450 



Messrs. L. Hill and M. Flack. 



[May 29, 



disappears more quickly, a result attributed to the increased surface of the 

 iris. 



To Ehrlich has been attributed the suggestion that an appreciable amount 

 of intraocular fluid may be secreted directly into the anterior chamber by 

 the anterior surface of the iris (Starling and Henderson, also Parsons). We 

 find nothing to confirm this in Ehrlich's paper. He describes the fluorescein 

 as coming round the edge of the iris, the context clearly showing that he 

 conceives the secretion as taking place from the ciliary processes. "Aus 

 diesem leicht auszufiihrenden und geradezu nicht verfehlenden Versuche 

 ergiebt sich ohne Weiteres, dass bei der Eegeneration des Kammerwassers 

 zunaehst die Vorderflache der Iris vollkommen unbetheiligt ist, und dass 

 diese ausschliesslich von der hinteren Kammer aus erfolgt." 



That there can be no difference of fluid pressure inside the eyeball, and 

 therefore, that the aqueous is a true secretion, we have shown by a series of 

 experiments in which the flow of blood is observed from the venas vorticosse 

 during alterations in the pressure of the fluid in the anterior chamber. The 

 rim of the orbital cavity is carefully cut away and the exit of one of the 

 vortex veins exposed. Our needle is then carefully introduced into the 

 anterior chamber and the pressure measured. A snick is now made in the 

 vortex vein so that the blood flows freely out. Upon increasing the pressure 

 in the eyeball by raising the pressure bottle the flow of blood becomes less 

 and less until finally it ceases to flow.* 



Measurement of the pressure at which this cessation of the flow occurs 

 shows that it corresponds closely with the carotid pressure of the same side. 

 Thus, to give an illustrative example, it was found that it required 160 cm. 

 of water (120 mm. Hg) to stop the flow of blood from an eye the normal 

 aqueous pressure of which was 69 cm. of water (51*5 mm. Hg). The carotid 

 pressure of the same side taken immediately afterwards was 118 mm. Hg. 



V. Schultenf carried out a somewhat similar experiment in order to 

 measure the pressure in the ophthalmic artery. He inserted a cannula into 

 the vitreous and drove in saline solution under increasing pressure until the 

 blood flow in the retinal arteries was just stopped as observed ophthalmoscopi- 

 cally. It was found to be only a few (2-15 mm. Hg) below that in the large 

 arteries. 



In these experiments the fluid pressure is equally distributed throughout 

 the eyeball, and the venous pressure rises pari passu with the fluid pressure, 

 for the veins are reduced in volume and blood expressed until the whole 



* The iris dilates when the pressure is raised, and this dilatation is prevented by 

 section of the cervical sympathetic nerve, 

 t Parsons, loc. cit., vol. 3, p. 1046. 



