he foon relapfes into a ftate of inattention to every
thing about him. Whilft in the former he is perfedtly fenfible to
every thing external, but has the voluntary powers of his mind in-
tenfely exerted on fome particular object of his defire or averfion, he
harbours in his thoughts a fufpicion of all mankind, left they fliould
counterad his defigns ; and while he keeps his intentions, and the

motives

Sect. XXXIV. 2. DISEASES OF VOLITION. 4:^^

motives of his aftions profoundly fecret ; he is perpetually fludying
the means of acquiring the objedt of his wifti, or of preventing or re-
venging the injuries he fufpedls.

3. A late French philofopher, Mr. Helvetlus, has deduced almofi:
all our aftions from this principle of their relieving us from the ennui
or tcEdium vit^ej and true it is, that our defires or averfions are the
motives of all our voluntary adlions ; and human nature feems to ex-
cel other animals in the more facil ufe of this voluntary power, and
on that account is more liable to infanity than other animals. But
in mania this violent exertion of volition is expended on midaken ob-
jects, and would not be relieved, though we were to gain or efcape
the objefts, that excite it. Thus I have feen two inftances of mad-
men, who conceived that they had the itch, and feveral have believed
they had the venereal infedlion, without in reality having a fymptom
of either of them. They have been perpetually thinking upon this
fubjeft, and fome of them were in vain fahvated with defign of con-
vincing them to the contrary.

4. In the minds of mad people thofe volitions alone exift, which
are unmixed with fenfation ; immoderate fufpicion is generally the
firft fymptom, and want of fhame, and want of delicacy about clean-
linefs. Sufpicion is a voluntary exertion of the mind arifing from the
pain of fear, which it is exerted to relieve : fhame is the name of a
peculiar difagreeable fenfation, fee Fable of the Bees, and delicacv
about cleanhnefs arifes from another difagreeable fenfation. And
therefore are not found in the minds of maniacs, which are employed
folely in voluntary exertions. Hence the moft modeft women in
this difeafe walk naked amongft men without any kind of concern,
ufe obfcene dilcourfe, and have no delicacy about their natural eva-
cuations.

5. Nor are maniacal people more attentive to their natural appe-
tites, or to the irritations which lurround them, except as far as may
refped their fufpicions or defigns ; for the violent and perpetual ex-

5 K ertions

434 DISEASES OF VOLlTIOlSr. Sect. XXXIV. 2.

ertions of their voluntary powers ofmind prevents their perception of
almoft every other obje6l, either of irritation or of fenfation. Hence
it is that they bear cold, hunger, and fatigue, with much greater
pertinacity than in their fober hours, and are lefs injured by thena in
refpedt to their general health. Thus it is aOTerted by hiflorians, that
Charles the Twelfth of Sweden flept an the fnow, wrapped only in
his cloak, at the fiege of Frederickfhad, and bore extremes of cold,
and hunger, and fatigue, under which numbers of his foldiers perifh-
ed ; becaufe the king was infane with ambition, but the foldier had
no fvich powerful ftimulus to preferve his fyllem from debility and
death.

6. Befides the infanities arifing from exertions in confequence of
pain, there is alfo a pleafureable infanity, as well as a pleafureable
delirium ; as the infanity of perfonal vanity, and that of religious fa-
naticifm. When agreeable ideas excite into motion the fenforial
power of fenfation, and this again caufes other trains of agreeable
ideas, a conftant ftreani of pleafureable ideas fucceeds, and produces
pleafureable delirium. So when the fenforial power of volition ex-
cites ao-reeable ideas, and the pleafure thus produced excites more vo-
lition in its turn, a conftant flow of agreeable voluntary ideas fuc-
ceeds ; which when thus exerted in the extreme conftitutes in-
fanity.

Thus when our mufcular acSlions are excited by our fenfations of
pleafure, it is termed play ; when they are excited by our volition,
it is termed work ; and the former of thefe is attended with lefs fa-
tlo-ue, becaufe the mufcular adlions in play produce in their turn
more pleafureable fenfation ; which again has the property of pro-
ducino- more mufcular a6tion. An agreeable inftance of this I faw
this morning. A little boy, who was tired with walking, begged of
"his papa to carry him. " Here," fays the reverend doctor, " ride
upon my gold-headed cane ;" and the pleafed child, putting it be-
tween his legs, gallopped away with delight, and complained no

Sect.XXXIV.2. diseases OF VOLITION, ^35

more of his fatigue. Here the aid of another fenforial power, that
of pleafureablefenfation, fuperadded vigour to the exertion of exhaufted
voiition. Which could othervvife only have been excited by additional
pain, as by the lafli of flavery. On this account where the whole
lenforial power has been exerted on the contemplation of the promifed
joys of heaven, the faints of all pcrfecuted religions have borne the
tortures of martyrdom with otherwife unaccountable firmnefs.

7. There are fome difeafes, which obtain at leaft a temporary relief
from the exertions of infanity ; many inftances of dropfies being thus
for a time cured are recorded. An elderly woman labouring with
afcites I twice faw relieved for fom.e weeks by infanity, the dropfy
ceafed for feveral weeks, and recurred again alternating with the in-
fanity. A man affli£ted with difficult refpiration on lying down, with
Very irregular pulfe, and oedematous legs, whom I faw this day, has
for above a week been much relieved in refpedt to all thofe fymptoms
by the acceflion of infanity, which is fhewn by inordinate fufpicion,
and great anger.

In cafes of common temporary anger the increafed action of the ar-
terial fyftem is feen by the red fkin, and increafed pulfe, with the
immediate increafe of mufcular activity. A friend of mine, when he
was painfully fatigued by riding on horfeback, was accuftomed to call
up ideas into his mind, which ufed to excite his anger or indignation, .
and thus for a time at leaft relieved the pain of fatigue. By this tempo-
rary infanity, the efte£l of the voluntary power upon the whole of his
fyftem was increafed ; as in the cafes of dropfy above m.entioned, it
would appear, that the increafed adion of the voluntary faculty of
the fenforiura afFeded the abforbent fyfiem, as v/ell as the fecernino-
one.

8. In refped to relieving inflammatory pains, and removing fever,
1 have feen many inftances, as mentioned in Sed. XII. 3. 4. One
.lady, whom I attended, had twice at fome years interval a locked

3 K 2 jaw^

43^ DISEASES OF VOLITION. Sect. XXXIV. 2.

jaw, which reheved a pain on her fternum with peripneumony. Two
other ladies I faw, who towards the end of violent peripneumony, in
which they frequently loft blood, were at length cured by infanity
fupervening. In the former the increafed voluntary exertion of the
mufcles of the jaw, in the latter that of the organs of fenfe, removed
the difeafe ; that is, the difagreeable fenfation, which had produced
the inflammation, now excited the voluntary power, and thefe new
voluntary exertions employed or expended the fuperabundant fenforial
power, which had previoufly been exerted on the arterial fyftem, and
eaufed inflammation.

Another cafe, which I think worth relating, was of a young man
about twenty j he had laboured under an irritative fever with debility
for three or four weeks, with very quick and very feeble pulfe, and
other ufual fymptoms of that fpecies of typhus, but at this time com-
plained much and frequently of pain of his legs and feet. When thofe
who attended him were nearly in defpair of his recovery, I obferved
with pleafure an infanity of mind fupervene : which was totally dif-
ferent from delirium, as he knew his friends, calling them by their
names, and the room in which he lay, but became violently fufpici-
ous of his attendants, and calumniated with vehement oaths his ten-
der mother, who fat weeping by his bed. On this his pulfe became
{lower and firmer, hut the quicknefs did not for fome time intirely
cea{e,,aad he gradually recovered. In this cafe the introdufi^ion of an
increafed quantity of the power of volition gave vigour to thofe move-
ments of the fyftem, which are generally only a£luated by the power
of irritation, and of affociation.

. Another cafe I recolleft of a young man, about twenty-five, who
had the fcarlet-fever, with very quick pulfe, and an_ univerfal erup-
tion on his ikin, and was not without reafoa efteemed to be in great
danger of his life. After a few days an infanity fupervened, which
4iis friends miftook for delirium, and he gradually recovered, and the
6> cuticlft

Sect. XXXIV. 5- DISEASES OF VOLITION. 437

cuticle peeled off. From thefe and a few other cafes I have always
efteemed infanity to be a favourable figu ia fevers, and have cautioufly
<lifl:ingui(hed it from delirium.

III. Another mode of mental exertion to relieve pain, is by pro-
ducing a train of ideas not only by the efforts of volition, as in infa-
nity ; but by thofe of fenfation likewife, as in delirium and fleep.
This mental effort is termed reverie, or fomnambulation, and is de-
fcribed more at large in Sedt. XIX. on that fubje6t. But I fhall here
relate another cafe of that wonderful difeafe, which fell veflerday
■under my eye, and to which I have ieen many analogous alienations
of mind, though not exadlly fimilar in all circumftances. But as alL
of them either began or terminated with pain or convullion, there-
can be no doubt but that they are of epileptic origin, and coaftitute-
another mode of mental exertion to, relieve fome painful fen^-
lation.

I. Mailer A. about nine years old, had been feized at feven every
morning for ten days with uncommon fits, and had had flight re-
turns ia the afternoon. They were fuppofed to originate from
worms, and had been in vain attempted to be removed by vermi-
fuge purges. As his fit was expe6led at feven yeflerday morning,,
I faw him before that hour ; he was afleep, feeraed free from pain^
and his pulie natural. About feven he began to complain of pain
about his navel, or more to the left fide, and in a few. minutes had
exertions of his arms and legs like fwimming. He then for half
an hour hunted a pack of hounds ; as appeared by his hallooine,
and calling the dogs by their names, and difcourfing with the at-
tendants of the chafe, defcribing exadlly a day of hunting,, which
(I was informed) he had witneffed a year before, going through
all the mofl minute circumflances of it ; calling to people, who
were then prefent, and lamenting the abfence of others, who were
^hen alfo. abfent. After this, fcene he imitated, as he lay. ia bed;

feme.

43S DISEASES OF VOLITION. Sect. XXXIV. 3.

fome of the plays of boys, as fwimming and jumping. He
then fung an Englifli and then an Italian fong ; part of which
with his eyes open, and part with them clofed, but could not
be awakened or excited by any violence, which it was proper
to ufe.

After about an hour he came fuddenly to himfelf with ap-
parent furprife, and feemed quite ignorant of any part of what
had paffed, and after being apparently well for half an hour, he
fuddenly fell into a great fbupor, with flower pulfe than natural, and
a flow moaning refpiration, in which he continued about another half
hour, and then xecovered.

The fequel of this difeafe was favourable ; he was direded one
grain of opium at fix every morning, and then to rife out of
bed ; at half paft fix he was direfted fifteen drops of laudanum in
a glafs of wine and water. The firfh day the paroxyfm became
fhorter, and lefs violent. The dofe of opium was increafed to one-
half more, and in three or four days the fits left him. The bark and
filings of iron were alfo exhibited twice a day ; and I believe the com-
plaint returned no more.

2. In this paroxyfm it muft be obferved, that he began with pain, and
ended with flupor, in both circumfi:ances refembling a fit of epilepfy.
And that therefore the exertions both of mind and body, both the vo-
luntary ones, and thofe immediately excited by pleafureable fenfation,
were exertions to relieve pain.

The hunting fcene appeared to be rather an a£t of memory
than of imagination, and was therefore rather a voluntary exer-
tion, though attended with the pleafureable eagernefs, which was
the confequence of thofe ideas recalled by recoUeftion, and not the
caufe of them.

Thefe ideas thus voluntarily recoUefted were fuccceded by fen-

fations of pleafure, though his fenfes were unaffefted by the fi:i-

8 mull

Sect. XXXIV. 3. DISEASES OF VOLITION. 439

muli of vifible or audible objeils ; or fo weakly excited by them as
;iot to produce fenfatioa or attention. And the pleafure thus ex-
cited by volition produced other ideas and other motions in con-
fequence of the fenforial power of fenfatioa. Whence the mixed
catenations of voluntary and fenfitive ideas and mufcular motions
in reverie ; which, like every other kind of vehement exertion,
contribute to relieve pain, by expending a large quantity of fenforial
power.

Thofe fits generally commence during fleep, from whence I fup-
pole they have been thought to have feme connection with fleep,
and have thence been termed Somnambalifm ; but their commence-
ment during fleep is owing to our increafed excitability by internal
fenfations at that time, as explained in Se6t. XVIII. 14 and 15, and
not to any fimilitude between reverie and fleep.

3. I was once concerned for a very elegant and ingenious youno-
lady, who had a reverie on alternate days, which continued nearly
the whole day ; and as in her days of difeafe fhe took up the fame
kind of ideas, which fhe had converfed about on the alternate day
before, and could recoUeifl nothing of them on her well-day ; fhe
appeared to her friends to poflefs two minds. This cafe alfo was of
epileptic kind, and was cured, with fome relapfes, by opium admi-
niflered before the commencement of the paroxyfm.

4. Whence it appears, that the methods of relieving inflammatory
pains, is by removing all fliimulus, as by venefe6lion, cool air, mu-
cilaginous diet, aqueous potation, filence, darknefs.

The methods of relieving pains from defe£b of flimulus is by fup-
plying the peculiar fl:imulus required, as of food, or warmth.

And the general method of relieving pain is by exciting into a(flion
fome great part of the fyftem for the purpofe of expending a part
of the fenforial power. This is done either by exertion of the vo-
luntary ideas and mufcles, as in infanity and convulfion ; or by

exertins;

440 DISEASES OF VOLITION. Sect. XXXIV. 3.

exerting both voluntary and fenfitive motions, as in reverie ; or by
exciting the irritative motions by wine or opium internally, and
by the warm bath or blifters externally ; or laftly, by exciting
the fenfitive ideas by good news, affeding (lories, or agreeable

traffions.

SEC T.

-Sect.XXXV. I. DISEASES OF ASSOCIATION. 4^1

SECT. ^rxXV;

DISEASES OF ASSOCIATION.

I. I. Sympathy tn' conjent of parts. .Primary and fecondary parts of an qffbctatei
train of motions reciprccaHy affeSl each other, Farts of irritative trains of mo-
tion affeSl each other in four ways. Sympathies of thejkin and ftomach. Flujh-
ing of the face after a meal. Eruption of the fmall-pox on the face. Chihiefs
after a meal. 2. Vertigo from intoxication. 3. Abforption from the lungs and

pericardium by emetics. In vomiting the anions of the Jlomach are decreafed, not
increofed. Digeftion flrengthened after an emetic. Vomitting from deficiency of

Jenforial power. 4. Dyfpncea from cold bathing. Slow pulfe fro'm. digitalis.
Death from gout in the fiomach. II. i. Primary and fecondary parts of fen-

Jitive ajfociations affeU each ether. Pain from gall-flone, from urinary Jione.
Hetnicrania. Painful epilepfy. 2. Gout and red face from inflamed liver.
Shingles from inflamed kidney. 3.. Coryza from cold applied to the feet. Pleu-
rijy. Hepatitis. 4. Pain offhouldersfrom inflamed liver. III. Difeafes from
the qffociations of ideas,

I. I. MANY fynchronous and fucceffive motions of our mufcular
fibres, and of our organs of fenfe, or ideas, become aflbciated io as to
form Indiffoluble tribes or trains of adion, as fhewn in Seflion X. on
Affociate Motions. Some conftitutions more eafily eflablifh thefe af-
fociations, whether by voluntary, fenfitive, or irritative repetitions,
and fome more eafily lofe them again, as Ihewn in Section XXXI. on
Temperaments.

When the beginning of fuch a train of aftlons becomes by any
ineans <3ifordered, the fucceeding part is liable to become difturbed

3 L in

44a DISEASES OF ASSOGI ATION. Sject. XXXV: i ^

in confequence, and this is commonly termed fympath y. or confent of
parts by the writers of medicine. For the. more clear underftanding,
of thefe fympathies wc muft confidera tribe or train of actions as di-
vided into two parts, and call one of them the primary or original :
motions, and the other the fecondary or fympathetic ones..

The primary and fecondary parts of a train of irritative adlions may
reciprocally affedt each other in foiu* different, manners; i. They
may both be exerted with greater energy than natural. 2. The
former may zdi with greater, and the. latter with lefs energy.. 3;
The former may a6l with lefs, and the latter with greater energy,
4. They may both aO: with lefs energy than natural.- I fhaU now
give an example of each kind of thefe modes of a£tion, and endeavour
to fhew, that though .the primary and fecondary parts of thefe trains
of tribes of . motion . are conneft'ed by irtitative affobiation, or their
previous habits of a£ling. together, as defcribed in Beit. XX. on Ver-
tigo. Yet that th-eir ading.with fimilar or diffimilar degrees of ener- -
gy, depends on th,& greater or lefs quantity of feriforiarpower, which.;
the primary part of the train, expends in its exertions, .

The- axflions of. the ftomach con flit ute {d importanfa parrt of', the
affociations of both > irritative and fenfitive motions, .that it is faid to
fympathize with almoft every part of the body ; ^ the firfk example,
which I fhall adduce to fhew that both the- primary and fecondary.
parts of a train of irritative affociations of motion a£t with increafed
energy, is taken from the confent of-the.lkin with this organ. When
the adion of the fibres .of the flomach is- increafed, as by the fhimulus
of a full meal,, the. exertions of the cutaneous arteries of the face be- -
come increafed by their irritative affociations with' thofe of the flo-
mach, and a glow or flufbing of. the face fucceeds. For the fmall :
veffels of the fkin of. the face having been more accuflomed to the va-r
rieties. of adlion, from their frequent expofure to. various degrees of
cold and heat become more eafily excited into increafed adlion, than
thofe of the covered . parts of o.ur bodies, and thus ad with, more

3- energy

Sect.. XXXV. I. DISEASES OF ASSOCIATION, 443

energy from their irritative or fenfitive affociatiohs with the ftomach.
On this account in fmall-pox the eruption in confequence of the pre-
vious afFeclion of the ftomach breaks out a day fooner on the face than,
on the hands, and two days fooner than on the trunk, and recedes in
fimilar times after maturation.

But fecondly, in weaker conftitutions, that is, in thofe who pof-
fefs lefs fenforial power, fo much of it is expended in the increafed
adlions of the fibres of the flomach excited by the ftimulus of a meal,
that a fenfe of chihiefs fucceeds inftead of the univerfal glow above
mentioned ; and thus the fecondary part of the affociated train of mo-
tions is diminifhed in energy, in confe'quence of the increafed aftivity
of the primary part of it.

2. Another inflance of a fimilar kind, where the fecondary part of
the train aiSls with lefs energy in confequence of the greater exertions
of the primary part, is the vertigo attending intoxication ; in this
circumftance fo much fenforial power is expended on the ftomach,
and on its neareft or more ftrongly affociated motions, as thofe of the
fubcutaneous veffels, and probably of the membranes of fome inter-
nal vifcera, that the irritative motions of the retina become imper-
fe6tly exerted from deficiency of fenforial power, as explained in
Seft, XX. and XXI. on Vertigo and on Drunkennefs, and hence the
daggering inebriate cannot completely balance himfelf by fuch in-
diftindt vifion.

3. An inflance of the third circumftance, where the primary part
of a train of irritative motions a;cts with lefs, and the fecondary part
with greater energy, may be obferved by making the following ex-
periment. If a perfon lies with his arms and Ihoulders out of bed,
till they become cold, a temporary coryza or catarrh is produced ; fo
that the paffage of the noflrils becomes totally obftrudled ; at leafl
this happens to many people ; and then on covering the arms and
fhoulders, till they become warm, the paffage of the uortrils ceafes

J L 2 again

444 DISEASES OF ASSOCIATION. Sect. XXXV. i.

again to be bbftradled, and a quantity of mucus is difcharged fronl
them. In this cafe the quiefcence of the veffels of the fkin of the
arms and fhoulders, occaiioned by expofure to cold air, produces by
irritative affociation an increafed a£lion of the veffels of the membrane
of the noftrils ; and the accumulation of fenforial power during the
torpor of the arms and fhoulders is thus expended in producing a
terriporary coryza or catarrh.

Another inflance may be adduced from the fympathy or confent of
the motions of the ftomach with other more diftant links of the very
extenlive tribes or trains of irritative motions affociated with them,
defcribed in Seft. XX. on Vertigo. When the aftions of the fibres of
the flomach are diminifhed or inverted, the adtions of the abforbent
veffels, which take up the mucus from the lungs, pericardium, and',
other cells of the body, become increafed, and abforb the fluids accu-
mulated in them with greater avidity, as appears from the exhibition,
of foxglove, antimony, or other emetics in cafes of anafarca, attend*
ed with unequal pulfe and difficult refpiration.

That the a£l of naufea and vomiting is a decreafed exertion of the
fibres of the ftomach may be thus deduced ; when an emetic medi-
cine is adrainiftered, it produces the pain of ficknefs, as a difagreeable;
tafte in the mouth, produces the pain of naufea ; thefe pains, like that:
of hunger, or of cold,, or like thofe, which are ufually termed ner-
vous,, as the headrach or hemicrania, do not excite the organ into
greater aftion ; but In this cafe I imagine the pains of ficknefs or of.
aaufea eomiteraft or deftroy the pleafureable fenfation, which feems-
neceffary to digeftion, as flievvn in Se&. XXXIII. i^ i. The peri--
ft'altic motions of the fibres of the ftomach become enfeebled by the
want of this ftimulus of pleafureable fenfation, and in.confequence
ftop for a time, and then become inverted ; for they cannot become,
inverted without being previoufly ftopped. Now that this inverfioJi,
of the trains of motion of the fibres of the ftomach. is owing to the de-
6' ■ ficiency.

Sect. XXXV. I. DISEASES OF ASSOCIATION. 445

ficiency of pleafureable fenfation is evinced from this circumftancc,
that a naufeous idea excited by words will produce^ vomiting as effec-
tually as a naufeous drug.

Hence it appears^ that the a£l of nauiea or vomiting expends lefs-
fenforial power than the ufual periftaltic motions of the ftomach in
the digeftlon of our aliment ; and that hence there is a greater quan-
tity of fenforial power becomes accumulated in the fibres of the flo-
nvach, and more of it in confequence to fpare for the aftion of thofe
parts of the fyftem, which are thus aflbciated with the fhomach, as
of the whole abforbent feries of veflTels, and which are at the fame
time excited by their ufualftimuli.

From this we can underftand, how after the operation of an emetic
the flomach becomes more irritable and fenfible to the flimulus, and
the pleafure of food ; fince as the fenforial power becomes accumu=
lated during the naufea and vomiting, the digeflive power is after-
wards exerted more forceably for a time. It fhould, however, be
here remarked, that though vomiting is in general produced by the
defe6l of this flimulus of pleafureable fenfation, as when a naufeous
drug is adminiflered ; yet in long continued vomiting, as in fea-fick-
nefs, or from habitual dram-drinking, it arifes from deficiency of fen-
forial power, w^hich in the former cafe is exhaufled by the increafed^
exertion of the irritative ideas of viflon, and in the latter by the fre-
quent application of an unnatural ftimulus.

4. An example of the fourth circumftance above mentioned, where
both the primary and fecondary parts of a train of motions proceed
with energy lefs than natural, may be obferved in the dyfpacea,
which occurs in'going into a very cold bath, and which has been de-
fcribed andexplained in Se61:. XXXIL 3, 2.

And by the increafed debility of the pulfations of the heart and ar-
teries during the operation of an emetic. Secondly, . from the flow-
nefs and intermifHon of the pulfations of the heart from the iiiceilant;
efforts to vomit occafioned by an overdofe of digitalis. . And. thirdly,,

froru-;

44^ Di&EASES OF ASSOCIATION. Sect.XXXV.^.

from the total ftoppage of the motions of the heart, or death, in con-
fequence of the torpor of the ftomach, when affeded with the com-
mencement or cold paroxyfm of the gout. See Sect. XXV. 1 7.

II. I. The prinaary and fecondary ■ parts of the trains of fenfitive
aflbciation reciprocally affeit each other in different manners, i. The
increafed fenfation of the primary part may ceafe, when that of the
fecondary,part commences. 2. The increafed aftion of the primary
part may. ceafe, when that of the fecondary part commences. 3.
The primary, part may have increafed fen fatioii, and the fecondary
part increafed a6tion. 4. The primary part may have .increafed. ac-
tion, and the fecondary part increafed fenfation.

Examples of the firft .mode, M'here the increafed fenfation of the
primary part of a train of feniitive affociation ceafes, when that of
the fecondary part commences, are not unfrequent ; as this is the
general origin of thofe pains, which continue fome time without
being attended with inflammation, fuch as the pain at the pit of the
ftomach from a ftone at the neck of the gall-bladder, and the pain
of flrangury in the glans penis from a ftone at the neck of the urinary
bladder. In both thefe cafes the part, which is affefted fecondarily,
is believed to be much more fenfible than the part primarily afFe£l;ed,
as defcribed in the catalogue of difeafes, Clafs II. i. i. 10. and IV. 2.
1. 1, and IV. 2. I. 2.

The hemicrania, or nervous headach, as it is called, when it ori-
ginates from a decaying tooth, is another difeafe of this kind; as the
pain of the carious tooth always ceafes, when the pain over one eye
and temple commences. And it is probable, that the violent pains,
which induce convulfions in painful epilepfies, are produced in the
fame manner, from a more fenfible part fympathizing with a difeafed
one of lefs fenfibihty. See Catalogue of Difeafes, Clafs IV. 2. 1.5.
and III. 1.1.7.

The lafl: tooth, or dens fapientias, of the upper jaw moft frequents
ly decays firft, and is liable to produce pain over the eye and tempJe

STect. XXXV. t. DISEASES OF ASSOCIATION. 447

of that fide. The laft tooth of the under-jaw is alfo liable to produce
a fimilar hemicrania, when it begins to decay. When a tooth in the
\)pper-jaw is the caufe of the headach,.a {lighter pain is fometimes
perceived on the cheek-bone. And when a tooth in. the lower-jaw
is the caufe of headach, a pain fometimes affe£ls the tendons of the
mufcles of the neck,, v/hich are attached near the jaws. But the
clav^us hyftericus, or pain about the middle of the parietal bone on
one fide of the head, I have feen produced by the fecond of the mo-
lares, or grinders, of the under-jaw ; of which I (hall relate the foL-
lowing.cafe. See ClafsII. i.. i. 4, and IV. 2. i. 5.

MrSi , about 30 years of age, was feized with great paia

about the middle of the right, parietal bone, which had continued a
whole day before I faw her, and was fo violent as to threaten tooc-
cafion convulfions. Not being able to dete£t a decaying tooth, or a
tender one, by examination with my eye, or by ftriking them with
a tea-fpoon,.and fearing bad. confequences from her tendency to con-
vulfion, I advifed her to extract the laft tooth of the under-jaw on the
affefted fide ; which was done without any good effedc. She was
then diredled to lofe blood, and to take a brilk. cathartic ; and after
that had operated, about 60 drops.of laudanum, were given: her, with
J^rge dofes of bark; by vv^hich the pain . was removed .^ In about a
fortnight (he took a cathartic medicine by ill advice, and the pain re-
turned with greater violence in the fame place ; and, before I could
arrive, as flie lived 30 miles from me, fhe fufFered a paralytic ftroke-;
which afFedted her limbs and her face on one fide, and relieved. the
pain of her head..

About a year afterwards I was again called to her on account of a
pain as violent as before exaftly on the fame part of the other parietal
bone. On examining her mouth I found the fecond molaris of the
under-rjaw on the fide before affedled was now decayed, and con--
dxided, ."that this tooth had occafioned the ftroke of the palfy by the
pain and confequent exertion it had caufed. On this account I ear-

neftly

4|8 DISEASES OF ASSOCIATION. Sect. XXXV. 2,

iieftly entreated her to allow the found raolaris of the fame jaw op»
polite to the decayed one to be extraftcd ; which was forthwith done,
and the pain of her head immediately ceafed, to the aflonifhment of
■her attendants.

• In the cafes above related of the pain exifting in a part diilant from
:the feat of the difeafe, the pain is owing to defeft of the ufual mo-
tions of the painful part. This appears from the coldnefs, palenefs,
and emptinefs of the affedled veflels, or of the extremities of the body
in general, and from there being no tendency to inflammation. The
increafed aftion of the primary part of thefe affociated motions, as of
the hepatic termination of the bile-du£l from the flimulus of a gall-
ftone, or of the interior termination of the urethra from the ftimulus
of a {lone in the bladder, or laftly, of a decaying tooth in hemicrania,
deprives the fecondary part of thefe affociated motions, namely, the
exterior terminations of the bile-duQ: or urethra, or the pained mem-
branes of the head in hemicrania, of their natural (hare of fenforial
power : and hence the fecondary parts of thefe fenfitive trains of aflb-
ciation become pained from the deficiency of their ufual motions,
which is accompanied with deficiency of fecretions and of heat. See
Sea. IV. 5. XII. 5. 3. XXXIV. I.

Why does the pain of the primary part of the aflbciation ceafe,
when that of the fecondary part commences ? This is a queftion of
intricacy, but perhaps not inexplicable. The pain of the primary
part of thefe aflbciated trains of motion was owing to too great flimu-
lus, as of the ftone at the neck of the bladder, and was confequently
caufed by too great adtion of the pained part. This greater a£l:ion
than natural of the primary part of thefe aflbciated motions, by em-
ploying or expending the fenforial power[of irritation belonging to the
whole aflbciated train of motions, occafioned torpor, and confequent
pain, in the fecondary part of the aflbciated train ; which was pof-
fefled of greater fenfibility than the primary part of it. Now the
great pain of the fecondary part of the train, as foon as it commences,

employs

^»

Sect, XXXV. 2. DISEASES OF ASSOCIATION. 449

employs or expends the feiiforial power of fenfation belonging to the
whole affociated train of motions ; and in confequence the motions
of the primary part, though increafed by the ftimukis of aji extrane-
ous body, ceafe to be accompanied with pain or fenfation.

If this mode of reafoning be juft it explains a curious fatft, why
when two parts of the body are flrongly Simulated, the pain is felt
only in one of them, though it is poffible by voluntary attention it
may be alternately perceived in them both. In the- fame manner,
when two new ideas are prefented to us from the fiimulus of external
bodies, we attend to but one of them at a time. In other words,
when one fet of fibres, whether of the mufcles or organs of fenfe,
contraft {o ftrongly as to excite much fenfation ; another let of fibres
contra<9:ing more weakly do not excite fenlation at all, becaufe the
fenforial power of fenfation is pre-occupied by the firfc fet of fibres.
So we cannot will more then one efFedl at once, though by aflbcia-
tions previoufly formed we can move many fibres in combination.

Thus in the inftances above related, the termination of the bile
du£t in the duodenum, and the exterior extrernity of the urethra,
are more fenfible than their other terniinations. When thefe parts
are deprived of their ufual motions by deficiency of the fenforial
power of irritation, they become painful according to law the fifth
in Seftlon IV. and the lefs pain originally excited by the fllmulus of
concreted bile, or of a ftone at their other extremities ceafes to be
perceived. Afterwards, however, when the concretions of bile, or
the ftone on the urinary bladder, become more numerous or larger,
the pain from their increafed flimulus becomes greater than the
affociated pain ; and is then felt at the neck of the gall bladder or
urinary bladder; and the pain of the glans penis, or at the pit of the
ftomach, ceafes to be perceived.

2. Examples of the fecond mode, where the increafed adion of
the primary part of a train of lenfitive affociation ceafes, when that
of the fecondary part commences, are alfo not unfrequent; as this is

^ M the

450 PISEASES Of ASSOCIATION. Sect. XXXV. 2.

the ufual manner of the tranflation of inflammations from internal to
external parts of the fyftem, Tuch as when an inflammation of the
liver or floraach is tranilated to the membranes of the foot, and
forms the gout ; or to the fkln of the face, and forms the rofy drop,
or when an inflammation of the membranes of the kidneys is tranf-
lated to the Ikin of the loins, and forms one kind of herpes, called
fhingles ; in thefe cafes by whatever caufe the original inflammation
may have been produced, as the fecondary part of the train of fenfi-
tive aflbciation is more fenfible, it becomes exerted with greater vio-
lence than the firfl part of it ; and by both its increafed pain, and
the increafed motion of its fibres, fo far diminifhes or exhaufts the
fenforial power of fenfation ; that the primary part of the train being
lefs fenfible ceafes both to feel pain, and to aft with unnatural
energy.

3. Examples of the third mode, where the primary part of a train
of fenfitive aflbciation of motions may experience increafed fenfation,
and the fecondary part inaxafed aftion, are likewife not unfrequent ;
as it is in this manner that mofl: inflammations commence. Thus,
after {landing fome time in fnow, the feet become affefted with the
pain of cold, and a common coryza, or inflammation of the mem-
brane of the noftrils, fucceeds^ It is probable that the internal in-
flammations, as pleurifies, or hepatitis, which are produced after the
eold paroxyfm of fever, originate in the fame manner from the fym-
pathy of thofe parts with fome others, which were previoufly pained
from quiefcence;, as happens to various parts of the fyftem during-
the cold fits of fevers. In thefe cafes it would feem, that the fen-
forial power of fenfation becomes accumulated during the pain of
fiold, as the torpor of the veffels occafioned by the defeft of heat con--
tributes to the increafe or accumulation of the fenforial power of
irritation, and that both thefe become exerted on fome internal part,
which was not rendered torpid by the cold which afi^efted the external

partsj.

Sect. XXXV. 3- DISEASES OF ASSOCIATION. 451

parts, nor by its aflbciation with them; or which fooner recovered
its fenfibility.

4. An example of the fourth mode, or where the primary part of
a fenlitive aflbciation of motions may have increafed aftion, and the
fecondary part increafed fenfation, may be taken from the pain of the
fhoulder, which attends inflammation of the membranes of the Hver,
fee Hepatitis, Clafs IV. 2. 1.6. in this circumfl:ance fo much fenforial
power feems to be expended in the violent aftions and fenfations of
the inflamed membranes of the liver, that the membranes affociated
with them become quiefcent to their ufual ftimuli, and painful in
confequence.

There may be other modes in which the primary and fecondary
parts of the trains of aflbciated fenfitive motions may reciprocally
afFe6t each other, as may be feen by looking over Clafs IV. in the
catalogue of difeafes; all which may probably be' refolved into the
plus and minus of fenforial power, but we have not yet had fufficient
obfervations made upon them with a view to this doclrine.

III. The allociated trains of our ideas may have fympathies, and
their primary and fecondary parts afte6l each other in fome manner
iimilar to thofe above defcribed ; and may thus occafion various curi-
ous phenomena not yet adverted to, befides thofe explained in the
Seftions on Dreams, Reveries, Vertigo, and Drunkennefs ; and may
thus difturb the deductions of our reafonings, as well as the ftreams
of our imaginations ; prefent us with falfe degrees of fear, attach
unfounded value to trivial circnm fiances ; give occafion to our earl}'
prejudices and antipathies ; and thus embarrafs the happinefs of our
lives. A copious and curious harveft might be reaped from this pro-
vince of fcience, in which, however, I fliall not at prefent wield
my fickle.

3M 2 SECT.

•45^ PERipDS OF DISEASES. Sect, XXXVI. i.

SECT. XXXVL

OF THE PERIODS OF DISEASES.

L Mufchs excited hy volition foon ceaje to contraEl, or hyfenjation, or by irritation,,
owing to the exhauftion of Jenjorial ■power. Mufdes JubjeSfed to lefs fiimulus.
have their Jenjorial power accumulated. Hence the periods of Jome fevers..
Want of irritability after intoxication. II. i. Natural aSlions catenated with
daily habits of life. i. With Jolar periods. Periods oj Jleep. Of evacuating_
the bowels. 3. Natural anions catenated with lunar periods. Menflruation^
Venereal orgajm of animals. Barrennejs. III. Periods of dijeajed animal
aUions from flated returns of noSfurnd cold, from folar and lunar influence.
Periods of diurnal fever, helfic fever, quotidian,, tertian, quartan fever. Periods
ef gout, pleurijy, of fevers with arterial debility, and with arterial jlrength.
Periods of rhaphania, of nervous cough, hemicrania, arterial htemorrhages^.
btemorrboids, h^moptoe, epilepfy, paljy, apoplexy, tnadnejs. IV. Critical days-
depend en lunar periods. Lunar periods in tbejmall pox.

I. IF any of our mufcl'es be made to contrad violently by the
power of volition, as thofe of the fingers, when any one hangs by
his hands on a fwing, fatigue foon enfues %. and the mufcles ceafe to
aft owing to the temporary exhauftion of the fpirit of animation ; as
foon as this is again accumulated in the mufcles, they are ready to.
contraft again by the efforts of volition..

Thofe violent mufcular actions induced by pain become in the
fame manner intermitted and recurrent ; as in labour-pains, vomit-
ing, tenefmus, flrangury ; owing likewife to the temporary exhauf-
tion of the fpirit of animation, as above mentioned,

When.

Sect. XXXVI. r. PERIODS OF DISEASES. i^S

When any ftimulus continues long to a6t with unnatural violence,
fo as to produce too energetic a6lion of any of our moving, organs,
thofe motions loon ceai'e, though the ftimulus continues to acl ; as
in looking long on a bright objeft, as on an inch-fquare of red filk
laid on white paper in the funfhine. See Plate I. in Sed. HI. i..

