ANA T 
j 5, The ulnar nerve. 16, Small brandies coming through 
the holes in the back-part of the os lacrum running to 
the mufcl.es, See. there. 1.7, A fmall branch running out 
between the os facrum and os coccygis. 18, The end of 
the Cauda equina running through the canal at the back- 
part of the os facrum. 19,The fciatic nerve. 20, Branch¬ 
es from the fciatic nerve to the mufcles on the back-part 
of the pelvis. 21, Branches from the fciatic nei veto the 
mufcles, &c. about the anus. 22, Branches from the fci¬ 
atic nerve to tire gluttons maximus and mufcles, at the 
upper and back part of the thigh. 23, Trunk of the fci¬ 
atic nerve, fending off branches to the mufcles -on the 
back-part of the thigh. 24, The fibular nerve fent off 
from the fciatic one. 25, The pofferior tibial nerve, which 
is a continuation of the fciatic nerve. 
The Nerves of the Eye-ball are (hewn in a feparate 
figure. 
OF THE NERVOUS FLUID. 
The nature and properties of the fluid or liquor which 
paffes through the nerves, hath been a fubjed of Confi- 
derable debate among phyfiologuls. Some have.imagined 
the liquor of the nerves to be capable of vafi; explolion 
like gun-powder, or of violent bidden rarefaction like 
air, or of ftrong ebullition like boiling water, or of effer- 
vefcence like the mixture of acids with alkaline liquors. 
But, as the mafs of blood from which this fluid is derived 
is notpofieffed of any fuch properties, we cannot fuppofe 
the blood to furnifh what it has not in itfelf. Befides, all 
thefe operations are too violent for the brain or nerves to 
bear; and, when they are once begun, they are not fo 
quickly controuled or reftrained, as experience teaches us 
tire nerves can, which may be fuddcnly made to ceafe from 
acting. We are not lufficiently acquainted with the pro¬ 
perties of an tether, or eledrical effluvia, pervading eve¬ 
ry thing, to apply them juft'ly in the animal ceconomy; 
and it is as difficult to conceive how they fhould be retain¬ 
ed or conduced in a long nervous cord. Thefe are diffi¬ 
culties not to be furmounted. The fureft way of judging 
what kind of liquor this of "the nerves muft be, is to exa¬ 
mine the liquors of finrilar parts of the body. All the 
glands feparate liquors from the blood much thinner than 
the compound mafs itfelf; fuch is the liquor poured into 
the cavity of the abdomen, thorax, ventricles of the brain, 
the faliva, pancreatic juice, lymph, Sec. Wherever there 
is occafion for fecreted liquors being thick and vifeid, in 
order to anfwer better the ufes they are intended for, na¬ 
ture has provided refervoirs for them to ffagnate in, where 
their thinner parts may be carried off by the numerous 
abforbent veins difperfed on the fide of thofe cavities; or 
they may exhale where they are expofed to the open air. 
The mucus of the note becomes vifeid by ftagnation; 
for, when it is immediately fecreted, it is thin and watery, 
as appears from the application of fternutatories, Sec. The 
cerumen of the ears is of a watery confidence when jud 
fqueezing out, The mucus of the alimentary canal grows 
thick in the lacunas. The bile in the hepatic duct has 
little more confidence than lymph; that in the gall-blad¬ 
der is vifeid and drong. The urine is much more watery 
as it flows from the kidneys, than when it is excreted 
from the bladder. The feed is thin in the tefticles, and 
is conceded in the vedculae feminales, See. Hence we 
may fafely conclude, that a thin liquor is fecreted in the 
cortex encephali or fprnai marrow; and feeing the thin- 
' nefs of the fecreted liquors is generally, as the divifions 
of the velfels, into fmall fubtie branches, and that the 
ramifications within the fkuil are alniod infinitely fubtie, 
the liquor fecreted in the encephalon may be determined 
to be among the fined or thinned of fluids. 
