The dressings should not be disturbed for at least 24 hours. The lids are then cleansed with 1-6,000 perchloride of mercury lotion, and the lower one is pulled down so as to allow the escape of tears and to see if any discharge be present. The upper lid should not be touched. If no discharge be present the eye is re-dressed. If discharge be present the conjunctival sac should be washed out carefully with boric lotion. Most wounds with conjunctival flaps are shut off in 48 hours, after which time it is advisable to wash out the conjunctival sac twice a day with boric lotion. Great care should be taken to see that no undue pressure is made on the globe. The patient should be warned not to screw up the eyes or strain whilst the dressing is being performed. CHAPTER II OPERATIONS UPON THE LENS =Surgical anatomy.= The lens consists of fibres which are developed from cells originating in an inclusion of the fœtal epiblast. A normal lens is surrounded by a capsule, the anterior half of which is lined with a single layer of epithelial cells on its inner surface. In fœtal life the cells which line the posterior half of the capsule go to form the lens fibres, so that after birth the lens capsule is lined by cells only on its anterior surface. The lens capsule, which is deposited from the epithelial cells lining it, consists of a highly elastic membrane; small wounds in its continuity, therefore, gape widely. Throughout life the cells lining the capsule continue to become new lens fibres, but at the same time the bulk of the lens does not increase markedly. This is due to the fact that the lens fibres become more closely packed together and lose some of their watery constituents (sclerosis). The older central part of the lens is the first to undergo this process, with the result that a definite hard nucleus is found in the lenses of people about the age of thirty to thirty-five and upwards. [Illustration: FIG. 83. A LENS THREE WEEKS AFTER NEEDLING. The section shows the swelling and breaking up of the lens in the anterior chamber. The iris has become adherent to the needle puncture.] Chemically the lens fibres are composed of crystallin, which is closely allied to a serum globulin and is therefore soluble in salt solution. When the lens capsule has been opened, by operation or accident, the saline aqueous is admitted to the lens, which becomes opaque, swells up, and is gradually absorbed (Fig. 83). In those under the age of thirty, therefore, a simple incision into the capsule is all that is required to cause it to be absorbed. But, as has already been pointed out, the lens develops a hard nucleus after that age and will not then be absorbed satisfactorily by simply opening its capsule; to remove it, as is done in senile cataract, the hard nucleus must be extracted from the eye. [Illustration: FIG. 84. ANATOMY OF THE ANTERIOR SEGMENT OF THE EYE.