On the contrary, where lefs of the ftimulus of volition, fenfation,
or irritation, have been applied to a mufcle than ufual ; there ap-
pears to be an accumulation of the fpirit of animation in. the moving-
organ ; by which it is liable to a£l with greater energy from lefs
quantity of ftimulus, than was previoufly neceflary to excite it into fa
great adlion i as after having beei> immerfed in fnow the cutaneous
veffels of oui- hands are excited into ftronger a6lion by the ftimulus
of a lefs degree of heat^ than would previoufly have produced, that
effea.

From hence the periods of fome fever-fits may take their origin^,
either limply, or by their accidental coincidence with lunar and folar.
periods, or with the diurnal periods of heat and cold, to be treated,
of below; for during the cold fit at the commencement of a fever,,
from whatever caufe that cold fit may have been induced, it follows,.
I. That the fpirit of animation muft become accumulated in the:
parts, which exert during this cold fit lefs than their natural quanr
tity of a6lion. z. If the caufe producing the cold fit does not iri-
creafe, or becomes diminifhed ; the parts before benumbed or in-
active become now excitable by fmaller ftimulus, and are thence,
thrown iato more violent adiioa than is natural ; that is a hot fit fuc-
ceeds the cold one. 3. By the energetic adtion of the fyftem during
the hot fit, if it continues long, an exhauftion of the fpirit of ani-
mation takes place; and another cold fit is liable to fucceed, from the-
moving fyftem not being excitable into action from its ufual ftimulus.
This inirritability of the fyftem from a too great previous ftimulus,
and Gonfequent exhauftion of fenforial power, is the caufe of the
general debility,, and ficknefs, and head-ach, fome hours after in-
toxication*-

454 Periods' OF diseases-, sect, xxxvi. 2.

toxication. And hence we fee one of the caiifes of the periods of
fever-fits ; which however are frequently combined with the periods
of our diurnal habits," or of heat!' and cold, or of folar or lunar
periods.

When befides the tendency to quiefcence occafioned by the expen-
diture of fenforial power during the hot fit of fever, fome other caufe
of torpor, as the folar or lunar periods, is necefiary to the introduc-
tion of a fecond cold fit ; the fever becomes of the intermittent kind ;
that is, there is a fpace of time intervenes between the end of the
hot fit, and the commencement of the next cold one. But where
no exteriour caufe is necefiary to the introduction of the fecond cold
fit ; no fuch interval of health intervenes ; but the fecond cold fit
commences, as foon as the fenforial power is fufiSciently exhaufled
by the hot fit ; and the fever becomes continual.

II. I. The following are natural animal a£lions, which afe fre-
quently catenated with our daily habits of hfe, as well as excited by
their natural irritations. The periods of hunger and thifft become
catenated with certain portions of tinie, or degrees of exhauflion, df
other diurnal habits of life. And if the pain of hunger be not re-
lieved by taking food at the ufual time, it is liable to ceafe till the
next period of time or other habits recur ; this is not only true in
refpeft to our general defire of food, but the kinds Of it alfo itt
governed by this periodical habit ; infomuch that beer taken to break-
faft will difturb the digeftion of thofe, who have been acduftomed to
tea ; and tea taken at dinner will difagree with thofe, who have
been accuftomed to beer. Whence it happens, that thofe, who
have weak flomachs, will be able to digefl more food, if they take
their meals at regular hours ; becaufe they have both the fiimulus of
the aliment they take, and the periodical habit, to aflifi: their digef-
tion.

The periods of emptying the bladder are not only dependent on

the acrimony or diftention of the water in it, but are frequently

2 catenated

Sr.cT.XXXVI.2. PERIODS OF DISEASES. 455

catenated with external cold applied to the Ikin, as in cold bathings
or vvafhlng the hands ; or with other habits of life, as many .^re ac-
cuftomed to empty the bladder before going to bed, or into the houfe
after a journey, and this whether it be full or not.

Our times of refpiration are not only governed by the ftimulus of
the blood in the lungs, or our defire of frefli air, but aUb by our
attention to the hourly objedls before us. Hence when a perfon is
earneftly contemplating an idea of grief, he forgets to breathe, till,
the fenfation in his lungs becomes va-y urgent ; and then a figh fuc-
ceeds for the purpofe of more forceably pufhing forwards the blood,,
which is accumulated in the lun^s.

Our times of refpiration are alfo frequently governed in part by
our want of a fteady fupport for the adlions of our arms, and hands,
as in threading a needle, or hewing wood, or in fwimming ; when
we are intent upon thefe objefts, we breathe at the intervals of the
exertion of the pedloral mufcles.

2. The following natural animal aflions are influenced by folar
periods. The periods of fleep and of waking depends much on the
iblar period, for we are inchned to fleep at a certain hour, and to
awake at a certain hour, whether we have had more or lefs fatigue
during the day, if within certain limits; and are liable to wake at a
certain hour, whether we went to bed earlier or later within certain,
limits. Hence it appears, that thofe who complain of want of fleep,
will be liable to fleep better or longer, if they accuflom themfelves
to go to reft, and to rife, at certain hours.

The periods of evacuating the bowels are generally conne£ted with,
fome part of the folar day, as well as with the acrimony or diften—
tion occafioned by the feces. Hence one method of corredling cof-
tivenefs is by endeavouring to eflabhfh a habit of evacuation at a cer-
tain hour of the day, as recommended by Mr. Locke, which may
be accomplifhed by ufing daily voluntary efforts at thofe times, joined]
with the ufual flimulus of the. material to be evacuated.

5, The

456 PERIODS OF DISEASES. SEcr. XXXVI. 3.

3. The following natural animal actions are connefted with lunar
•periods, i. The periods of female menftruation are connetSted with
lunar periods to great exaftnefs, in fome inftances even to a few
hours. Thefe do not commence or terminate at the full or change,
or at any other particular part of the lunation, but after they have
commenced at any part of it, they continue to recur at that part
with great regularity, unlefs dillurlDed by fome violent circumftance,
as explained in Seft. XXXII. No. 6. their return is immediately caufed
by deficient venous abfocption, which is owing to the want of the
ftimulus, defigned by nature, of amatorial copulation, or of the
growing fetus. When the catamenia returns fooner than the period
of lunation, it fliews a tendency of the conftitution to inirritabi-
lity ; that is to debility, or deficiency of fenforial power, and is to be
relieved by fmall dofes of fteel and opium.

The venereal orgafm of birds and quadrupeds feems to commence,
or return about the moft powerful lunations at the vernal orautumnal
equinoxes ; but if it be difappointed of its obje£l:, it is faid to recur at
monthly periods ; in this refpedt refembling the female catamenia.
Whence it is believed, that women are more liable to become preg-
nant at or about the time of their catamenia, than at the intermediate
times ; and on this account they are feldom much miftaken in their
reckoning of nine lunar periods from the laft menftruation; the in-
attention to this may fometimes have been the caufe of fuppofed bar-
rennefs, and is therefore worth the obfervation of thofe, who wifh
to have children.

III. We now come to the periods of difeafed animal a£lions.
The periods of fever-fits, which depend on the ftated returns of noc-
turnal cold, are difcuffed in Seel. XXXII. 3. Thofe, which origi-
nate or recur at fdlar or lunar periods, are alfo explained in Section
XXXII. 6. Thefe we ihall here enumerate ; obferving, however, that
it isnot more furprifing, that the influence of the varying attractions
of the fan and moon, fliould raife the ocean into mountains, than

that

Sect. XXXVI. 3- PERIODS OF DISEASES. 457

that it fliould affe6t the nice feMfibihties of animal bodies ; though tha-
inanner of its operation -on them is difficult to be underflood. It is
probable however, that as this influence gradually leflens during the
courfe of the day, or of the lunation, or of the year, fome actions
of our fyftem become lefs and lefs ; till at length a total quiefcence
of fome part is induced; which is the commencement of the pa-
Toxyfm-sof fever, of menflruation, of pain wi:th decreafed adion of
the affetTted organ, and of confequent convulfion.

1. A diurnal fever in fome wealc people is diftinctly obferved to
■come on towards evening, and to ceafe with a moift Ikin early in the
■morning, obeying -the folar periods. Perfons of weak conftitutions
are liable to get into better fpirits at the accefs of the hot fit of this
•evening fever ; and are thence inclined to fit up late ; which by fur-
ther enfeebling them increafes the difeafe j whence they lofe their
ilrenp-th and their coloiiir,

2. The .periods of heftic fever, fuppofed to arife from abforption of
matter, obeys the diurnal periods like the above, having the exacer-
befcence towards evening, and its remiilion early in the morningy
with fweats, or diarrhoea, or urine with white fedimeiit.

. 3. The periods of quotidian fever are either catenated with folar
■time, and return at the intervals of twenty-four hours ; or with Ivsnar
■time, recurring at the intervals of about twenty-five Iiours. There is
great lafe in knowing with what circumftances the periodical return
of new morbid motions are conjoined, as the mofb effe6iual times of
exhibiting the proper medicines are thus determined. So if the tor-
por, which uftiers in an ague fit, is catenated with the lunar day: it
is know, when the bark or opium m:uil be given, fo as to exert ita.
principal effed about the time of the expedled return. Solid opium
fliould be given about an hour before the expeded cold fit ; liquid
opium and wine about half an hour ; the bark repeatedly for fix or
eight hours previous to the expeded return.

J N 4. The

458 PERIODS OF DISEASES. Sect. XXXVI. 3,

- 4. The periods of tertian fevers, reckoned from the commence-
ment of one cold fit to the commencement of the next cold fit, recur
with folar intervals of forty-eight hours, or with lunar ones of about
fifty hours. When thefe times of recurrence begin one or two hours
earlier than the folar period, it fliews, that the torpor or cold fit is
produced by lefs external influence ; and therefore that it is more li-
able to degenerate into a fever with only remiffions ; fo when men-
flruation recurs fooner than the period of lunation, it fhews a ten-
dency of the habit to torpor or inirritability.

5. The periods of quartan fevers return at folar intervals of feventy-
two hours, or at lunar ones of about feventy-four hours and an half.
This kind of ague appears moft in moift cold autumns, and in cold
countries replete with marfhes. It is attended with greater debility,
and its cold accefs more difficult to prevent. For where there is pre-
vioufly a deficiency of fenforial power, the conftitution is liable to
run into greater torpor from any further diminution of it ; two
ounces of bark and fome fteel fhould be given on the day before the
return of the cold paroxyfm, and a pint of wine by degrees a few
hours before its return, and thirty drops of laudanum one hour before
the expe£led cold fit.

6. The periods of the gout generally commence about an hour be-
fore fun-rife, which is ufually the coldeft part of the twenty- four
hours. The greater periods of the gout feem alfo to obferve the folar
influence, returning about the fame feafon of the year.

7. The periods of the pleurify recur with exacerbation of the pain
and- fever about fun-fet, at which time venefeftion is of mofi: fervice.
The fame may be obfcrved of the inflammatory rheumatifm, and
other fevers with arterial ftrength, which feem to obey folar periods;;
and thofe with debility feem to obey lunar ones.

8. The periods of fevers with arterial debility feem to obey the
lunar day, having their accefs daily nearly an hour later ; and have

.. . fometimes

Sect. XXXVI. 3- PERIODS OF DISEASES. 459

fometimes two acceffes ia a day, refembling the lunar effects upon the
tides. ■

9. The periods of rhaphania, or convulfions of the limbs from rheu-
matic pains, feem to be connedted with folar influence, returning at
nearly the fame hour for weeks together, tinlefs diflurbed by the ex-
hibition of powerful dofes of opium.

So the periods of Tuffis ferina, or violent cough with flow pulfe,
called nervous cough, recurs by folar periods. Five grains of opium
given at the time the cough commenced difturbed the period, from
{even in the evening to eleven, at which time it regularly returned
for fome days, during which time the opium was gradually omitted.
Then 120 drops of laudanum were given an hour before the accefs of
the cough, and it totally ceafed. . The laudanum was continued a
fortnight, and then gradually difcontinued.

10. The periods of hemicrania, and of painful epilepfy, are liable
to obey lunar periods, both in their diurnal returns, and in their
greater periods of weeks, but are alfo induced by other exciting
caufes.

11. The periods of arterial haemorrhages feem to return at folar
periods about the fame hour of the evening or morning. Perhaps the
venous haemorrhages obey the lunar periods, as the catamenia, and
haemorrhoids.

12. The periods of the haemorrhoids, or piles, in fome recur
monthly, in others only at the greater lunar influence about the equi-
noxes.

13. The periods of haemoptoe fometimes obey folar influence, re-
curring early in the morning for feveral days ; and fometimes lunar
periods, recurring monthly ; and fometimes depend on our hours of
lleep. See Clafs I. 2. i. 9.

14. Many of the firft periods of epileptic fits obey the rnonthly lu-
nation with fome degree of accuracy ; others recur only at the raofl
powerful lunations before the vernal equinox^ and after the autumnal

3 N 2 one ;

460 . PERIODS OF DISEASES.. Sect. XXXVI. 4.

one J but when the conftitution has o-ained a habit of relieving dif-
agreeable fenfations by this, kind of exertion, the fit recurs from any
flight caufe.

15.., The attack of palfy and apoplexy are known, to recur with
great frequency about the equinoxesi

16. There are nu^merous inftances of the efFe£t of the lunations upon
the periods of i»fanity, whence.- the name of lunatic has been given ta.
thofe afflidled with this-difeafe..

IV. The critical days, ia. which fevers arc fuppofed' to terminate^,
have employed the attention of medical philofophers from the days of
Hippocrates to the prefent time. In whatever part of a lunation a
fever commences, which owes either its whole caufe to folar and- lu-
nar influence, or to this m conjunftion' with other caufcs;., it would
feem, that tiie efFedt would be the gr^ateft at the full and new moon,
as. the tides rife higheft at thofe times, and would be the leafl: at the
quadratures-; th.u& if a. fever-fit fliould commence at the new or full
moon^ oecafioned by the folar and lunar attradl-ion diminifliing fome
chemical affinity of the particles of blood, and thence decreafing their
ftimukis on our fanguiferous fyftem, as- mentioned in- Seel. XXXIL 6.
this- effe6l' will' daily decreafe for the firft feven days, and will- then
increafe till about the fourteenth day, and wiliagaindecreafe till about
the twenty.-firft day, and increafe again till the end of the lunation;
If a fever-fit- from tile above- caufe (hould commence- on the feventh.',
day after- either- lunation,-: the revsrlfe of the above circumftances would
happen* Now. it; is, probable, that thofe fevers,, whofe crifis or- ter-
minations are influenced by lunations, may begin at one. or other of'
the above times, namely at the- changes -or quadi'aturesj though fuf-
^ficient obfervatioiis- have not been made- to afcertain this circumftance..
Hence I conclude,, that the_fmall-pox and^meafles have their critrcal,
days, not governed by the times required for; certain chemical changes-
in the blood,, which afFe6l or alter the flimulus of the contagious
matter, but from-, the daily- increafing or decreafing efteft of this luna?-
^] . link-:

Sect. XXXVI. 4. PERIODS OF MSEASES. 461

link of catenation, as explained in Seftion XVII. 3. 3. And as other
fevers terminate mofl frequently about the feventh, fourteenth-,
twenty-firft, or about the end of four \veek5, when no medical af-
fiftance ba& difturbed their periods, I conclude, that thefe crifes, or
terminations, are governed by periods of the lunations, though we are
ftill ignorant of their ma;nner of operation.

In. the diftinft fmall-pox the vefliges of lunation are very apparent,-
after inoculation a quarter c^ a- lunation precedes the commencement
of the fever, another quarter terminates with the complete eruption,-
aiiother quarter with the complete maturation, and another quarter
terminates the complete abforption of a material now rendered inoScixa-
£ve to the conftitutioiu

SECT,

46z DIGESTION, SECRETION, &c. Sect.XXXVII. i.

SECT. XXXVII.

OF DIGESTION, SECRETION, NUTRITION.

I. Cryftals increaje by the greater attraSfion of their fides. Accretion by chemical
preciptationsy by welding, by freffure, by agglutination. II. Hunger, dtgejiion,
why it cannot be imitated out of the body. LaEleals abfori by animal feleSfion,
or appetency. III. 'The glands and pores abforb nutritious particles by animal
feleSlion. Organic particles of Buffon. Nutrition applied at the time of elonga-
tion of fibres. Like inflammation. IV. Itfeems eafter to have preferved animals
than to reproduce them. Old age and death from inirritability . Three caufes of
this. Original fibres of the organs of fenfe and mufcles unchanged. V. Art of
producing long life.

I. THE larger cryftals of faline bodies may be conceived to arife
from the combination of fmaller cryftals of the fame form, owing to
the greater attractions of their fides than of their angles. Thus if
four cubes were floating in a fluid, whofe ffidioii or refiftance is no-
thing, it is certain the fides of thefe cubes would attract each other
ftronger than their angles ; and hence that thefe four fmaller cubes
would fo arrange themfelves as to produce one larger one.

There are other means of chemical accretion, fuch as the depofi- ■
tions of diflblved calcareous or filiceous particles, as are feen in the
formation of the ftaladtites of limeftone in Derbyftiire, or of calcedone
in Cornwall. Other means of adhefion are produced by heat and
preffure, as in the welding of iron-bars ; and other means by fimple
preffure, as in forcing two pieces of caoutchou, or elaftic gum, to ad-
here;

SECT.XXXVn.2. DIGESTION, SECRETION, &:c. 463

here ; and laftly, by the agglutination of a third fubftance penetrating
the pores of the other two, as in the agglutination of wood by means
of animal gluten. Though the ultimate particles of animal bodies
are held together during life, as well as after death, by their fpecific
attra£lion of cohefion, like all other matter; yet it does not appear,
that their original organization was produced by chemical laws, and
their produftion and increafe muft therefore only be looked for from
the laws of animation.

II. When the pain of hunger requires relief, certain parts of the
material world, which furround us, when applied to our palates, ex-
cite into aftion the mufcles of deglutition ; and the material is fwal-
lowed into the ftomach. Here the new aliment becomes mixed with
certain animal fluids, and undergoes a chemical procefs, termed di-
geftion ; which however chemiftry has not yet learnt to imitate
out of the bodies of living animals or vegetables. This procefs leems
very (imilar to the faccharine procefs in the lobes of farinaceous feeds,
as of barley, when it begins to germinate ; except that, along with
the fugar, oil and mucilage are alfo produced ; which form the chyle
of animals, which is very limilar to their milk.

The reafon, I imagine, why this chyle- making, or faccharine pro-
cefs, has not yet been imitated by chemical operations, is owing to
the materials being in fuch a fituation in refpecl to warmth, moifture,
and motion ; that they will immediately change into the vinous or
acetous fermentation ; except the new fugar be abforbed by the nu-
merous lacteal or lymphatic vefl'els, as foon as it is produced ; which
is not eafy to imitate in the laboratory.

Thefe lafteal veffels have mouths, which are irritated into aftion
by the ftimulus of the fluid, which furrounds them ; and by animal
fele£lion, or appetency, they abforb fuch part of the fluid as is agree-
able to their palate ; thofe parts, for inflance, which are already con-
verted into chyle, before they have time to undergo another change
by a vinous or acetous fermentation. This animal abforption of fluid
8 is

4H DIGESTION, SECRETION, &c. Sect.XXXVIL 3,

is almoft -vifible to the naked eye in the adlon of the pun£la laory-
•,malia.; which imbibe the tears from the eye, and difcharge them
,again into the noftrils.

•III. The arteries conftitute another refervoir of a changeful fluid;
•from which, after its recent oxygenation in the lungs, a further ani-
mal feledlion of various fluids is abforbed by the numerous glands ;
.thefe felefl: t^eir refpe£tive fluids from the blood, which is perpetu-
ally undergoing a chemical change ; but the feleclion by thefe glands,
.like that of the ia<£leals, which open their mouths into the digeflin^
_aliment in the flomach, is from animal appetency, not from chemical
affinity ; fecretion cannot therefore be imitated in the laboratory, as
it confifls in a fele£lioa of part of a fluid during the chemical change
of that fluid.

The mouths of the lafteals, and Iym]3ha-tlcs, and t;he ^dtimate ter^
jnination-s of the glands, are finer than can eafily ,be conceived ; yet
it is probable, that the pores, or interftices of the parts, or coats,
which conftitute thefe ultimate veflels, may ftill have greater tenuity;
and that thefe pores from the above analogy muft poflefs a fimilar
power of irritability, and abforb by their living energy the particles of
fluid adapted to their purpofes, whether to replace the parts abraded
or diflblved, ,or to elongate and .enlarge themfelves. Not only every
kind of gland is thus£iidued with its peculiar appetency, and feledls
the material agreeable to its tafte from the blood, but every individual
pore acquires ,by animal feletlion the material, which it wants ; and
thus nutrition fe.ems to be performed in a manner fo fimilar to fecre-
tion ; that they only differ in the one retaining, ^ and the other
parting. again with the particles, which they hav.e felei3:ed from the
.blood.

This \yay of accounting for nutrition from ftimulus, and the con-
f^quent aninial fele6tion of particles, is much more analogous to other -
phenomena of the animal microcofm, than by having recourfe to the
.raicrofcopic aaioialcu-la, or wganic particles of Buffi?n and Needham ;

wliieh.

Sect.XXXVILj. digestion, secretion, &:c. 465

which being already compounded mufl themfelves require nutritive
particles to continue their own exiftence. And muft be liable to un-
dergo a change by our digeftive or fecretory organs ; otherwife man-
kind would foon refemble by their theory the animals, which they
feed upon. He, who is nouriflied by beef or venifon, would in time
become horned ; and he, who feeds on pork or bacon, would gain a
nofe proper for rooting into the earth, as well as for the perception of
odours.

The whole animal fyilem may be considered as confiding of the
extremities of the nerves, or of having been produced from them ; if
we except perhaps the medullary part of the brain refiding in the
head and fpine, and in the trunks of the nerves. Thefe extremities
of the nerves are either of thofe of locomotion, which are termed
mufcular fibres ; or of thofe of fenfation, which conftitute the im-
mediate organs of fenfe, and which have alfo their peculiar motions.
Now as the fibres, which conftitute the bones and membranes, pof-
fcffed originally fenfation and motion ; and are liable again to poflefs
them, when they become inflamed ; it follows, that thofe were,
when firft formed, appendages to the nerves of fenfation or locomo-
tion, or were formed from them. And that hence all thefe folid
parts of the body, as they have originally confifted of extremities of
nerves, require an appofition of nutritive particles of a fimilar kind,
contrary to the opinion of Buffon and Needham above recited.

Laftly, as all thefe filaments have poffeffed, or do poffefs, the
power of contraftion, and of confequent inertion or elongation ; it
feems probable, that the nutritive particles are applied during their
times of elongation ; when their original conftituent particles are re-
moved to a greater diftance from each other. For each mufcular or
fenfual fibre may be confidered as a row or firing of beads ; which
approach, when in contraftion, and recede during its reft or elonga-
tion ; and our daily experience fhews us, that great adtion emaciates
the fyftem, and that it is repaired during reft.

3 O Something

466 DIGESTION, SECRETION, &c. Sect. XXXVII. 3.

Something like this is feen out of the body j for if a hair, or a
lingle untwifted fibre of flax or filk, be foaked in water ; it becomes
longer and thicker by the water, which is abforbed into its pores.
Now if a hair could be fuppofed to be thus immerfed in a- folution of
particles fimilar to thofe, which compofe it ; one may imagine, that
it might be thus increafed in weight and magnitude ; as the particles
of oak- bark increafe the fubflance of the hides of beafts in the procefs
of making leather. I mention thefe not as philofophic analogies, but
as fimiles to facilitate our ideas, how an accretion of parts may be ef-
fefted by animal appetences, or feledions, in a manner fomewhat
fimilar to mechanical or chemical attraftions.

If thofe new particles of. matter, previoufly prepared by digeftion
and fanguification, only fupply the places of thofe, which have been,
abraded by the adions of the fyflem, it is properly termed nutrition.
If they are applied to the extremities of the nervous fibrils, or in fuch
quantity as to increafe the length or craflitude of them, the body be-
comes at the fame time enlarged, and its growth is increafed, as well
as- its deficiences repaired.

In this laft cafe fomething more than a fimple appofition or felec-
tion of particles feems to be neceffary ; as many parts of the fyfiem
durino- its growth are caufed to recede from thofe, with which they
were before in contad ; as the ends of the bones, or cartilages, recede
from each other, as their growth advances : this procefs refembles
inflammation, as appears in ophthalmy, or in the produftion of nevir
flefli in ulcers, where old veflels are enlarged, and new ones pro-
duced ; and like that is attended with fenfation. In this fituation the
veflels become diftended with blood, and acquire greater fenfibility^
and may thus be compared to the erection of the penis, or of the
nipples of the breafts of women ; while new particles become added
at the fame time ; as in the procefs of nurition above defcribed.

When only the natural growth of the various parts of the body
are produced, a pleafureable fenfation attends it, as in youth, and

perhaps

Sect. XXXVII. 4. DIGESTION, SECRETION, &c. 467

perhaps in thofe, who are in the progrefs of becoming fat. When
an unnatural growth is the confequence, as in inflammatory difeafes,
a painful fenfation attends the enlargement of the fyftem,

IV. This appofition of new parts, as the old ones difappear, fe-
lefted from the aliment we take, firil: enlarges and flrengthens our
bodies for twenty years, for another twenty years it keeps us in
health and vigour, and adds flrength and folidity to the fyflem ;
and then gradually ceafes to nourifh us properly, and for another
twenty years we gradually fuik into decay, asid finally ceafe to ad,
and to exift.

On confidering this fubjeft one fhould have imagined at firfl view,
that it might have been eafier for nature to have fupported her pro-
geny for ever in health and life, than to have perpetually reproduced
them by the wonderful and myfterious procefs of generation. But
it feems our bodies by long habit ceafe to obey the ffimulus of the
aliment, which fhould fupport us. After we have acquired our
height and folidity we make no more new parts, and the fyflem
obeys the irritations, fenfations, volitions, and afTociations, with
lefs and lefs energy, till the whole finks into inadion.

Three caufes may confpire to render our nerves lefs excitable,
which have been already mentioned, i. If a flimulus be oreater
than natural, it produces too great an exertion of the Simulated
organ, and in confequence exhaufts the fpirit of animation • and
the moving organ ceafes to adl, even though the ftimulus be con-
tinued. And though reft will reeruit this exhauflion, yet fome de-
gree of permanent injury remains, as is evident after expoiino- the
eyes long to too flrong a light. 2. If excitations weaker than na-
tural be applied, fo as not to excite the organ into adion, (as when
fmall dofes of aloe or rhubarb are exhibited,) they may be gradually
increafed, without exciting the organ into a£lion ; which will thus
acquire a habit of difobedieiice to the flimulus ; thus by iocreafuig the

3 O 2 dofc

468 DIGESTION, SECRETION, &c. Sect. XXXVII. 5.

dofe by degrees, great quantities of opium or wine may be taken
without intoxication. See Se£l. XII. 3. i.

3. Another mode, by which life is gradually undermined, is when
irritative motions continue to be produced in confequence of ftimulus,
but are not fucceeded by fenfation ; hence the ftimulus of contagious
matter is not capable of producing fever a fecond time, becaufe it is
not fucceeded by fenfation. See Sect. XII. 3. 6. And hence, owing
to the want of the general pleafureable fenfation, which ought to at-
tend digeftion and glandular fecretion, an irkfomenefs of life enfues ;
and, where this is in greater excefs, the melancholy of old age oc-
curs, with torpor or debility.

From hence I conclude, that it is probable that the fibrill«, or
moving filaments at the extremities of the nerves of fenfe, and the
fibres which conftitute the mufcles (which are perhaps the only parts
of the fyftem that are endued with contra6lile life) are not changed,
as we advance in years, like the other parts of the body ; but only
enlarged or elongated with our growth ; and in confequence they be-
come lefs and lefs excitable into a£lion. Whence, inftead of gradu-
ally changing the old animal, the generation of a totally new one
becomes neceffary with undiminifhed excitability; which many years
will continue to acquire new parts, or new folidity, and then lofing
its excitability in time, perifh like its parent.

V. From this idea the art of preferving long health and life may be
deduced ; which muft confift in ufing no greater ftimulus, whether
of the quantity or kind of our food and drink, or of external circum-
ftances, fuch as heat, and exercife, and wakefulnefs, than is fuf-
ficient to preferve us in vigour ; and gradually, as we grow old toin-
creafe the ftimulus of our aliment, as the inirritability of our fyflem
increafes.

The debilitating efFefts afcribed by the poet Martial to the ex-

ceffive ufe of warm bathing in Italy, may with equal propriety be ap-

8 plied

Sect. XXXVII. 5. DIGESTION, SECRETION, &c. 469

plied to the warm rooms of England ; which, with the general ex-
ceffive ftimulus of fpirituous or fermented liquors, and in fome in-
fiances of immoderate venery, contribute to (horten our lives.

Balnea, vhta, venns, conttmpunt corpora nojira,
Atfaciunt vitam balnea, vina, venus !

-Wine, women, warmth, againfl: our lives combine ;
But what is life without warmth, women, wine !

SECT.

47« OXYGENATION OP BLOOD, Sect. XXXVIII.

SECT. XXXVIII.

OF THE OXYGENATION OF THE BLOOD IN THE LUNGS,
AND IN THE PLACENTA.

I. Blood abjorhs oxygene from the air, whence fhofphork acid, changes its iolour, gives
out heat, and feme fhlogijiic material, and acquires an etherial fpirit, which is
diffipated in fibrous motion. II. The placenta is a pulmonary organ like the gills
offijb. Oxygenation of the blood from air, from water, by lungs, hy gills, by
the placenta ; neceffity of this oxygenation to quad^-upeds, to fijh, to the fcetus in
utero. Placental vejjels infer ted into the arteries of the mother, life of cotyledons
in cows. Why quadrupeds have not Janguiferous lochia. Oxygenation of the
chick in the egg, of feeds. III. The liquor amnii is not excrementitious. It is
nutrititious. It is found in the ejophagus and flomach, and forms the meconium.
Monjlrous births without beads, ^ejlion of Dr. Harvey,

I. FROM the recent difcoveries of many ingenious philofophers it*
appears, that during refpiration the blood imbibes the vital part of the
air, called oxygene, through the membranes of the lungs; and that
hence refpiration may be aptly compared to a flow combuftion. As
in combuftion the oxygene of the atmofphere unites with fome phlo-
giftic or inflammable body, and forms an acid (as in the production of
vitriolic acid from fulphur, or carbonic acid from charcoal,) giving
out at the fame time a quantity of the matter of heat ; fo in refpira-
tion the oxygene of the air unites with the phlogiftic part of the blood,
and probably produces phofphoric or animal acid, changing the colour

Sect. XXXVIII. I. OXYGENATION OF BLOOD. ^yt

of the blood from a dark to a bright red ; and probably fome of the
matter of heat is at the fame time given out according to the theory
of Dr. Crawford. But as the evolution of heat attends almofl: all che-
mical combinations, it is probable, that it alfo attends the fecretions
of the various fluids from the blood ; and that the conftant combina-
tions OK produ(5lions of new fluids by means of the glands conftitute
the more general fource of animal heat ; this feems evinced by the
univerfal evolution of the matter of heat in the blufli of fliame or of
anger ; in which at the fame time an increafed fecretion of the per-
fpirable matter occurs ; and the partial evolution of it from topical in-
flammations, as in gout or rheumatifm,. in which there is a, fecretion
of new blood-veflels.

Some medical philofophers. have afcrlbed the heat of animal bodies
to the friction of the particles of the blood againfl the fides of the vef-
fels. But no perceptible heat has ever been produced by the agitation
of water, or oil, or quickfilver, or other fluids ; except thofe fluids
have undergone at the fame time fome chemical change, as in agitat-
ing milk or wine, till they become four.

Befides the fuppofed produdion of phofphoric acid, and change of
colour of the blood, and the production of carbonic acid, there would
appear to be ibmething of a more fubtile nature perpetually acquired
from the atmofphere ; which is too fine to be long contained in ani-
mal vefTels, and therefore requires perpetual renovation ; and without
which life cannot continue longer than a minute or two ; this ethe-
real fluid is probably feereted from the blood by the -brain, and
perpetually dillipated in the adions of the mufcles and organs of
fenfe.

That the blood acquires fomething from the air, which is imme-
diately neceflary to life, appears from an experiment of Dr. Hare
(Philof. Tranfaft. abridged, Vol. III. p-. 239.) who found, " that
birds, mice, &c. would live as long again in a veflel, where he had
crowded in double the quantity of air by a condenfing engine, than

3 t^ey

4/2 OXYGENATION OF BLOOD. Sect. XXXVIII. 2.

they did when confined in air of the common denfity." Whereas if
feme kind of deleterious vapour only was exhaled from the blood in
refpiration ; the air, when condenfed into half its compafs, could not
be fuppofed to receive fo much of it.

11. Sir Edward Hulfe, a phyfician of reputation at the beginning of
the prefent century, was of opinion, that the placenta was a refpira-
tory organ, like the gills of fifh ; and not an organ to fupply nutri-
ment to the foetus ; as mentioned in Derham's Phyfico-theology.
Many other phyiicians feem to have efpoufed the fame opinion, as
noticed by Haller. Elem. Phyfiologiie, T. i. Dr. Gipfon publilhed
a defence of this theory in the Medical Eflays of Edinburgh, Vol. I.
and II. which doftrine is there controverted at large by the late Alex-
ander Monro ; and fince that time the general opinion has been, that
the placenta is an organ of nutrition only, owing perhaps rather to the
authority of fo great a name, than to the validity of the arguments
adduced in its fupport. The fubje£t has lately been refumed by Dr.
James Jeffray, and by Dr. Foreflrer French, in their inaugural differ-
tations at Edinburgh and at Cambridge; who have defended the con-
trary opinion in an able and ingenious manner; and from whofeThefes
I have extra£l:ed many of the following remarks.

Firft, by the late difcoveries of Dr. Prieflley, M. Lavoifier, and
other philofophers, it appears, that the bafis of atmofpherical air,
called oxygene, is received by the blood through the membranes of
the lungs ; and that by this addition the colour of the blood is changed
from a dark to a light red. Secondly, that water poflefles oxygene
alfo as a part of its compofition, and contains air likewife in its pores;
whence the blood of fifh receives oxygene from the water, or from
the air it contains, by means of their gills, in the fame manner as the
blood is oxygenated in the lungs of air-breathing animals ; it changes
its colour at the fame time from a dark to a light red in the vefTels of
their gills, which conflitute a pulmonary organ adapted to the me-
dium in which they live. Thirdly, that the placenta confifls of ar-
teries

Sect. XXXVIII. 2. OXYGENATION OF BLOOD. 473

teries carrying the blood to its extremities, and a vein bringing it
back, refembling exa£liy in ftruflure the lungs and gilla above men-
tioned ; and that the blood changes its colour from a dark to a light
red in paffing through thele veflels.

This analogy between the lungs and gills of animals, and the pla-
centa of the fetus, extends through a great variety of other circum-
ftances ; thus air-breathing creatures and R{h can live but a fev/ mi-
nutes without air or water ; or when they are confined in fuch air or
water, as has been fpoiled by their own refpiration ; the fame hap-
pens to the fetus, which, as foon as the placenta is feparated from the
uterus, muft either expand its lungs, and receive air, or die. Hence
from the ftru6lure, as vvell as the ufe of the placenta, it appears to be
a refpiratory organ, like the gills of fiih, by which the blood in the
fetus becomes oxygenated.

From the terminations of the placental veflels not being obferved
to bleed after being torn from the uterus, while thole of the uterus
efFufe a great quantity of florid arterial blood, the terminations of the
placental veflels would feem to be inferted into the arterial ones of the
mother ; and to receive oxygenation from the pafling currents of her
blood through their coats or membranes ; which oxygenation is proved
by the change of the colour of the blood from dark to light red in its
palTage from the placental arteries to the placental vein.

The curious flrufture of the cavities or lacunas of the placenta,
demonftrated by Mr. J. Hunter, explain this circumftance. That in-
genious philofopher has fhewn, that there are numerous cavities or
lacunas formed on that fide of the placenta, which is in conta£l with
the uterus ; thofe cavities or cells are filled with blood from the ma-
ternal arteries, which open into them; vi/hich blood is again taken up
by the maternal veins, and is thus perpetually changed. While the
terminations of the placental arteries and veins are fpread in fine reti-
culation on the fides of thefe cells. And thus, as the growing fetus

3 P requires

474 OXYGENATION OF BLOOD. Sect. XXXVIII. 2.

requires greater oxygenation, an apparatus is produced refembling
exa6lly the air-cells of the lungs.

In cows, and other ruminating animals, the internal furface of the
uterus is unequal like hollow cups, which have been called coty-
ledons ; and into thefe cavities the prominencies of the numerous pla-
centas, with which the fetus of thofe animals is furniflied, are in-
ferted, and iT:rl£lly adhere ; though they may be extra£led without
efFufion of blood. Thefe inequalities of the uteri^is, and the nu-
merous placentas in confequence, feem to be deligned for the purpofe
of expanding a greater furface for the terminations of the placental
veffels for the purpofe of receiving oxygenation from the uterine ones ;
as the progeny of this clafs of animals are more completely formed
before their nativity, than that of the carnivorous claffes, and mufl:
thence in the latter weeks of pregnancy require greater oxygenation.
Thus calves and lambs can walk about in a few minutes after their
birth ; while puppies and kittens remain many days without opening
their eyes. And though on the feparation of the cotyledons of ru-
minating animals no blood is efFufed, yet this is owing clearly to the
greater power of contraction of their uterine lacun2e or alveoli. See
Medical Effays, Vol. V. page 144. And from the fame caufe they
are not liable to a fanguiferous menftruation.

