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



a product of the two factors, formation and absorption, and that the main- 

 tenance of the pressure at a constant height must be determined by an 

 accurate balance between these two processes. The problem which lies 

 before us is to determine the mechanism of formation of this fluid. 



The intraocular fluid is a clear, colourless solution containing a proportion 

 of salts similar to that of the blood plasma, but having an osmotic pressure 

 which is somewhat higher than the blood plasma, and containing the merest 

 trace of proteids.* 



I. Metlwds of Research. 



The animals used were mostly cats. In a few cases dogs were employed, 

 and in one experiment a rabbit. In the case of the cats the anaesthetic 

 used was always ether, with the addition in some cases of a small dose of 

 morphia. In a few experiments, after the induction of full anaesthesia, 

 a small dose of curare was given. The administration of the anaesthetic was 

 continued during the experiment by an air-pump connected with a cannula 

 in the trachea. For the dogs the A.C.E. mixture was employed. 



A record of the blood pressure was kept in all experiments. In some it 

 was taken continuously, but in the greater number of experiments a short 

 record was taken every few minutes in order to avoid trouble with clotting 

 in the cannula. In the cats the blood pressure was taken in the lower part 

 of the abdominal aorta, in the dog in the femoral artery. 



The apparatus we employed for measuring the intraocular pressure was 

 very similar to that described in a former paper (3). A graduated tube with 

 internal bore of about 0'5 mm., and about 50 cm. long, is provided with 

 a lateral tube near each end. One end of the tube is connected by india- 

 rubber tubing, by means of a T--piece, with a reservoir containing Ringer's 

 solution (or any other fluid the absorption of which is to be determined), and 

 also with a manometer. The other end is connected by a second (glass) tube 

 with a gilt steel hollow needle, which is introduced into the anterior chamber 

 of the eye. The needle may be open at the end, or be closed at the end and 

 provided with a lateral opening. To each of the side tubes a rubber capsule 

 is attached. The capsule nearest the reservoir contains air, while that 

 towards the eye is filled with fluid. By means of screw-clamps, fluid or air 

 may be driven from either of the two capsules into the graduated tube. 

 Before introducing the needle into the anterior chamber, the pressure in the 

 apparatus is adjusted by raising the reservoir to about 25 cm. H 2 0, which 

 represents the average intraocular pressure. While the fluid is dropping from 



* Full details of various analyses of intraocular fluid are given by Leber (2), p. 207, 

 et seq. 



