Clinical tonography, described by Grant10in 1950, has proved of value for the study of the mechanism of aqueous flow under physiological and pathological conditions. It is of great help in the diagnosis of glaucoma and in the evaluation of the therapeutic effect of drugs and of surgery in glaucoma. Though the simplifying assumption involved in the interpretation and calculation from the tonographic tracings necessarily introduces some systematic errors, these do not detract appreciably from the value of tonography as a means of exploring problems of aqueous flow. The purpose of this study was to investigate under experimental conditions one vascular factor which might influence aqueous flow and to see whether tonography in experimental rabbits could be used as an effective tool for the analysis of the effects. Tonography in rabbits was reported only briefly by Grant.10He stated that recordings were made on rabbit eyes in the