The neceffity of the oxygenation of the blood in the fetus is farther
illufl:rated by the analogy of the chick in the egg ; which appears to
have its blood oxygenated at the extremities of the veffels furround-
ing the yolk ; which are fpread on the air-bag at the broad end of the
egg, and may abforb oxygene through that moifl: membrane from the
air confined behind it ; and which is fhewn by experiments in the ex-
haufted receiver to be changeable through the Ihell.

This analogy may even be extended to the growing feeds of vege-
tables ; which were fliewn by Mr. Scheele to require a renovation of
the air over the water, in which they were contined. Many vege-
j; table

Sect. XXXVIII. 3- OXYGENATION OF BLOOD. 475

table feeds are furrou tided with air in their pods or receptacles, as
peas, the fruit of ftaphylea, and lichnis veficaria ; but it is probable,
that thofe feeds, after they are (lied, as well as the fpawn of filh,
by the fituation of the former on or near the moill: and aerated iurface
of the earth, and of the latter in the ever-changing and ventilated
water, may not be in need of an apparatus for the oxygenation of their
firft blood, before the leaves of one, and the gills of the other, are
produced for this purpofe.

III. I. There are many arguments, befides the ftridl analogy be-
tween the liquor amnil and the albumen ovi, which {hew the former
to be a nutritive fluid ; and that the fetus in the latter months of
pregnancy takes it into its ftomach ; and that in confequence the pla-
centa is produced for fome other important purpofe.

Firft, that the liquor amnii is not an excrementitious fluid is
evinced, becaufe it is found in greater quantity, when the fetus is
young, decreafuig after a certain period till birth. Haller afferts,
*' that in fome animals but a fmall quantity of this fluid remains at
the birth. In the eggs of hens it is confumed on the eighteenth day,
fo that at the exclufion of the chick fcarcely any remains. In rabbits
before birth there is none." Elem. Phyliol. Had this been an ex-
crementitious fluid, the contrary would probably have occurred.
Secondly, the Ikin of the fetus is covered with a whitifh cruft or pel-
licle, which would feem to preclude any idea of the liquor amnii
being produced by any exfudation of perfpirable matter. And it can-
not conllft of urine, becaufe in brute animals the urachus pafles
from the bladder to the alantois for theexprefs purpofe of carrying oiF
that fluid ; which however in the human fetus feems to be retained
in the diftended bladder, as the feces are accumulated in the bowels of
all animals.

2. The nutritious quality of the liquid, which furrounds the fetus,
appears from the following conGderations. i. It is coagulable by heat,
by nitrous acid, and by fpirit of vvine, like raiik, ferum of blood, and

2 P 2 other

476 OXYGENATION OF BLOOD. Sect. XXXVIII. 3,

-other fluids, which daily experience evinces to be nutritious. 2. It
has a ialtifh tafte, according to the accufate Baroa Haller, not unUke
the whey of milk, which it even refembles in fmell. 3. The white
of the ees which conftitutes the food of the chick, is fhewn to be nu-
tritious by our daily experience ; befides the experiment of its nutri-
tious efFeils mentioned by Dr. Fordyce in his late Treatife on Digef-
tion, p. 178 ; who adds, that it much refembles the eflential parts of
the ferum of blood.

3. A fluid fimilar to the fluid, with which the fetus is furrounded,
except what little change may be produced by a beginning digefrion,
is found in the ftomach of the fetus ; and the white of the egg is found
in the fame manner in theftomach of the chick.

Numerous hairs, fimilar to thofe of its Ikin, are perpetually found
among the contents of the ftomach in new-born calves ; which muft
therefore have licked themfelves before their nativity. Blafii Anatom.
See Sea. XVI. 2. onlnftina.

The chick in the egg is feen gently to move in its furrounding fluid,
and to open and fhut its mouth alternately. The fame has been ob-
ferved in puppies. Haller's El. Phyf. I. 8. p. 201.

A column of ice has been feen to reach down the cefophagus from
the mouth to the ftomach in a frozen fetus ; and this ice was the liquor
amnii frozen.

The meconium, or firfl: faeces, in the bowels of new-born infants
evince, that fomething has been digefted ; and what could this be but
the liquor amnii together with the recrements of the gaflric juice and
gall, which were neceffary for its digeftion ?

There have been recorded fome monftrous births of animals with-
out heads, and confequently without mouths, which feem to have been
dehvered on doubtful authority, or from inaccurate obfervation. There
are tv/o of fuch monftrous produ£lions however better attefted ; one
of a human fetus, mentioned by Gipfon in the Scots Medical Eflays ;
which having the gula impervious was furn^lhed with an aperture into

■ the

Sect. XXXVIII. 3- OXYGENATION OF BLOOD. 477

the wind-pipe, which communicated below into the gullet ; by means
of which the liquor amnii might be taken into the ftomach before na-
tivity without danger of fuiFocation, while the fetus had no occaiion to
breathe. The other monftrous fetus is defcribed by Vander Wiel,
who afferts, that he faw a monftrous lamb, which had no mouth ; but
inftead of it was furniflied with an opening in the lower part of the
neck into the ftomach. Both thefe inftances evidently favour the doc-
trine of the fetus being nourifhed by the mouth ; as otherwife there
had been no neceffity for new or unnatural apertures into the ftomach,
when the natural ones were deficient ?

From thefe fa£ls and obfervations we may fafely infer, that the
fetus in the womb is nourifhed by the fluid which furrounds it ; which
during the iirft period of geftation is abforbed by the naked lacleals;
and is afterwards fwallowed into the ftomach and bowels, when thefe
organs are perfeded ; and laftly that the placenta is an organ for the
purpofe of giving due oxygenation to the blood of the fetus ; which
is more necefl'ary, or at leaft more frequently neceffary, than even the
fupply of food.

The queftion of the great Harvey becomes thus eafily anfwered.
" Why is not the fetus in the womb fuffocated for want of air, when
it remains there even to the tenth month w'ithout refpiration : yet if
it be born in the leventh or eighth month, and has once refpired, it
becomes immediately fuffocated for want of air, if its refpiration be
obftruded ?"

For further information on this fubje£l, the reader is referred to
the Tentamen Medicum of Dr. JefFray, printed at Edinburgh in
17S6. And it is hoped that Dr. French willfome time give his thefes
on this fubjeS: to the pubhc.

SECT.

478 GENERATION. Sect.XXXIX.

SECT. XXXIX.

OF GENERATION.

Felix, qui caufas alta caligine merfas

Pandit, et evolvit tenuiffima vincula rerum. Anon.

I. Habits of aEling and feeling of individuals attend the foul into a future life, and at-
tend the new einhryon at the time of its produElion. The new fpeck of entity ah-
Jorbs nutriment i and receives oxygene. Spreads the terminations of its vejfels on
cells, which communicate with the arteries of the uterus ; fometimes with thoje of
the peritoneum. Afterwards it fwallows the liquor amnii, which it produces by
its irritation from the uterus, or peritoneum. Like infeSts in the heads of calves
and floeep. Why the white of egg is of two conftfiencies. Why nothing is found
in quadrupeds fimilar to the yolk, nor in mofi vegetable feeds. II. i . Eggs of
frogs andfifJd impregnated out of their bodies. Eggs of fowls which are not fecun-
dated, contain only the nutriment for the embryon. 1'he embryon is produced by
the male, and the nutriment by the female. Animalcula in femine. Profufion of
nature's births. 2. Vegetables viviparous. Buds and bulbs have each a father
hut no mother. Vejjfels of the leaf and bud inofculate. The paternal offspring ex-
aSlly refembles the parent. 3. InfeSis impregnated for fix generations. Polypus
branches like buds. Creeping roots. Viviparous flowers. 'Tania, volvox. Eve
from Adam's rib. Semen not a fiimulus to the egg. III. i. Embryo7is not ori-
ginally created within other embryons. Organized matter is not Jo minute.
2. All the parts of the embryon are not formed in the male parent. Crabs pro-
duce their legs, worms produce their heads and tails. In wens, cancers, and in-
flammations, new veffels are formed. Mules partake of the forms of both parents.
Hair and nails grow by elongation, not by diflention. 3. Organic particles of
Buffon. IV. I. Rudiment of the embryon a fimple living filament, becomes a
living ring, and then a living tube. 2. It acquires new irritabilities, andjenfiibili-

ties

Sect. XXXIX. GENERATION. 479

ties with new organizations^ as in wounded Jnails, ply-pi, moths, gnats, tadpoles.
Hence new parts are acquired by addition not by diftention. 3. All parts of the
body grow if not confined. 4. Fetufes deficient at their extremities, or ha'-je a du-
plicature of parts. Monfirous births. Double parts of vegetables. 5. Mules
cannot be formed by diftention of the Jeminal ens. 6. Families of animals from a
mixture of their orders. Mules imperfeSt. 7. Animal appetency like chemical
affinity. Vis fabricatrix and medicatrix of nature. 8. The changes of animals
before and after nativity. Similarity of their Jru^iure. Changes in them froin,
lift, hunger, and danger. All warm-blooded animals derived from one living
filament. Cold-blooded animals, infeEis, worms, vegetables, derived alfo from one
living filament. Male animals have teats. Male pidgeon gives milk. The
world itfelf generated. The caufe of caifes. A ft ate of probation and refpmfi-
hility. V. I . Efficient caife of the colours of birds egg;, and of hair and fes-
tbers, which become white infnowy countries. Imagination of the female colours
the egg. Ideas or motions of the retina imitated by the extremities of the nerves of
touch, or rete mucofum. 2. Nutriment Jupplied by the female of three kinds.
Her imagination can only affeSt the firft kind. Mules how produced, and mulat*
toes. Organs of reproduSfion why deficient in mules. Eggs with double yolks.
VI. I. Various Jecretions produced by the extremities of the veffiels, as in the
glands. Contageous matter. Many glands affected by pleafurable ideas, as thoje
which fecrete thefemen. 1. Snails and worms are hermaphrodite, yet cannot im-
pregnate themf elves. Final caufe of this. j. The imagination of the male forms
the /ex. Ideas, or motions of the nerves of vifion or of touch, are imitated by the
ultimate extremities of the glands of the teftes, which mark thefex. This effeSi of
the imagination belongs only to the male. The Jex of the embryon is not ozvino- to
accident. 4. Caifes of the changes in animals from imagination as in monftrrs.
From the male. From the female. 5. Mif carriages from fear. 6. Power of
the imagination of the male over the colour, form, and Jex of the prc^eny. An in-
' fiance of. 7. AEi of generation accompanied with ideas of the male or female
form. Art of begetting beautiful children of either Jex. VII. Recapitulation.
VIII. Conclujion. Of cauje and effeSl. The atomic philojophy leads to a firft
cauje.

I. THE

48o GENERATION. Sect. XXXIX. i,

I. THE ingenious Dr. Hartley ia his work on man, and fome
other philofophers, have been of opinion, that our immortal part ac-
quires during this life certain habits of aftion or of fentiment, which
become -for ever indilToluble, continuing after death in a future ftate
of exigence ; and add, that if thefe habits are of the malevolent kind,
they muft render the poffeflbr miferable even in heaven. I would
apply this ingenious idea to the generation or production of the em-
bryon, or new animal, which partakes fo^much of the form and pro-
penfities of the parent.

Owing to the imperfeftion of language the offspring is termed a
new animal, but is in truth a branch or elongation of the parent ;
lince apart of the embryon-animal is, or was, a part of the parent;
and therefore in ftriift language it cannot be faid to be entirely new at
the time of its production ; and therefore it may retain fome of the
habits of the parent-fyllem.

At the earlieft period of its exiilence the embryon, as fecreted from
the blood of the male, would feem to confifl: of a living filament with
certain capabilities of irritation, fenfation, volition, and affociation ;
and alfo with fome acquired habits or propenfities peculiar to the pa-
rent : the former of thefe are in common with other animals ; the
latter feem to ditlinguifh or produce the kind of animal, whether
man or quadruped, with the fimilarity of feature or form to the pa-
rent. It is difficult to be conceived, that a living entity can be fepa-
rated or produced from the blood by the aClion of a gland ; and which
Ihall afterwards become an animal fimilar to that in whofe veflels it
is formed ; even though we fliould luppofe with fome modern theo-
' rifts, that the blood is alive; yet every other hypothefis concerning
generation refts on principles itill more difficult to our comprehenfion.

At the time of procreation this fpeck of entity is received into an
appropriated nidus, in which it miift acquire two circumftances ne-
cefiary to its life and growth ; one of thefe is food or fuftenance,
which is to be received by the abforbent mouths of its veffels ; and

the

Sect.XXXIX. r. GENERATION. 481

the other is that part of atmofpherical air, or of water, which by the
new chemiftry is termed oxygene, and which affeds the blood by
pafling through the coats of the veflels which contain it. The fluid
furrounding the embryon in its new habitation, which is called liquor
amnii, fupplies it with nourifhment ; and as fome air cannot but be in-
troduced into the uterus along with the new embryon, it would feem
that this fame fluid would for a fhort time, fuppofe for a few hours,
fupply likewife a fufficient quantity of the oxygene for its immediate
exiftence.

On this account the vegetable impregnation of aquatic plants is
performed in the air j and it is probable that the honey-cup or neflary
of vegetables requires to be open to the air, that the anthers and
ftigmas of the flower may have food of a more oxygenated kind than
the common vegetable fap-juice.

On the introdudlion of this primordium of entity into the uterus
the irritation of the liquor amnii, which furrounds it, excites the ab-
forbent mouths of the new veflels into a6lion ; they drink up a part
of it, and a pleafurable fenfation accompanies this new a£lion ; at the
fame time the chemical affinity of the oxygene a£ls through the vef-
fels of the rubefcent blood ; and a previous want, or difagreeable fen-
jfation, is relieved by this procefs.

As the want of this oxygenation of the blood is perpetual, (as ap-
pears from the inceflant neceffity of breathing by lungs or gills,) the
veflels become extended by the efforts of pain or delire to feek this
neceflary obje£l of oxygenation, and to remove the difagreeable fen-
fation, which that want occalions. At the fame time new particles
of matter are abforbed, or applied to thefe extended veflTels, and they
become permanently elongated, as the fluid in conta£l with them fooa
loofes the oxygenous part, which it at firfl poflTefled, which was ow-
ing to the introduction of air along with the embryon. Thefe new
blood-veflels approach the fides of the uterus, and penetrate with their
fijie terminations into the veflels of the mother ; or adhere to them,

3 Q^ acquiring

482 GENERATION. Sect.XXXIX. r.

acquiring oxygene through their coats from the paffing currents of the
arterial blood of the mother. See Se6l. XXXVIII. 2.

This attachment of the placental veffels to the internal fide of the
uterus by their own proper efforts appears further illuftrated by the
many inflances of extra-uterine fetufes, which have thus attached or
inferted their veffels into the peritoneum ; or on the vifcera, exadlly
in the fame manner as they naturally infert or attach them to the
uterus.

The abforbent veffels of the embryon continue to drink up nou-
rifhment from the fluid in which they fwim, or liquor amnii ; and
which at firft needs no previous digeftive preparation ; but which,
when the whole apparatus of digeftion becomes complete, is fwal-
lovved by the mouth into the ftomach, and being mixed with faliva,
gaftric juice, bile, pancreatic juice, and mucus of the inteftines, be-
comes digefted, and leaves a recrement, which produces the firfl
feces of the infant, called meconium.

The liquor amnii is fecreted into the uterus, as the fetus requires
it, and may probably be produced by the irritation of the fetus as an
extraneous body ; fince a fimilar fluid is acquired from the peritoneum
■in cafes of extra-uterine geflation. The young caterpillars of the
gadfly placed in the Ikins of cows, and the young of the ichneumon-
fly placed in the backs of the caterpillars on cabbages, feem to pro-
duce their nourifhment by their irritating the (ides of their nidus..
A vegetable fecretion and concretion is thus produced on oak-leaves-
by the gall-infect, and by the cynips in the bedeguar of the rofe ; and
by the young grafshopper on many plants, by which the animal fur-
rounds itfelf with froth. But in no circumftance is extra-uterine gef-
tation fo exaftly refembled as by the eggs of a fly, which are de-
polited in the frontal fmus of ftieep and calves. Thefe eggs float in
feme ounces of fluid colle£ted in a thin pellicle or hydatide. This
bao- of ftuid compreffes the optic nerve on one fide, by which the
vifion being lefs diftind in that eye, the animal turns in perpetual
8 circles

Sect. XXXIX. i. GENERATION. 4«.^

circles towards the fide afFefted, in order to get a more accurate view
of objects ; for the fame reafon as in fquinting the afFedted eye is
turned away from the obje£l contemplated. Slieep in the warm
months keep their nofes clofe to the ground to prevent this fly from
fo readily getting into their noftrils.

The liquor amnii is fecreted into the womb as it is required, not
only in refpe£l to quantity, but, as the digeftive powers of the fetus
become formed, this fluid becomes of a different confiftence and qua-
lity, till it is exchanged for milk after nativity. Haller. Phyfiol. V.
I. In the egg the white part, which is analogous to the liquor amnii
of quadrupeds, confifts of two diftincl parts ; one of which is more
vifcid, and probably more difficult of digeftion, and more nutritive
than the other ; and this latter is ufed in the lafl: week of incubation.
The yolk of the egg is a ftill ftronger or more nutritive fluid, which
is drawn up into the bowels of the chick juft at its exclufion from the
(hell, and ferves it for nourifhment for a day or two, till it is able to
digeft, and has learnt to chufe the harder feeds or grains, which are to
afford it fuftenance. Nothing analogous to this yolk is found in the
fetus of laftiferous animals, as the milk is another nutritive fluid ready
prepared for the young progeny.

The yolk therefore is not neceflary to the fpawn of fifh, the eggs
of infe£ls, or for the feeds of vegetables ; as their embryons have
probably their food prefented to them as foon as they are excluded
from their fliells, or have extended their roots. Whence it happens
that fome infects produce a living progeny in the fpring and fummer,
and eggs in the autumn ; and fome vegetables have living roots or
buds produced in the place of feeds, as the polygonum viviparum,
and magical onions. See Botanic Garden, p. ii. art. anthoxanthum.

There feems however to be a refervoir of nutriment prepared for
fome feeds befides their cotyledons or feed-leaves, which may be fup-
pofed in fome m.eafure analogous to the yolk of the egg. Such are the
faccharine juices of apples, grapes and other fruits, which fupply nu-

3 0^2 trition

484 GENERATION. Sect. XXXIX. 2.

trition to the feeds after they fall oa the ground. And fuch is the
milky juice in the centre of the coco-nut, and part of the kernel of
it ; the fame I fuppofe of all other monocotyledon feeds, as of the
palms, grafles, and lilies.'

II. I, The procefs of generation is ftill involved in impenetrable
obfcurity, conjeftures may neverthelefs be formed concerning fome of
its circumftances. Firft, the eggs of fifli and frogs are impregnated,
after they leave the body of the female ; becaufe they are depofited in
a fluid, and are not therefore covered with a hard (hell. It is how-
ever remarkable, that neither frogs nor fi(h will part with their fpawn
without the prefence of the male ; on which account female carp and
gold-filli in fmall ponds, where there are no males, frequently die
from the diftention of their growing fpawn. 2. The eggs of fowls,
which are laid without being impregnated, are feen to contain only
the yolk and white, which are evidently the food or fuftenance for
the future chick. 3. As the cicatricula of thefe eggs is given by the
cock, and is evidently the rudiment of the new animal ; we may con-
clude, that the embryon is produced by the male, and the proper
food and nidus by the female. For if the female be fuppofed to form
an equal part of the embryon, why (hould fhc form the whole of the
apparatus for nutriment and for oxygenation ? the male in many ani-
mals is larger, ftronger, and digefls more food than the female, and
therefore fliould contribute as much or more towards the reproduc-
tion of the fpecies ; but if he contributes only half the embryon,
and none of the apparatus for fuftenance and oxygenation, the divifion
is unequal ; the flrength of the male, and his confumption of food
are too great for the efFe6t, compared with that of the female, which
is contrary to the ufual courfe of nature.

In objection to this theory of generation it may be faid, if the ani-
malcula in femine, as feen by the microfcope, be all of them rudi-
ments of homunculi, when but one of them can find a nidus,
what a wafte nature has made of her productions ? I do not aflert

tha£

Sect. XXXIX. 2. GENERATION. 485

that thefe moving particles, vilible by the microfcope, are horaun-
ciones ; perhaps they may be the creatures of ftagnation or putridity,
or perhaps no creatures at all ; but if they are fuppofed to be rudi-
ments of homunculi, or embryons, fuch a profulion of them correl-
ponds with the general eitorts of nature to provide for the continu-
ance of her fpecies of animals. Every individual tree produces innu-
merable feeds, and every individual fifh innumerable fpawn, in fuch
inconceivable abundance as vi'ould in a fhort fpace of time crowd the
earth and ocean with inhabitants ; and thefe are much more per-
fect animals than the animalcula in femine can be fuppofed to be, and
perifh in uncounted millions. This argument only fliews, that the
productions of nature are governed by general laws ; and that by. a
wife fuperfluity of provifion (he has enfured their continuance.

2. That the embryon is fecreted or produced by the male, and not
by the conjundion of fluids from both male and female, appears from
the analogy of vegetable feeds. In the large flowers, as the tulip,
there is no fimilarity of apparatus between the anthers and the ftigraa : .
the feed is produced according to the obfervations of Spallanzani long
before the flowers open, and in confequence long before it can be im-
pregnated, like the egg in the pullet. And after the prolific duft is
fhed on the ftigma, the feed becomes coagulated in one point firfl, like
the cicatricula of the impregnated egg. See Botanic Garden, Part I.
additional note 38. Now in thefe fimple products of nature, if the
female contributed to produce the new embryon equally with the male,
there would probably have been fom.e vilible fimilarity of parts for this
purpofe, befides thofe neceflary for the nidus and luftenance of the
new progeny. Befides in many flowers the males are more numerous
than the females, or than the feparate uterine cells in their germs,
which would fhew, that the office of the male was at leaft as impor-
tant as that of the female ; whereas if the female, befides producing
the egg or feed, was to produce an equal part of the embryon, the of-
iice of reprodudion would be unequally divided between them.

Add

-486 GENERATION. Sect. XXXIX. 2.

Add to this, that in the moft fimple kind of vegetable reprodudion,
I mean the buds of trees, which are their viviparous offspring, the
leaf is evidently the parent of the bud, which rifes in its bofom, ac-
cording to the obfervation of Linnasus. This leaf eonfifts of abfor-
bent veflTels, and pulmonary ones, to obtain its nutriment, and to ini-
pregnate it withoxygene. This fimple piece of living organization is
alfo furniOied with a power of reprodu<Slion ; and as the new offspring
is thus fupported adhering to its father, it needs no mother to fupply
it with a nidus, and nutriment, and oxygenation ; and hence no fe-
male leaf has exiftence.

I conceive that the veflels between the bud and the leaf communi-
cate or inofculate ; and that the bud is thus ferved with vegetable blood,
that is, with both nutriment and oxygenation, till the death of the
parent-leaf in autumn. And in this refpedl it differs from the fetus of
viviparous animals. Secondly, that then the bark-veffels belonging
to the dead-leaf, and in which I fuppofe a kind of manna to have
been depofited, become now the placental veffels, if they may be fo
called, of the new bud. From the vernal fap thus produced of one
fugar-maple-tree in New-York and in Pennfylvania, five or fix
pounds of good fugar may be made annually without deflroying the
tree. Account of maple-fugar by B. Rufh. London, Phillips. (See
Botanic Garden, Part I. additional note on vegetable placentation.)

Thefe veffels, when the warmth of the vernal fun hatches the
young bud, ferve it with a faccharine nutriment, till it acquires leaves
of its own, and flioots a new fyftem of abforbents down the bark
and root of the tree, jufl: as the farinaceous or oily matter in feeds,
and the faccharine matter in fruits, ferve their embryons with nutri-
ment, till they acquire leaves and roots. This analogy is as force-
able in fo obfcure a fubjed, as it is curious, and may in large buds,
as of the horfe-chefnut, be almoft feen by the naked eye ; if with a
penknife the remaining rudiment of the lafl year's leaf, and of the
new bud in its bofom, be cut away flice by (lice. The feven ribs of

the

Sect.. XXXIX. 2. GENERATION. . 487

the laft year's leaf will be feen to have arifen from the pith in feveu
diftixi£t points making a curve ; and the new bud to have been pro-
duced in their centre, and to have pierced the alburnum and cortex,
and grown without the affiftance of a mother. A fimilar procels
may be feen on differing a tulip-root in winter ; the leaves, which
inclofed the laft year's flower-ftalk, were not neceflary for the flower ;
but each of thefe was the father of a new bud, which may be now
found at its bafe ; and which, as it adheres to the parent, required no
mother.

This paternal offspring of vegetables, I mean their buds and bulbs,
i& attended with a very curious circumftance ; and that is, that they
exaftly refemble their parents, as is obfervable in grafting fruit-trees,
and in propagating flower-roots ; whereas the feminal offspring of
plants, being fupplied with nutriment by the mother, is liable to per-
petual variation. Thus alfo in the vegetable clafs dioicia, where the
male flowers are produced on one tree, and the female ones on ano-
ther ; the buds of the male trees uniformly produce either male flow-
ers, or other buds fimilar to themfelves ; and the buds of the female
trees produce either female flowers, or other buds fimilar to them-
felves ; whereas the feeds of thefe trees produce either male or fe-
• male plants. From this analogy of the produftion of vegetable buds
without a mother, I contend that the mother does not contribute to
the formation of the living ens in animal generation, but is neceffary
only for fupplying its nutriment and oxygenation.

There is another vegetable fa£l publiflied by M. Koelreuter, which
he calls " a complete metaniorphofis of one natural fpecies of plants
into another," which fliews, that in feeds as well as in buds, the em-
bryon proceeds from the male parent, though the form of the fubfe-
quent mature plant is in part dependant on the female. M. Koelreuter
impregnated a ftigma of the nicotianaruftica with the farina of the ni-
cotiana paniculata, and obtained prolific feeds from it. With the
plants which fprung from thefe feeds, he repeated the experiment,

impregnating

4«« GENERATION. Sect. XXXIX. 2.

impregnating them with the farina of the nicotiana paniculate. As
the mule plants which he thus produced were prolific, he continued
to impregnate them for many generations with the farina of the ni-
cotiana paniculata, and they became more and more like the male pa-
rent, till he at length obtained fix plants in every refpeft perfe£lly fi-
milar to the nicotiana paniculata ; and in no refpeft refembling their
female parent the nicotiana ruftica. Blumenbach on Generation.

.3. It is probable that the infedls, which are faid to require but one
impregnation for fix genei'ations, as the aphis (fee Amenit. Academ.)
produce their progeny in the manner above defcribed, that is, without
amother, and not without a father ; and thus experience a lucina fine
concubitu. Thofe who have attended to the habits of the polypus,
which is found in the flagnant water of our ditches in July, affirm,
that the young ones branch out from the fide of the parent like the
buds of trees, and after a time feparate themfelves from them. This
is fo analogous to the manner in which the buds of trees appear to be
produced, that thefe polypi maybe confidered as all male animals, pro-
ducing embryons, which require no mother to fupply them with a
nidus, or with nutriment, and oxygenation.

This lateral or lineal generation of plants, not only obtains in the
buds of trees, which continue to adhere to them, but is beautifully
feen in the wires of knot-grafs, polygonum aviculare, and in thofe of
ftrawberries, fragaria vefca. In thefe an elongated creeping bud is
protruded, and, where it touches the ground, takes root, and pro-
duces a new plant derived from its father, from which it acquires both
nutriment and oxygenation ; and in confequence needs no maternal
apparatus for thefe purpofes. In viviparous flowers, as thofe of al-
lium magicum, and polygonum viviparum, the anthers and the flig-
mas become effete and perifh ; and the lateral or paternal offspring
fucceeds inflead of feeds, which adhere till they are fufficiently ma-
ture, and then fall upon the ground, and take root like other bulbs.

The lateral produdionof plants by wires, while each new plant is

thus

Sect. XXXIX. 3. GENERATION. 489

thus chained to its parent, and continues to put forth another and ano-
ther, as the wire creeps onward on the ground, is exailly refembled
by the tape-worm, or taenia, fo often found in the bowels, ftretch-
ing itfelf in a chain quite from the llomach to the re6lum. Linnaeus
aflerts, " that it grows old at one extremity, while it continues to ge-
nerate young ones at the other, proceeding ad infinitum, like a root of
grafs. The feparate joints are called gourd-worms, and propagate
new jointslike the_ parent without end, each joint being furniflied
with its proper mouth, and organs of digeftion." Syftema natura?.
Vermes tenia. In this animal there evidently appears a power of re-
produ<5lion without any maternal apparatus for the purpofe of fupply-
ing nutriment and oxygenation to the embryon, as it remains at-
tached to its father till its maturity. The volvox globator, which is a
tranfparent animal, is laid by Linnaeus to bear within it fons and
grand-fons to the fifth generation. Thefeare probably living fetufes,
produced by the father, of different degrees of maturity, to be de-
truded at difTerent periods of time, like the unimpregnated eggs of
various fizes, which are found in poultry ; and as they are produced
without any known copulation, contribute to evince, that the living
embryon in other orders of animals is formed by the male-parent, and
not by the mother, as one parent has the pou'er to produce it.

This idea of the reproduftion of animals from a fingle living fila-
ment of their fathers, appears to have been fhadowed or allegorized in
the curious account in facred writ of the formation of Eve from a rib
of Adam.

From all thefe analogies I conclude, that the embryon is produced
folely by the male, and that the female fupplies it with a proper nidus,
with fuftenance, and ^yith oxygenation ; and that the idea of the fe-
men of the male conflituting only a flimulus to the egg of the fe-
male, exciting it into hfe, (as held by fome philofophers; has no fup-
port from experiment or analogy.

III. I. Many ingenious philofophers have found fo great difficulty

3 R in

49'o GENERA T I O N. Sect. X-XXIX. ..3. „

iti conceiving the manner of the reprodu6lion of animals, that they
have fuppofed all the numerous progeny to have exifted in miniature
in the animal originally created ; and that thefe infinitely minute forms
are only evolved or diftended, as the embryon increafes in the womb.
This idea, befides its being unfupported by any analogy we are ac-
quainted with, afcribes a greater tenuity to organized matter, than
we can readily admit ; as thefe included embryons a«re fuppofed each of
them to confift of the various and complicate parts of animal bodies :
they mufl polTefs a much greater degree of minutenefs, than that
which was afcribed to the devils that tempted St. Anthony ; of
whom 20,000 were faid to have been able to dance a faraband on the
point of the fined needle without incommoding each other,

2. Others have fuppofed, that all the parts of the embryon are
formed in the male, previous to its being depofited in the egg or ute-
rus ; and that it is then only to have its parts evolved or diftended as
mentioned above ; but this is only to get rid of one difficulty by pro-
pofing another equally incoraprehenfibl-e : they found it, difficult to
conceive, how the embryon could be formed in the uterus or egg,
and therefore Vi'iflied it to be formed before it came thither. In
anfwer to both thefe doctrines it may be obferved, ift, that fome ani-
mals, as the crab-fifh, can reproduce a whole limb, as a leg which.
has been broken off; others, as worms and fnails, can reproduce a
head, or a tail, when either of them has been cut away^ and that;
hence in thefe animals at leaft a part can be formed anew, which can-
not be fuppofed to have exifted previoufly in miniature.

Secondly, there are new parts or new veffels produced in many dif-
eafes, as on the cornea of the eye in ophthalmy, in wens and cancers^
v^hich cannot be fuppofed to have had a prototype or original minia-
ture in the embryon.

Thirdly, how could mule-animals be produced, which partake of
the forms of both the parents, if the original embryon was a miniai
ture ex^fting ia the femea of the male pareat ? if an embryon of the

TO ale-

Sect. XXXIX. 3. GENERATION. 49 r

male afs was only expanded, no refemblance to the mare could exift
iii the mule.

This miftaken idea of the extenfion of parts Teems to have had its
rife from the mature man refembling the general form of the fetus ;
and from thence it was believed, that the parts of the fetus were
diftended into the m.an ; whereas they have increafed 100 times in
weight, as well as 100 times in lize ; now no one will call the ad-
ditional ^^ parts a diftention of the original one part in refpe6t to
weight. Thus the uterus during pregnancy is greatly enlarged in
thickhefs and folidity as well as in capacity, and hence muft have ac-
quired this additional lize by accretion of new parts, not by an ex-
tenfion of the old ones ; the familiar a<£l of blowing up the bladder of
an animal recently flaughtered h:is led our imaginations to apply this
idea of diftention to the increafe of fize from natural growth ; which
however muft be owing to the appofition of new parts ; as it is evinc-
ed from the increafe of weight along with the increafe of dimenfion ;
and is even vifible to our eyes in the elongation of our hair from the
colour of its ends ; or when it has been dyed on the head ; and in the
growth of our nails from the fpecks fometimes obfervable on them ;
and in the increafe of the white crefcent at their roots, and in the
growth of new flefh in wounds, which confifts of new nerves as well
as of new blood-veflels.

3. Laftly, Mr. Buffon has with great ingenuity imagined the ex-
iftence of certain organic particles, which are fuppofed to be partly
alive, and partly mechanic fprings. The latter of thefe were dilco-
vered by Mr. Needham in the milt or male organ of a fpecies of cuttle
fifh, called calmar; the former, or living animalcula, are found in
both male and female fecretions, in the infufions of feeds, as of pep-
per, in the jelly of roafted veal, and in all other animal and vegetable
fubftances. Thefe organic particles he fuppofes to exift in the fper-
matic fluids of both fexes, and that they are derived thither from
every part of the body, and muft therefore refemble, as he fuppofes,

3 R 2 the

49^ GENERATION. Sect. XXXIX. 4.

the parts from \A' hence they are derived. Thefe organic part^jcles he
believes to be- in conflant aftivity, till they become mixed in the
womb, and then they inflantly join and produce an embryon or fetus
Similar to the two parents.

Many obje^lions might be adduced to this fanciful theory, I fhall
only mentioii two. Firft, that it is analogous to no known animal
laws. And lecondly, that as thefe fluids, replete v/ith organic par-
ticles derived both from the male and female organs, are fuppofed to
be iimilar ; there is no reafon why the mother fliould not produce a
female embryon without the affiftance of the male, and reahze the
lucina fine concubitu.

IV. 1. I conceive the prlmordium, or rudiment of the embryon,
as fecreted from the blood of the parent, to conlift of a fimple living
filament as a mufcular fibre ; which I fuppofe to be an extremity of a
nerve of loco-motion,, as a fibre of the retina is an extremity of a nerve
of fenfation ; as for inftance one of the fibrils, which compofe the
mouth of an abforbent veflel ; I fuppofe this living filament, of
whatever form it may be, whether, fphere, cube, or cylinder, to be
endued with the capability of being excited into a£lion by certain
kinds of ftimulus. By the ftimulus of the furrounding fluid, in which
it is received from the male, it may bend into a ring; and thus form,
the beginning of a tube. Such moving filaments, and fuch rings,
are defcribed by thofe, who have attended to.microfcoplc animalcula..
This liv.ing ring may now embrace or abforb a nutritive particle of
the fluid, in which it fwims ; and by. drawing it into its pores, or
ioinino' it by compreilion to its extremities, may increafe its own
lenp-th or craflitude ;. and by degrees the living ring may become a

living tube.

2, With this new organization, or accretion of parts, new kinds
of irritability may commence ; for fo long as there was but one living
oy^&n, it could only be fuppofed to poffefs irritabiUty ; fince fenfibility
may be. conceived to bean extenfionof the efFed of irritability over

the

Sect.XXXIX.4. generation. 493

the reft of the fyftem. Thefe new kinds of irritability and of fenfi-
bility in coiifequence of new organization, appear from variety of
facts in the more mature animal ; thus the formation of the teftes,
and confequent fecretion of the femen, occafion the paffion of luftj
the lungs mufb be previoufly formed before their exertions to obtain
frefti air can exift ; the throat or csfophagus muft be formed previous
to the fenfition or appetites of hunger and thirft ; one of which
feems to refide at the upper end, and the other at the lower end of
that canal.

Thus alfo the glans penis, when it is diftended with blood, ac-
quires a new fenfibility, and a new appetency. The fame occurs to
the nipples of the breafts of female animals, when they are diflended
■with blood, they acquire the new appetency of giving milk. So in-
flamed tendons and membranes, and even bones, acquire new fenfa-
tions ; and the parts of mutilated animals, as of wounded fnails, and
polypi, and crabs, are reproduced; and at the fame time acquire fen-
lations adapted to their fituations. Thus when the head of a fnail is
reproduced after decollation with a fliarp rafor, thofe curious telefco-
pic eyes are alfo reproduced, and acquire their fenfibility to light, as
well as their adapted mufcles for retraction on the approach of
injury.

