440 



Messrs. L. Hill and M. Flack. 



[May 29, 



intraocular pressure greatly, and considerable pressure may be required at 

 the moment of insertion. The method also permits the entry of fluid into the 

 eye should the pressure of the fluid employed be greater than that of the 

 aqueous. 



We have measured the aqueous pressure by means of a specially constructed 

 hollow needle, used in conjunction with the method employed by one of us 

 (L. H.) when measuring the intracranial or cerebro-spinal fluid pressure.* The 

 needle (fig. 1) consists of two hollow tubes, one revolving within the other. 



A 



Fig. 1 



One end of the outer tube has a solid needle point attached. Each tube has 

 a side eyehole, which in one position correspond one with the other. On 

 revolving the inner tube through a quarter of a circle the holes no longer 

 correspond and are closed. An index arm attached to the inner tube shows 

 when the needle is closed and when open. This L.H. needle — as we shall call 

 it — is connected by rubber tubing to a short length of capillary glass tubing, 

 which in turn is connected by a T-piece with a manometer and with a pressure 

 bottle. The pressure bottle is balanced by a weight and can be raised or 

 lowered with ease (fig. 2). The whole system is filled with Einger's solution, 

 and an air bubble introduced within the capillary glass tube to act as an 

 index. We find it convenient to introduce this air bubble by means of a 

 hypodermic syringe, the needle of which is inserted through the rubber tube at 

 its junction with the capillary glass tube. The zero position of the air bubble 

 is marked while the needle is held open at the level of the eye of the animal, 

 the surface of the solution in the pressure bottle being at the same level. The 

 needle is then closed and made to transfix the cornea ; the inner tube is turned 

 so as to open the needle, while, at the same time, the pressure bottle is raised 

 until the air index is restored to the zero mark and the pressure of the aqueous 

 compensated. The reading of the manometer gives the pressure in centimetres 

 * Leonard Hill, 'The Cerebral Circulation.' «T. and A. Churchill, London, 1896. 



