1912.] Relation between Capillary Pressure and Secretion. 441 



of water. The method of counterbalancing the pressure prevents the entry of 

 aqueous into the manometer. The same method was employed by v. Schulten 

 and by E. E. Henderson and Starling. These last two researchers, however, 

 introduced the air bubble index after the needle had been inserted, and then 

 found the pressure which kept it stationary. Taking this into consideration, 

 also the fact that they inserted the needle with fluid flowing from it at a 



Fig. 2. 



pressure conjectured to be greater than the aqueous pressure, we conclude 

 that their measurements do not give with certainty the normal intraocular 

 pressure. 



In some preliminary experiments carried out by Thomson Henderson and 

 one of us (L. H), an open needle was used and readings were obtained which 

 seemed to show that the intraocular pressure approximated to the intra- 

 cranial pressure ; the two varied in the same way concomitantly with changes 

 in the general circulatory pressure. It seemed not unlikely that these 

 readings were vitiated by the escape of fluid during insertion, or afterwards, 

 along the track of the needle, and were thus too low. The fluid may escape 

 when the open eyehole of the needle is half inside and half outside the cornea. 

 Also, when the small cylindrical needle has been passed through, it is difficult 

 to prevent the leakage of fluid along its track. Any loss of fluid lowers the 