With every new change, therefore, of organic form, or additioa..
of organic parts, I fuppofe a new kind of irritability or of feniibility
to be produced ; fuch varieties of irritability or of fenfibility exift i:i
our adult ftate in the glands ; every one of which is furniflied with an.
irritability, or a tafte, or appetency, and a confequent m.ode of acliou.
peculiar to itlelf.

In this manner I conceive the velTels of the jaws to produce thofe

of the teeth, thofe of the fingers to produce the nails, thofe of the

-ikm to produce the hair; in the fame manner as aftei'wards about the

age of puberty the beard and other great changes in the form of the

body, and dilpoiition of the mind, are-produced in confequence of the

new

■A9\ GENERATION. Sect. XXXIX. 4.

new fecretion of femen ; for if the animal is deprived of this fecretioii
thofe changes do not take place. Thefe changes I conceive to be
formed not by elongation or diftention of primeval ftamina, but by
appofition of parts ; as the mature crab-fifh, when deprived of a limb,
in a certain fpace of time has power to regenerate it ; and the tadpole
puts forth its feet long after its excllifion from the fpawn ; and the
caterpillar in changing into a butterfly acquires a new form, with
new powers, new fenfations, and new defires.

The natural hiiliory of butterflies, aiid moths, and beetles, and
gnats, is full of curlofity ; fome of them pafs many months, and
others even years, in their caterpillar or grub ftate ; they then reft
many weeks without food, fufpended in the air, buried in the earth,
or fubmerfed in water; and change themfelves -during this time into
an animal apparently of a different nature; the ftomachs of fome of
them, Vi'hich before dlgefted vegetable leaves or roots, now only di-
geft honey ; they have acquired wings for the purpofe of feeking this
new food, and a long probofcis to colle£t it from flowers, and 1 fup-
pofe a fenfe of fmell to detedl the fecret places in flowers, where it is
formed. The moths, which fly by night, have a much longer pro-
bofcis rolled up under their chins like a watch fpring ; which they^
extend to colled; the honey from flowers in their fleeping ftate ; when
they are clofed, and the neftaries in confequence more difficult to be
plundered. The beetle kind are furniihed with an external covering
of a hard material to their wings, that they may occaiionally again
make holes in the earth, in which they paffed the former flate of their
exiftence.

But what moft of all diflinguiflies thefe new animals is, that they
are new furnlflied with the powers of reproduilion ; and that they
now differ from each other in fex, which does not appear in their
caterpillar or grub ftate. In fome of them the change from a cater-
pillar into a butterfly or moth feems to be accomplifhed for the fole
pnrpofe of their propagation ; fince they immediately die after this is

finifhed.

S£CT. XXXIX. 4. GENERATION. 495

fitiiflied, and take no food in the interim, as the filk-worm in this
climate ; though it is poffible, it might take honey as food, if it was
prefented to it. For in general it would feem, that food of a more
Simulating kind, the honey of vegetables inftead of their leaves, was
ncceffary for the purpofeof the feminal reproduction of thefe animals,
exadlly fimilar to what happens in vegetables; in thefe the juices of
the earth are fufficient for their purpofe of reproduftion by buds or
bulbs ; in which the new plant feems to be formed by irritative mo-
tions, like the growth of their other parts, as their leaves or roots ;
but for the purpofeof leminal or amatorial reprodu6lion, where fenfa-
tion is required, a more Simulating food becomes neceflluy for the
anther, and ftigma ; and this food is honey ; as explained in Seft. XIII.
on Vegetable Animation.

The gnat and the tadpole referable each other in their change from
natant animals with oriUs into aerial animals with lunos; and in their
change of the ekment in which they live ; and probably of the food,
with which they are fupported ; and laftly, with their acquiring in
their new ftate the difference of fex, and the organs of feminal or ama-
torial reprodudlion. While the polypus, v/ho is their companion in
their former ftate of life, not being allowed to change his form and
element, can only propagate like vegetable buds by the fame kind of
irritative motions, which produces the growth of his own body, with-
out the feminal or amatorial propagation, which requires fenfation ;.
and which in gnats and tadpoles feems to require a change both of
food and of refpiratlon.

From hence I conclude, that with the acquiiition of new parts,
new fenfations, and new defires, as well as new powers, are pro-
duced ; and this by accretion to the old ones, and not by diflention of
them. And finally, that the moft efiential parts of the fyftem, as
the brain for the purpofe of diftributing the power of life, and the
placenta for the purpofe of oxygenating the blood, and the additional
abforbent veffels for the purpofe of acquiring aliment, are firft formed

49^ G E N E R A T I O'N. Sect. XXXIX. 4.

by the in itA'cions above mentioned, and by the pleafureable fenfations
attending thofe irritations, and by the exertions in confequence of
painful fenfations, fimilar to thofe of hunger and fuffocation. After
thefe an apparatus of limbs for future ufes, or for the purpofe of
nioving the body in its prefent natant flate, and of lungs for future
refpiration, and of teftes for future reprodudtion, are formed by the
irritations and fenfations, and confequent exertions of the parts pre-
viouily exifting, and to which the new parts are to be attached.

3. In confirmation of thefe ideas it may be obferved, that all the
parts of the body endeavour to grow, or to make additional parts to
themfelves throughout our lives ; but are reflrained by the parts im-
mediately containing them ; thus, if the fkin be taken away, the
flethy parts beneath foon ihoot out new granulations, called by the
vulgar proud flefli. If the periofteum be removed, a fimilar growth
commences from the bone. Now in the cafe of the imperfect embryon,
the containing or confining parts are not yet fuppofed to be formed,
and hence there is nothing to reflrain its growth.

4. By the parts of the embryon being thus produced by new ap-
pofitions, many phenomena both of anim.al and vegetable produdlions
receive an eatier explanation ; fuch as that many fetufes are deficient
at the extremities, as in a finger or a toe, or in the end of the tongue,
or in v/hat is called a hare-lip with deficiency of the palate. For if
there fiiould be a deficiency in the quantity of the firft nutritive par-
ticles laid up in the egg for the reception of the firft living filaiYient,
the extreme parts, as being laft formed, muft fhew this deficiency by
their being imperfect.

This idea of the growth of the embryon accords alfo with the pro-
duftion of fome monflrous births, which confift of a duplicature of
the limbs, as chickens with four legs ; which conld not occur, if the
fetus was formed by the diflention of an original flamen, or minia-
ture. For if there (hould be a fuperfiuity of the firfl nutritive par-
ticles laid up in the egg for the firii living filament ; it is eafy to con-
5 ceive.

Sect. XXXTX. 4. GENERATION. "497

ceive, that a dupllcature of fome parts may be formed.. And that
fuch fuperPiuous nouriftimeat fometimes exlfts, is evinced by the
double yolks in fome eggs, which I fuppofe were thus formed previ-
ous to their impregnation by the exuberant nutriment of the hen.

This idea is confirmed by the analogy of the monfters in the ve-
getable world alfo ; in which a duplicate or triplicate production of
various parts of the flower is obfervable, as a triple neiflary in fome
columbines, and a triple petal in fome prim.rofes ; and which are fup-
pofed to be produced by abundant nourifiiment.

5. If the embryon be received into a fluid, whofe fl:imulu3 is dif-
ferent in fome degree from the natural, as in the produftion of mule-
animals, the new irritabilities or fenfibilities acquired by the increafing
or growing organized parts may differ, and thence produce parts not
fimilar to the father, but of a kind belonging in part to the mother ;
and thus, though the original flamen or living ens was derived totally
from the father, yet new irritabilities or fenfibilities being excited, a
chano-e of form correfponditig with them will be produced. Nor
could the produdtion of mules exlfl:, if the ftamen or miniature of all
the parts of the embryon is previoufly formed in the male femen, and
is only diftended by nourifliment in the female uterus. Whereas this
difficulty ceafes, if the embryon be fuppofed to confifl: of a living fila-
ment, which acquires or makes new parts with new irritabilities, as
it advances in its o-rowth.

The form, foliditv, and colour, of the particles of nutriment laid
vip for the reception of the firfl: living filament, as well as their pecu-
liar kind of ftimulus, may contribute to produce a difference in the
form, folidity, and colour of the fetus, fo as to refemble the mother,
as it advances in life. This alfb may efpecially happen during the
flrfl flate of the exiflence of the embryon, before it has acquired or-
gans, which can change thefe firfl nutritive particles, as explained in
No. 5. 2. of this Sedion. And as thefe nutritive particles are fup-

3 S' ' pofed

498 GENERATION. Sect. XXXIX. 4.

pofed to be fimilar to thofe, which are formed for her own nutrition,
it follows that the fetus fliould fo far refemble the mother.

This explains, why hereditary difeafes may be derived either from
the male or female parent, as well as the peculiar form of either of
their bodies. Some of thefe hereditary difeafes are limply owing to a
deficient aftivity of a part of thefyftem, as of the abforbent veffels,
which open into the cells or cavities of the body, and thus occafion
dropfies. Others are at the fame time owing to an increafe of fenfa-
tion, as in fcrophula and confumption ; in thefe the obftruftion of the
fluids is firft caufed by the inirritability of the veflels, and the inflam-
mation and ulcers which fucceed, are caufed by the confequent in-
creafe of fenfation in the obftru6led part. Other hereditary difeafes,
as the epilepfy, and other convulfions, confift in too great voluntary
exertions in confequence of difagreeable fenfation in fome particular
difeafed part. Now as the pains, which occafion thefe convulfions,
are owing to defed of the a£lion of the difeafed part, as fliewn ia
Se6l. XXXIV. it is plain, that all thefe hereditary difeafes may have
their origin either from defedive irritability derived from the father,
or from deficiency of the ilimulus of the nutriment derived from the
mother. In cither cafe the effefl would be fimilar; as a fcrophulous
race is frequently produced among the poor from the deficient ftimu<-
lus of bad diet, or of hunger ; and among the rich, by a deficient ir-
ritability from their having been long accuftomed to. too great ftimulus,
as of vinous fpirit.

6. From this account of reprodudion it appears, that all animals
have a fimilar origin, viz. from a fingle living filament ; and that the
difference of their fornrts and. qualities has arifen only from the dif-
ferent irritabilities and fenfibilities, or voluntarities, or affociabilities,
of this original living filament ; and perhaps in fome degree from the
different forms of the particles of the fluids, by which it has been at
firft Simulated into activity. And that from hence, as Linnaeus has

conjedured

Sect. XXXIX. 4. GENERATION. 499

conjeflured ia refpedt to the vegetable world, it is not impoflible,
but the great variety of fpecies of animals, which now tenant the
earth, may have had their origin from the mixture of a few natural
orders. And that thofe animal and vegetable mules, which could
continue their fpecies, have done fo, and conftitute the numerous
families of animals and vegetables which now exilt ; and that thole
mules, which were produced with imperfeft organs of generation,
periflied without reproduAion, according to the oblervation of Arl-
i^otle ; and are the animals, which we now call mules. See Botanic
Garden, Part II. Note on Dianthus.

Such a promifcuous intercourfe of animals is faid to exift at this
day in New South Wales by Captain Hunter. And that not only
amongft the quadrupeds and birds of different kinds, but even amongft
tlie nili, and, as he believes, amongft the vegetables. He Ipeaks of
an animal between the opoffum and the kangaroo, from the (ize of a
flieep to that of a rat. Many fifli feemed to partake of the fhark ;
ibme with a Ikait's head and Ihoulders, and the hind part of a Ihark ;
others with a fl-iark's head and the body of a mullet ; and fome with a
fliark's head and the flat body of a fting-ray. Many birds partake of
the parrot ; fome have the head, neck, and bill of a parrot, with
long ftraight feet and legs ; others with legs and feet of a parrot, with
head and neck of a fea-guU. Voyage to South Wales by Captain John
Hunter, p. 68.

7. All animals therefore, I contend, have a fimilar caufe of their
organization, originating from a fingle living filament, endued indeed
with different kinds of irritabilities and fenfibilities, or of animal ap-
petencies ; which exift in every gland, and in every moving organ of
the body, and are as effential to living organization as chemical affini-
ties are to certain combinations of inanimate matter.

If I might be indulged to make a fimile in a philofophical work, I
fhould fay, that the animal appetencies are not only perhaps lefs nu-
merous originally than the chemical affinities ; but that like thefe lat«

3 S 2 ter.

5PO GENERATION. Sect. XXXIX. 4,

ter, they change with every new combination ; thus vital air and
azote, when combined, produce nitrous acid ; which now acquires
the property of diffolving filver ; fo with every new additional part to
the embryon, as of the throat or lungs, I fuppofe a new animal ap-
petency to be produced.

■ In this early formation of the embryon from the irritabilities, fen-
fibilities, and affociabilities, and confequent appetencies, the faculty
of volition can fcarcely be fuppofed to have had its birth. For about
what can the fetus deliberate, when it has no choice of objefls ? But
in the more advanced ftate of the fetus, it evidently pofleffes volition ;
as it frequently changes its attitude, though it feems to deep the
greateft part of its time ; and aftervv'ards the power of volition con-
tributes to change or alter many parts of the body during its grov^^th
to manhood, by our early modes of exertion in the various depart-
ments of life. All thefe faculties then conftitute the vis fabricatrix,
and the vis confervatrix, as well as the vis medicatrix of nature, fo
much fpoken of, but fo little underftood by philofophers.

S. When we revolve in our minds, firft, the great changes, which
we fee naturally produced in animals after their nativity, as in the
produftion, of the butterfly with painted wings from the crawling ca-
terpillar ; or of the refpiring frog from the fubnatant tadpole ; from
the feminine boy to the bearded man, and from the infant girl to the
,k£l:efcent woman ; both which changes may be prevented by certain
mutilations of the glands neceflary to reproduftion.

Secondly, when we think over the great changes introduced into
various animals by artificial or accidental cultivation, as in horfes,
which we have exercifed for the different purpofes of ftrength or
fwiftnefs, in carrying burthens or in running races ; or in dogs,
which haye been cultivated for ftrength and courage, as the bull-dog;
or for acutenefs of his fenfe of fmell, as the hound and fpaniel ; or for
the fwiftnefs of his foot, as the greyhoand ; or for his fwimming in
the water, or for drawing fnow-fledges, as the rough-haired dogs of
2 the

Sect. XXXIX. 4. GENERATION. 501

the north ; or laftly, as a play-dog for children, as the lap-dog ; with
the changes of the forms of the cattle, which have been domefticated
from the greateft antiquity, as camels, and fheep ; which have un-
dergone fo total a transformation, that we are now ignorant from
what fpecies of wild animals they had their origin. Add to thefe the
great changes of fhape and colour, which we daily fee produced in-
fmaller animals from our domeftication of them, as rabbits, or pid-
geons ; or from the difference of climates and even of feafons ; thus
the fheep of warm climates are covered with hair inftead of wool ;
and the hares and partridges of the latitudes, which are long buried in
fnow, become white during the winter months ; add to thefe the
various changes produced in the forms of mankind, by their early
modes of exertion ; or by the difeafes occafioned by their habits of
life ; both of which became hereditary, and that through many ge-
nerations. Thofe who labour at the anvil, the oar, or the loom, as
well as thofe who carry fedan-chairs, or who have been educated to
dance upon the rope, are diftinguifliable by the fhape of their limbs ;
and the difeafes occafioned by intoxication deform the countenance
with leprous eruptions, or the body with tumid vifcera, or the joints-
with knots and diflortions.

Thirdly, when we enumerate the great changes produced in the
fpecies of animals before their nativity j thefe are fuch as refemble
the form or colour of their parents, which- have been altered by the
cultivation or accidents above related, and are thus continued to their
pofterity. Or they are changes produced by the mixture of fpecies as
in mules ; or changes produced probably by the exuberance of nou-
rifliment fupplied to the fetus, as in monftrous births with additional
limbs ; many of thefe enormities of fhape are propagated, and conti-
nued as a variety at lead, if not as a new fpecies of animal. I have
feen a breed of cats with an additional claw on every foot ; of poultry
alfo with an additional claw, and with wings to their feet; and of
others without rumps. Mr. Buffon mentions a breed of dogs without

tailsj.

502 GENERATION. Sect*. XXXIX 4.

tails, which are common at Rome and at Naples, which he fuppofes
to have been produced hy a cuftom long efrabliflied of cutting theif
tails clofe off. There are many kinds of pidgeons, admired for their
peculiarities, which are monfters thus produced and propagated. And
to thefe mud be added, the changes produced by the imagination of
the male parent, as will be treated of more at large in No. VI. of this
Section.

When we confider all thefe changes of animal form, and innumer-
able others, which may be colle6ted from the books of natural hiftory ;
we cannot but be convincedj that the fetus or embryon is formed by
appolition of new parts, and not by the diftention of a primordial neft
of germs, included one within another, like the cups of a conjurer.

Fourthly, when we revolve in our minds the great fimilarity of
flrufture, which obtains in all the warm-blooded animals, as well
quadrupeds, birds, and amphibious animals, as in mankind ; from the
moufe and bat to the elephant and whale ; one is led to conclude, that
they have alike been produced from a fimilar living filament. In feme
this filament in its advance to maturity has acquired hands and fingers,
with a fine fenfe of touch, as in mankind. In others it has acquired claws
or talons, as in tygers and eagles. In others, toes with an intervening
web, or membrane, as in feals and geefe. In others It has acquired
cloven hoofs, as in cows and fwine ; and whole hoofs in others, as
in the horfe. While in the bird kind this original living filament has
put forth v^'ings inflead of arms or legs, and feathers inflead of hair.
In fome it has protruded horns on the forehead inflead of teeth in the
fore part of the upper jaw ; in others tuflies inftead of horns ; and in
others beaks inftead of either. And all this exactly as is daily feen in
the tranfmutations of the tadpole, which acquires legs and lungs,
when he wants them ; and lofes his tail, when it is no longer of fer-
vice to him.

Fifthly, from their firft rudiment, or primordium, to the termi-
nation of their lives, all animals undergo perpetual transformations ;

which

Sect. XXXIX. 4. GENERATION. 503

which ai'e in part produced by their own exertions in confcquence of
their defires and averfions, of their pleafures and their pains, or of ir-
ritations, or of affociations ; and many of thefe acquired forms or pro-
penfities are tranfmitted to their pofterity. See Sed. XXXI. i.

As air and water are fupplied to animals in fufficient profufion, thj
three great objeils of dcfire, which have changed the forms of many
animals by their exertions to gratify them, are thofe of luft, hunger,
and fecurity. A great want of one part of the animal world has con-
fined in the defire of the exclufive poflefiion of the females ; and thefs
have acquired weapons to combat each other for this purpofe, as the
very thick, fhield-like, horny Ikin on the fhoulder of the boar is a de-
fence only againffc animals of his own fpecies,. who ftrike obliquely
■upwards, nor are his tuflies for other purpofes, except to defend him-
felf, as he is not naturally a carnivorous aninaal. So the horns of ths
Sag are (harp- to offend his adverfary, but are branched for the pur-
pofe of parrying or receiving the thrufts of horns fimilar to his own»
and have therefore been formed for the purpofe of combating other
flags for the exclufive pofleffion of the females ; v-^ho are obferved',
like the ladies in the times of chivalry^ to attend the car of ths
victor.

The birds, which do not carry food to their young, and do not
therefore marry, are armed with fpurs for the pxirpofe of fighting for
the exclufive pofleffion of the females, as cocks and quails. It is cer-
tain that thefe weapons are not provided for their defence againft other
adverfaries, becaufe the females of thefe fpecies are without this ar-
mour. The final caufe of this conteft amongft the males feems to be,
that the flrongeft and mofl aftive animal fhould propagate the fpeciesj,,
which fhould thence become improved.

Another great want confiftsin the means of procuring food, which
has- diverfified the forms of all fpecies of animals. Thus the nofe of
the fwine has become, hard for the purpofe of turning up the foil in

fearch-,

504 GENERATION. Sect. XXXIX. 4.

fearch of infe£ts and of roots. The trunk of the elephant is an elonga-
tion of the nofe for the purpofe of pulling down the branches of trees
for his food, and for taking up water without bending his knees.
Beafts of prey have acquired ftrong jaws or talons. Cattle have ac-
quired a rough tongue and a rough palate to pull off the blades of grafs,
as cows and flieep. Some birds have acquired harder beaks to crack
nuts, as the parrot. Others have acquired beaks adapted to break the
harder feeds, as fparrows. Others for the fofter feeds of flowers, or
the buds of trees, as the finches. Other birds have acquired long
beaks to penetrate the moifter foils in fearch of infefts or roots, as
woodcocks J and others broad ones to filtrate the water of lakes, and
to retain aquatic infedts. All which feem to have been gradually pro-
duced during many generations by the perpetual endeavour of the crea-
tures to fupply the want of lood, and to have been delivered to their
pofterity with couftant improvement of them for the purpofes re-
quired.

The third great want amongft animals is that of fecurity, which
feems much to have diverfified the forms of their bodies and the colour
of them; thefe confift in the means of efcaping other animals more
powerful than themfelves. Hence fome animals have acquired wings
inftead of legs, as the fmaller birds, for the purpofe of efcape. Others
great length of fin, or of membrane, as the flying fiih, and the bat.
Others great fwiftnefs of foot, as the hare. Others have acquired
hard or armed {hells, as the tortoife and the echinus marinus.

The contrivances for the purpofes of fecurity extend even to ve-
getables, as is feen. in the wonderful and various means of their con-
cealing or defending their honey from infedls, and their feeds from
birds. On the other hand fwiftnefs of wing has been acquired by
hawks and fwallows to purfue their prey ; and a probofcis of admirable
flrufture has been acquired by the bee, the moth, and the humming
bird, for the purpofe of plundering the nectaries of flowers. All

which

Sect. XXXIX. 4. GENERATION. 505

which feem to have been formed by the original living filament, ex-
cited into action by the neceffities of the creatures, which poffefs
them, and on which their exiftence depends.

From thus meditating on the great fimilarity of the flrudlure of the
warm-blooded animals, and at the fame time of the great changes they
undergo both before and after their nativity; and by confidering in
how minute a portion of time many of the changes of animals above
defcribed have been produced ; would it be too bold to imagine, that
in the great length of time, fince the earth began to exift, perhaps
miUions of ages before the commencement of the hiftory of mankind,
would it be too bold to imagine, that all warm-blooded animals have
arifen from one living filament, which the gb.eat First Cause
endued with animality, \vith the power of acquiring new parts, at-
tended with new propenfities, diredled by irritations, fenfations, vo-
litions, and aflbciations ; and thus poffeffing the faculty of continuing
to improve by its own inherent activity, and of delivering down
thofe improvements by generation to its pofterity, world without
end !

Sixthly, The cold-blooded animals, as the fifh-tribes, which are
furnifhed with but one ventricle of the heart, and with 2:ills inftead
of lungs, and with fins inftead of feet or wings, bear a great fimila-
rity to each other ; but they diiter, neverthelefs, fo much in their
general flruilure from the warm-blooded animals, that it may not
feem probable at firft view, that the fame living filament could have
given origin to this kingdom of animals, as to the former. Yet are
there fome creatures, which unite or partake of both thefe orders of
animation, as the whales and feals ; and more particularly the fros:,
who changes from an aquatic animal furnifhed with gills to an aerial
one furnifhed with lunsis.

The numerous tribes of infects without wings, from the fpider to
the fcorpion, from the flea to the lobfter ; or with wings, from the
gnat and the ant to the wafp and the dragon-fly, differ fo totally from

^ T each

5o6 GENERATION. Sect. XXXIX. 4,

eaeh other, and from the red-blooded claffes above defcribed, both in
the forms of their bodies, and their modes of hfe ; befides the organ
of fenfe, which they feem to pofiefs in their antennae or horns, to
M'hich it has been thought by fome naturaUfts, that other creatures
have nothing fimilar ; that it can fcarcely be fuppofed that this na-
tion of animals could have been produced by the fame kind of living
filament, as the red-blooded clafles above mentioned. And yet the
changes which many of them undergo in their early ftate to that of
their maturity, are as different, as one animal can be from another.
As thofe of the gnat, which paffes his early ftate in water, and then
ftretching out his new wings, and expanding his new lungs, rifes in
the air J as of the caterpillar, and bee-nymph, which feed on ve-
getable leaves or farina, and at length burfting from their felf-formed
graves, become beautiful winged inhabitants of the Ikies, journey-
ing from flower to flower, and nourifhed by the ambrofial food of
honey.

There is ftill another clafs of animals, which are termed vermes
by Linnaeus, which are without feet, or brain, and are hermaphro-
dites, as worms, leeches, fnails, fhell-fi(h, coralline infeds, and
fponges ; which polTefs the fimpleft ftrufture of all animals, and ap-
pear totally different from thofe already defcribed. The fimplicity
of their ftru£lure, however, can afford no argument againft their
having been produced from a living filament as above contended.

Laft; of all the various tribes of vegetables are to be enumerated
amongil: the inferior orders of animals. Of thefe the anthers and
itigmas have already been ftiewn to poiTefs fome organs of fenfe, to be
nourifhed by honey, and to have the power of generation like infedls,
and have thence been announced amongfl the animal kingdom in
Seft. XIII. and to thefe mufl be added the buds and bulbs which con-
flitute the viviparous offspring of vegetation. The former I fuppofe
to be beholden to a fingle living filament for their feminal or amato-
Tval procreation ; and the latter to the fame caufe for their lateral or

branching

Sect. XXXIX. 4. GENERATION. 507

branching generation, which they poffefs in common with the poly-
pus, tsnia, and volvox ; and the fimplicity of which is an argument
in favour of the fimilarity of its caufe.

Linn^us fuppofes, in the Introdudion to his Natural Orders, that
very few vegetables were at firft created, and that their numbers
were increafed by their intermarriages, and adds, fuadent hsec Crea-
toris leges a fimplicibus ad compofita. Many other changes feem to
have arifen in them by their perpetual conteft for light and air above
ground, and for food or moifture beneath the foil. As noted in Bo-
tanic Garden, Part II. Note on Cufcuta. Other changes of veo-e-
tables from climate, or other caufes, are remarked in the Note on
Curcuma in the fame work. From thefe one might be led to ima-
gine, that each plant at firfl: confifted of a fingle bulb or flower to
each root, as the gentianella and daify ; and that in the conteft for air
and light new buds grew on the old decaying flower ftem, fhootino-
down their elongated roots to the ground, and that in procefs of ao-es
tall trees were thus formed, and an individual bulb became a fwarm
of vegetables. Other plants, which in this conteft for light and air
were too flender to rife by their own ftrength, learned by deo-rees to
adhere to their neighbours, either by putting forth roots like the ivy,
or by tendrils hke the vine, or by fpiral contortions like the honey-
fuckle ; or by growing upon them like the mifleto, and taking nou-
riftiment from their barks ; or by only lodging or adhering on them,
and deriving nourifhment from the air, as tillandlia.

Shall we then fay that the vegetable living filament was originally
different from that of each tribe of animals above defcribed ? And that
the produdive living filament of each of thofe tribes was difi^erent ori-
ginally from the other ? Or, as the earth and ocean were probably
peopled with vegetable produftions long before the exiftence of ani-
mals ; and many families of thefe animals long before other families
of them, fhall we conjefture, that one and the fame kind of living
filaments is and has been the caufe of all organic life ?

3 T 2 This

5o8 GENERATION. Sect.XXXIX. 4.

This idea of the gradual formation and improvement of the animal
world accords with the obfervations of feme modern philofophers,
who have fuppofed that the continent of America has been raifed out
of the ocean at a later period of time than the other three quarters of
the globe, which they deduce from the greater comparative heights
of its mountains, and the confequent greater coldnefs of its refpeftive
climates, and from the lefs fize and ftrength of its animals, as the
tygers and allegatbrs compared with thole of Afia or Africa. And
laftly, from the lefs progrefs in the improvements of the mind of its
inhabitants in refpeft to voluntary exertions.

This idea of the gradual formation and improvement of the animal
world feems not to have been unknown to the ancient philofophers.
Plato having probably obferved the reciprocal generation of inferior
animals, as fnails and worms, was of opinion, that mankind with all
other animals were originally hermaphrodites during the infancy of
the world, and were in proceis of time feparated into male and female.
The breafts and teats of all male quadrupeds, to which no ufe can
be now affigned, adds perhaps fome fhadow of probability to this opi-
nion. Linnaeus excepts the horfe from the male quadrupeds, who
have teats ; which might have fhewn the earlier origin of his ex-
iftence ; but Mr. T. Hunter afferts, that he has difcovered the vef-
tises of them on his flieath, and has at the fame time enriched natural
hiftory with a very curious faft concerning the male ptdgeon ; at the
time of hatching the eggs both the male and female pidgeon undergo
a great change in their crops ; which thicken and become corrugated,
and fecrete a kind of milky fluid, which coagulates, and with which
alone they for a few days feed their young, and afterwards feed them
with this coagulated fluid mixed with other food. How this refem-
bles the breafts of female quadrupeds after the production of their
young ! and how extraordinary, that the male Ihould at this time
give milk as well as the female ! See Botanic Garden, Part II. Note
on Curcuma,

The

Sect. XXXIX. 5. GENERATION. 509

The late Mr. David Hume, in his pofthumous works, places the
powers of generation much above thofc of our boafted reafon ; and
adda, that reafon can only make a machine, as a clock or a (hip, but
the power of generation makes the maker of the machine ; and pro-
bably from having obferved, that the greateft part of the earth has
been formed out of organic reci'ements ; as the immenfe beds of lime-
flone, chalk, marble, from the (hells of fifh ; and the extenfive pro-
vinces of clay, fandltone, ironflone, coals, from decompofed ve-
getables ; all which have been firft produced by generation, or by the
lecretions of organic life ; he concludes, that the world itfelf might
have been generated, rather than created ; that is, it might have been
gradually produced from very fmall beginnings, increafi'ng by the ac-
tivity of its inherent principles, rather than by a fudden evolution of
the whole by the Almighty fiat. — What a magnificent idea of the in-
finite power of the Great Architect ! The Cause of Causes !
Parent of Parents ! Ens Entium ! . ,

For if we may compare infinities, it would feem to require a
greater infinity of power to caufe the caufes of effects, than to caufe
the effeds themfelves. This idea is analogous to the improving ex-
cellence obfervable in every part of the creation ; fuch as in the pro-
greffive increafe of the folid or habitable parts of the earth from water ;
and in the progreflive increafe of the wifdom and happinefs of its in-
habitants ; and is confonant to the idea of our prefent fituation being
a ftate of probation, which by our exertions we may improve, and are
confequently refponfible for our adlions.

V. I. The efficient caufe of the various colours of the egsfs of
birds, and of the hair and feathers of animals, is a fubje£l fo curious,
that I fhall beg to introduce it in this place. The colours of many
animals feem adapted to their purpofes of concealing themfelves either
to avoid danger, or to fpring upon their prey. Thus the fnake and
wild cat, and leopard, are fo. coloured as to referable dark leaves and
their lighter interfaces ; birds refemble the colour of the browa

ground.

5IO GENERATION. Sect.XXXIX. 5.

ground, or the green hedges, which they frequent ; and moths and
butterflies are coloured like the flowers which they rob of their honey.
Many iailauces are mentioned of this kind in Botanic Garden, p. 2.
Note on Rubia.

Thefe colours have, however, in fome inftances another ufe, as
the black diverging area from the eyes of the fwan j which, as his
eyes are placed leis prominent than thofe of other birds, for the con-
venience of putting down his head under water, prevents the rays of
light from being reflefted into his eye, and thus dazzling his fight,
both in air and beneath the water ; which muft have happened, if that
furface had been white like the reft of his feathers.

There is a ftill more wonderful thing concerning thefe colours
adapted to the purpofe of concealment ; which is, that the eggs of
birds are fo coloured as to refemble the colour of the adjacent objefts
and their interftices. The eggs of hedge-birds are greenifli with dark
fpots ; thofe of crows and magpies, which are feen from beneath
through wicker nefts, are white with dark fpots ; and thofe of larks
and partridges are ruffet or brown, like their nefts or fituations.

A thing ftill more aftonhhing is, that many animals in countries
covered with fnow become white in winter, and are faid to change
their colour again in the warmer months, as bears, hares, and par-
trido-es. Our domefticated animals lofe their natural colours, and
break into great variety, as horfes, dogs, pidgeons. The final
caufe of thefe colours is eafily underftood, as they ferve fome purpofes
of the animal, but the efficient caufe would feem almoft beyond con-
jedlure.

Firft, the choroid coat of the eye, on which the femitranfparent
retina is expanded, is of different colour in different animals j in thofe
which feed on grafs it is green ; from hence there v/ould appear fome
connexion between the colour of the choroid coat and of that con-
ftantly painted on the retina by the green grafs. Now, when the
fround becomes covered with fnow, it would feem, that that adion

Sect. XXXIX. 5. GENERATION. 511

of the retina, which is called whitenefs, being conftantly excited in
the eye, may be gradually imitated by the extremities of the nerves
of touch, or rete mucofum of the Ikin. And if it be fuppofed, that
the a£lion of the retina in producing the perception of any colour con-
fifts in fo difpofing its own fibres or furface, as to refit 61 thofe colour-
ed rays only, and tranfmit the others like foap-bubbles ; then that
part of the retina, which gives us the perception of fnow, muft at
that time be white ; and that which gives us the perception of grafs,
mufl: be green.

Then if by the laws of imitation, as explained in Se(Elion XII. 33,
and XXXIX. 6. the extremities of the nerves of touch in the rete
mucofum be induced into fimilar action, the Ikin or feathers, or hair,
may in like manner fo difpofe their extreme fibres, as to refle£l white;
for it is evident, that all thefe parts were originally obedient to irrita-
tive motions during their growth, and probably continue to be fo ;
that thofe irritative motions are not liable in a healthy ftate to be fuc-
ceeded by fenfation ; which however .is no uncommon thing in their
difeafed ftate, or in their infant ftate, as in plica polonica, and in very
young pen-feathers, which are ftill full of blood.

It was (hewn in Section XV. on the Produftion of Ideas, that the
moving organ of {enfe in fome circumftances refembled the objedt
which produced that motion. Hence it may be conceived, that the
rete mucofum, which is the extremity of the nerves of touch, may
by imitating the motions of the retina become coloured. And thus,
like the fable of the camelion, all animals may poffefs a tendency to
be coloured fomewhat like the colours they moft frequently infpect,
and finally, that colours may be thus given to the egg-fhell by the
imagination of the female parent ; which fhell is previouily a mucous
membrane, indued with irritability, without which it could not cir-
culate its fluids, and increafe in its bulk. Nor is this more wonder-
ful than that a fingle idea of imagination fhould in an inftant colour
the whole furface of the body of a bright fcarlet, as in the blu{h of

ill a me.

512 GENERATION. Sect. XXXIX. 5,

fliame, though by a very different procefs. In this intricate fubjeit
nothing- but loofe analogical conjeftures can be had, which may how-
ever lead to future difcoveries ; but certain it is that both the change
of the colour of animals to white in the winters of fnowy coun-
tries, and the fpots on birds eggs, muft have fome efficient caufe ;
fince the uniformity of their produdlion fhews it cannot arife from a
fortuitous concurrence of circumftances; and how is this efficient
caufe to be deteded, or explained, but from its analogy to other ani-
mal facts ?

2. The nutriment fupplied by the female parent in viviparous ani-
mals to their young progeny may be divided into three kinds, corre-
fponding with the age of the new creature, i. The nutriment con-
tained in the ovum as previoufly prepared for the embryon in the
ovary. 2. The liquor amnii prepared for the fetus in the uterus,
and in which it fwims ; and laftly, the milk prepared in the pe<5loral
glands for the new-born child. There is reafon to conclude that
variety of changes may be produced in the new animal from all thefe
fources of nutriment, but particularly from the firft of them.

The organs of digeftion and of fanguification in adults, and after-
wards thofe of fecretion, prepare or feparate the particles proper for
iiouriftiment from other combinations of matter, or recombine them
into new kinds of matter, proper to excite into adlion the filaments,
which abforb or attradl them by animal appetency. In this procefs
we muft attend not only to the a£tion of the living filament which
receives a nutritive particle to its bofom, but alfo to the kind of par-
ticle, in refpeft to form, or fize, or colour, or hardnefs, which is
thus previoufly prepared for it by digeftion, fanguification, and fecre-
tion. Now as the firfi: filament of entity cannot be furnifhed with
the preparative organs above mentioned, the nutritive particles, which
are at firft to be received by it, are prepared by the mother ; and de-
pofited in the ovum ready for its reception. Thefe nutritive particles
muft be fuppofed to di^er in fome refpefts, when thus prepared by
different animals. They may differ in fize, folidity, colour, and form ;

and

Sect. XXXIX. 5- GENERATION. s'3

and yet may be fufficiently congenial to the living filament, to Vv-hidi
they are applied, as to excite its activity by their flimulus, and its ani-
mal appetency to receive them, and to combine them with itfclfiijio
■organization. '" ^ •"

'By this firft nutriment thus prepared for the embryou-is not meant
the liquor amnii, which is produced afterwards, nor the larger exte-
rior parts of the white of the egg; but the fluid prepared, 1 fuppoie,
in the ovary of viviparous animals, and that which immediately fur-
rounds the cicatricula of an impregnated egar, and is vifible to the eve
in a boiled one.

