THE OSMOTIC relation between blood and aqueous humor is a factor which plays an important and well-recognized part in governing the intraocular pressure.1 Duke-Elder2 and associates showed in 1938 that the aqueous is slightly hypertonic to blood; this observation was further elaborated by Duke-Elder3 and Davson4 and substantiated by Kinsey,5 In 1948 Duke-Elder and Davson3 wrote: "It may be that the maintenance of this osmotic gradient is of considerable importance in the mechanism of the intraocular pressure. This factor has not been fully explored." A unified concept for the maintenance of the intraocular pressure was proposed by Kinsey6 in 1950; here, again, emphasis was on the osmotic interrelationship of blood and aqueous humor. The attention of the above-mentioned investigators was focused mainly on the intraocular pressure, while other aspects of aqueous humor dynamics were not explored. The introduction of Grant's * aqueous outflow test