316 



Messrs. L. Hill and M. Flack. [Apr. 23, 







mm. Hg. 

 140 

 138 

 133 



mm. Hg. 

 72 

 92 

 88 



The structural mechanisms visible in the kidney seem to us altogether 

 opposed to the doctrine that fluid is filtered from the blood into the capsule 

 by the force of the blood-pressure. There are membranae propria? which confine 

 the tubules, but no rigid structures which can sustain the capillary wall and 

 convert it into a membrane capable of sustaining a difference of hydrostatic 

 pressure. The glomerulus is a lobulated structure the lobules of which hang 

 in the capsule, just as the ciliary processes hang in a bath of aqueous within 

 the posterior chamber of the eye. We believe that the passage of fluids is 

 determined in both cases by a secretory force acting from the cells which 

 line the vascular processes. The pressure of the fluid within the capsule and 

 of the blood within the glomerular vessels must be the same. In the case of 

 the brain the choroidal fringes secrete the cerebro-spinal fluid ; the venous 

 pressure and that of this fluid correspond and are always one and the same. 

 The pressure of the brain against the wall of the skull is also the same ; the 

 slightest increase of pressure exerted on the brain squeezes the blood out of 

 the capillaries. If the pressure be made to rise in the cerebral veins, that of 

 the cerebro-spinal fluid rises to the same extent. Suppose fluid be injected, 

 or in some inflammatory state cerebro-spinal fluid be secreted at a higher 

 pressure, then the venous pressure rises concomitantly, since the veins are 

 narrowed by the injected or secreted fluid. We shall show in a subse- 

 quent paper that in the eye the same conditions hold good. The ciliary 

 processes are held to secrete the aqueous, and the circulatory pressure 

 in the veins within the eyeball is adjusted to the secretory pressure 

 of the aqueous. The aqueous takes up so much of the total volume 

 and the veins are narrowed to such an extent that the intra-ocular pressure 

 is raised to a considerable figure, some 30-40 mm. Hg. The pressure, both 

 intra-ocular and intra-cranial, depends on the circulation, and ceases 

 with the circulation, but its height is regulated by the secretory action 

 of the cells. In the eye and brain we have the delicate secreting fringes 

 lying in a bath of the secreted fluid, and there exists no supporting structure 

 which can bear off any part of the pressure. We cannot imagine that the 

 fringes are held open as it were by wire springs. The pressure of the 

 -secretion outside and of the blood within the capillaries and veins must be 



