444 



Messrs. L. Hill and M. Flack. 



[May 29, 



or that of the cerebro-spinal fluid, at the same time as the intraocular 

 pressure. We find that we can pass another needle of similar construction 

 through the occipito-atlantal membrane and thus compare under the same 

 conditions the aqueous and the cerebro-spinal fluid pressure. In this part 

 of the research we used cats and a few dogs. The animal is anaesthetised 

 with ether, and after a tracheal cannula has been inserted, it is placed belly 

 downwards on a flat, hot-water tin with its head over the end of the tin. 

 The occipito-atlantal membrane is exposed by separating the muscles from the 

 occipital bone after making a median longitudinal incision ; weighted hooks 

 are used, two to keep open the sides of the incision, one, fastened to the 

 anterior end of the wound and passed over the snout, to keep the head 

 in position. The needle is passed through the membrane from side to side 

 so that its eyehole opens into the bath of cerebro-spinal fluid. The pressure 

 of the aqueous is much higher than that of the cerebro-spinal fluid, or intra- 

 cranial pressure, e.g. one may be 5-10 cm. of water, the other 30-60 cm. 

 The air indices in either case pulse with each heart beat, but while the 

 index of the cerebral instrument follows with large excursions the respiratory 

 variations of the venous pressure, that of the eye remains unaffected. The 

 pressure of the aqueous is so high that the variations of venous pressure do 

 not influence it. 



Starling and E. E. Henderson also noted the fact that the intraocular 

 pressure is not affected by changes in the general venous pressure. 



The observations of others (v. Schulten, Starling and Henderson, etc.) show 

 that the intraocular pressure varies in the same direction as the arterial 

 pressure. In this respect the aqueous and the cerebro-spinal pressures go 

 together. Ligation of the carotid artery on the same side lowers the aqueous 

 pressure 5-10 mm. Hg; compression of the abdominal aorta raises it 

 10-20 mm. Hg ; section of the spinal cord in the cervical region lowers it 

 10-15 mm. Hg ; stoppage of the heart lowers it 10-12 mm. Hg. 



In general we confirm the above results. Thus, tightening a string round 

 the neck caused a fall of 15 mm. Hg in the intraocular pressure. During 

 stimulation of the depressor nerve the arterial pressure fell 36 mm. Hg, the 

 intraocular 8 mm. Hg. Stimulation of the cervical sympathetic caused a 

 rise of intraocular pressure of 1-2 mm. Hg, followed by a fall of 

 4-5 mm. Hg. Starling and E. E. Henderson ascribe the rise to contraction 

 of the orbital muscle and the fall to vaso-constriction of the intraocular 

 arteries. Dr. W. T. Lister examined the eye of one of our cats with the 

 ophthalmoscope and was unable to note any constriction of the retinal vessels 

 during stimulation which produced full dilatation of the pupil. We would 

 point out that dilatation of the pupil must cause expulsion of the blood in the 



