448 



Messrs. L. Hill and M. Flack. 



[May 29, 



unconvincing nature of the results so obtained, and turned to another method 

 of enquiry. After introducing a hollow needle, and balancing the pressure, 

 they divided the heart of the animal, and measured the rate of movement 

 inwards of the air index ; they say : " This rate must be equal to the rate of 

 production of fluid previously obtaining in the eye under normal conditions 

 of circulation." Parsons says:* "That constant reabsorption of the fluid 

 secreted is taking place is shown by the injection of an indifferent fluid into 

 the anterior chamber of a freshly removed eye under constant pressure." . . . 

 " The fluid can be seen to exude from the cut ends of the anterior ciliary 

 and vortex veins, and the pericorneal region becomes injected with the 

 coloured fluid (Priestley Smith)." Again, " The difference between the 

 amounts of fluid entering the living and the dead eye will give the amount 

 of fluid secreted by the eye at the given pressure (Adamuk, Jesner, 

 Niesmanoff)."f 



In our opinion these are amazing claims to make, and show how far the 

 authors are from what we hold to be a true conception of the conditions in the 

 living eyeball. As in the case of the brain, the mean capillary-venous 

 pressure and the intraocular pressure are one and the same. Each pulse 

 keeps up the pressure, brings into play the elasticity of the eye and maintains 

 the onflow and outflow of blood. Evidence shows that the aqueous is secreted 

 by the ciliary processes and absorbed by the capillary- venous network of the 

 iris and the iridial angle. Nuel and BenoitJ have traced the paths of 

 absorption by injecting Chinese ink into the living eye. There is nothing in 

 the structure of the iris, ciliary processes, or retina which can act as a rigid 

 membrane and allow an inequality of pressure between the blood in the 

 capillaries and veins and the fluid in the aqueous or vitreous outside. 

 Measurement has shown that the vitreous and aqueous pressures are the 

 same (Bellarminoff, Hamburger, Priestley Smith). The whole eyeball must 

 be at one and the same fluid pressure, namely, the lowest hydrostatic pressure, 

 and this is the pressure in the veins at their exit through the sclerotic. In 

 the case of the brain we know there is no difference of pressure on either side 

 of the capillary membrane ; measurement has proved this, the capillary- venous 

 pressure and cerebro-spinal fluid pressure are the same. When, as Starling 

 and E. E. Henderson did. we divide the heart of the animal, the air index moves 

 towards the needle in the anterior chamber, first because the blood at once 

 leaves the eyeball, secondly, because the veins are no longer filled and there is 

 within them no pressure to counter that of the aqueous outside. The spaces 



* Log. tit., vol. 3, p. 966. 



t Parsons, loc. cit, vol. 3, p. 967. 



X 'Arch. f. Ophthal.,' 1895, vol. 41. 