Now thefe ultimate particles of animal matter prepared by the
glands of the mother may be fuppofed to refemble the fimiilar ultimate
particlei, which were prepared for her own nourifliment ; that is, to
the ultimate particles of which her ewn organization confifls. And
that hence when thefe become combined with a new embryon, which
in its early ftate is not furniflied with ftomach, or glands, to alter
them ; that new embryon will bear fome refemblance to 'th-e
mother.

This feeras to be the origin of the compound forms of mules.,
which evidently partake of both parents, but principally of the
male parent. In this produ6lion of chimeras the antients feem to
have indulged their fancies, whence the'fphinxes, griffins, dragons,
centaurs, and minotaurs, which are ^vanifhe'd from . modern cre-
dulity.

It would feem, that in Ihefe tinnafural conjunftions, v/hen the
nutriment depofited by the female was fo ill adapted to ftimulate the
living filament derived from the male into adtion, and to be received,
or embraced by it, and combined with it into organization, as not to
produce the organs neceffary to life, as the brain, or heart, or flo-
mach, that no mule was prodxiced. Where all the parts neceffary to
.life in thefe compound animals were formed fufficiently perfe(3:, ex-

3 U cept

514 GENERATION. Sect. XXXIX. 5.

cept the parts of generation, thofe animals were produced, which are
HOW called mules.

The formation of the organs of fexual generation, in contradiftinc-
tion to that by lateral buds, in vegetables, and in fome animals, as
the polypus, the taenia, and the volvox, feems the chef d'oeuvre, the
mafter-piece of nature ; as appears from many flying iafeas, as in
moths and butterflies, who feem to undergo a general change of their
forms folely for the purpofe of fexual reprodudtion, and in all other
animals this organ is not complete till the maturity of the creature.
Whence .it happens that, in the copulation of animals of different
fpecies, the parts neceffary to life are frequently completely formed ;
but thofe for the purpofe of generation are dsfeftive, as requiring a
nicer organization ; or more exadl coincidence of the particles of nu-
triment to the irritabilities or appetencies of the original living fila-
ment. Whereas thofe mules, where all the parts couH be perfedllj
formed, may have been produced in early periods of time, and may
have added to the numbers of our various fpecies of animals, as before
obferved.

As this production of mules is a conftant effe£t from the conjunc-
tion of different fpecies of animals, thofe between the horfe and the-
female afs always refembling the horfe more than the afs ; and thofe,.
on the contrary, between the male afs and the mare, always refem-
blino- the afs more than the mare ; it cannot be afcribed to the ima-
•^ination of the male animal which cannot be fuppofed to operate Co
uniformly ; but to the form of the firfl nutritive particles, and t>
their peculiar flimulus exciting the living filament to feledl and com-
bine them with itfelf. There is a fimilar uniformity of effed in re-
fpeft to the colour of the progeny produced between a white man,
and a black woman, which, if I am well informed, is always of the
mulatto kii:id, or a mixture of the two; which may perhaps be im-
puted to the peculiar form of the particles of nutriment fupplied to the
embryon by the mother at the early period of its exigence, and their

peculiar

Sect. XXXIX. 5. GENERATION. 515

peculiar ftimulus ; as this efFed, like that of the mule progeny above
treated of, is uniform and confident, and cannot therefore be afcribed
to the imagination of either of the parents.

When the embryon has produced a placenta, and furnifihed itfelf
with veffels for feleftion of nutritious particles, and for ox^'^genatioa
of them, no great change in its form or colour is likely to be pro-
duced by the particles of faflenance it now takes from the fluid, in
which it is immerfed ; becaufe it has now acquired organs to alter or
new combine them. Hence it continues to grow, whether this fluid,
in which it fwims, be formed by the uterus or by any other cavity of
the body, as in extra- uterine geftation; and which would feem to be
produced by the ftimulus of the fetus on the fides of the cavity,
where it is found, as mentioned before. And thirdly, there is ftill
lefs reafon to expedl any unnatural change to happen to the child after
its birth from the difference of the milk it now takes ; becaufe it has
acquired a ftomach, and lungs, and glands, of fufHcient power to
decompofe and recombine the milk ; and thus to prepare from it the
various kinds of nutritious particles, which the appetencies of the va-
rious fibrils or nerves may require.

From all this reafoning I would conclude, that though the imagi-
nation of the female may bs fuppofed to affeft the embryon by pro-
ducing a difference in its early nutriment ; yet that no fuch power
■can effesft it after it has obtained a placenta, and other organs ; which
may feledl or change the food, which, is prefented to it either in the
liquor amnii, or in the milk. Now as the eggs in pullets, like the
feeds in vegetables, are produced gradually, long before they are im-
pregnated^ it does not appear how any fudden effeft of imagination of
the mother at the time of impregnation can produce any confiderable
change in the nutriment already thus laid up for the expefted or de-
fired embryon. And that hence any changes of the embryon, except
thofe uniform ones in the produftion of mules and mulattocs, more
probably depend on the imagination of the male parent. At the fame

3 U 2 «. time

5 1 6 GENERATION. Sect. XXXlX. 6;

time it feems manifeft, that thofe moriftrous births, which confifl m
fome deficiencies only, or fome redund'aneies- of parts, originate from
the deficiency or redundance of the firft nutriment prepared in the-
ovary, or in the part of the egg immediately furrounding. the cicatri-
cula, as defcribed above ; and which continues fome time to excite the-
firfV living filament into adtien, after the fimple animal is completed;,
. or ceafes to- excite it, before the complete form is accomplidied. The
former of thefe eircumftances is evinced- bsy the eggs with double,
^yolks, which, frequently happen to our domeflicated' poultry,, and-
which, I believe, are fo formed before impregnatioii,-but which would;
be well worth attending to, both before and after impregnation; as-
it is probable, fomething valuable on this fubje£l might be learnt from-
them. The latter circumfi:anee,-.or that of deficiency of origirial nn-^
triment, may be deduced from reverfe analogy.

There are^ however, other kinds of monft'fous births^ which ?
neither depend on deficiency of parts, nor fupernumerary ones ; nor.
are owing to the conjundtionofanimals of different fpecies ; but whichcj
appear to be new conformations, or new difpofitions of parts in refpefi:
to each other, and which, like the variation of colours and forms o£
our domefticated animals, and probably the fexual parts of all animals,
may depend on the imagination of the male parent, which we. now-
come to confider.-

VI. I. The nice a(£tions of the extremities of our various glands.-
are exhibited in their various productions, which are believed to be;
made by the gland,, and not previoufly tx» exifl as fuch in the blood..
Thus the glands, which' conftitute the liver, make bile ; thofe of the'
ftomach make gaflric acid ; thofe beneath; the jaw, faliva ; thofe of
the ears, ear-wax; and the like. Every kind of gland muft pofTefs a.
peculiar irritability, and probably a fenfibility, at the early ftate of its.
exiftence ; and muft be furnifhed with a nerve of fenfe,.or of motion,,
to perceive, and to fele£t, and to combine the particles, which com-
pofe the fluid it fecretes. And this nerve of fenfe which perceives

th6

S2CT. XXX-IX. 6. GENERATION. 517

the different articles which compofe the blood, mull at lead be con-
ceived to be as fine and fubtile an organ, as the optic or auditory nerve,
which perceive light or found. See Soft. XIV. 9.

But in nothing; is this nice a£lion of the extremities of the blood'
veflels fo wonderful, as in the produ6lion of contagious matter. A
fmall drop of variolous contagion difflifed in the blood, or perhaps only
by being inferted beneath the cuticle, after a time, (as about a quar-
ter of a lunation,) excites the extreme veflels of the Ikin into certain
motions, which produce a fimilar contagious material, filling with it.
a thoufand puilides. So that by irritation, or by fen fat ion in confe-
quence of irritation, or by aflbciation of motions, a material is formed"
by the extremities of certain cutaneous veflels, cxadtly fimilar to the
flimulating.material, which caufed the irritation, or confequent fen-
fation, or- aflbciation.

Many glands of the. body have their motions, and in. confequence
their fecreted fluids, affefted by pleafurable or painful ideas, fince they,
are ia- many inftances influenced by fenfitive aflbciations, as well as by
the irritations of the particles of the pafling blood.. Thus the idea of
meat, excited in the minds of hungry dogs, by their fen fe of vlfion,
or of fmell, increafes the difcharge of faliva, both in quantity and vif-
cidity ; as is feen in its hanging down, in threads from their mouths^ ,
as they ftand round a dinner-table. The fenfations of pleafure, or of
pain, of peculiar kinds, excite in the fame manner, a greaLdifcharge of
tears ;.. which appear alfo to be. more faline at the time of their fecre-
tion, from their inflaming the eyes and eye-lids. The palenefs from
fear, aad the blufli of fliame, and of joy, are other inftances of the
effedls of painful, or pleafurable fenfations, on the ex:tremities of the
arterial fyftem.

It is probable, that the pleafurable fenfatlon excited'in the ftomach'
by food, as welL as its irritation, contributes to excite into aftion the
gaftric glands, and to produce a greater fecretion of their fluids. The
fame probably occurs in the fecretion of bile ; that is, that the pleafur-
able

•5 1 S GENERATION. Sect. XXXIX. 6.

able fenfation excited in the ftomach, affects this fecretioa by fer.fitive
afiociation, as vvel! as by irritative affociation.

And laftly it would feem, that all the glands la the body have their
fecreted fluids affe£led, in quantity and quality, by the pleafurable or
painful fenfations, which produce or accompany thofe fecretions.
And that the pleafurable fentations arifing from thefe fecretions may
conftitute the unnamed pleafure of exiftence, which is contrary to
what is meant by taedium vitas, or ennui ; and by which we fomc-
times feel ourfelves happy, without being able to afcribe it to any
mental caufe, as after an agreeable meal, or in the beginning of in-
toxication.

Now it would appear, that no fecretlon or excretion of fluid is at-
tended with fo much agreeable fenfation, as that of the femen ; and it
would thence follow, that the glands, which perform this fecretion,
are more likely to be much affedted by their catenations with pleafur-
able fenfations. This circumflance is certain, that much more of this
fluid is produced in a given time, when the olye£l of its exclufion is
agreeable to the mind.

2. A forceable argument, which fhews the neceffity of pleafurable
fenfation to copulation, is, that the a6t cannot be performed without
it ; it is eaiily interrupted by the pain of fear or badifulnefs ; and no
efforts of volition or of irritation can effeft this procefs, except fuch as
induce pleafurable ideas or fenfations. See Se£t. XXXIII. i. i.

A curious analogical circumftance attending hermaphrodite infedls,
as fnails and worms, flill further illuftrates this theory ; if the fnail or
worm could have impregnated itfelf, there might have been a faving
of a large male apparatus ; but as this is not fo ordered by nature, but
each fnail and worm reciprocally receives and gives inripregnation, it
appears, that a pleafurable excitation feems alfo to have been required.

This wonderful circumftance of many infedts being hermaphro-
dltes, and at the fame time not having power to impregnate them-
ielvcs, is attended to by Dr. Lifter, in his Exercltationes Anatom. de

Linaacibus,

Sect. XXXIX. 6. GENERATION. 519

Limacibus, p. 14.5 ; who, amongfl: many other final caufes, which he
adduces to account for it, adds, ut tam triftibiis et frigidis animalibus
majori cum voluptate perficiatur veniis.

There is, however, another final caufe, to which this circumflance
may be imputed: it was obferved above, that vegetable buds and
bulbs, which are produced without a mother, are always exa6l re-
femblances of their parent; as appears in grafting fruit-trees, and in
the flower-buds of the dioiceous plants, which are always of the fame
fex on the fame tree ; hence thofe hermaphrodite infe6ts, if they
could have produced young without a mother, would not have been
capable of that change or improvement, which is feen in all other
animals, and in thofe vegetables, which are procreated by the male
embryon received and nourifhed by the female. And it is hence pro-
bable, that if vegetables could only have been produced by buds and
bulbs, and not by fexual generation, that there would not at this time
have exifted one thoufandth part of their prefent number of fpecies i
which have probably been originally mule-produ6lions ; nor could
any kind of improvement or change have happened to them, except
by the difference of foil or climate..

3. I conclude, that the imagination of the mate at the time of co-
pulation, or at the time of the fecretion of the femen, may fo affedi
this fecretion by irritative or fenfitive afToclation, as defcnbed in No.
5. I. of this fe(51:ion, as to caufe the produtlion of fimi'arity of form
and of features, with the diffcindion of fex ;. as the moti j-as-of the chif-
fel of the turner imitate or correfpond with thofe or the ideas of the
artifl. It is not here to be underfliood, that the firfl living fibre,
which is to form an animal, is produced with any fimilarity of form
to the future animal; but with propenfities, or appetencies, which
Ihall produce by accretion of parts the fimilarity of form, feature, or
fex, correfponding to the imagination of the father.

Our ideas are movements of the nerves of feafe, as of the optic

nerve in recoUefting vifible ideas^ fuppofe of a triangular piece of

3 ivory.

7;2^ GENERATION. -Sect. XXlCIX/S..

ivory. "The fiae moving fibres of the retina aft in a manner to which
i give the name of white ; and this action is conhiied to a defined part
of it ; to which figure I give the -ftame of triangle. And it is a pre-
ceding pleafurable fenfation exifting in my mind, which occafions me
to produce this particular motion of the retina, when no triangle is
prefent. Now it is probable, that the afting fibres of the ultimate
terminations of the lecreting apertures of the veflels of the teftes, arc
as fine as thofe of the retina; and that they are liable to be thrown
into that peculiar adtion, which marks the fex of the fecreted errt-
bryon, by fympathy with the pleafurable motions of the nerves of
vlfion, or of touch ; that is, with certain ideas of imagination^ ' From
hence it would appear, that the world has long hetn miftaken in
afcribing great power to the imagination of the female, whereas from
this account ot it, the real power of imaginatioiv, in t'he adt of gene-
ration, belongs folely to the male. See Se£l. XII. 3. 3.

It may be objefted to this theory, that a man may be fuppofed to
have in his mind, the idea of the form and features of the female,
rather than his own, and therefore there fhould be a greater number
of female births. On the contrary, the general idea of our own form
occurs to every one almofl: perpetually, and is termed confcioufnefs of
Gur exiftence, and' thus may effeft, that the number of males furpafles
that of females. 'See Se6t. XV. 3. 4. and XVIH. 13. And what
.further confirms this idea is, that the male children moft frequently
refemble the father in form, -or feature, as well as in fex ; and the fe-
male moft- frequently relcmble the mother, in feature, and form, as
well ^as in fex.

■It 'may again be objefted, if a female child fometimes refembles the
father, and a male child the mother, the ideas of the father, at the
time of procreation, muft fuddenly change from himfelf tothe mo-
ther, at the very inftant, when the embryon is fecreted or formed.
This difficulty ceafes when we confider, that it is as eafy to form an
idea of feminine features with male organs of reprodudion, or of male

.features

Sect. XXXIX. 6. GENERATION. 521

features with female ones, as the contrary ; as we conceive the idea
of a fphinx or mermaid, as eafily and as diftin£tly as of a woman.
Add to this, that at the time of procreation the idea of the male or-
gans, and of the female features, are often both excited at the fame
time, by contacl, or by vifion.

I aflc, in my turn, is the fex of the embryon produced by accident ?
Certainly whatever is produced has a caufe ; but when this caufe is
too minute for our comprehenfion, the efte£t is faid in common lan-
guage to happen by chance, as in throwing a certain number ou dice.
Now what caufe can occafionally produce the male or female charac-
ter of the embryon, but the peculiar adions of thofe glands, which
form the embryon ? And what can influence or govern thefe actions
of the gland, but its aflbciations or catenations with other fenfitive
motions ? Nor is this more extraordinary, than that the catenations
of irritative motions with the apparent vibrations of objefts at fea
Ihould produce ficknefs of the ftomach ; or that a naufeous ftory
Ihould occafion vomitino;.

4. An argument, which evinces the efFe<3: of imagination on the
firfl rudiment of the embryon, may be deduced from the produdion
of fome peculiar monfters. Such, for inftance, as thofe which have
two heads joined to one body, and thofe which have two bodies joined
to one head; of which frequent examples occur amongft our domefti-
cated quadrupeds, and poultry. It is abfurd to fuppofe, that fuch
forms could exift in primordial germs, as explained in No. IV. 4. of
this fedion. Nor is it pofTible, that fuch deformities could be pro-
duced by the growth of two embryons, or living filaments; which
(hould afterwards adhere together ; as the head and tail part of differ-
ent polypi are faid to do (Blumenbach on generation, Cadel, Lon-
don) ; lince in that cafe one embryon, or living filament, muft have
begun to form one part firft, and the other another part firfl. But
fuch monflrous conformations become lefs difficult to comprehend,
when they are confidered as an effedl of the imagination, as before

3 X explained.

5212 GENERATION. Sect. XXXIX. 6.

explained, on the living filament at the time of its fecretion ; and that
fuch duplicature of limbs were produced by accretion of new parts,
in confequence of propeniities, or animal appetencies thus acquired
from the male parent.

For inftance, I can conceive, if a turkey-cock fhould behold a rab-
bit, or a frog, at the time of procreation, that it might happen, that
a forcible or even a pleafurable idea of the form of a quadruped might
fo occupy his imagination, as to caufe a tendency in the nafcent fila-
ment to refemble fuch a form, by the appofition of a duplicature of
limbs. Experiments on the production of mules and monfters would
be worthy the attention of a Spallanzani, ajid might throw much
light upon this fubjecl, which at prefent muft be explained by con-
jedlural analogies.

The wonderful effed of imagination, both in the male and female
parent, is fhewn in the produftion of a kind of milk in the crops
both of the male and female pigeons after the birth of their young,
as obferved by Mr. Hunter, and mentioned before. To this fhould
be added, that there are fome inftances of men having had milk fe-
creted in their breafts, and who have given fuck to children, as re-
corded by Mr. Buffon. This efFe6t of imagination, of both the male
and female parent, feemstohave been attended to in very early times;
Jacob is faid not only to have placed rods of trees, in part flripped of
their bark, fo as to appear fpotted, but alfo to have placed fpotted
lambs before the flocks, at the time of their copulation. Genefis,

chap. xxx. verfe 40.

5. In refpeft to the imagination of the mother, it is difficult to-
comprehend, how this can produce any alteration in the fetus, ex-
cept by affefting the nutriment laid up for its firll: reception, as de-
fcribed in No. V. 2. of this feftion, or by affefting the nourishment
or oxygenation with which fhe fupplies it afterwards. Perpetual
anxiety may probably affeft the fecretion of the liquor amnii into the
uterus, as it enfeebles the whole fyftem ; and fudden fear is a frequent

cau

Sect. XXXIX. 6. GENERATION. 523

caufe of mifcarriagc ; for fear, contrary to joy, decreafes for a time
the adlion of the extremities of the arterial iyftem ; hence fuddeii
palenefs fucceeds, and a fhrinking or contra6lion of the veffels of the
(kin, and other membranes. By this circumftance, I imagine, the
terminations of the placental veffels are detached from their adhefions,
or infertions, into the membrane of the uterus ; and the death of the
child fucceeds, and confequent mifcarrlage.

Of this I recolle£t a remarkable inftance, which could be afcribed
to no other caufe, and which I fliall therefore relate in few words.
A healthy young woman, about twenty years of age, had been about
five months pregnant, and going down into her cellar to draw fome
beer, was frighted by a fervant-boy ftarting up from behind the bar-
rel, where he had concealed himfelf with defign to alarm the maid-
fervant, for whom he miftook his miftrefs. She came with difficulty
up ftairs, began to flood immediately, and mifcarried in a few hours.
She has fince borne feveral children, nor ever had any tendency to
mifcarry of any of them.

In refpe£t to the power of the imagination, of the male over the
form, colour, and fex of the progeny, the following inftances have
fallen under my obfervation, and may perhaps be found not very un-
frequent, if they were more attended to. I am acquainted with a
gentleman, who has one child with dark hair and eyes, thouo-h his lady
and himfelf have hght hair and eyes ; and their other four children are
like their parents. On obferving this diffimilarity of one child to the
others he affured me, that he believed it was his own imagination, that
produced the difference ; and related to me the following ftory. He
laid, that when his lady lay in of her third child, he became attached
to a daughter of one of his inferior tenants, and offered her a bribe for
her favours in vain ; and afterwards a greater bribe, and was equally
unfuccefsful ; that the form of this girl dwelt much in his mind for
fome weeks, and that the next child, which was the dark-ey'd youno-

3 X z lady

524 GENERATION. Sect. XXXIX. 6.

lady above mentioned, was exceedingly like, in both features and
colour, to the young woman who refufed his addrefles.

To this inftance I muft add, that I have known two families, in
which, on account of an intailed eflate in expeftation, a male heir
was moil eagerly defired by the father ; and on the contrary,, girls
were produced to the feventh in one, and to the ninth in another j
and then they had each of them a fon. I conclude, that the great defire
of a male heir by the father produced rather a difagreeable than an
ao-reeable fenfation ; and that his ideas dwelt more on the fear of ge-
neratino- a female, than on the pleafurable fenfations or ideas of his
own male form or organs at the time of copulation, or of the fecretion
of the femen ; and that hence the idea of the female charadler was
more prefent to his mind than that of the male one ; till at length
in defpair of generating a male thefe ideas ceafed, and thofe of the
male charafter prefided at the genial hour.

7. Hence I conclude, that the aft of generation cannot exifl with-
out beino- accompanied with ideas, and that a man muft have at that
time either a general idea of his own male form, or of the form of
his male organs ; or an idea of the female form, or of her organs ;,
and that this marks the fex, and the peculiar refemblances of the
ehlid to either parent. From whence it would appear, that the phalli,
which were hung round the necks of the Roman ladies, or worn in
their hair, might have efFed in producing a greater proportion of
male children ; and that the calipzedia, or art of begetting beautiful
children, and of procreating either males or females, may be taught
by affefting the imagination of the male- parent ; that is, by the fine
extremities of the feminal glands imitating the anions of the organs
of fenfe either of fight or touch. But the manner of accomplifhing
this cannot be unfolded with fufficient delicacy for the public eye ;
but may be worth the attention of thofe, who are ferioufly interefted
in the procreation of a male or female child,

Recaptulation..

Sect. XXXIX. 7- GENERATION. 525

Recapitulation.

VII. 1. A certain quantity of nutritive particles are produced by
the female parent before impregnation, which require no further di-
geftion, fecretion, or oxygenation. Such are feen In the unimpreg-
iiated eggs of birds, and in the unimpregnated feed-veffels of vege-
tables.

2. A living filament is produced by the male, which being inferted
amldfl thefe firfl: nutritive particles, is Simulated Into adion by them ;
and in confequence of this adlion, fome of the nutritive particles are
embraced, and added to the original living filament; in the fame
manner as common nutrition is performed in the adult animal.

3. Then this new organization, or additional part, becomes simu-
lated by the nutritive particles in its vicinity, and fenfation is now
fuperadded to irritation; and other particles are in confequence em-
braced, and added to the living filament ; as is i^tn. in the new gra-
nulations of flefh in ulcers.

By the power of aflbciation, or by irritation, the parts already
produced continue their motions, and new ones are added by fenfa-
tion, as above mentioned ; and laftly by volition, which laft fenforial
power is proved to exift In the fetus in its maturer age, becaufe It
has evidently periods of aftivity and of fleeping ; which lafl is another
word for a temporary fufpenfion of volition.

The original living filament may be conceived to pofTefs a power
of repulfing the particles applied to certain parts of it, as well as of
embracing others, which flimulate other parts of it ; as thefe powers
exifl in different parts of the mature animal ; thus the mouth of
every gland embraces the particles of fluid, which fuits Its appetency;
and its excretory dudl repulfes thofe particles, which are difagreeable
to it.

4. Thus

526 GENERATION. Sect. XXXIX. 7.

4. Thus the outline or miniature of the new animal is produced
gradually, but in no great length of time ; becaufe the original nu-
tritive particles require no previous preparation by digeftion, fecre-
tion, and oxygenation: but require limply the fele6lion and appofi-
tion, which is performed by the living filament. Mr. Blumenbach
fays, that he poffeffes a human fetus of only five weeks old, which
is the fize of a common bee, and has all the features of the face,
every finger, and every toe, complete ; and in which the organs of
generation are diilinftly feen. P. 76. In another fetus, whofe head
was not larger than a pea, the whole of the bafis of the Ikull with
all its depreffions, apertures, and proceffes, were marked in the moll
Iharp and diftinil manner, though without any offification. lb.

5. In fome cafes by the nutriment originally depofited by the mo-
ther the filament acquires parts not exadlly fimilar to thofe of the fa-
ther, as in the produdion of mules and mulattoes. In other cafes,
the deficiency of this original nutriment caufes deficiencies of the ex-
treme parts of the fetu5, which are lafl: formed, as the fingers, toes,
lips. In other cafes, a duplicature of limbs are caufed by the fuper-
abundance of this original nutritive fluid, as in the double yolks of
eggs, and the chickens from them with four legs and four wings.
But the produftion of other mbnfters, as thofe with two heads, or
with parts placed in wrong fituations, feems to arife from the ima-
gination of the father being in fome manner imitated by the extreme
veffels of the feminal glands ; as the colours of the fpots on eggs,
and the change of the colour of the hair and feathers of animals by do-
meftication, may be caufed in the fame manner by the imagination of
the mother.

6. The living filament is a part of the father, and has therefore
certain propenfities, or appetencies, which belong to him ; which
may have been gradually acquired during a million of generations,
even from the infancy of the habitable earth ; and which now pof-
feffes fuch properties, as would render, by the appofition of nutritious

particles.

Sect. XXXIX. 7. GENERATION. 527

particles, the new fetus exactly fimilar to the father; as oc-
curs in the buds and bulbs of vegetables, and in the polypus, and
taenia or tape-worm. But as the firft nutriment is fupplied by the
mother, and therefore refembles fuch nutritive particles, as have
been ufed for her own nutriment or growth, the progeny takes in
part the likenefs of the mother.

Other fimilarity of the excitability, or of the form of the male
parent, fuch as the broad or narrow flioulders, or fuch as conftitute
certain hereditary dileafes, as fcrophula, epilepfy, infanity, have
their origin produced in one or perhaps two generations; as in the
progeny of thofe who drink much vinous fpiritsj and thofe heredi-
tary propenfities ceafe again, as I have obferved, if one or two fober
generations fucceed ; otherwife the family becomes extin£t.

This living filament from the father is alfo liable to have its pro-
penfities, or appetencies, altered at the time of its produ6lion by the
imagination of the male parent ; the extremities of the feminal glands
imitating the motions of the organs of fenfe; and thus the lex of the
embryon is produced ; which may be thus made a rriale or a female
by affefting the imagination of the father at the time of impregnation.
See Se6l. XXXIX. 6. 3. and 7.

7. After the fetus is thus completely formed together with its uni-
bihcal veffels and placenta, it is now fupplied with a different kind of
food, as appears by the difference of conliftency of the different
parts of the white of the egg, and of the liquor amnii, for it has
now acquired organs for digeftion or fecretion, and for oxygenation,
though they are as yet feeble ; which can in fome degree change, as
well as feleft, the nutritive particles, which are now prefented to it.
But may yet be afFe6led by the deficiency of the quantity of nutri-
tion fupplied by the mother, or by the degree of oxygenation fupplied
to its placenta by the maternal blood.

The augmentation of the complete fetus by additional particles of
nutriment is not accomplifhed by diilention only, but by appolition

528 GENERATION. Sect. XXXIX. 7.

to every part both external and internal; each of which acquires by
animal appetencies the new addition of the particles which it wants.
And hence the enlarged parts are kept fimilar to their prototypes,
and may be faid to be extended ; but their extenfion muft be conceived
only as a neceffary confequence of the enlargement of all their parts
by apportion of new particles.

Hence the new appofition of parts is not produced by capillary at-
trailion, becaufe the whole is extended ; whereas capillary attradion
would rather tend to bring the fides of flexible tubes together, and
not to diftend them. Nor is it produced by chemical affinities, for
then a folution of continuity would fucceed, as when fugar is dif-
folved in water ; but it is produced by an animal procefs, which is
the confequence of irritation, or fenfation ; and which may be termed
animar appetency.

This is further evinced from experiments, which have been infti-
tuted to fhew, that a living mufcle of an animal body requires
o-reater force to break it, than a fimilar mufcle of a dead body.
Which 'evinces, that befides the attraflion of cohefion, which all
matter poffeffes, and befides the chemical attra£lions of affinities,
which hold many bodies together, there is an animal adhefion, which
adds vigour to thefe common laws of the inanimate world.

8. At the nativity of the child it depofits the placenta or gills,
and by expanding its lungs acquires more plentiful oxygenation from
the currents of air, which it muft now continue perpetually to re-
fpire to the end of its life ; as it now quits the liquid element, in
which it was produced, and like the tadpole, when it changes into
a frog, becomes an aerial animal.

9. As the habitable parts of the earth have been, and continue to
be, perpetually increafing by the produdlion of fea-fhells and coral-
lines, and by the recrements of other animals, and vegetables ; fo
from the beginning of the exiftence of this terraqueous globe, the
7 animals,

Sect. I^.XXIX. 8. G E N E R A T I O :t<r. 5^5

animals, which inhabit it, have conftantly improved, aivd are ftilj iu
a flate of progreffive improvement.

This idea of the gradual generation of all tWngs feems to have
been as familiar to the ancient philofophers as to the modern ones.;
and to have given rife to the beautiful hieroglyphic figure of the
vr^oTov caov, or firfl: great egg, produced by night, that is, whofc
origin is involved in obfcurity, and animated by e^o^, that is, by-Dr-
viNE Love ; from whence proceeded all things which exift.

Concliiri(M,

VIIL T. Cause and effect -may be confidered as the prb-
greffion, or fucceffive motions, of the parts of the ^'eat fyflem of
Nature. The flate of things at this moment is the effedl of the flatc
■of things, which exifled in the preceding moment ; and the caiafe of
the flate of things, wiiich fhall exift in the next moment.

Thefe caufes 2nd efteds may be more eafily comprehended, if mo-
tion be confidered as a change of the figure of a group of bodies, as
propofed in Sedt. XIV. 2. -2. inafmuch as our ideas of vifible or tan-
gible objects are more difrindl, -than our abfl:ra£ted -ideas of their mo-
tions. Now the change of the configuration of the fyflem of nature
at this moment muiT: be an efFedl of the preceding configuration, for
-a change of configuration cannot exifl without a previous configu ration, j
-and the proximate caufe of every efFe<St mufl immediatelj/ precede that
etteft. For example, a moving ivory -ball could not proceed onvvards,
unlels-it had previoufly began to -proceed J or unlefs an impulfe had
been previously given it ; which previous motion or impulfe conflitutes
•a part of the laft fituation of things.

As the effe£ls produced in this moment of time becom.c caufes in
■the next, w€ may confider the progrefiive motions of objeds as a

.3 ^ chaiu

5 JO GENERATION. Sect. XXXIX. E.

chala of caufcs only; v/hofe firft link proceeded from the great Cre-
ator, and which have exifted from the beginning of *he created iini-
verfe, and are perpetually proceeding.

2. Thefe caufes may be conveniently <livided into two kinds, ef^
ficient and inert caufes, according y^^ith the two kinds of entity fup-
pofed to exift in the natural world, which may be termed matter and
fpirit, as propofed in Sed. I. and further treated of in Sed:. XIV".
The efUcient caufes of motion, or new configuration, confift either-
of the principle of general gravitation, vi^hich adluates the fun and
planets ; or of the principle of particular gravitation, as in, ele£tricity,
magnetifm, heat ; or of the principle of chemical affinity, as in com-
buftion, fermentation, combination; or of the principle of organic
life-, as in the contra£tlon of vegetable and animal fibres. The Inert
caufes of motion, or new configuration, confiil of the parts of mat-
ter, which are in-t reduced within the fpheres of adlivity of the prin-
ciples above defcribed. Thus, when an apple falls on the ground,
the principle of gravitation is the efficient caufe, and the matter of
.the apple the inert caufe. If a bar of iron be approximated to a niag-
net, it may be termed the inert caufe of the motion, which brings
thefe two bodies into contaft ; while the magnetic principle may be
termed the efficient caufe. In the fame manner the fibres, which
conftitute the rethia may be called the inert caufe of the motions of
that organ ia vifion, while the fenforial power may be termed the ef-
ficient caufe..

3. Another more common diftrlbution of the perpetual chain of'
caufes and efFeds, which conftitute the motions, or changing con-
figurations, of the natural world, is into aftive and pafilve. Thus^
if" a ball in motion impinges againft another ball at reft, and commu-
nicates its motion to it, the former ball is faid. to aft, and the latter
to be.adled upon. In this fenfe of the words a magnet is faid to at-

.traft iron ; and the prick of a fpur to ftimulate a horfe into exertion 1
fo that in this view of the works of nature all things may be faid ei-
ther

Sect. XXXIX. 8.. G E 1-7 E R A T I O N. 531

ther (imply to exift, or to exift as caufes, or to exift as effeds ; that
is, to exift cither in an zQiive or paflive ftate.

This diftributiou of objefts, and their motions, or changes of po-
fltion, has been found fo convenient for the purpofes of common life,
that on this foundation refts the whole conftruftion or theory of lan-
guage. The names of the things themfelves are termed by gram-
marians Nouns, and their modes of exiftence are termed Verbs. The
nouns are divided into fubftantives, which denote the principal things
fpoken of ; and into adjectives, which denote fome circumftances, or
lefs kinds of things, belong-ing to the former. . The verbs are divided
'into three kinds, fuch as denote the exiftence of things fimply, as, to
be ; or their exiftence in an adlive ftate, as, to eat ; or their ex-
iftence in a paflive ftate, as, to be eaten. Whence it appears,
that all languages confift only of nouns and verbs, with theif
abbreviations for the greater expedition of communicating our
thoughts ; as explained in the ingenious work of Mr. Home Tooke,
who has unfolded by a fingle flafh of light the whole theory of lan-
guage, which had fo long lain buried beneath the learned lumber of
the fchools. Diverfions of Parley. Johnfon. London.

4. A third divifion of caufes has been into proximate and remote ;
thefe have been much fpoken of by the writers on medical fubjefts,
but without fafticient precifion. If to proximate and remote caufes
we add proximate and remote efFecls, we fhall include four links of
the perpetual chain of caufation ; which will be more convenient for
the difcuflion of many philofophical fubjedls. .^

Thus if a particle of chyle be applied to the mouth of a laCleal vef-
fel, it may be termed the remote cauie of the motions of the fibres,
which compofe the mouth of that lafteal. veftel ; the fenforial power
is the proximate caufe ;-the contraclion of the fibres of the mouth of
the veffel is the proximate eifeit; and their embracing the particle of
chyle is the remote effe£b ; and thefe four links of caufation conftitute
.ablorption.

Thus when we attend to the rifing fun, firft the yellow rays of

3 Y 2 light

5J2; G' E N" E R A T r O N. Sect. XXXIX. fe.

KgHf ffiraulate the fenforiar power redding in the extremities of the-
optic nerve, this is the remote caufe. 2. The fenforial power is
excited into a ftate of a6iivity, this is the proximate Gaufe. 3. The
fibrous extremities of the optic nerve ace contracled, this is the prox-
imate efFeft. 4. A- pleafureabfe cr painfirl fenfation is produced ill
eonfequence of the coiitra6liou of thefe fibresof the optic nerve, this,
is the remote efFe6b ; a-nd thefe four links of the ehain-of caufatiou
Gonftitute the fenfitive idea, or what is commonly termed the fenfa-
tion of the rifin? fun.-

5. Other caufes have been announced by medical writers under the
names of caufa procataritica, and caufa proegumina, and caufa fine-
qua non. All which are links more or lefs diilant of the chain of re-
mote caufes..

To thefe muft be added the final caufe, fo called by many. authorSi^
'#vhieh means the motive, for the accomplifhment of which the pre-
ceding chain of caufes was put into adlion.. The idea:of a final caufe^,
therefore, includes that of a rational mind, which employs means to
^fFedl its purpofes ; thus the defire of preferving himfelf from the pain*
of cold,- which he has frequently experienced, induces the favage to
eonftrud his hut;, the fixing flakes into the ground for walls, branches-
of trees for rafters,, and turf for a cover, are aferies of fuccefilve vo-
luntary exertions ; which are fo many means to produce a certain ef-
fed. This effeft of preferving himfelf from cold, is termed the finaE
caufe ; the conftrudlion of the hut is the remote efFe£t ; the adion of,
«|he mufcular fibres of the man, is the proximate efFe6l ; the volition,.,
or activity of defire to preferve himfelf from cold, is the proximate-,
caufe ; and^jae pain-of cold, which excited that defire^ is the remote,
jeaufe.

6. This perpetual chain of caufes and efFeas, whofe firfl: link is~
rivetted to the throne of God, divides itfelf into innumerable diverg-
ing branches, which, like the nerves arifing from the brain, permeate-
.the moft- minute.and moil remote extremities of the fyftem, difFufing-

^ motioa.

Sect. XXXIX- §. GENERATION: 5-3

motioa and fenfation to the whole. As every caufe is fuperior in
power to the efFeft, which it has produced, fb our idea of the power
of the Almighty Creator becomes more elevated and fublime, as we.
trace the operations of nature from caufe to caufe, climbing up the-
links of thefe chains of being, till we afcend to the Great Source of all.
things.

