Let us consider the first of the three procedures just mentioned--_iridectomy_--introduced by von Graefe. The mechanism of its mode of cure is best studied in cases of acute primary glaucoma, when there is apposition of the periphery of the iris to the cornea. In these acute cases there is probably only a mere _apposition_, and the blocking up of the sclero-iridian angle is largely mechanical. Here the root of the iris is readily removed in its entirety and a really peripheral iridectomy is easily done. When, however, a true _adhesion_ between corneal and iridic tissue takes place the filtration angle is not so easily opened. True peripheral adhesions are not readily broken up or separated, and the iridectomy is, for that reason at least, not effective. Moreover, this form of anterior synechia (resulting from a true union of iris and cornea) is so intimate that the iris root is, by the iridectomy, torn away only at the sclero-iridian angle at the anterior border of the adhesion--and does not open up a channel into Schlemm's canal. It is not, therefore, difficult to understand why iridectomy alone in any of the forms of chronic glaucoma fails to open up the true filtration spaces and does not provide a drain that permits of an escape of fluid from the posterior chamber through the loose tissue that surrounds it into the canal of Schlemm. Treacher Collins found, after a careful examination of eyes upon which iridectomy had been performed for glaucoma, that it is extremely rare for the initial section to pass through the pectinate ligament, while Schlemm's canal invariably escapes. Moreover, since the sclero-corneal incision is uniformly oblique, the position and extent of the external wound does not always furnish evidence of the character of the internal wound. In all likelihood many cases of relief or cure following iridectomy are those due to the formation of cystoid scars or minute fistulae, rather than as a result of the removal of a portion of the iris periphery. The best brief tabulation of the results obtained by iridectomy, in glaucoma, is to be found in Weeks' textbook on _Diseases of the Eye_, page 417: "Sulzer reports as follows: Acute glaucoma, 149 cases; improved, 72.5 per cent; serviceable vision preserved, 11.3 per cent; vision impaired at once, 4.08 per cent; very little vision, 12.12 per cent. "Zentmeyer and Posey: In simple glaucoma central vision increased in 60 per cent; remained the same in 20 per cent; diminished in 20 per cent.