296 Mr. E. E. Henderson and Prof. E. H. Starling. [Nov. 23, 



the end of the needle, this latter is thrust through the lateral part of the 

 cornea, so as to lie in the middle of the anterior chamber. A bubble of air 

 is introduced into the graduated tube by compression of one capsule, and 

 brought to the middle of the tube by relaxing the clamp on the capsule at 

 the end towards the eye. The reservoir is then rapidly adjusted to such 

 a height that the bubble remains stationary. 



In some of the later experiments a platino-iridium cannula, with a solid 

 steel point made slightly conical, was found to be an improvement, as, in the 

 event of any leaking occurring, it could be pushed in further. 



In introducing the cannula great care must be used, as, should the needle 

 catch in or tear the iris, or wound the lens, the eye would be rendered useless 

 for the purposes of the experiment. The needle, being comparatively large 

 and blunt, requires considerable force for its introduction. We have found 

 it safer to make a small perforation with the point of a cataract knife and, 

 without letting the aqueous humour escape, to introduce the cannula in the 

 hole thus made. Should the exact spot be lost sight of, a little fluorescine 

 will stain it. A fine silk thread passed through the episcleral tissue, as in the 

 operation for advancement of a rectus tendon, gives a better hold than fixation 

 forceps, and is somewhat less in the way. 



The fluid employed in the apparatus was usually Einger's solution, in some 

 cases normal saline. Whichever fluid was employed, it was filtered through a 

 Berkefeld candle before the experiment, in order that no foreign body might 

 be present which could lodge in and block the filtration channels. 



The intraocular fluid must play a twofold function in the eye. In the 

 first place, by keeping up the intraocular pressure, it lends rigidity to the 

 supporting structures of the eyeball, and furnishes therefore a fixed point for 

 the intraocular muscles to contract against, besides maintaining the proper 

 distances between the various refractive media. In the second place, it is 

 the only source of nourishment to certain of the structures of the eye, 

 namely, the middle and back part of the cornea, the lens and suspensory 

 ligament, and the vitreous humour. The question that we have to decide 

 is whether this fluid is formed by a process of secretion by the cells covering 

 the ciliary processes, or whether it is a transudation similar to lymph. The 

 question presents many analogies to that with regard to the secretion of urine. 

 In each case we have a possible source of transudation in the capillary 

 blood-vessel network and also an absorbing mechanism. We can only arrive 

 at a conclusion by determining the physiological conditions under which 

 we may alter either the production or the absorption of the intraocular 

 fluid. 