Hence the modern difcoveries in chemiftry and in geology,, by
having traced the caufes of the combinations of bodies to remoter, ori-
gins, as well as thofe in aftronomy, which dignify the pfefent age,
contribute to enlarge and amplify our ideas of the power of the Great
jFirfl Caufe. And had thofe ancient philofophers, who contended that
the world was formed from atoms, afcribed their combinations to cer-
tain immutable properties received from the hand of the Creator, fuch:
as general gravitation,, chemical affinity, or animal appetency, inflead
of aferibing them to a blind chance ; the doftrine of atoms,-as confli~
tuting or compofing the material world by the variety of their com-
binations, fo far from leading the mind to atheifm, would ftrengthea-.
the deraonftration of the exiftence of a Deity,, as the firft caufe of all
things; becaufe the analogy. refulting from our perpetual experience of
caufe and effed would- have thus been exemphfied through univerfal;
nature.

I^he- heavens declare the glory of God, and the firmament Jheweih his
handy work I One day telietb another^ and one night certifieth another;
they have neither fpeech nor language, yet their voice is gom^ forth into
all lands, and their words into the ends of tlje world. Manifold are thy.
'^mrks.y O Lord ! in.wifdomhajl thou made them alL. Pfal. xix. civ-

SECT.

33*

OCULAR SPECTRA. Sect. XL.

SECT. XL.

On the. Ocular Spectra of Light and Colours, by Dr.R.W.
Darwin, of Shrewfbury. Reprinted, by Permiflion, from the
Philofophical Tranfaaions, Vol. LXXVI. p. 313.

SpeSfra of four kinds, i. AElivity of the retina in vifion. 1. Spe5ira from defeS
offenfibility. "t^. SpeSra from excefs of fenfMity. 4. Of direSf ocular fpeSra.
5, Greater ftimulus excites the retina into fpafmodic anion. 6. Of reverfe ocular
fpeSfra. 7. Greater fiimulus excites the retina into various fuccejjive fpafmodic
aElions. 8. Into fixed Jpafmodic a5iion. 9. Into temporary paralyfis. 10. Mif-
cellaneous remarks; i. TiireSi and reverfe JpeSira at the fame time. J fpeSlrd
halo. Rule to predetermine the colours of fpeSira. 1. Variation of fpeSira from
extraneous light. 3. Variation of fpeSlra in numher, figure, and remiffioru
4. Circulation of the blood in the eye is vifible. 5. A new way of magnifying
Bhje5is. Conchifion.

WHEN any one has long and attentively looked at a bright ob-
ject, as at the fetting fun, on clofing his eyes, or removing them, an
image, which refembles in form the obje£l he was attending to, con-
tinues fome time to be vifible : this appearance in the eye we fhall
call the ocular fpe£trum of that objedl.

Thefe ocular fpeftra are of four kinds : J ft. Such as are owing to a

lefs fenfibility of a defined part of the retina ; ox fpeUlrafrom defeSi of

Jenftbility. 2d, Such as are owing to a greater fenfibility of a defined

part of the retina ; ox JpeElra frwn excefs of Jenftbility. 3d, Such as

referable their object in its colour as well as form ; which may be

termed

Sect. XL. I, OCULAR SPECTRA. S3y

tenned dire^ ocu/ar Jpe&ra. 4t:h, Sucli as are of a colour contrary to
that of their obje£l ; which may be termed reverje ociclar Jpetlr a.

The laws of light have been moft fuccefsfully explained by the.
great Newton, and the perception, of vifible objecls has been ably in-
veftigated by the ingenious Dr. Berkeley and M. Malebranche ; but
thefe minute phsenomena of vifion have yet been thought reducible to
no theory, though many philofophers have employed a confiderable
degree of attention upon them : among thefe are Dr. Jurin, at ths
end of Dr. Smith's Optics ; M. iEpinus, in the Nov. Com. Petropol.
V. lo. ; M. Beguelin, in the Berlin Memoires,. V. U. 1771; M..
d'i\.rGy, in- the Hiftoire de I'Acad. des Scienc. 1765 ; M. de la Hire ;
and, laftly, the celebrated M. de BufFon, in the Memoires de I'Acadi.
des Scien. who has termed them accidental colours, as if fubje£led to
no eftabliflied laws, Ac. Par. 1743. M. p. 215.

I muft here apprize the reader, that it is very difficult for different
people to give the fame names to various fhades of colours ; \\'hence,
in the follov-^ing pages, fomething mufl be allowed, if on repeating the
experiments the colours here mentioned fhould not accurately cor-
refpond with his own names of them..

L AEiivity of the Reiiha in Vtjibh. .

From the fubfequent experiments it appears, that the retina is ia
an a61:ive not in a paffive ilate during the exifteiice of thefe ocular
fpeiflra ; and it is thence to be concluded, that all vifion is owing to
the aftivity of this organ.

I. Place a piece of red filk, about an inch in diameter, as in plate i,
at Se£l. III. I, on a flieet of white paper, in a flrong light ; look
fleadily upon it from about the diftance of half a yard for a minute ;
then doling your eyelids cover them with your hands,, and a green.

fpedlrum.

5i6 OCULAR SPECTRA. Sect. XL. r.

fpeif^rum will be feen in your eyes, refembllng in form the piece of
-red filk : after fome time, this fpedlrum will difappear and fliortly re-
appear; and this alternately three or four times, if the experiment is
well made, till at length It vanifhes entirely.

2. Place on a flieet of white paper a circular piece of blue filk,
about four inches in diameter, in the funfliine ; cover the center of
this with, a circular piece of yellow filk, about three inches in dia-
meter ; and the center of the yellow filk with a circle of pink filk,
about two i-nches in diameter; and the center of the pink filk with a
circle of green filk, about one inch in diameter; and the centre of
this with a circle of indigo, about half an inch in diameter ; make a
fraali fpeck with ink in the very center of the whole, as in plate 3, at
Sedl. III. 3. 6.; look llieadily for a minute on this -central fpot, and
tlien clofing your eyes., and applying your hand at about an inch dif-
tance before them., fo as to prevent too -much or too little light from
paffing through the eyelids, you will fee the moft beautiful circles of
colours that imagination can conceive, which are moft refembled by
the colours occafioned by pouring a drop or twocif oil on a ftill lake
in a bright day.; but thefe circular irifes of colours are not only different
from the colours of the filks above mentioned, but are at the fame
time perpetually changing. as long as they exrft.

3. When anyone in the dark prefles either corner of his eye with
"his finger, and turns his eye away from his finger, he will fee a circle
.of colours like thofe in a peacock's tail: and a fudden flafli of light is

excited in the eye by a ftroke on tt. (Newton's Opt. C^i6.)
> 4. When any ORe turns round rapidly on one foot, till he becomes
dl^zy, and fails upon the ground, the fpeftra of the ambient objeds
continue to prefent themfelves in rotation, or appear to hbrate, and he
feeras to behold them for fome tim.e ftill in motion.

From .all thefe experiments it appears, that the fpedra in the eye
are not owing^ to the mechanical impulfe of light imprefled on the
retina, nor to its chemical combination with that organ, iior to the

abforption

Sect. XL. I. OCULAR SPECTRA, 53;,

abforption and emiflion of light, as is obferved in many bodies ; for
in all thefe cafes the fpeftra muft either remain uniformly, or gra-
dually diminifli ; and neither their alternate prefence and evanefcence
as in the firft experiment, nor the perpetual changes of their colours
as in the fecond, nor the flafli of light or colours in the prefled eye as
in the third, nor the rotation or libration of the fpeclra as in the fourth,
.could exiift.

Jt is not abfurd to conceive, that the retina may be ftimulated into
motion, as well as the red and white mufcles which form our limbs
and v^eflels; fince it confifts of fibres, like thofe, intermixed with it*
medullary fubllance. To evince this itruclure, the retina of an ox's
•eye was fiafpended in a glafs of warm water, and forcibly tern in a
•few places ; the edges of thefe parts appeared jagged and hairy, and
did not contrail, and become fmooth like iimple mucus, when it is
diftended till it breaks ; which {hews that it confifts of fibres ; and
this its fibrous conftruftion became ftill more diftinct to the fight, by
adding fome cauftic alkali to the water, as the adhering mucus was
firfl eroded, and the hair-like fibres remained floating in the velTel.
Nor does the degree of tranfparency of the retina invalidate the evi-
dence of its fibrous ftru6lure, fince Leeuwenhoek has (hewn that
the cryftalline hunwur itfelf oonfifls of fibres. (Arcana Naturze,
V. I. p. 70.)

Hence it appears, that as the mufcles have larger fibres intermixed
with a fmaller quantity of nervous medulla, the organ of vifion has a
greater quantity of nervous medulla intermixed with fmaller fibres j
and it is probable that the locomotive mufcles, as well as the vafcular
ones, of microfcopic animals have much greater tenuity than thefe of
the retina.

And befides the fimilar laws, which will be fiiewn in this paper
to govern alikethe actions of the retina and of the mufcles, there are
many other analogies which exift between them. They are both ori-
ginally e-xcited into aftion by irritations, both aft nearly in the fame

3 Z quantity

53S- OCULAR SPECTRA. Sect.XL. 2,

quantity of time, are alike ftrengthcned or fatigued by exertion, are
alike painful if excited into a6lion when they are in an inflamed ftale^
are alike liable to paralyfis, and to the torpor of old age.

II. Of spectra FP^Oivr defect o.f sENsiBiLrTr.

^he retina is- notfo eafily excited into aEllon hy lefs Irritation after havinr,
been lately- fubjeSied. to greater^

J. When any one pafTes from the bright daylight into a darkened
room, the irifes of his eyes expand themfelves to their utmofl extent
fn a few feconds of time j but it is very long before the optic nerve,
after having been ftlmulated by the greater light of the day, becomes-
fenfible of the lefs degree of it in the room ; and, if the room is not
too obfcure, the irifes will again contra£t them.felves in feme de-
gree, as the fenfibility of the retina returns.

2. Place about half aivinch fc[uare of white paper on a black hat,,
and looking fteadily on the center of it for a minute, remove your eyes
to a iheet of white paper ; and after a fecond or two a dark fquare
will be feen on the white paper, which will continue fome time. A
limilar dark fquare will be feen in the elofed eye, if light be admitted
through the eyelids.

So after looking at any luminous objecfl of a fmall fize, as at the-
fun, for a fhort time, fo as not much to fatigue the eyes, this part of
the retina becomes lefs fenfible to fmaller quantities of light ; hence,.
when the eyes are turned on other lefs luminous parts of the Iky, a
dark fpot is feen refembling the fhape of; the fun, or other luminous
object which we laft beheld. This is the fource of one kind of the
dark-colouredjwa/tftfc volitantes. If this dark fpot lies above the center
of the eye, we turn our eyes that way, expeding to bring it into
3 -- . the

Sect. XL. 2. OCULAR SPECTRA, r-o

the center of the eye, that we may view it more di{lin£lly ; and in
this cafe the dark fpedrnm feems to move upwards. If the dark
fpedtrum is found beneath the centre of the eye, we purfiie it from
the fame motive, and it feems to move downwards. This has wjveii
rife to various conje£tures of fomething floating in the aqueous hu-
mours of the eyes; but whoever, in attending to thefe fpots, keeps
his eyes unmoved by looking fteadily at the corner of a cloud, at the
fame time that he obferves the dark fpedra, will be thoroughly con-
vinced, that they have no motion but what is given to them by the
.movement of our eyes in purfuit of them. Sometimes the .form of
the fpe£lrum, when it has been received from a circular luminous
-body, will become oblong; and fometimes it will be divided into tuo
circular fpeclra, which is not owing to our changing the angle made
by the two optic axifes, according to the diftance of the clouds or
other bodies to which the fpe6lrum is fuppofed to be contiguous, but
to other caufes mentioned in No.X. 3. of this fedlion. The apparent
lizs of it will alfo be variable according to its fuppofed diftance.

As, thefe fpedra are more eafily obfervable when our eyes are a
-little weakened by fatigue, it has frequently happened, that people of
dehcate conftitutions have been much alarmed at them, fearino- a be-
ginning decay of their fight, and have thence fallen into the hands of
ignorant oculifts ; but-I believe they never are a prelude to any other
difeafe of the eye, and that it is from habit alone, and our want of at-
tention to them, that we do not fee them on all obje(5ts every hour of
our lives. But as the nerves of very weak people lofe their fenfibility,
in the fame manner as their mufcles lofe their a£livitv, by a fmall
time of exertion, it frequently happens, that fick people in the ex-
treme debility of fevers are perpetually employed in picking fomethins-
from the bed-clothes, occafioned by their miftaking the appearance
of thefe mufcce volitantes in tbeir eyes, Benvenuto Celini, an Italian
artift, a man of ftrong abilities, relates, that having paiTed the whole
night on a dillant mountain with fome companions and a conjurer,

3 Z 2 and

540- OCULAR SPECTRA. Sect. XL. 3.

and performed many ceremonies to raife the devil, on their return iiv
the morning to Rome, and looking up when the fun began to rife,
they faw numerous devils run on the tops of the houfes, as they paffed
along ; fo much were the fpeftra of their weakened eyes magnified
by fear, and made fubfervient to the purpofes of fraud or fuperftition.
(Life of Ben. Celini.)

3. Place afquare inch of white paper on a large piece of ftraw-
coloured filk ; look fteadily fbme time on the white paper, and their ■
move the center of your eyes on the filk, and a fpeftrum of the form
of the paper will appear on the filk, of a deeper yellow than the other
part of it : for the central part of the retina, having been fome time
expofed to the ftimulus of a greater quantity of white light, is become
lefs fenfible to a fmaller quantity of it, and therefore fees only the
yellow rays in that part of the ftraw-coloured filk.

Fafts fimilar to thefe are obfervable in other parts of our fyftem :
thus, if one hand be made warm, and the other expofed to the cold,
and then both of them immerfed in fubtepid water, the water is per-
ceived warm to one hand, and cold to the other ; and we are not able
to hear weak founds for fome time after we have been expofed to loud'
ones ; and we feel a'chillinefs orr coming into an atmofphere of tem-
perate warmth, after having been fome time confined in a very warm-
room : and hence the flomach, and other organs of digeftion, of thofe
who have been habituated to the greater ftimulus of fpirituous liquor^
are not excited into their due a£tion by the lefs ftimulus of common
food alone ; of which the immediate confequence is indigeftion anc?
hypochondriacifmo

nu GfP

Sect. XL. J. OCULAR SPECTRA. 54^

III. Of spectra from excess of sensibility.

Tie retina is irwre eajily excited into afiion by greater irritation after
having been lately fiibjecied to lefs^

T. If the eyes are clofed, and covered perfe6lly with a bat, for a
minute or two, in a bright day; on removing the hat a red or crimfon
light is feen through the eyelids. In this experiment the retina, after
being fome tinae kept in the dark^ becomes fo fenfible to a fmall quan-
^ tity of light, as to perceive difl:in£Uy the greater quantity of red rays-
than of others which pafs through the eyelids. A limilar coloured,
light is feen to pafs through the edges of the fingers,^ when the open,
hand is oppofed to the flame of a candle.

2. If you look for fome minutes fteadily on a window in the be-
ginning of the evening twilight,, or in a dark day, and then move,
your eyes a little,, io that thofe parts of the retina,, on which the dark,
frame- work of the window was delineated,, may now fall on the glafs
part of it, many luminous^ lines, reprefenting the frame- work, will
appear to lie acrofs the glafs panes : for thofe parts of the retina, which,
•were before leaft Simulated by the dark frame- work, are now more-,
feniible to light than the other parts of the retina which were expofed
to the more luminous parts of the window,.

3. Make with ink on white paper a very black fpot, about half aa
inch in diameter, with a. tail- about an inch in length, fo as to repre-
fent a tadpole, as in plate 2, at Se<£t. III. 8.3.; look, fteadily for a
minute on this fpot, aad, on moving the eye a little,,- the figure of
the tadpole will be feen on the white part of the paper, which figure
of the tadpole will appear whiter or more luminous than the other
parts of tha white paper; for the part of the retina on which the tad-
pole was delineated, is now more feniible to light than the other parts

542 ■ OCULAR SPECTRA. S.irT.XL.3.^

of it, which were expofed to the white paper. This experiment 13
mentioned by Dr. Irwin, but is not by him afcribed to the true caufe^
namely, the greater fenfibility of that part of the retina which hasbeeii
expofed to the black fpot,,than of the other parts which had received
the white field of paper, which is put beyond a doubt by the next
experiment.

4. On clofing the eyes after viewing the black fpot on the white
paper, as in the foregoing- experiment, a red fpot is feen of the form
of the black fpot: for that part of the retina, on which the black
fpot was delineated, being novN' more fenfible to light than the other
parts of it, which were expofed to the white paper, is capable of per-
ceiving the red raj-s which penetrate the eyelids. If this experiment
be made by the light of a tallow candle, the" fpot will be yellow in-
flead of red; for tallow candles abound much with yellow light,
which paffes in greater quantity and force through the eyelids than
blue light; hence the difficulty of diftinguifliing blue and green by
this kind of candle light. The colour of the fpedrum may pofilbly
vary in the daylight, according to the different colour of the meri-
dian or the morning or evening light.

M. Beguelin, in the Berlin Memoires, V. II. 1771, obferves, that,
when he held a book fo that the fun' fhone upon his half-clofed eye-
lids, the black letters, which, he had long infpe6ted, became red,
which muft have been thus occafioned. Thofe parts of the retina
which had received for fome time the black letters, were fo much
more fenfible than thofe parts which had been oppofed to the white
paper, that to the former the red light, which pafTed through the
eyelids, v.'as perceptible. There is a limilar ftory told, I think, in
M. de Voltaire's Hifi:orical Works, of a Duke of Tufcany, who was
playing at dice with the general of a foreign army, and, believing he
faw bloody fpots upon the dice, portended dreadful events, and retired
in conx"ufion. Tlie obfer-ver, after looking for a minute on the black

fpots

Sect. XL. 3. OCULAR SPEC T R A. 543:

fpots of a die, and carelefsly clofing his eyes, on a bright day, would
lee the image of a die with red fpots upon it, as above explained.

5. On emerging from a dark cavern, where we have long conti-
luied, the light of a bright day becomes intolerable to the eye for a
Gonfiderable time, owing to the excefs of fenfibility exifting in the-
eye, after having been long expofed to little or no ftimulus. This
©ccafions iis immediately, to contrad; the iris to its fmalleft aperture,
which becomes again gradually dilated, as the retina becomes accuf-
tomed to the greater fhimulus of the daylight.

The twinkling of a bright flar, or of a diftant candle in the night,.
is perhaps owing to the fame caufe. While we continue to look, upon
thefe luminous objeds^ their central, parts gradually appear paler,,
owing to the decreafing fenfibilitv of the part of the retina expofed to
their light; whilft, at the fame time, by the unfleadinefs of the ej^e,,
the edges of them are perpetually falling on parts of the retina that;
were juft before expofed to the darknefs of the night, and therefore.-
tenfold more fenfible to light than the- part on which, the flar cr candle
had been for fome time delineated. This pains the eye in a iimilar-
manner as when we come fuddenly from a dark 'room into bright,
daylight, and gives the appearance of bright fcintillations. Hence,
the ftars twinkle moft when the night is darkeft, and do not twinkle _-
through telefcopes, as obferved by MuiTchenbroeck; and.it will after-
wards be feen why this twinkling is forrietimes of different colours
when the objecb is very bright, as Mr. Meivill obferved in looking at
Si'rius. For the opinions of others on this fubjeft, fee Dr.Prieftley's
valuable Hiftory of Light and Colours, p. 494*

Many facts obfervable in the animal fyftera are fimilar to thefe; as-
the hot glow occaiioned by the ufual warmth of the air, or our
clothes, on coming out of a cold bath ;. the pain of the fingers on ap-
.proaching the fire after having handled fnowj and the inflamed heels
from walking in fnow. Hence thofe who have been expofed to much
.cold, have died on being Drought to a fire, .or their limbs have become,
' ' - fo

344 OCULAR SPECTRA. SccT.XL.4,

-fo much inflamed as to mortify. Hence much food or wine given
fuddenly to thofe who have almoft periftied by hunger has deftroyed
them } for all the organs of the famiflied body are now become To
■much more irritable to the ftimulus of food and wine, which they
have long been deprived of, that inflammation is excited, which ter-
minates in gangrene or fever*

IV. Of direct ocular spectra.

^ quantity of fiimulus fomewhat greater than natural excites the retina
into Jpafmodic aUion^ which ceajes in a few feconds .

A CERTAIN duration and energy oftheflimulus of light and colours
excites the perfe£l a£iion of the retina in vifion ; for very quick mo-
tions are imp-erceptible to us, as well as very flow ones, as the
■whirling of a top, or the Ihadow on a fun-dial. So perfe£l darknefs
does not afFe£b the eye at all ; an-d excefs of hght produces pain, not
-vifion.

I. When a fire-coal is whirled round in the dark, a lucid circle

remains a confiderable time in the eye; and that with fo much vivacity

of light, 'that it is miftaken for a continuance of the irritation of the

•objed. 'In the fame manner, when a fiery meteor fhoots acrofs the

night, it appears to leave a long lucid train behind it, part of which,

and perhaps fometimes the whole, is owing to the continuance of the

a^Sion of the retina after having been thus vividly excited. This is

"beautifully illuflrated by the following experiment: fix a paper fail,

three or four inches in diameter, and made like that of a fmoke jack,

in a tube of pafteboard ; on looking through the tube at a diflrant pro-

•fpeft, fome disjointed parts of it will be feen through the narrow inter-

rvals between the fails; but as the fly begins t^ revolve, thefe interval-s

•appear

Sect. XL. 4. OCULAR SPECTRA. 545

appear larger ; and when it revolves quicker, the whole profped: is
feen quite as diftindt as if nothing intervened, though lefs luminous.

2. Look through a dark tube, about half a yard long, at the area
of a yellow circle of half an inch diameter, lying upon a blue area of
double that diameter, for half a minute; and on clofuig your eyes the
colours of the fpeftrum will appear fimilar to the two areas, as ia
fig. 3.; but if the eye is kept too long upon them, the colours of the
fpeftrum v/ill be the reverfe of thofe upon the paper, that is, the in-
ternal circle will become blue, and the external area yellow ; hence
fome attention is required in making this experiment.

3. Place the bright flame of a fpermaceti caudle before a black ob-
je<St in the night ; look fteadily at it for a ITiort time, till it is obferved
to become fomewhat paler ; and on doling the eyes, and covering
them carefully, but not fo as to comprefs them, the image of the
blazing candle will continue diftlndlly to be vifible.

4. Look fleadily, for a fhort time, at a window in a dark day, as in
Exp, 2. Sedl. III. and then clofingyour eyes, and covering them with
your hands, an exaS: delineation of the window remains for fome time
%'ifible in the eye. This experiment requires a little practice to make
it fucceed well ; fince, if the eyes are fatigued by looking too long on
the window, or the day be too bright, the luminous parts of the win-
dow will appear dark in the fpeftrum, and the dark parts of the
frame-work will appear luminous, as in Exp. 2. Sedl. III. And it is
even difficult for many, who firft try this experiment, to perceive the
fpeclrum at all ; for any hurry of mind, or even too great attention to-
the fpeftrum itfelf, will difappoint them, till they have had a little
experience in attending to fuch fmall fenfations.

The fpciStra defcribed in this feftion, termed direct ocular fpectra,
are produced without much fatigue of the eye ; the irritation of the
luminous objedl being foon withdrawn, or its quantity of light being
not fo great as to produce any degree of uneafineis in the organ of
vifion; which diflinguifhes them from the next clafs of ocular fpeclra,

4 A which

546 OCULAR SPECTRA. SECT.XL.5.

which are the confequence of fatigue. Thefe diredl fpedra are beft
obferved in fuch circumftances that no light, but what comes from
the objeft, can fall upon the eye ; as in looking through a tube, of
half a yard long, and an inch wide, at a yellow paper on the fide of a
room, the dire£l fpeftrum was eafily produced on clofing the eye with-
out takino; it from the tube : but if the lateral light is admitted through
the eyelids, or by throwing the fpedlrum on white paper, it becomes
a reverfe fpe£lrum, as will be explained below.

The other fenfes alfo retain for a time the impreffions that have
been made upon them, or the aiSlions they have been excited into.
So if a hard body is preffed upon the palm of the hand, as is pra«9:ifed
in tricks of legerdemain, it is not eafy to diftinguifh for a few fecoiids
whether it remains or is removed j and taftes continue long to exift
vividly in the mouth, as the fmoke of tobacco, or the tafte of gentian,
after the fapid material is withdrawn.

V. A quantity of Jlhnulus fomewbat greater than the lajl mentioned
excites the retina into fpafmodlc a£llon^ which ceafes and recurs'
alternately.

1. On looking for a time on the fetting fun, fo as not greatly to
fatigue the fight, a yellow fpedtrum is feen when the eyes are clofed
and covered, which continues for a time, and then difappears and re-
curs repeatedly before it entirely vanifhes. This yellow fpedrum of
the fun when the eyelids are opened becomes blue ; and if it is made
to fall on the green grafs, or on other coloured objedls, it varies its
own colour by an intermixture of theirs, a-s will be explained in ano-
ther place.

2. Place a lighted fpermaceti candle in the night about one foot
from your eye, and look fleadily on the centre of the flame, till your

eye

Sect.XL.6. ocular SPECTRA. 547

eye becomes much more fatigued than in Sedl. IV. Exp. 3. ; and 0:1
clofing your eyes a reddifh fpetlrum will be perceived, which will
ceafe and return alternately.

The adlion of vomiting in like manner ceafes, and is renewed by
intervals, although the emetic drug is thrown up'with the firft effort :
fo after-pains continue fome time after parturition ; and the alternate
pulfations of the heart of a viper are renewed for fome time after it is
cleared from its blood.

VI. Of reverse ocular spectra.

S'he ret'ma after having been excited into action by a (iimuliis fomeivhat
greater than the laji mentioned falls into oppojite fpafmodic adtion.

The aftions of every part of animal bodies may be advantageoufly
compared with each other. This ftrict analogy contributes much to
the inveftigation of truth ; while thofe loofer analogies, which com-
pare the phenomena of animal life with thofe of cheraiftry or me-
chanics, only ferve to miflead our inquiries.

When any of our larger mufcles have been in long or in violent
adion, and their antagonifls have been at the fame time extended, as
foon as the action of the former ceafes, the limb is ftretched the con-
trary way for our eafe, and a pandiculation or yawning takes place.

By the following obfervations it appears, that a fimilar circumftance
obtains in the organ of vifion ; after it has been fatigued by one kind
of action, it fpontaneoufly falls into the oppofite khid.

]. Place a piece of coloured filk, about an inch in diameter, on a
fheet of white paper, about half a yard from your eyes; look fleadily
upon it for a minute ; then remove your eyes upon another part of the
white paper, and a fpeclrum will be feen of the form of the filk
thus infpeded, but of a colour oppofite to it. A, fpedrum nearly

4 A 2 fimilar

548 OCULAR SPECTRA. Sect.XL.6,

fimilar will appear if the eyes are clofed, and the eyelids (haded by ap-
proaching the hand near them, fo as to permit fome, but to prevent
too much light falling on them.

Red filk produced a green fpedlrum.

Green produced a red one.

Orange produced blue.

Blue produced orange.

Yellow produced violet.

Violet produced yellow.
That in thefe experiments the colours of the fpe£tra are the reverfe
of the colours which occafioned them, may be feen by examining the
third figure in Sir Ifaac Newton's Optics, L. II. p. i, where thofe
thin lamin;£ of air, which reflefted yellow, tranfmitted violet ; thofe
which refle£led red, tranfmitted a blue-green ; and fo of the reft,
agreeing with the experiments above related.

2. Thefe reverfe fpe£tra are fimilar to a colour, formed by a com-
bination of all the primary colours except that with which the eye
has been fatigued in making the experiment : thus the reverfe
fpeiflrum of red muft be fuch a green as would be produced by a com-
bination of all the other prifmatic colours. To evince this fadl the
following fatisfadlory experiment was made. The prifmatic colours
were laid on a circular pafteboard wheel, about four inches in dia-
meter, in the proportions defcribed in Dr. Prieflley's Hiflory of Light
and Colours, pi. 12. fig. 83. except that the red compartment was
entirely left out, and the others proportionably extended fo as to com-
plete the circle. Then, as the orange is a mixture of red and yellow,
and as the violet is a mixture of red and indigo, it became neceffary
to put yellow on the wheel inftead of orange, and indigo inflead of
violet, that the experiment might more exaftly quadrate with the
theory it was defigned to eftablifli or confute; becaufe in gaining a
green fpedlrum from a red objeft, the eye is fuppofed to have become
infenfible to red light. This wheel, by means of an axis, was made

6 to

Sect.XL. 7. OCULAR SPECTRA. 549

to whirl like a top ; and on its being put in motion, a green colour
was produced, correfponding with great exadnefs to the reverfe
fpe£trum of red.

3. In contemplating any one of thefe reverfe fpeclra in the clofed
and covered eye, it difappears and re-appears feveral times fiicceflively,
till at length it entirely vanifhes, like the diredl fpeclra in Se£l. V, ;
but with this additional circumftance, that when the fpedlrum be-
comes faint or evanefcent, it is inftantly revived by removing the
hand from before the eyelids, fo as to admit more light : becaufe
then not only the fatigued part of the retina is inclined fpontaneoufly
to fall into motions of a contrary direftion, but being ftill fenfible to
all other rays of light, except that with which it was lately fatigued,
is by thefe rays at the fame time Simulated into thofe motions which
form the reverfe fpeiftrum.

From thefe experiments there is reafon to conclude, that the fa-
tigued part of the retina throws itfelf into a contrary mode of adlion,
like ofcitation or pandiculation, as foon as the ftimulus which has fa-
tigued it is withdrawn ; and that it flill remains fenfible, that is, liable
to be excited into action by any other colours at the fame time, ex-
cept the colour with which it has been fatigued.

VII. The retina after having been excited itito aSlion by a fiimulus fome-
what greater than the laji mentioned falls into various fiiccefrce
fpafmodtc aciiofis.

I. On looking at the meridian fun as long as the eyes can well
bear its brightnefs, the difk firfl becomes pale, with a luminous
crefcent, which feems to librate from one edge of it to the other,
owing to the unfteadinefs of the eye; then the whole phafis of the
fun becomes blue, furrounded with a white halo; and on clofins: the
eyes, and covering them with the hands, a yellow fpectrum is
feen, which in a little time changes into a blue one.

M. de

550 OCULAR SPECTRA. Sect. XL. 7,

M. de la Hire obferved, after looking at the bright fun, that the
impreffion in his eye firft affumed a yellow appearance, and then,
green, and then blue ; and wifhes to afcribe thefe appearances to
ifome afFedlion of the nerves. (Porterfield on the Eye, Vol. I.

P- 343-)

2. After looking fleadily on about an inch fquare of pink filk,

placed on white paper, in a bright funfliine, at the diftance of a foot
from my eyes, and clofing and covering my eyelids, the fpeftrum of
the filk was at firft a dark green, and the fpeftrum of the white paper
became of a pink. The fpe£tra then both difappeared ; and then the
internal fpeftrum was blue ; and then, after a fecond difappeararrce,
became yellow, and laftly pitik, whilfl the fpe£trum of the field va-
ried into red and green.

Thefe fucceffions of different coloured fpeftra were not exaftly the
lame in the different experiments, though obferved, as near as could
•be, with the fame quantity of light, and other fimilar circumftances ;
owing, I fuppofe, to trying too many experiments at a time ; fo that
the eye was not quite free from the fpeftra of the colours which were
previoufly attended to.

The alternate exertions of the retina in the preceding fe£lion re-
fembled the ofcitation or pandiculation of the mufcles, as they were
performed in dire6lions contrary to each other, and were the confe-
quence of fatigue rather than of pain. And in this they differ from
the fucceffive diflimilar exertions of the retina, mentioned in this fec-
tion, which refemble in miniature the more violent agitations of the
limbs in convulfive difeafes, as epilepfy, chorea S. Viti, and opiftho-
tonos ; all which difeafes are perhaps, at firft, the confequence of
pain, and have their periods afterwards eftiablifiied by habit.

VIII. The

Sect.XL.8.9. ocular SPECTRA* 551

VIII. 'TBs retina, after having been excited into aEiion by a flimulus fonte'
what greater than the lajt mentioned^ J alls into a fixed fpafmodic
a£liony which continues for fame days,

I. After having looked long at the meridian fun, in making fome
of the preceding experiments, till the diiks faded into a pale blue, I
frequently obferved a bright blue fpe6trum of the fun on other objeds
all the next and the fucceedlng day, which conftantly occurred when I
attended to it, and frequently when I did not previoufly attend to it.
When I clofed and covered my eyes, this appeared of a dull yellow;
and at other times mixed with the colours of other objefls on which
it was thrown. It may be imagined, that this part of the retina was
become infenfible to white light, and thence a bluifli fpedlrum became
vifible on all luminous objefts ; but as a yellowifli fpeftrum was alfo
feen in the clofed and covered eye, there can remain no doubt of this
being the fpedlrum of the fun. A fimilar appearance was obferved b^
M. ^pinus, which he acknowledges he could give no account of.
(Nov. Com. Petrop. V. 10. p. 2. and 6.)

The locked jaw,, and fome cataleptic fpafms, are refembled by this
phenomenon ; and from hence we may learn the danger to the eye by
infpedling very luminous objeds too long a time.

IX. A quantity of jiimulus greater than the preceding induces a temporary
paralyfis of the organ ofvifion.

I. Place a circular piece of bright red filk, about half an inch in
diameter, on the middle of a fheet of white paper ; lay them on the
floor in. a bright funfliine, and fixing your eyes fteadily on the. center
of the red circle, for three or four minutes, at the diftance of four 01:

• fix

«;52 'OCULAR SPECTRA, Sect.XL.io.

fix feet from the obje£l, the red filk will gradually become paler, and
finally ceafe to appear red at all.

2. Similar to thefe are many other animal fa(5ls ; as purges, opiates,
and even poifons, and contagious matter, ceafe to ftimulate our fyftem,
after we have been habituated to their ufe. So fome people deep un-
difturbed by a clock, or even by a forge hammer in their neighbour-
hood : and not only continued irritations, but violent exertions of any
kind, are fucceeded by temporary paralyfis. The arm drops down
after violent aftion, and continues for a time ufelefs; and it is probable,
that thofe who have perifhed fuddenly in fwimming, or in fcating on
the ice, have owed their deaths to the paralyfis, or extreme fatigue,
which fucceeds every violent and continued exertiono

X. Miscellaneous Remarks,

There were fome circumftances occurred in making thefe experi-
tnents, which were liable to alter the refults of them, and which I
fhall here mention for the affiftance of others, who may wifli to re-
peat them.

J. Of SreSi and inverfe fpeBra extjiing ai the fame time', of reciprocal
dlredi fpe&ra-, of a cofnbination of direct and inverfe fpeBra ; of a
fpediral halo ; rules to fre- determine the colours of fpedlra,

n. When an area, about fix inches fquare, of bright pink Indian
paper, had been viewed on an area, about a foot fquare, of white
writing paper, the internal fpedlrum in the clofed eye was green,
beino- the reverfe fpeftrum of the pink paper ; and the external fpec-
trum was pink, being the dired fpedrum of the pink paper. The

fame

Sect.XL/io. CCULAR spectra. 553

fame circumilance happened when the internal area was white, and
external one pink ; that is, the internal fpeftrum was pink, and the
external one green. All the fanie appearances occurred when the pink
paper was laid on a black hat.

b. When fix inches iquare of deep violet pohOTed paper was viewed
on a foot fquare of Vv^hite writing paper, the internal fpedrum was
yellow, being the reverfe fpcLlrum of the violet paper, and the
external one was violet, being the dired fpedrum of the violet
paper.

c. When fix inches fquare of pink paper was viewed on a foot
fquare of blue paper, the internal fpeclrum was blue, and the exter-
nal fpeftrum was pink ; that is, the internal one was the dire6l fpec-
trum of the external object, and the external one was the direct fpec-
trum of the internal objedl, inftead of their being each the reverfe
fpedlrum of the objects they belonged to.

d. When fix inches fquare of blue paper were viewed on a foot
fquare of yellow paper, the interior fpedtrum became a brilliant yel-
low, and the exterior one a brilliant blue. The vivacity of the
fpe£tra was owing to their being excited both by the itimulus of the
interior and exterior objects ; fo that the interior yellow fpectrum
was both the reverfe fpedtrum of the blue paper, and the direct
one of the yellow paper ; and the exterior blue fpeftrum was both
the reverfe fpedtrum of the yellow, paper, and the diredt one of the
blue paper.

e. When the internal area was only a fquar-e half- inch of red paper,
laid on a fquare foot of dark violet paper, the internal fpe£trum was
green, with a reddifli-blue halo. When the red internal paper was
two inches fquare, the internal fpeitrum was a deeper green, and the
external one redder. When the internal paper was fix inches fquare,
the fpe£trum of it became blue, and the fpedbrura of the extertial paper
was red.

4B /.When

S;54- OCULAR SPECTRA. Sect. XL. t o.

J\ When a fquare half-inch of blue paper was laid on a fix-inch
fquare of yellow paper, the fpe«3:rum of the central paper in the
clofed eye vvas yellow, incircled with a blue halo. On looking long
©n the meridian fun, the dilk fades in-to a pale blue furrounded with a.
whitifli halo.

