Bauhaus-Universität Weimar

OBSERVATIONS ON SENSIBILITY. 
Iefs fenfible tlian the cornea, by to-aching both, not only with my 
linger, but with a bit of foft filk or linen *. 
H AviNG been lately prefent at the extradion of the cryftalline 
lens in Mr Sharp’s method f, I inquired particularly of the' patient,, 
whether he felt any pain when the cornea was firft pierced with 
the knife? he told me he thought the pain was much the fame with 
what he ufed to feel when the fkin of his arm was cut in bleeding.. 
It ought however to be remarked, that though the Ikin and cornea 
have both a confiderable degree of fenfibility ; yet, when they are cut. 
quickly with a very fliarp infiniment, there is lefs pain felt than one- 
would imagine. Thus, when the Ikin is Rightly wounded in Ilia- 
ving, the blood that follows is often the fiflt thing that lets one^ 
know of the accident : and this, together with the pain occafioned: 
by holding the eye firm in its orbit, and the concern the patients* 
are generally under, may well account for their being fometimes« 
fcarce fenfible of any pain when the cornea is pierced with a Iharp 
needle. But upon the whole, it appears, that the cornea is poflefled 
of a remarkable degree of fenfibility ; and confequently, that M. de 
Hallers? 
* M* de Hallèr remarks, that in thefe experiments, I only touched the conjunaiva (a), which ; 
is certainly true ; nor was I ignorant of this. But as M. de Haller had pronounced the cor- 
nea in general to be infenfible, and had made no exception in favour of the conjunaiva which» 
covers it, my experiments were certainly in point, and the conclufion from them juft : and its 
wiil be found very difficult to prove by any experiment, that the pain occafioned by cutting - 
the cornea is not partly owing to this membrane, as well as to the conjunaiva.. 
M. de Haller, unwilling to allow fenfibility even to the conjunaiva, afcribes the pain oc^* 
cafioned by touching the cornea to fmall branches of the fifth pair of nerves which'run be¬ 
tween thefe membranes. But fuppofing the exiftenee of nervous branches between the cor 
nea and conjunaiva, as well as between this laft and the fclerotic, akho’ no anatomift has-^ 
yet demonftrated the former ; yet the pain occafioned by touching the,cornea, very gently 
the fenfation produced by the cool air blowing on it, cannot well be conceived to be owin? to. 
any thing, elfe than the fenfibility of its exterior covering. Nay, if the ««« itfeif were not; 
more fenfible than the fclerotic, why ffiould the conjunaiva feel more accutely where it co 
vers the former, than where it is contiguous to the latter ? The conjunaiva; where it cover," 
the cornea, is certainly one of the moft fenfible parts of the whole body, and léaft able to bear 
any hurt, or the application of any acrid fubftance Nor could its fenfibility be fo great ifi 
it were owing folely to fome branches of nerves running between it and the «ww*,- § ’ ' 
t Philofoph tranfa
    

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