1905.] On the Production of Intraocular Fluid. 303 



determined the rate of inflow when the pressure in his cannula was raised 

 to 50 mm., 75 mm., and 100 mm. Hg. He then killed the animal, and again 

 determined the rate at which the fluid would flow in under these various 

 pressures. He found that above 50 mm. Hg the rate of inflow was the same 

 in the dead as in the riving animal. He therefore concluded that 50 mm. Ho; 

 represented the intracapillary pressure. In coining to this conclusion he was 

 guided by the assumption that, when the intraocular pressure was raised so as 

 to be equal to the intracapillary pressure, the transudation of intraocular 

 fluid would cease, and above this pressure the rate of inflow for his reservoir 

 would be, therefore, the same in the living and dead eye. It is impossible, 

 however, by this method to determine intracapillary pressure. The globe 

 of the eyeball is practically rigid. As the intraocular pressure is raised, 

 the intraocular fluid will press upon the veins of the ciliary processes, and 

 the blood pressure will therefore rise in the capillaries and in the veins 

 until it is greater than the intraocular pressure. "With successive rises in the 

 intraocular pressure the pressure in capillaries and veins must get larger and 

 larger in order that any circulation of blood may be maintained, and the 

 circulation through the capillaries will cease only when the intraocular 

 pressure is very nearly as high as the arterial pressure. If the circu- 

 lation in Mesnamoffs experiments ceased at 50 mm. Hg, it is evident 

 that the normal intracapillary pressure, when the intraocular pressure is 

 25 mm. Hg, must be considerably below 50 mm. Hg. How then are we 

 to explain the very definite figures obtained by Niesnamoff ? This observer 

 apparently performed very few experiments. In his paper he gives the 

 results of only one such experiment as that here described. On repeating 

 his experiments we found it impossible to obtain anything like such definite 

 figures — and this for various reasons. In the first place, a considerable rise 

 of intraocular pressure, such as to 50 or 70 mm. Hg, exercises an abnormal 

 stretching effect upon the filtering apparatus of the eyeball, so that the 

 channels at the anterior angle of the eye are gradually opened up, and in 

 many experiments we observed a consequent gradual increase in the rate 

 of inflow of the fluid. In most experiments, for example, the rate of inflow 

 was greater with descending pressures than with ascending pressures. This 

 is well shown in experiment No. 2, on p. 301. 



The following experiment shows the dilatation consequent on a preliminary 

 raising of the intraocular pressure : — 