Thefe circumftances, though they very much perplexed the ex-
periments till they were inveftigated, admit of a fatisfailory explana-
tion ;. for while the rays from the bright internal objedl in exp. a. fall
with their full force on the center of the retina, and, by fatiguing
that part of it, induce the reverfe fpedtrum, many fcattered rays, from
the fame internal pink paper, fall on the more external parts of the
retina, but not in fuch quantity as to occafion much fatigue, and
hence induce the dired fpedlrum of the pink colour in thofe parts of
the eye. The fame reverfe and direft fpe£tra occur from the violet
paper in exp. ^. .* and in exp; c. the fcattered rays from the central
pink paper produce a diredl fpedrum of this colour on the external
parts of the eye, while the fcattered rays from the external blue
paper produce a diredl fpeftrum of that colour on tke central part of
the eye, inftead of thefe parts of the retina falling reciprocally into
their reverfe fpedra. In exp. d. the colours being the reverfe of each,
other, the fcattered rays from the exterior objeft falling on the cen-
tral parts of the eye, and there exciting their direct fpedtrum, at the
fame time that the retina was excited into a reverfe fpeftrum by the
central objeft, and this diredt and reverfe fpe6lrum being of fimilar
colour, the fuperior brilliancy of this fpeftrum was produced. la
exp. e. the efFeit of various quantities of ftimulus on the retina, from
the different refpeftive fizes of the internal and external areas,, induced:
a fpe£lrum of the internal area in the center of the eye, combined of
the reverfe fpeftrum of that internal area and the direct one of the ex-
ternal area, in various (hades of colour, from a pale green to a deep
blue, with fimilar changes in the fpedtruna of the external area,. For

the.

Sect. XL. lo. OCULAR SPECTRA. 555

the fame reafons, when an internal bright obje6t was fmall, as in
,exp. y^ inflead of the whole of the fpe6trunn of the external objeft
being reverfe to the colour of the internal objeft, only a kind of halo,
or radiation of colour, fimilar to that of the internal objeft, was
fpread a little way on the external fpeftrum. For this internal
blue area being fo fmall, the fcattered rays from it extended but a lit-
tle way on the image of the external area of j^ellow paper, and could
therefore produce only a blue halo round the yellow fpeftrum in the
center.

if any one fhould fufpedl that the fcattered rays from the exterior
coloured obje6l do not intermix with the rays from the interior co-
loured object, and thus affeft the central part of the eye, let him look
through an opake tube, about two feet in length, and an inch in di-
ameter, at a coloured wall of a room with one eye, and with the
other eye naked ; and he will find, that by fliutting out the lateral
light, the area of the wall feen through a tube appears as if illumi-
nated by the funfhine, compared with the other parts of it; from
whence arifes the advantage of looking through a dark tube at diftaut
paintings.

Hence we may fafely deduce the following rules to determine be-
■ fore-hand the colours of all fpedlra. i. The dire6l fpedlrum without
any lateral light is an evanefcent reprefentation of its abje6t in the un-
fatigued eye. 2. With forne lateral light it becomes of a colour com-
bined of the dire£t fpeftrum of the central obje6t, and of the circum-
jacent obje6ls, in proportion to their refpedtive quantity and brilli-
ancy. 3. The reverfe fpedtrum without lateral light is a reprefenta-
tion in the fatigued eye of the form of its objedls, with fuch a colour
as would be produced by all the primary colours, except that of the
objeft. 4. With lateral light the colour is compounded of the re-
verfe fpeftrum of the central objecfl, and the direft fpedlrum of the
circumjacent objefts, in proportion to their refpe<£liVe quantity and
brilliancy.

■4 B 2 2. Variation

556 OCULAR SPECTRA. Sect, XL. lo.

z. Variation and vlvaciiy of the fpecira occajioned by extraneous light.

The reverfe fpedrura, as has been before explained, ia fimilar to a
colour, formed by a combination of all the primary colours, except
tha-t with which the eye has been fatigued in making the experiment :
fo the reverfe fpectrum of red is fuch a gretn as would be produced
by a combination of all the other. prifmatic colours. Now it muft be
obferved, that this reverfe fpedrum of red is therefore the dired fpec-
trum of a combination of all the other prifmatic colours, except the
red ; whence,- on removing the eye from a piece of red filk to a fheet
of white paper, the green fpedrum, which is perceived,, may either
be called the reverfe fpeftrum of the red filk, or the dire6l fpeclrum'
of all the rays from the white paper,, except the red ; for in truth it
is both. Hence we fee the reafon why it is not eafy to gain a dtredl
fpeftrum of any coloured objeil in the day-time, where there is much
lateral light, except of very bright objefts, as of the fetting fun, or.
by looking through an opake tube j becaufe the lateral external light
falling alfo on the central part af the retina, contributes to induce the
reverfe fpe(3:rum, which is at the fame time the diredl fpedrum-o£
that lateral light, dedudling only the colour of the central objedl which
we have been viewing. And for the fame reafon, it is difficult to
oain the reverfe fpedrum, where there is no lateral light to contri-
bute to its formation. Thus, in looking through an opake tube on a
yellow wall, and clofing my eye, without admitting any lateral light,
the fpedlra were all at firft yellow ; but at Length changed into blue.
And on looking in the fame manner on red paper, I did at length get
a ^reen fpe£lrum ; but they were all at firfl red ones : and the fame
after looking at a candle in the night.

- The reverfe fpedrum was formed with greater facility when the
/ eye

Sect. XL. lo. OCULAR SPECTRA.. 557

eye was thrown from the object on a fheet of vshite paper, or when
light was admitted through the clofed eyelids; becaufe not only the
fatigued part of the retina was inclined fpontaneoufly to fall into mo-
tions of a contrary diredion ; but being ftill fenfible to all other rays of
light except that v/lth which it was lately fatigued, was by thefe rays
Simulated at the fame time into thofe motions which form the reverfe
fpedrum. Hence, when the reverfe fpedtrum of any colour became
faint, it was wonderfully revived by admitting more light through
the eyelids, by removing the hand from before them : and hence, on
covering the clofed eyelids, the fpeclrum would often ceaie for a time»
till the retina became fenuble to the ftimulus of the fmaller quantity
of light, and then it recurred. Nor was the fpeclrum only changed
in vivacity, or in degree, by this adinifiion of light through the ej'^e-
lids ; but it frequently happened, after having viewed bright obje6ls».
that the fpedrum in the clofed and covered eye was changed into a
third fpedrum, when light was admitted through the eyelids : whiclx
third fpedrum was compofed of fuch colours as could pafs through
the eyelids, except thofe of the objedt- Thus, when an area of halF
an inch diameter of pink paper was viewed, on a fheet of white paper
in the funfhine, the fpedrum with clofed and covered eyes was green j
but on removing the hands from before the clofed eyelids, the fpec-
trum became yellow, and returned infiiantly again to green, as often
as the hands were applied to cover tke eyelids, or removed from them :
for the retina being now infenfible to red light, the yellow rays paff-
ing through the eyelids in greater quantity than the other colours,.
induced a yellow Ipeclrum ; whereas if the fpeftrum was thrown on
white paper, with the eyes open, it became only a lighter green.

Though a certain quantity of light facilitates the formation of the
reverfe fpeftrum, a greater quantity prevents its formation, as the
more powerful ftimulus excites even the fatigued parts of the eve into
aftion ; otherwife we fhould fee the fpeclrum of the laft viewed objeil
as.oiten as we turn our eyes. Hence the reverfe fpedra are beil leai

558 OCULAR SPECTP.A. Sect. XL. lo.

hy gradually approaching the hand near the clofed eyelids to a certain
diftance only, which mufl be varied with the brightnefs of the day,
or the energy of the fpedrum. Add to this, that all dark fpedtra, as
black, blue, or green, if light be admitted through the eyelids, after
they have been fotne time covered, give reddifh fpe£tra, for the i-ea-
fons given in Se£l. III. Exp. i.

From thefe circumflances of the extraneous light coinciding with
the fpontaneous efforts of the fatigued retina to produce a reverfe fpec-
trum, as was obferved before, it is not eafy to gain a direft fpeftrum,
except of obje6ts brighter than the ambient light ; fuch as a candle ia
the night, the fetting fun, or viewing a bright obje6t through an
-opake tube ; and then the reverfe fpedlrum is inftantaneoufly produced
by the admiflion of fome external light ; and is as inftantly converted
again to the diredl fpeilrum by the exclufion of it. Thus, on look-
ing at the fetting fun, on clofing the eyes, and covering them, a yeU
low fpeftrum is feen, which is the diredl fpedlrum of the fetting fun ;
but on opening the eyes on the Iky, the yellow fpe£lrum is immedi-
ately changed into a blue one, which is the reverfe fpedlrum of the
yellow fun, or the diredt fpedlrum of the blue Iky, or a combination
, of both. And this is again transformed into a j^ellow one on clofing
the eyes, and fo reciprocally, as quick as the motions of the opening
and clofing eyelids. Hence, when Mr. Melvill obferved the fcintilla-
tions of the flar Sirius to. be fometimes coloured, thefe were probably
the diredl fpedlrum of the blue iky on the parts of the retina fa-
tigued by the white light of the ftar. (Effays Phyfical and Literary,
p. 8 1. V. 2.)

When a diredl fpedlrum is thrown on colours darker than itfelf, it
mixes with them ; as the yellow fpedlrum of the fetting fun, thrown
on the green grafs, becomes a greener yellow. But when a diredl
fpedlrum is thrown on colours brighter than itfelf, it becomes inftant-
ly changed into the reverfe fpedlrum, which mixes with thofe brighter
colours. So the yellow fpedlrum of the fetting fun thrown on the

luminous

Sect. XL. 10. OCULAR SPECTRA.^ 559.

luminous Ikv becomes blue, and changes with the colour or bri'j;ht-
iiels of the clouds on which it ajjpears. But tlie reverfe fpedtium
mixes with eveiy kind of colour on whicli it is thrown, whether
brighter than itlelf or not : thus the reverfe fpectrum, obtained by-
viewing a piece of yellow filk, when tlirown on white paper, was a.
lucid blue green ; when thrown on black Turkey leather, becomes a.
deep violet. And the fpedrum of blue filk, thrown on white paper,
was a light yellow ; on black filk was an obfcure orange ; and the
blue fpedrum, obtained from orange-coloured filk, thrown on yellow^
became a sireen^

In thefe cafes the retina is thrown into adivity or fenfatlon by the
fliimulus of external colours, at the fame time that it continues the-
aftivity or fenfation which forms the fpedlra ; in the fame manner as
the prifmatic colours, painted on a whirling top, are feen to mix to- •
gether. Whenthefe colours of external objects are brighter than the
direft fpeftrum which is thrown upon them, they change it into the
reverfe fpedtrum, like the admiffion of external light oil a diredl fpec-
trum, as explained above. When they are darker than the dired fpec-
trum, they mix with it, their weaker flimulus being iufufficieiit ta
iiiduce the reverfe fpedrum*

3. Variation offpeSira in refpefi to number^ and figure, and reimjjion^.

When we look long and attenttively at any objeft, the eye cannot
always, be kept entirely motionlefs 5 hence, on infpedling a circular
area of red filk placed on white paper, a lucid crefcent or edge is i^tn.
to librate on one fide or other of the red circle : for the exterior parts
of the retina fometimes falhng on the edge of the central filk, and
lometimes on the white paper, are lefs fatigued with red light than
the central part of the retina, which is conilantly expofed to it ; and
3 therefore.

560 OCULAR SPECTRA. Sect. XL. to.

therefore, when they fall on the edge of the red filk, they perceive it
more vividly. Afterwards, when the eye becomes fatigued, a green
fpeftrum in the form of a crefcent is feen to librate on one fide or .
other of the central circle, as by the unfteadinefs of the eye a part of
the fiitigiied retina falls on the white paper ; and as by the increafing
fatigue of the eye the central part of the filk appears paler, the edge on
which the unfitigued part of the retina occafionally falls will appear
of a deeper red than the original filk, becaufe it is compared with the
pale internal part of it. M. de Bufton in making this experiment ob-
ferved, that the red edge of the filk was not only deeper coloured than
the original filk ; but, on his retreating a little from it, it became ob-
long, and at length divided into two, which muft have been owing to
his obferving it either before or behind the point of ihterfeftion of the
two optic axifes. Thus, if a pen is held up before a diftant candle, when
we look intenfely at the pen two candles are feen behind it ; when we
look intenfely at the candle two pens are feen. If the fight be un-
fleady at the time of beholding the fun, even though one eye only be
ufed, many images of the fun will appear, or luminous lines, when
the eye is clofed. And as fome parts of thefe will be more vivid than
others, and fome parts of them will be produced nearer the center of
the eye than others, thefe will difappear Iboner than the others ; and
hence the number and fhape of thefe fpeclra of the fun will continually
vary, as long as they exift. The caufe of fome being more vivid than
others, is the unfteadinefs of the eye of the beholder, fo that fome
parts of the retina have been longer expofed to the funbeams. That
fome parts of a complicated fpe6trum fade and return before other parts
of it, the following experiment evinces. Draw three concentric cir-
cles ; the external one an inch and a half in diameter, the middle one
an inch, and the internal one half an inch ; colour the external and
internal areas blue, and the remaining one yellow, as in Fig. 4. ; after
having looked about a minute on the center of thefe circles, in a bright
light, the fpedrum of the external area appears firil in the clofed eye,

then

Sect. XL. 10. OCULAR SPECTRA. 561

then the middle area, and laftly the central one ; and then the central
one difappears, and the others in inverted order. If concentric circles
of more colours are added, it produces the beautiful ever changing
lpe<£lrum in Sedl. I. Exp. 2.

From hence it would feem, that the center of the eye produces
quicker remifTions of fpeftra, owing perhaps to its greater fenfibility ;'
that is, to its more energetic exertions. Thefe remifhons of fpeftra
bear fome analogy to the tremors of the hands, and palpitations of the ,
heart, of weak people : and perhaps a criterion of the flrength of any
mufcle or nerve may be taken from the time it can be continued in
exertion.

4. Variation offpecira In reJpeSl to briU'iancy, the vijibllity of the c'lrcu-'

lation of the blood in the eye.

1. The meridian or evening light makes a difference in the colours
of fome fpedra j for as the fun defcends, the red rays, which are lefs
refrangible by the convex atmofphere, abound in great quantity.
Whence the fpedlrum of the light parts of a window at this time, or
early in the morning, is red ; and becomes blue either a little later or
earlier ; and wliite in the meridian day ; and is alfo variable from the
colour of the clouds or iky which are oppofed to the window.

2. All thefe experiments are liable to be confounded, if they are
made too foon after each other, as the remaining fpedrum will mix
with the new ones. This is a very troublelbrae circumflance to
painters, who are obliged to look long upon the fame colour ; and in
particular to thofe whofe eyes, from natural debilitj, cannot long
continue the fame kind of exertion. For the fame reafon, in makino-
thefe experiments, the refult becomes much varied if the eyes, after
viewing any objeft, are removed on other objeds for but an inftant of
time, before we clofe them to view the fpedrum ; for the light from

4C the

563 OCULAR SPECTRA. Sect.XL. 10.

the object, of which we had only a franfient view, in the very time of -
clofing our eyes ads 'as a ftimulus on the fatigued retina ; and for a
time prevents the defired fpedrum from appearing, or mixes its own
fpe6lrum with it. Whence, after the eyelids are clofed, either a
dark field, or fome unexpe£^ed colours, are beheld for a few feconds,,
before the defired fpeftrum becomes diftinftly vifible.

3. The length of time taken up in viewing an objeft, of which we
are to obferve the fpe6trum, makes a great difference in the appearance
of the fpeftrum, not only in its vivacity, but in its colour ; as the

. direft fpedrum of the central objeft, or ofthe circumjacent ones, and;
alfo the reverfe fpedra of both, with their various combinations, as
well as the time of their diaration in the eye, and of their remifllons-
or alternations, depend upon the degree of fatigue the retina, is fuhjedt-
ed to. The Chevalier d'Arcy conftrufted a machine by which a coal
of fire was whirled round in the dark, and found, that when a lu-
minous body made a revolution in. eight thirds, of tin>e, it prefented to
the eye a complete circle of fire ; from whence he concludes, that the.
imprefl^ion continues on the organ about the feventh part of a fecond.
(Mem. de I'x'^cad, des Sc. 1765.) This,, however, is. only to be coi>-
fidered as the fhortefl: time of the duration, of thefe dli-eft.fpeclra ; fince
-in the fatigued eye both the dire£l and reverfe fpeilra, with their ia-
termifllons, appear to take up many feconds of time, and feem very
variable in proportion to the circumftances of fatigue or energy.

4. It fometimes happens, if the eyeballs have been rubbed hard.
with the fingers, that lucid fparks are feen in quick motion amidfl the
Ipearum we are attending to. This is funilar to the flaflies of fire
from a liroke ou the eye in fighting, and is refembled by the warmth
and glow, which appears upon. the ikin after friftion, and is probably
ovvino- to an acceleration ofthe arterial blood into the veffels emptied

CD-

by the previous prefl'are. By being accuflomed to obferve fuch fmall
fenfations in the eye, it is eafy to fee the circulation of the blood in
this organ. I hare attended to this frequently,. Vi'hcn 1 have obferved

BANKS.

Sect. XL. 10. OCULAR SPECTRA. 563

my eyes more than commonly fenfible to other fpeclra. The circu-
lation may be feen either in both eyes at a time, or only in one of
them ; for as a certain quantity of light is neceflary to produce this
curious phenomenon, if one hand be brought nearer the clofed eyelids
than the other, the circulation in that eye will for a time difappear.
For the eafier viewing the circulation, it is fometimes neceflary to
rub the eyes with a certain degree of force after they are clofed, asid
to hold the breath rather lonsfer than is agreeable, which, hv accu-
mulating more blood in the eye, facilitates the experiment ; but in
general it may be feen- diftinclly after having examined other fpeAra
•with your back to the light, till the eves become wearv; then having
covered your clofed eyelids for half a minute, till the fpectrum is
faded away which you were examining, turn your face to the light,
and removing your hands from the eyelids, by and by again fhade them
a little, and the circulation becomes curiouily diilinct. The flreams
of blood are however generally feen to unite, which fliews it to be the
venous circulation, owing, I fuppofe, to the greater opacity of the
colour of the blood in thefe vefiels ; for this venous circulation is alfo
much .more.eafily ieen by the microfcope in the tail of a tadpole.

3. 'Variation of fpeclra in refpeB to dijlincinefs andji^e; zvith a new ixiav

of magriifying ohjecis.

I. It was before obferved, that when the two colours viewed- to-
gether were oppofite to each other, as yellow aiid blue, red and green,
&c. according to the table of refleftions and tranfmiffions of light in
Sir Ifaac Newton's Optics, B. II. Fig. 3. the fpefira of thofe colours
were of all others the moft brilliant, and beft defined; becaufe they
were combined of the reverie fpe^rum of one colour, and of the direct
fpedrum of the other. Hence, in books printed with fmall tvpes, or
ui the minute graduation of thermometers, or of clock-faces, which

_4 C 2 are

564 OCULAR SPECTRA. Sect. XL. 10.

are to be feeii at a diftance, if the letters or figures are coloured with
orange, and the ground with indigo ; or the letters with red, and the
ground with green ; or any other lucid colour is ufed for the letters,
the fpedlrum of which is fimilar to the colour of the ground ; fuch let-
ters will befeen much more diftindly, and with lefs confufion, thaa
in black or white : for as the fpeclrum of the letter is the fame colour
with the ground on which they are feen, the unfteadinefs of the eye
in long attending to them will not produce coloured lines by the edges
of the letters, which is the principal caufe of their confufion. The
beauty of colours lying in vicinity to each other, whofe fpeftra are
thus reciprocally fimilar to each colour, is owing to this greater eafe
that the eye experiences in beholding them diftindlly; and it is pro-
bable, in the organ of hearing, a fimilar circumftance may conftitute
the pleafure of melody. Sir Ifaac Newton obferves, that gold and
indigo were agreeable when viewed together ; and thinks there may
be fome analogy between the fenfations of light and found. (Optics,
Qu. 14.)

In viewing the fpeftra of bright objefts, as of an area of red filk of
half an inch diameter on white paper, it is eafy to magftify it to ten-
fold its fize : for if, when the fpeftrum is formed, you flill keep your
eye fixed on the filk area, and remove it a few inches further from
you, a green circle is feen round the red filk : for the angle now fub-
tended by the filk is lefs than it was when the fpedrum was formed,
but that of the fpe£lrum continues the fame, and our imagination
places them at the fame diftance. Thus when you view a fpe£trum
on a fheet of white paper, if you approach the paper to the eye, you
may dimini(h it to a point ; and if the paper is made to recede from
the eye, the fpeflrum will appear magnified in proportion to the dif-

tance.

I was furprifed, and agreeably amufed, with the following experi-
ment. I covered a paper about four inches fquare with yellow, and
with a pen filled with a blue colour wrote upon the middle of it the

word

Sect. XL. 10. OCULAR SPECTRA. 565

word BANKS in capitals, as in Fig. 5, and fitting with my back to
the fun, fixed my eyes for a minute exadlly on the center of the let-
ter N in the middle of the word ; after clofing my eyes, and (hading
them fomewhat with my hand, the word was diftindtly feen in the
fpedlrum in yellow letters on a blue field ; and then, on opening my
eyes on a yellowifh wall at twenty feet diftance, the magnified name
of BANKS appeared written on the wall in golden characlers.

Conclujion.

It was obferved by the learned M. Sauvages (Nofol. Method.
CI. VIII. Ord. I.) that the pulfations of the optic artery might be per-
ceived by looking attentively on a white wall well illuminated. A
kind of net- work, darker than the other parts of the wall, appears and
vaniflies- alternately with every pulfation. This change of the colour
of the wall he well afcribes to the compreffion of the retina by the di-
aftole of the artery. The various colours produced in the eye by the
prelTure of the finger, or by a fliroke on it, as mentioned by Sir Ifaac
Newton, feem like wife to originate from the unequal preffure on va-
rious parts of the retina. Now as Sir Ifaac Newton has (hewn, that
all the different colours are refledled or tranfmitted by the kminse of
foap bubbles, or of air, according to their different thicknefs or thin-
nefs, is it not probable, that the efFe£l of the activity of the retina may
be to alter its thicknefs or thinnefs, fo as better to adapt it to refleft or
tranfmit the colours which ftimulate it into ailion ? May not muf-
cular fibres exift in the retina for this purpofe, which may be lefs mi-
nute than the locomotive raufcles of microfcopic animals ? May not
thefe mufcular actions of the retina conftitute the fenfatiou of light
and colours ; and the voluntary repetitions of them, when the objed

5^^ OCULAR SPECTRA. Sect. XL. lo.

is withdrawn, conftitute our memory of them ? And laflly, may not
the laws of the fenfations of light, here inveftigated, be appUcable to
all our other fenfes, and much contribute to elucidate many phenomena
of animal bodies J^oth in their healthy and difeafed ftate ; and thus ren-
der this inveftigation well worthy the attention of the phyfician, the
metaphyflcian, and the natural philofopher ?

November i, 1785.

ADDITIONS.

At Page 120, after Line 19, pleafe to' add.

From the experiments above mentioned of Galvani, Volta, Fow-
ler, and others, it appears, that a plate of zinc and a plate of filver have
greater efFe6l than lead and filver. If one edge of a plate of filver
about the fize of half a crown-piece be placed upon the tongue, and
one edge of a plate of zinc about the fame fize beneath the tongue,
and if their oppofite edges are then brought into contadl before the
point of the tongue, a tafte is perceived at the moment of their comino-
into conta£t ; fecondly,^ if one of the above plates be put between the
•upper lip and the gum of the fore-teeth, and the other be placed under
the tongue, and their exterior edges be then brought into contadl in a-.
darkilTi room, a flafli of light is perceived in the eyes.

Thefe effe6ls I imagine only fliew the fenfibility of our nerves of
fenfe to very fmall quantities of the eledtric fluid, as it paffes through
them; for I fuppofe thefe fenfations are occafioned by flight eledric
fnocks produced in the following manner. By the experiments pub-
lifhed byMr. Bennet, with his ingenious. doubler of ele£lricity, which
is the greateft difcovery made in that fcience fince the coated jar, and
tlie ediidion of lightning froni the Ikies, it appears, that zinc was
3 . alwavs

•568 ADDITIONS.

always found minus, and filver was always found plus, when both of
them were in their feparate ftate. Hence, when they are placed in the
manner above defcribed, as foon as their exterior edges come nearly
into contaft, fo near as to have an extremely thin plate of air between
them, that pla,te of ,a1r be'cbmes charged in the fame manner as a plate
of coated glafs ; and is at the fame inftant difcharoed throug-h the

O ' Do

nerves of tafte or of fight, and gives the fenfations, as above defcribed,
of light or of faporocity; and only fhcws the great fenfibihty of thefe
organs of fenfe to the ftimulus of the eledtric fluid in fuddenly paffing
■through them.

At Page 160, after Line 29, pleafe to add.

Thefe animals feem to poflefs fomething like an additional fenfe by
means of their whilkers; which have perhaps fome analogy to the
antennae of moths and butterflies. The whiflcers of cats confifl: not
only of the long hairs on their upper lips, but they have alfo four or
five long hairs ftanding up from each eyebrow, and alfo two or three
on each cheek; all which, when the animal ere£ls them, make with
their points fo many parts of the periphery of a circle,-of an extent at
leaft equal to the circumference of any part of their own bodies. With
this inftrument, I conceive, by a little experience, they can at once
determine, whether any aperttire amongft hedges or fhrubs, in which
animals of this genus live in their wild ftate, is large enough to admit
their bodies ; which to them is a matter of the greateft confequence,
whether purfuing or purfued. They have likewife a power of erect-
ing and bringing forward the whilkers on their lipsj which probably
is for the purpofe of feeling, whether a dark hole be further per-
meable,

6 The

ADDITIONS. $69

The antennae, or horns, of butterflies and moths, who have awk-
ward wings, the minute feathers of which are very Uable to injury,
ferve, I fuppofe; a (imilar purpofe of meafuring, as they fly or creep
amongft the leaves of plants and trees, whither their wings can pafs
without touching them.

In Sea. XXXIX. f/eafe to add.

Dr. Thunberg obferves, in his Journey to the Cape of Good Hope,
tliat there are fome families, which have defcended from blacks in the
female line for three generations. The firft generation proceeding
from an European, who married a tawny flave, remains tawny, but
approaches to a white complexion ; but the children of the third
generation, mixed with Europeans, become quite white, and are
'often remarkably beautiful. V.i. p. 112.

Additional Obfervations on Vertigo, which ought to have been inferted
in Seel. XX. 6. after the Words " optic nerve," at the End of the
fecond Paragraph.

After revolvmg with your eyes open till you become vertiginous,
as fooii as you ceafe to revolve, not only the circum-ambient objefts
appear to circulate round you in a diredtion contrary to that, in which
you have been turning, but you are liable to roll your eyes forwards
-and backwards ; as is well obferved, and ingenioufly demonftrated by
Dr. Wells in a late publication on vifion. The fame occurs, if you
revolve with your eyes clofed, and open them immediately at the
time of your ceafing to turn ; and even during the whole time of re-
volving, as may be felt by your hand preffed lightly on your clofed

4 D eyelids.

S:p. ADDITIONS.

eyelids. To thefe movements of the eyes, of which he fuppofes the
obferver to be inconfcious, Dr. Wells afcribes the apparent circum-
gyration of objeds on cealjug to revolve.

The caufe of thus turning our eyes forwards, and then back again,
after our body is at reft, depends, I imagine,, on the fame circum-
ftance, which induces us to follow the indiftin£t fpedlra,. which are
formed on* one fide of the center of the retina., when weobferve them,
apparently on clouds, as defcribed in- Seft. XL. 2. 2-. ; and then not
being able to gain a more diftin6t vifion of them, we turn our eyes
back, and again and again purfue the flying fhade.

But this rolling of the eyes, after revolving till we become verti-
ginous, cannot caufe the apparent circumgyration of objefts, in a di-
rection contrary to that in which we have been revolving, for the
following reafons. i. Becaufe in purfuiug a fpecjlrura^ ia the iky,, or
on the ground, as above mentioned,, we perceive no retrograde mo-
tions of objeil's. 2. Becaufe the apparent retrograde motions of ob-
jefts, when we have revolved till we are vertiginous, continues much,
longer than the rolling of the eyes above defcribed.,

3. When we have revolved from right to left, the apparent motion
of objeds, when we flop, is from left to right ; and" when we have
revolved from left to. right, the apparent circulation of objects is from'
rlo-ht to left; yet in both thefe cafes the eyes of die revolver are feen
equally to roll forwards and backwards..

4. Becaufe this rolling of the eyes backwards and forwards takes
place during our revolving, as may be perceived by the hand lightly
prefled on the clofed eyejids, and. therefore exifts before the eifeft-
afcribed to. it.

And fifthly, I now come to relate an experiment, in which the-
roUing of the eyes does not take place at all after revolving, and yet-
the vertigo is more diflreffing than in the fituations above mentioned.
If any one looks fleadily at a fpot in the ceihng over his head^ or in- ■
deed at his own finger held-up high over his beadj and;in that fitu-

atioa.

ADDITIONS. 571

ation turns round till he becomes giddy; and then flops, and looks
, horizontally ; he now finds, that the apparent rotation of obje£ls is
from above downwards, or from below upwards ; that is, that the
apparent circulation of objefts is now vertical inftead of horizontal,
making part of a circle round the axis of his eye ; and this without
any rolling of his eyeb.dls. The reafbn of there being no rolling of
the eyeballs perceived after this experiment, is, becaufe the images of
objefts are formed in rotation round the axis of the eye, and not from
one fide to the other of the axis of it ; fo that, as the eyeball has not
power to turn in its focket round its own axis, it cannot follow the
apparent motions of thefe evanefcent fpeftra, either before or after
the body is at reft. From all which arguments it is manifeft, that
thefe apparent retrograde gyrations of obje6ts are not caufed by the
rolling of the eyeballs ; firft, becaufe no apparent retrogreffion of ob-
je£ts is obferved in other rollings of the eyes : iecondly, becaufe tJie
apparent retrogreffion of objeds continues many feconds after the
rolling of the eyeballs ceafes. Thirdly, becaufe the apparent retro-
greffion of objefts is fomeftimes one way, and fometniies another,
yet the rolling of the eyeballs is t'he fame. Fourthly, becaufe the
rolling of the eyeballs exifts "before the apparent retrograde motions of
objefts is obferved ; that is, before the revolving perfon flops. And
fifthly, becaufe the apparent retrograt3e gyration of objefts is produced,
when there is no roiling of the eyeballs at all.

Do£lor Wells imagines, that no fpcdlra can be gained in the eye,
if a perfon revolves with his eyelids clofed, and thinks this a fufficient
argument againft the opinion, that the apparent progreffion of the
fpe£lra of light or colours in the eye can caufe the apparent retro-
greffion of objeds in the vertigo above defcribed ; but it is certain,
when any perfon revolves in a light room with his eyes clofed, that
he neverthelefs perceives differences of light both in quantity and co-
lour through his eyeUds, as he turns round ; and readily gains fpedra
of thofe differences. And thefe fpedlra are not very different except

4D 2 ■ ^ in

S^z ADDITIONS.-

iii vivacity from fbofe, which he acquires, when he revolves witfe
iinclofed eyes, fmce if he then revolves very rapidly the colours and
forms of furrounding objefts are as it were mixed together in his eye \.
as when the prifmatic colours are painted on a wheel, they appear
white as they revolvq. The truth of this is evinced by the ftaggering
or vertigo of men perfectly blind, when they turn round ; which is
not attended with apparent circulation of objecfts, but is a vertiginous
diforder of the fenfe of touch. Blind men balance themfelves by their
fenfe of touch ; which, being lefs adapted for perceiving fmall devi-
ations from their perpendicular, occafions them to carry themfelves
more ereft in walking. This method of balancing themfelves by the
dire£tion of their preffure againft the floor^ becomes difordered by the
\inufual mode of adion in turning round, and they begin to lofe their
perpendicularity, that is, they become vertiginous; but without anjp
apparent circular motions of vifible objefts.

It will appear from the following experirnents, that the apparent
progreflion of the ocular fpefbra of light or colours is the caufe of the
apparent retrogreffion of objedts, after a perfon has revolved, till he is
vertiginous.

Firft, when a perfon turns round in a light room with his eyes
open, but clofes them before he flops, he wUl feem to be carried foi"-
wards in the dire£lion he was turning for a fhort time after he flops.
But if he opens his eyes again, the objefts before him inflantly appear
to move in a retrograde dire<flion, and he lofes the fenfation of beina:
carried forwards. The fame occurs if a perfon revolves in a light room
with his eyes clofed ; when he flops, he feems to be for a time car-
ried forwards, if his eyes are flill clofed ; but the inftant he opens
them, the furrounding obje<£ls appear to move in retrograde gyration.
From hence it may be concluded, that it is the fenfation or imagina-
tion of our continuing to go forwards in the dire6tion in which we
were turning, that caufes the 'apparent retrograde circulation of ob-

jefts.

^ Secondlyj

ADDITIONS. siZ

Secondly, thougli there is an audible vertigo, as is known by the
feattement, or undulations of found in the ears, which many verti-
ginous people experience ; and though there is alfo a tangible vertigo,
as when a blind perfon turns round, as mentioned above ; yet as this
circumgyration of objefts is an hallucination or deception of the lenfe
of fight, we are to look for the caufe o^ our appearing to move for-
ward, when we Hop with our eyes doled after gyration, to fome af-
fedion of this fenfe. Now, thirdly, if the fpeftra formed in the eye
during our rotation, continue to change, when we (land ftill, like
the fpeftra defcribed in Se61:.III. 3. 6. fuch changes muft fuggefi to
us the idea or fenfation of our flill continuing to turn round ; as is the
cafe, when we revolve in a light room, and clofe our eyes before w'e
jftop.. And laftly, on opening our eyes in the fituation above de-
fcribed, the objects we chance to view amid thefe changing fpedlra
in the eye, muft feem to move in a contrary dire6tion j, as the moon
fometimes appears to move retrograde, when fwift-gliding clouds are
paffing forwards fo much nearer the eye of the beholder.

To make obfervations on faint ocular fpe£lra requires fome degree
of habit, and compofure of mind, and even patience ; fome of thofe
defcribed in Sect. XL. vi'ere found difficult to fee, by many, who
tried them ; now it happens, that the mind, during the confufion of
vertigo, when all the other irritative tribes of motion, as well as thofe
of vifion, ape in fome degree difturbed, together with the fear of fall-
ing, is in a very unfit flate for the contemplation of fuch weak fenfa-
tions, as are occafioned by faint ocular fpeftra. Yet after freqiientlv
revolving, both with my eyes clofed, and with them open, and at-
tending to the fpedtra remaining- in them, by (hading the light from
my eyelids more or lefs with my hand, I at length ceafed to have the
idea of going forward, after I flopped with my eyes clofed ; and faw
changing fpe6tra in my eyes, which feemed to move, as it were,
over the field of vifion ; till at length, by repeated trials on funny
days, I perfuaded myfelf, on opening my eyes, after revolvipg fome

time.

574 ADDITIONS.

time, on a fhelf of gilded books in my library, that I could perceive
the fpedra in my eyes move forwards over one or two of the books,
like the vapours in the air of a fummer's day ; and could fo far unde-
ceive myfelf, as to perceive the books to ftand flill. After more trials
I fometimes brought myfelf to believe, that I faw changing fpedlra
of lights and fnades moving in my eyes, after turning round for fome
time, but did not imagine either the fpeftra or the obje<£l:s to be in a
flate of gyration. I fpeak, however, with diffidence of thefe fa6ls,
as I could not always make the experiments fucceed, when there was
not a flrong light in my room, or when my eyes were not in the moil
proper (late for fuch obfervations.

The ingenious and learned M. Savage has mentioned other theories
to account for the apparent circumgyration of objedls in vertiginous
people. As the retrograde motions of the particles of blood in the op-
tic arteries, by fpafm, or by fear, as is feen in the tails of tadpoles,
and membranes between the fingers of frogs. Another caufe he thinks
may be from the librations to one fide, and to the other, of the crys-
talline lens in the eye, by means of involuntary adlions of the mufcles,
which conftitute the ciliary procefs. Both thefe theories lie under
the fame obje6lion as that of Dr. Wells before mentioned ; namely,
that the apparent motions of objedls, after the obferver has revolved
for fame time, fliould appear to vibrate this way and that ; and not
to circulate uniformly in a diredion contrary to that, in which the
obferver had revolved,

M. Savage has, laftly, mentioned the theory of colours left in the
eye, which he has termed imp<-eflions on the retina. He fays, " Ex-
perience teaches us, that impreflions made on the retina by a vifible
obje£t remain lome feconds after the objedl is removed ; as appears
from the circle of fire which we fee, when a fire-flick is whirled
round in the dark ; therefore when we are carried round our own axis
in a circle, we undergo a temporary vertigo, when we flop : becaufe
the impreflions of the circumjacent objeds remain for a time after-
wards

ADDITIONS. S75

wards on the retina." Nofolog. Method. Claf. VIII. i. i. We have
before obferved, that the changes of thefe colours remaining in the
eye,, evinces them to be motions of the fine terminations of the retina,
and not impreffions on it ; as impreffions on a paffive fubflance muft-
either remain, or ceafe intirely..

