202 



EYE. 



Fig. 126. 



dow of the iris may often be seen in acrescentic 

 form on a cataract ; and in such persons, whe- 

 ther from this cause or from the inflammation 

 not being of the adhesive character, blindness 

 is more frequently attended with dilated pupil. 

 In breaking up cataracts through the cornea, 

 I have repeatedly satisfied myself of the con- 

 tact or close vicinity of the two surfaces by 

 placing the needle between them. The an- 

 nexed outline section, from the work of Som- 

 merring, shews how 

 small he considered the 

 space between the iris 

 and lens, and displays 

 accurately how the 

 posterior chamber is 

 formed by the iris an- 

 teriorly, the lens pos- 

 teriorly, and the cili- 

 ary processes at the 

 circumference, with the 

 small circular portion 

 of the hyaloid mem- 

 brane of the vitreous 

 humour between the 

 ciiliary processes of 

 the choroid and the 

 circumference of the 

 lens. 



It appears to me unaccountable why sur- 

 geons, with these anatomical facts before them, 

 still continue to introduce the needle into the 

 posterior chamber, to break up cataracts, in- 

 stead of passing it through the cornea into the 

 anterior chamber, where ample space exists, 

 and a full view is obtained of all the steps of 

 the operation. In doing so the needle is thrust 

 through opaque parts among delicate structures, 

 into a narrow cavity, where, hidden by the iris, 

 it can be used with little certainty of correct 

 application. At the same time, instead of 

 penetrating the simple structure of the cornea, 

 which bears injury as well as any other struc- 

 ture of the body, the instrument pervades the 

 fibrous sclerotic, a structure impatient of in- 

 jury and prone to inflammation, punctures the 

 ciliary ligament at the imminent risk of in- 

 juring one of the ciliary nerves or even wound- 

 ing the long ciliary artery, and finally passes 

 through one of the most vascular parts in the 

 body, the corpus ciliare. The practice appears 

 a signal instance of the influence of education, 

 habit, and authority in setting improvement at 

 defiance. The proofs afforded of the close 

 vicinity of the margin of the pupil to the cap- 

 sule of the lens, should remind the surgeon 

 that one of the greatest dangers to be ap- 

 prehended in iritis is the adhesion of these two 

 parts, and that one of the first steps in the 

 treatment should be to separate them by the 

 application of belladonna, which, by its pecu- 

 w influence on the pupil, dilates that aper- 

 ture, nn j ; consequently, brings its margin 

 more opposite the circumference of the lens 

 and at a gi-eater distance from the prominent 

 central portion . 



The aqueous humour, although constituting 

 so essential a part of vhe optical mechanism of 

 the eye, is but small in quiantity ; according to 



Petit not more than four or five grains. Its 

 specific gravity and refractive power scarcely 

 differ from that of water; and according to 

 Berzelius, 100 parts contain 98.10 of water, 

 1.15 of chloruret of soda with a slight trace 

 of alcoholic extract, 0.75 of extractive matter 

 soluble in water only, and a mere trace of 

 albumen. It is perfectly transparent, but is 

 said to be milky in the foatus. 



The source from which this fluid is derived 

 has been the subject of controversy in con- 

 sequence of Nuck, a professor of anatomy at 

 Leyden, having asserted that he had discovered 

 certain ducts through which it was transmitted, 

 and published a small treatise to that effect, 

 which ducts were proved to be vesssels by a 

 cotemporary writer, Chrouet, in which deci- 

 sion subsequent authors have concurred. In 

 the present day this fluid is generally believed 

 to be secreted by a membrane lining the cavity, 

 as the fluid which lubricates the serous cavities 

 is secreted by their lining membranes. Al- 

 though this is in all probability the fact, the 

 circumstances are not exactly the same in both 

 cases. In the serous cavities, merely as much 

 fluid as moistens the surface is poured out, 

 while in the chamber of the aqueous humour 

 sufficient to distend the cavity is secreted. In 

 the serous cavities the membrane from which 

 they derive their name can be demonstrated ; 

 in the chamber of aqueous humour this can 

 scarcely be accomplished. I have resorted to 

 various methods to enable me to demonstrate 

 the existence of the membrane of the aqueous 

 humour on the back of the elastic cornea, 

 such as maceration, immersion in hot water, 

 soaking in alcohol, and treating with acids, 

 alkalis, and various salts, but without effect.' 

 In describing the structure of the cornea, I 

 have shewn that the elastic cornea itself can- 

 not for a moment be considered the membrane 

 in question, on account of its strength, thick- 

 ness, elasticity, and abrupt termination; and 

 I do not think that the demonstration of a 

 serous membrane expanded on such a struc- 

 ture as transparent cartilage is to be expected, 

 inasmuch as the demonstration of the synovial 

 membrane on the cartilages of incrustation in 

 the joints is attended with much difficulty. 

 The pathological fact which tends most to 

 prove the existence of such a membrane here, 

 is, that in iritis, especially that of a syphilitic 

 character, the aqueous humour appears often 

 very muddy, especially in the inferior half of 

 the chamber; this, however, in the latter stages 

 may be found to arise from a delicate speckled 

 opacity on the back of the cornea, which re- 

 mains permanently, and injures vision con- 

 siderably. Analogy also favours the inference 

 that the whole cavity of the chamber must be 

 lined by serous membrane, inasmuch as all 

 structures, of whatsoever nature they may be, 

 in the serous or synovial cavities, are so covered 

 or lined. This provision is so universal, that 

 if such various structure, as the elastic cornea, 

 iris, capsule of the lens, ciliary processes, and 

 hyaloid membrane, which enter into the con- 

 struction of the chamber of aqueous humour, 

 be exposed to the contact of the fluid without 



