1912.] Relation between Capillary Pressure and Secretion. 459 



Summary. 



(1) The intraocular pressure is 35-65 mm. Hg in cats and in dogs under 

 ether. To the finger, the tension of the human eye seems to be about the 

 same as in these animals. 



(2) The tension varies with the arterial pressure ; a residual pressure of 

 some 13-18 mm. Hg remains for a short time after the heart beat has stopped. 



(3) The tension is primarily due to the secretory action of the cells which 

 line the ciliary processes ; this secretory pressure regulates the capillary- 

 venous pressure pertaining in the eyeball ; the pressure of the aqueous and 

 the capillary-venous pressure are always one and the same. Sudden abolition 

 of this equality of pressure by escape of the aqueous causes congestion of the 

 iris and ciliary body, and haemorrhage then results from the iris when the 

 blood pressure is raised. 



(4) The circulatory conditions in the eye resemble those in the intra- 

 cranial cavity, with the exception that the intraocular is much higher than 

 the intracranial pressure, and therefore is not affected by changes in the 

 general venous pressure. 



(5) When the intraocular pressure is raised by injection of Einger's 

 solution into the anterior chamber, the circulation through the eyeball 

 continues until the intraocular pressure just exceeds the arterial pressure. 



(6) It is suggested that the increased tension in glaucoma is due to 

 increased imbibition and secretion of fluid, resulting from an altered 

 metabolism of the ocular tissues, leading to compression of the veins and 

 to a rise in the capillary -venous pressure, and therefore intraocular pressure. 

 The operative relief of glaucoma depends not on the relief of the tension 

 per se, but on the increased transudation of tissue lymph with its immunising 

 properties. Acute glaucoma resembles an inflammatory condition in any 

 other part of the body, e.g. a boil. 



(7) The essential factor in the act of accommodation is the transference of 

 the aqueous from the front of the lens to the circumlental region, which 

 allows the forward expansion of the fluid exterior part of the lens. 