The liquor or fluid in the nerves moves conflantly, 
equally, and (lowly, unlefs when its courfe is altered by 
the influence of the mind, or by the pred’ure of fome 
neighbouring ndive organ. We have not, however, and 
perhaps cannot have,- any idea of the manner in which 
the mind and body ad upon each other: but, if we ah 
Voh. 1 . No. 40. 
o M y. hr 
low that the one is affected by the other, which none de¬ 
ny, and that the fluid of the nerves (whatever name peo¬ 
ple pleafe to give it) is a principal indrument which the 
mind makes ufe of to influence the actions of the body, 
or to inform itfelf of the impreffions made on the body, 
we mud allow that the mind can dired this indrument 
differently, particularly as to quantity and celerity, tho' 
we mud remain ignorant of the manner how many pheno¬ 
mena, depending on this connedion of mind and body, 
are produced. Thus we would in vain attempt to account 
for animals continuing, after their heads were ftruck off 
or their hearts were cut out, to perform addons begun be¬ 
fore they differed any injury. 
All objeds of f’enfe, when applied to their proper or¬ 
gans, ad by impulfe; and this adion is capable of being 
increafed by increadng the impelling force. In tangible 
objeds, it is clearly evident, that theclofer they are preff. 
ed to a certain degree, the more di(tin£t does the percep¬ 
tion come. Odorous particles need the alliftance of air 
moved rapidly to affed our nofe : fapid fubfiances, that 
are fcarcely diffident to give us an idea of their tafte by 
their own weight, are a (tiffed by the preffure of the tongue 
upon the palate: tlie rays of light colleded drive light 
bodies before them : found communicates a vibration to 
all bodies in harmonic proportion with it. The impulfes 
made thus by any of thefe objeds on the nerves, which 
are full of liquor, prefs their fides or extremities, and 
their liquor is prevented from flowing fo freely as it did. 
The canals being all full, this refinance mud inflantane- 
oully affed the whole column of fluids in the canals that 
are prelfed, and their origins, and have the fame effed 
as if the impulfe had been made upon the origin itfelf. 
To illuftrate this by a'grofs comparifon, Let any one puffy 
water out of a fyringe, through a long flexible pipe fixed 
to the fyringe; and he is fenfible of refiffance or a pufh 
backwards, the moment any one flops the orifice of the 
pipe, or clofes the fides of it with his fingers. This im¬ 
pulfe made on the nerves, and thus communicated to their 
origin, varies according to the firength or weaknefs, the 
quicknefs or flownefs, the continuance or fpe'edy removal, 
the uniformity or irregularity, the conftancy or altera¬ 
tion, &c. with which objeds are applied to the nerves. 
The various kinds of impulfes which the different clalfes 
of objeds make, occafion in animals, which ought to have 
accurate perceptions of each objed, a neceffity of having 
the different organs of the fenfes varioufly modified, fo 
that the feveral impulfes may be regularly applied to the 
nerves in each organ ; or, in other words, we muft have 
different organs of the fenfes fitted to the different claffes 
of objeds. As the objeds have one common property of 
impulfe, fo all the organs have moil of the properties of 
the organ of touching in fommon with the papillae of the 
(kin. This is evident in the nofe and tongue : wecanal- 
fo perceive it in fome operations of the eyes, as we may 
likewife do in fome cafes where matter is colleded in the 
internal ear. 
Thefe properties common to the different objeds and 
organs, occafion frequently uncommon efteds in the ap¬ 
plication of an objeit,to an organ proper to another objed: 
of fenfation ; for, fometimes we have the fame idea as if 
the objed had been applied to its own proper organ; at 
other times the objed is as it were changed, and we have 
the idea as if the organ had had its own proper objed ap¬ 
plied to it. Thus, for example, light is the proper ob¬ 
jed to be applied to the eye, to give us an idea of colours; 
yet, when all light is excluded from the eyes, an idea of 
light and colours may be excited in 11s by coughing, 
fneeziiig, rubbing or (triking the eye-ball. A cane vi¬ 
brating, fo as not to excite found perceptible to the ear, 
applied to the teeth, raifes a ffrong idea of found ; as ar 
little infed creeping in the meatus auditorius. al'fo does, 
The fingers applied to two rough furfaces, rubbing on 
each other, are fenfible of the found they make; fur get) ns 
of any pradice in the cure of fradured bones can bear 
vvjtaels to the truth of this. The fingers dipped in acid 