Dum, Liber! aflra petis volitans trepklantibus alls,
Irniis immemori, parvula gutta, mari.

Me quoque, me cun-ente rota revolubilis setas
Volverit in tenebras, — i. Liber, ipfe fequor.

END OF TBE FIRST VOLUME..

INDEX

TO THE

SECTIONS OF PART FIRST.

Absorption of folids, xxxiii. 3. r. xxxvii.

of fluids in anafarca, xxxv. 1.3.

Abforbent velTels, xxii. 2. xxix. i.
......... regurgitate theif fluids, xxix. 2.

their valves, xxix. 2.

communicate with vena portaruir.,

xxvii. 2.
Accumulation of Tenforial povsrer, iv. 2. xii.

Aftivity of fyftem too great, cure of, xii. 6.

too fmall, cure of, xx. ^.

Age, old, xii. 3. 1. xxxvii. 4.
Ague-fit, x.ii. 7. I. xxxii. 3.4. Xxxii. 9.
.-... .... how cured by bark, xii. 3. 4.

periods, how occafioned, xii. 2. 3.

xxxii. 3. 4. xvii. 3. 6.
Ague cakes, xxxii. 7. xxxii. g.
Air, feiife of frefh, xiv. 8.
. . . mjurcs ulcers, xxviii. 2.
. . . injeftcd into veins, xxxii. 5.
Alcohol deleterious, xxx- 3.
Alliterations, why agreeable, xxii. 2.
Aloas in leflened dofes, xii. 3. i.
American natives indolent, xxxi. '2.
... . . . , . , ....... narrow'fhouldered, xxxi. i.

Analogy intuitive, xvii. 3. 7.

Animals ief& liable to madnefs, xxxiii. i.

....... lefs liable to contagion, xxxiii. i.

how to teach, xxii. 3. 2.

their fimilarity to each other, xxxix.

4. 8.
....... their changes after nativity, xxxix.

4. 8.
their changes before nativity, xxxlx.

. . ..... lefs liable to contagious difeafes, why

xxxiii. I. 5.
lefs liable to delirium and infanity,

why, xxxiii. 1.5.
eafier to preferve than to reproduce,

xx.xvii.

food, dlflafte of, xxxviii, i.

....... appetency, xxxix. 4. 7.

Antipathy, x. 2. 2.

Appetites, xi. 2. 2. xiv. 8.

Aphthse, xxviii.

Apoplexy, xxxiv. 1.7.

........ not from deficient irritation, xxxii.

2. I.
ArchiteiSlure, xii. 3. 3. xvi. ib.
Arts, fine, xxii. 2.
Afparagus, its fmell in urine, Xxix.

4 E Afibciation

57S I N D

Affociation defined, ii. il. iv. 7. v. 2.

aflbciate motions, x.

, ftrongerthan irritative ones, xxiv.

2.8.

formed before nativity, xi. 3.

with irritative ones, xxiv. 8. ^

with retrograde ones, xxv. 7.

XXV. 10. xxv. 15.

difeafes from, xxxv.

Afthma, xviii. 15.

Attention, language of, xvi. 8. 6.

Atrophy, xxviii.

Averfion, origin of, xi. 2. 3.

/ ■ - -■ -*■

Balance ourfelves by vifion, xx. i.

Bandage increafes abforption, xxxiii. 2. !*■. "

Barrennefs, xxxvi. 2. 3.

Battement of founds, xx. 7

Bath, cold. See Cold Bath.

Beauty, fenfe of, xvi. 6. xxii.2»^

Bile-dufls, XXX. ""!''. ^ .' .

... .ftones, XXX. 3.

.... regurgitates into the blood, Xav.' 2; 7.

.... vomiting of, x-kx. 3.

Birds of paflage, xvi. 12;

. . . . nefts of, xvi. 13.

.... colour of their eggs, xxxix, 5,

Biting in pain, xxxiv. i. 3.

of mad animals, xxxiv. 1. 3-

Black fpots on dice appear red, xl. 3.
Blidder, communication of with the intef-

tines, xxix. 3.
...... of fifh, xxiv. 1.4.

Blood, transfufion of in nervous fevers,
'■ xxxii. 4.

deficiency of, xxxii. 2. and 4.

from the vena portarum into the in-

teftines, xxvii. 2.

its momentum, xxxii. 5. 2.

momentum increafed by venefe£tion,

xxxii 54
..... drawn in nervous pains, xxxii. 5. 4.

its oxygenation, xxxviii.

Breathing, how learnt, xv. 4.

Breaftsof men, xiv. 8.

Brutes dilTer from men, xi. 2, 3. xvi. 17.

EX.

Brutes, See Animals.
Buxton bath, why it feels warm, xii. 2. l.
xxxii. 3. 3.

Capillary veflels are glands, xxvl. I.

Catalepfy, xxxiv. i. 5.

Catarrh from cold ikin, xxxv. i. 3. xxxv.

from thin caps in fleep, xviii. 15.

Catenation of motions defined, ii. 11. iv. 7.
'w> i •). . . .,' caufe.of them, xvii. I. 3.

, defcribed, xvii,

continue fometime after their pro-

duftion, xvii. i. 3.

voluntary ones difievered in fleep,

■ xvii. I. J2. xvii- 3. 13.
Cathartics, external, their operation, xxix.

Caufation, animal, defined, ii. 11. iv. 7.

Caufe of caufes, xxxix. 4. 8.

Caufes inert and efficient, xxxix. 8. 2.

a£tive and paflive, xxxix. 8. 3.

proximate and remote, xxxix. 8. 4.

Chick in the egg, oxygenation of, xxxviii; a;
Child riding on a ftick, xxxiv. 2. 6. " ''
Chilnefs after meals, xxi. 3. xxxv. j.- r; ■ ■ •

Cholera, cafe of, xxv. 13.

Circulation in the eye vifible, xl. io.'4.'

Cold in the head, xii. 7- 5.

.... perceived by- the teeth, xxxii. 3. i,

xiv. 6.

. . air, ufes of in fevers, xxxiii 3. 3,

.. feet, produces coryza, xxxv. 2. 3„

xxxv. I. 3.

.. bath, why it ftrengthens, xxxii. 3.. 2.

.. fhort and cold breathing in it, xxxii.

3- 2-

.. produce? a fever-fit, xxxii. 3. 2

. . fit of fever the confequence of hot fir,

xxxii. 9. 3- »

. . bathing in pulmonary hemorrhage,

xxvii. I.

... fits of fever, xxxii, 4. xxxii. 9. xvii.

^ ■3- 3- . . ,

Comparmg ideas, xv, 3.

Confcioufnefs, xv. 3. 4.

Confcioufiiefe

I N' D ^E X.

519

Confcioufnefs in dreams, xviii. 13.
Confumption, its temperament, xxxi; I.

and 2.

of dark-eyed patients, xxvii. z.

of light-eyed patients, xxviii. 2.

is contagions, xxxiii. 2. 7.

Confent of parts. See Sympatliy. '''/i

Contagion, xii 3. 6. xix. 9 xxxiii. 2. ''6;

and S. xxii. 3- 3.
does not enter the blood, xxxiii.

2. 10. xxii. 3. 3.
Contradiion and attraflion, iv. I.
of fibres produces fenfation, iv, 5.

xii. I. 6.

continues fome time, xii. r. 5.

alternates with relaxation, Xii.

Convulfion, xvii. i. 8. xxxiv. i. i. and 4.

iii. 58.

of particular mufcles, xvii. i. 8.

periods of, xxxvi. 39-

Colours of animals, efficient caule of, xxXix. 5.
, of eggs from female iuiagination,

xxxix. 5.
, of the choroid coat of the eye, xxxix.

5-
of birds nefts, xvi. 13.

Coryza. See Catarrh.

Cough, nervous, periods of, xXxVi. 3. 9.

Cramp, xviii. 15. xxiv. 1.7.

Critical days from lunations, xxxvi. 4.

Darkifh room, why we fee well in it, xii.

2. I.
Debility fenforial and flimulatory, xii 2. i.
direft and indirect of Dr. Brown,

xii. 2. I. xxxii. 3. 2.

, See Weaknefs.

, from drinking fpirits, cure of, xii.

7.8.^

in fevers^ cure of, xii. 7. S.

Deliberation, what, xxxiv, i.
Defire, origin of, xi. 2. 3.
Diabetes explained, xxix, 4.

^ with bloody urine, xxvii. 2.

Diarrhoea, xxix. 4.

Digeftion, xxxiii. i. xXxvii.

(Irengthened by emetics, xxxv.

I- 3
ftrengthened by regular hourj,

why, xxxvi 2. r. »

Digitalis, ufe of in dropfy, xxix. 5.2.
Dilirium, two kinds of, xxxiii. i. 4- xxxiv.

2. 2.

cafes of, iii. 5. 8

prevented by dreams, xViii 2.

Diftention a£ts as a ftimulus, xxxii 4.

. . , See Extenfion.

Diftinguifhing, xv. 3.

Diurnal circle of a£lions, xxv. 4.

Doubting, XV. 3.

Dreams, vili. I 2. xlv. 2. 5.

their inconfiftency, xviii. 16.

no furprife in them, xviii. 17.

much novelty of combination, xviii,

9-
Dropfies explained, xxix. 5. i.
Dropiy cured by infanity, xxxiv. 2.7.
..... Cure of, xxix. 5. 2.
Drunkennefe. See Intoxication, xxi.

» diminifhed by attention, xxi. 8»

Drunkards weak till next day, xvii. i. 7.
I ftammer, and dagger, and weep,

xii. 4. I. xxi. 4.
........ fee objedls double, why, xxi. 7.

.^...... tecome delirious, fleepy, ftupid,

xxi. 5.
Dvfpnoea in coH bath, xxxii. 3. 2.

Eaf, a good one, xvi. 16.

. . . nolfe in, xx. 7.

Eggs of frogs, fiili, fowl, xxxix. 2.

. -. . . of birds, why fpotted, xxxix. 5.

-i . . . with tlouble yolk, xxxix. 4. 4.

Eleflricity, xii. I. xiv. g.

jaundice cured by it, xxx. 2;

Embryon produced, by the male, xxxiji. 2i

i coniifts cf a living fibre, xxxix. 4*

, i -. abforbs nutriment, receivesoxygcn,

xxxix. I.
i ...... . its aftions and fenfations, x\i. 2.

Emetic. See Vomiting.-^-"

4 E 2 Emotions

58o

INDEX.

Emotions, xi. 2. 2.

Ennui', or taedium vitae, xxxiv. 2. 3. xxxiii.

I. I. xxxix. 6. Clafs ii. i. I.
Epileptic fits explained, xxxiv. i. 4. xxvii.2.

. .9 in fleep, why, xviii. 14. & 15.

Equinoxial lunations, xxxii. 6.
Excitability perpetually varies, xii. i. 7,
fynonymous to quantity of fen-

forial power, xii.. i. 7.
Exercife, its ufe, xxxii. 5. j.
Exertion of fenforial power defined, xii. 2.1.
Exiflencein fpace, xiv. 2. 5.
Extenfion, fenfe of, xiv. 7.
Eyes become black in Ibme.epilepfies, xxvii. 2>.

Face, flufhing of after dinner, xxxv. i. I.
, . , . why firft affedled in fmall-pox, xxxv.

I. I.
.... red from inflamed liver, xxxv. 2. 2.
Fainting fits, xii. 5. i. xiv. 7.
Fear, language of, xvi. 8. i.
.... a caufe of fever, xxxii. 8.
.... caufe of, xvii. 3. 7.
Fetus. See Embryon, xvi. 2. xxxix. I.
Fevers, irritative, xxxii. i.

intermittent, xxxii. i. xxxiu 3.

.. ... fenfitive, xxxiii. I.

..... not an effort of nature for relief,

xxxii- 10.
..,,. paroxyfms of, xii. 7. r. xii. 2. 3;

xii. 3- 5
why fome intermit and not others,

xxxvi. I.
cold fits of, xxxii. 4. xxxii. g. xvii.

3. 3.
..... periods of, xxxvi. 3.

have foiar or lunar periods, xxxii. 6.

fource of the fymptoms of, xxxii. i.

...... proftration of ftrength in, xii, 4. u

xxxii. 3. 2.
..... cure of, xii. 6. i.

how cured by the bark, xii. 3. 4.

cured by increafcd vohtioa, xii. 2. 4.

xxxiv. 28.
. . , . . beft quantity of ftimulvis \q, xii. 7. 8.
Fibres. See Mufcles.

Fibres, their mobility, xii. r. 7. xK. I. I..
..... contradtions of, vi, xii. i. i.

four clafles of their motions, vi.

..... their motions diftinguifhed from fent»

forial ones, v. 3.
Figure, xiv. 2. 2. iii. r.
Fifh, their knowledge, xvi. 14.
Foxglove, its ufe in dropfies, xxix. ^. Z',

overdofe of, xxv. 17.

Free-will, xv. 3. 7.

Gall-ftone, xxv. 17, See Bile-ilonesi

Generation, xxxiii. I. xxxix.

Gills of fifh, xxxviii. 2.

Glands, xxii. 1. conglobate glands,.' xxii. 2.

. . . . . . have their peculiar ftimulus, xi. r.

...... their fenfes, xiv. 9. xxxix. 6.

invert their motions, xxv. 7.

...... increafe. their motions, xxv. 7.

Golden rule for exhibiting wine, xii. 7. 8.

for leaving off wine, xii. 7. 8.

Gout from inflamed liver, xxxv. 2. 2. xviii.

ij xxiv. 2. 8.
.... in the flomach, xxiv. 2. 8. xxv. 17.
.... why it returns after evacuations, xxxii. 4.
.... owing to vinous fpirit only, xxi. 10.
.... periods of, xxxvi. 3, 6.
Grinning in pain, xxxiv. i. 3.
Gyration, on one fbot, xx. 5. and 6..

Habit defined, ii. 11. iv. 7.
Hemorrhages, periods of, xxxvi. 3-. V3i
............ from paraly fis of veins,. xxviE.

I. and 2.
Harmony, xxii. 2.
Head-achs, xxxv. 1, i.-
Hearing, xiv. 4.

Heat, fenfe of, xiv. 6. xxxii, 3,-14 .
.... produced by the glands, xxii. 3,

.... external and internal, xxxii. 3. r.

.... atmofphere of heat, xxxii. 3. i.

.... increafes during fleep, xviii. 15.

Bemicrania, xxxv. 2. i..

H^raicrama.

INDEX. 58J

Remicrania from decaying teeth, xxxv. 2. i. Inflammation not from pains from defeft of
Hepatitis, caufe of, xxxv. 2. 3. ftimulus, xxxiii. 2. 3.

Hereditary difeafes, xxxix. 7. 6, of parts previoufly infenfible.

Hermaphrodite infedls^ xxxix. 5. xii. 3. 7.

Herpes, xxviii. 2. often diftant from its caufcj-

from inflamed kidney, xxxv. 2. 2. xxiv. 8.

Hunger, fenfe of, xiv. 8. obferves folar days^ xxxii. 6.

Hydrophobia, xxii. 3. 3. of the eye, xxxiii. 3. i.

Hypochondriacifm, xxxiii. i. i..xxxiv. 2. 3 of the bowels prevented by their

continued a£lion in deep, xviii. 2.
Inoculation with blood, xxxiii. 2. lO.

^' Infane people,, their great ftrength, xii. i.
Infanity (fee Madnefs) plealureable one,
Ideas defined, ii. f. xxxiv. 2. 6.

.... are motions of the organs of fenfe, iii.4.- Infedls, their knowledge, xvi. 15. and ;6.

xviii. 5. xviii. 10. xviii. 6. in the heads of calves, xxxix. 1.

♦ . . . analogous to mufcular motions, iii. 5. clafs of, xxxix. 4. 8.

^. .. continue fome time, XX. 6. Inftinftive adlions defined, xvi.r.

.... new ones cannot be invented", iii. 6. i. Inteflines, xxv. 3.

.... abftrafted ones, iii. 7. 4. Intoxication relieves pain, why, xxi. 3.-
. . . . inconfiftent trains of, xviii. 16. from food after fatigue, xxi. 2-

.... perifh with the organ of fenfe, iii. 4. 4. . difeafes from it, xxi. 10.

»... painfuUrom inflammation of the organ> _ See Drunkennefs,

iii. 5. 5- Intuitive analogy, xvii. 3. 7.

♦-. . . irritative ones, vii. 1. 4. vii. 3. 2. xv. 2. Invention, xv. 3. 3.

XX. 7. Irritability increafes during fleep, xviii. 15,

... , . of refemblance, contiguity, caufation. Itching, xiv. 9.

viii. 3. 2. x. 3. 3.
.... refemble the figure and. other properties

of bodies, xiv. 2. 2. , /»-

.... received in tribes, xv. i.

.... of the. fame, fenfe eafier combined,- xv. jaw-locked, xxxiv. i . 5..

u I. Jaundice from paralyfis of the liver, xxx. 2.

.... of refleftion,. xv. i. 6. ii. 12. ....... cured by electricity, xxx. 2^

Ideal. prefence, XV. I. 7. . Judgment, xv. j

Identity, xv. 3. ^. xviii. 13^.

Iliac paflion, xxv. 15.

Imagination, viii. I. 2. xv. 1, 7, xv. 2. 2. ^'

.......... of the male forms the fex, xxxix.

6. Knowledge of various animals, xvi . .1 1 ,
Immaterial beings, xiv. 1. xiv. 2. 4. '
Imitation, origin of, xii. 3. 3. xxxix. 5, xxLi.

3 xvi. 7. ■*-"•

Impediment of fpeech, xvii. i. 10. xvii. 2^

JO. Lacrymal fa'ck^ xvi. 8. xxiv. 2:.' and 7..

Infeftion. See Contagion. Lafteals, paralyfis of, xxviii. See Abfor-
Inflammation, xii. 2. 3. xxxiii. 2. 2; bents.

^ , , . . great vafcukr exertion in, xii. Lady playing on the harpfichord,' xvii, 2.

2.. I. ,..,, . diftrefredforherdyingbird,.xvii. 2. lo.

Language-,

^Sl

I N D E X.

Language, natural, its oi-'igin, xvl. 7. & 8.
........ of various paffxons defcribed, xvi, 8.

artificial, of various animals, xvi. 9.

theory of, xxxix. 8. 3.

Lapping of puppies, xvi. 4.

Laughter explained, xxxiv. i. 4,

....... 'from tickling, xvii. 3. 5. xxxi\r.

1.4.
, from frivolous ideas, xxxiv. i. 4.

xviii. 12.
Life, long, art of producing, xxxvii.
Light has no momentum, lii. 3. i.
Liquor amnii, xvi, xxxviii 2.

is nutritious, xxxviii. 3.

frozen, xxxviii. 3.

Liver, paralyfis of, xxx, i . 4.

large of geefe, xxx. i . 6.

Love, fentimental, its origin, xvi. 6.

animal, xiv. 8. xvi. ^,

Lunar periods affeft difeafes, xxxii. 6.

Lufl, xiv. 8. xvi. 5.

Lymphatics, paralylls of, xxviii. See Ab-

forbents.

Moon and fun, their influence, xxxii. 6.

Mortification, xxxiii. g. 3.

Motion is either caufe or effecl:, i. xiv. 2. 2.

primary and fecundary, i.

animal, i. iii. i.

..;... propenfity to, xxii.i.

animal, continue fome time after their

produ£lion, xvii. i. 3.
defined, a variation of figure, iii. i.

xiv. 2. 2. xxxix. 7.
Mucus, experiments on, xxvi. i.

fecretion of, xxvi. 2.

Mules, xxxix. 4. 5. and 6. xxxix. 5. 2.
Mule plants, xx.\ix. 2.
Mufcaj volitantes, xl. 2. ' '

Mufcles conftitutc an organ of fcnfe, xiv. 7.

ii. 3.
ftimulatcd by extenfion, xi. i.

xiv. 7.
...... contrail by fpirit of animation, xii,

I. 1. and 3.
Mufic, xvi. 10. xxii. 2.
Mufical time, why agreeable, xii. 3. 3.

Mad-dog, bite of, xxii. 3. 3. Naufea, xxv. 6.

Madnefs, xxxiv. 2. I. xii. 2. I. Nerves and brain, ii. 2. 3.

Magnetifm, xii. i. i. ...... extremitiesof form the whole fyfienij

Magnifying Gbje>5ls, new way of, xl. 10. 5. xxxvii. 3.

Male animals have teats, xxxix. 48. are not changed With age, xxxvii. 4,

.... pigeons give milk, xxxix. 4.8. Nervous pains defined, xxxiv. 1. i.

Man diftinguiihed from brutes, xi. 2. 3. Number defined, xiv. 2. 2.

xvi. I 7 Nutriment for the embryon, xxxix. 5. 2.

Material world, xiv. i. xiv. 2. 5. xviii. 7. Nutrition owing to ftimulus, xxxvii. 3.

Matter, penetrability of, xiv. 2.3. ........ by animal feledlion, xxxvii. 3.

punilent, xxxiii. 2.4. ...... when the fibres are elongated, xxxvii,

Meafles, xxxiii. 2. 9. 3.

Membranes, xxvi. 2. like inflammation, xxxvii. 3.

Memory defined, ii. 10. xv. i. 7. xv. 3.

Menftruation by lunar periods, xxxii. 6.

Mifcarriage from fear, xxxix. 5. "*

Mobility of fibres, xii. 1.7.

Momentum of the blood, >.xxii 5. 2. 'ObjeiSs long Viewed become faint, iii. -3. 2,

fometimes increafed by venefeC- Ocular fpedtra, xl.

tion, xxxii. 5. 4. Oil externally in diabaetes, xxix. 4.

Monfters, xxxix. 4. 4 and 5. 2. Old age from inirritability, xxxvii.

without heads, xxxviii. 3. Opium is rtimulant, xxxii. 2. 2.

3 Opium

INDEX.

58J

Opiotn promotes abforption after evacuation,

xxxiii. 2. 10.

ill increafing dofes, xii. 3. 1.

Organs of fenfe, ii. 5. and 6.

Organs when deftroyed ceafe to produce ideas,

iii. 4. 4. _
Organic particlesof Buflbn, xxxvii. 3. xxxix.

Organ-pipes, xx, 7.

Oxygenation of the blood, xxxviii,

Pain from excefs and defeft of motion, iv. 5.
xii. 5. 3. xxxiv. 1. XXXV. 2. 1.

». . not felt during exertion, xxxiv. i. 2.

» . . from greater contradiion of fibres, xii. 1 . 6.

. . . from accumulation of fenforial power,
xii, 5. 3. xxiii. 3. I.

. . . from light, prelTure, heat, cauftics,
xiv. 9.

... in epilepfy, xxxv. 2. i.

. . . diftant from its caufe, xxiv. S.

. . . from ftone in the bladder, xxxv. 2. r;

► , ► of head and back, from defedl, xxxii. 3.

. , . from a gall-ftone, xxxv. 2.1. xxv. 17..

, . . of the itomach in gout, xxv. 17.

... of thoulder in hepatites, xxxv, 2. 4.

,>.. produces volition, iv. 6.

Palenefs in cold fit, xxxii. 3. 2,

Palfies explained, xxxiv. i. 7,

Paralytic limbs ftretch from irritation, vi i. i . 3,

»,...... patients move their found limb

much, xii. 5, I.

Paralyfis from great exertion, xii. 4. 6.

from lets exertion, xii. 5. 6.^

-. of the la£leals, xxviii,

. . ..',,. of the liver, xxx. 4.

of the right arm, why, xxxiv. 1 . 7.

of the veins, xxvii. 2.

Particles of matter wiU not approach, xii. I . I,.

Paffions, xi. 2. 2.

........ connate, xvi. i.

Pecking of chickens, xvi. 4,

Perception defined, ii. §. xv. 3.1.

periods of agues, how formed, xxxii, 3. 4»

,. of difeales, xxxvi.

of natural aftions and of difeafed ac-
tions,, xxxvi.

Perfpiration in fever-fits, xxxii. 9. SeeSwreat.

Petechia, xxvii. 2.

Pigeons fecrete milk in their ftomachs,.

xxxix. 4. 8.
Piles, xxvii. 2.

Placenta a pulmonary organ, xxxviii. 2.
Pleafure of life, xxxiii i. xxxix. 5
,. from greater fibrous contradtions,

xii. I. 6.

what kind caufes laughter, xxxiv. r. 4.

....... what kind" caufes fleep, xxxiv. i. 4..

Pleurify, periods of, xxxvi. 3.7.

» caufe of, xxxv. 2. 3.

Prometlieus, ftory of, xxx. 3.

Proftration of flrength in fevers, xii. 4. r.

Pupils of the eyes large, xxxi. i.

Pulfe quick in fevers with debility,- xii. i. 4- .

xii. 5. 4. xxxii. 2. I.
. , . , in fevers with flrength, xxxii. 2.
.... from defedl of blood, xxxii. 2. 3. xii.

1.4.
. . . . weak from emetics, xxv. 1 7.

Quack advertlfements injurious. Apologv..
Quadrupeds have no fanguiferous lochia,.

xxxviii. 2.
have nothing fmiilar to the yolk

of egg, xxxix, I,-

Rhaphania, periods of; xxxvi. 3. 9..
Reafon, ix. I. 2. xv. 3.
Reafoning, xv, 3,

Recolle6tion, ii. 10. ix. 1.-2; xv. 2. 3.
Relaxation and bracing, xxxii. 3.. 2.
Repetition, why agreeable, xii. 3. 3. xxii.2i
Refpiration afFefted by attention, xxxvi. 2.1.
Reftleffnefs in fevers, xxxiv. i. 2.
Retrograde motions, xii. 5. 5. xxv. 6. xxix. .11..

of theflomach, xxv. 6.

. of the fkin,- xxv, 3.

of fluids,, how diftlnguifhed,.

xxix. 8.
,.,,.,... how caufed,^- xxix. i ii 5..

Retrograde

.■5»4 '^ N" D-

Retrograde dlfeafes, fynopfis of, xxix. g.

Retina is fibrous, iii. 2. xl. i.

..... ."is aftive in vifion, iii. 3. xl. r.

excited into fpafmodic motions, xl. 7.

is fenfible during ilcep, xviii.5. xix. 8.

-Reverie, xix. i. xxxiv. 3.

cafe of a lleep-walker, xix. 2.

isari epileptic difeafe, xix. g.

Rocking young children, xxi. 4.

Rot in flieep, xxxi'. y.

Ruminating animals, xxv. r.

Rhymes in poetry, why agreeable, xxii. 2.

Saliva produced by mercury, xxiii.

..... by food, xxiii. i.

by ideas, xyiii. 2. and 5.

..... by difordered volition, xxiii. J.

Schirrous tumours revive, xii. 2. 2.

Screaming iir pain, xxxiv. 1,2,

Scrophula, its temperament, xxxi. i.

xxviii. 2. xxxix. 4. 5.

Scurvy of the lungs, xxvii. 2.

Sea-ficknefs, xx. 4.

ftopped by attention, xx. 5.

■Secretion, xxxui. i. xxxvii.

increafed during fleep, xviii. 16.

Seeds require oxygenation, xxxviii. 2.

Senfation defined, li. 9. v. 2. xxxix. 8. 4.

d.feaffs of, xxxiii.

from fibrous contraflions, iv. 5.

x}i. 1. 6.

in an amputated limb, iii. 7. 3.

-.affedls the whole'fenrorium, xi. ^.

, produces volition, iv. 6.

.Senfibility increafss during fleep, xviii. 1-5.

Senfitive motions, viii. xxxiii. 2. xxxiv. 1.

'fevers of two kinds, xxxiii. .1.2.

ide.is, XV. 2. 2.

Senforium defined, ii. I.

Senfes corrciSl one another, xviii. 7.

diftinguiihedfrom appetites, xxxiv. 1. 1.

,Sv;nfjrial power. See Spirit of Animation.

great expcnce of in the vital mo-

•tlons, xxxii. 3. 2.

two kinds of exerted in feafitive fe-
sters, XAxiii. I. 3.

E X.

Senforial powers defined, v. r.

motions diftinguiflred from fibrous

motions, v. 3.
not much accumulated in deep,

xviii. 2. —

pow^ers, accumulation of, xii. 5. i.

exhauftion of, xii. 4. i .

wrafted below natural in hot fits,

xxxii. g. 3.
lels exertion of produces pain, xii.

5- 3- ^ ...

, lefs quantity of it, xii. 5. 4.

Senfual motions diftinguifliedfrom mufcular,

iu7.
Sex owing to the imagination of the father,

xxxiv. 5.
. . . xxxix. 7. 6. xxxix. 6. 3. xxxix. 6. 7.
Shingles from inflamed kidney, xxxv. 2. 2.
Shoulders broad, xxxi. i. xxxix. 7. 6
Shuddering from cold, xxxiv. i. i. and 2.
Sight, its accuracy in men, xvi. 6.
Skin, (kurfonit, xxvi. i.
Sleep fufpends volition, xviii. I.
.... defined, xviii. 21.
.... remote caufes, xviii. 20.
.... fenfation continues in it, xviii. 2.
.... from food, xxi. i.
.... from rocking, uniform founds, xxi. i.
.... from wine and opium, xxi. 3.
.... why it invigorates, xi'. j. ]..
.... pulfe flower and fuller, xxxii. 2. 2.

interrupted, xxvii. 2.

. . . . from breathing lefe oxygene, xiiii. 20.
.... from being whirled on a millflone,

xviii. 20.
.... from application of cold, xviii. 20.
Sleeping animals, xii. ■2.2.
Sleep-walkers. See Reverie, xix. r.
Small-pox, xxxiii. 2. 6. xxxiv. 6. r.
eruption firfl: on the face, why,

XXXV. r. I. xxxiii. 2. 10.
the blood will not infedl, xxxiii.

2. 10.

obeys lunations, xxxvi. 4.

Smell, ;;!'. 5. xvi. ^
Sir.iling, origin of, xvi. 8. 4.
Solidity, xiv. 2. 1.

Somnambulation. See Reverie, xix, I,
Space, xiv. 2. 2.

Spafm,

I N D

Spafm, dofirine of, xxxli. 10.

Spectra, ocular, xl.

miftaken for fpe(51;res, xl. 2.

...... vary from long infpeftion, ili. 3. 5.

Spirit of animation. See Scnforial Power.

.... of animation caufes fibrous contraction,
iv. 2. ii. I . xiv. 2. 4.

.... polTeffes folidity, figure, and other pro-
perties of matter, xiv. 2. 3. .

Spirits and angels, xiv. 2. 4.

Stammering explained, xvii. i. 10. xvii. 2. 10.

Stimulus defined, ii. 13. iv. 4. xii. 2. i.

of various kinds, xi. r.

with leflened effeft, xii. 3. I.

....... with greater effedt, xii. 3. 3.

ceafes to produce fenfation, xii. 3. 3.

Stomach and inteftines, xxv.

. , inverted by great flimulus, xxv. 6.

its adlions decreafed in vomiting,

XXXV. I. 3.

a blow on it occafions death, xxv. 1 7 .

Stools black, xxvii. 2.
Strangury, xxxv. 2. i. .

Sucking before nativity, xvi. 4.
Suckling children, fenfe of, xiv. 8.
Suggeflion defined, ii. 10. xv. 2. 4.
Sun and moon, their influence, xxxii. 6.
■Surprife, xvii. 3. j.- xviii. 17.
Sufpicion attends madnefs, xxxiv. 2. 4.
Swallowing, a£t of, xxv. i. xvi. 4.
Sweat, cold, xxv. 9. xxix. 6.

in hot fit of fever, xxxii. 9.

in a morning, why, xviii. 15.

Sweaty hands cured by lime, xxix. 4. g.
Swinging and rocking, why agreeable, xxi. 3.
Sympathy, xxxv. i.
Syncope, xii. 7. i. xxxiv. i. 6.

E X. 585

Teeth decaying caufe headachs, xxxv. 2. i.
Temperaments, xxxi.
Theory of medicine, wanted. Apology.
Thirfl, fenfe of, xiv. 8.

why in dropfies, xxix. 5.

Tickle themfeh'cs, children cannot, xvii. 3. 5.

Tickling, xiv. g.

Time, xiv. 2. 2. xviii. 12.

. . . . . lapfe of, XV. 3. 6.

poetic and mufical, why agreeable,

xxii. 2.

dramatic, xviii. 12.

Tasdium \-\tas. See Ennui.
Tooth-edge, xvi. 10. iii.4. 3. xii. 3. 3.
Touch, fenfe of, xiv. 2. i.

liable to vertigo, xxi. g.

of various animals, xvi. 6.

Trains of motions inverted, xii. 5. 5.
Transfufion of blood in nervous lever, Xxxii. 4. .
Tranflations of matter, xxix. 7.
Typhus, beftquantity of ftimulus in, xii, 7. 8.
....... periods ofobferve lunar days, xxxii. 6.

Ulcers, art of healing, xxxiii. 3.2.

of the lungs, why difficult to heal,

xxviii. 2.
Uniformity in the fine arts, why agreeable,

xxii. 2.
Urine pale in intoxication, xxi. 6.

paucity of in anafarca, why, xxix. 5.

its paflage from inteftines to bladder,

xxix. 3.
copious during fleep, xviii. 15.

. *: Variation, perpetual, of irritability, xii. 2. r.

Tape-worm, xxxix. 2. Vegetable buds are inferior animals, xiii. I.

Talte, fenfe of, xiv. 5. exadtly refemble their parents.

Tears, fecretion of, xxiv. xxxix.

from grief, xvi. 8. 2. ' pofTefs fenfation and volition, xiii. 2.

froiri tender pleafure, xvi. 8.3. have affociate and retrograde mo-

..... from lUmulus of nafal dudi:, xvi. 8. tions, xiii. 4. xxix. g.

xxiv. 4. their anthers and ftigmas are alive,

by volition, xxiv. 6. xiii. 5.

4 F Vegetables

586

INDEX.

Vegetables haveorgans of fenfe and ideas,xiii. 5.

contendforlightandair, xxxix.4. 8,

...,..., duplicature of their flowers, xxxix.

4. 4.
Veins are abforbents, xxvii. i.
.... paralyfis of, xxvii. I.
Venereal orgafm of brutes, xxxii. 6.
Venfefeftion in nervous pains, xxxii. 5. 4.
Verbs of tliree kinds, xv. 3. 4.
Verfes, their meafure, xxii. 2.
Vertigo, xx. defined, xx. 11.

in looking from a tower.

XX. I.

....... ma fliip at fea, xx. 4.

of all the fenfes, xxi. g.

by intoxication, xxxv. 1.2.

Vibratory motions perceived after failing, xx.

5. XX. 10.
Vis medicatrix of nature, xxxix. 4. 7.
Villon, fenfe of, xiv. 3.
Volition defined, v. 2. xxxiv. 1.

afFetls the whole fenforiura, xi. 2.

....... difeafes of, xxxiv.

Voluntarity, x. 2. 4.

Voluntary motions, ix. xxxiv. 1,

Voluntary ideas, xv. 2. 3.

........ criterion of, xi. 2. 3. Xxxlv. J,

Vomiting from vertigo, xx. 8.

from drunkennefs, xx, 8. xxi. 6.

, by intervals, xxv. 8.

... o ... . by voluntary efforts, xxv. 6.

■. . or two kinds, xxxv. i. 3.

in cold fit of fever, xxxii. 9. r.

flopped by quickfilver, xxv. i6»

weakens the pulfe, xxv. 1 7.

Waking, how, xviii. 14.
Walking, how learnt, xvi. 3.
Warmth in lleep, why, xviii. 15.
Weaknefs defined, xii. i. 3. xil. 2. i. xxxii.
3. 2.

cure of, xii. 7. 8. See Debility.

Wit producing laughter, xxxiv. I. 4.
World generated, xxxix. 4. S.
Worm-fluke, xxxii.- 7.

DIRECTIONS TO THE BINDER.

1. Pleafe to place the Plate confifting of one red fpot, at Se£t. III. i.

2. Confifting of one black fpot, at Se£l. III. 3. 3.

3. Confiftlng of five concentric coloured circles, at Se£t. III.

4. Confifting of one yellow circle furrounded by one blue one,

at Sea. XL. 4. 2.

5. Confining of one yellow circle and two blue ones, at Sedl.

XL. 10. 3.

6. Confifting of the word BANKS in blue on a yellow ground,

at Sed. XL. 10. 5.

ERRATA.

Page 178. line 24. yir autennse, nW antennae.
1S3. — l.yirhave, j-mrfhas.
341. in line fixth of tlie Latiii verfcs_. for incutitu;-, rw^ impelliim--

ADVEHTISEMENT.

The publication of the Second Volume of this Work, containing
a diftribution of the difeafes, both of mind and body, into four
natural clafles, with their fubfequent orders, genera, and fpecies,
their immediate caufes, and their- methods of cure, together with a
new arrangement of the articles of the Materia Mediea, their quali-
ties, and modes of operation, is poftpoaed till next year, on account
of the more neceUary avocations of the writer; and that by revifing
it during the fummer months he may make it more worthy the ac-
ceptance of the Public.

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Full text of "Zoonomia ; or, The laws of organic life"

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