1912.] Relation between Capillary Pressure and Secretion. 447 



secretion. Under these circumstances, the eye is temporarily a rigid box, 

 and, as is shown to be the case in the brain by Leonard Hill, the venous 

 pressure is equal to the intracranial pressure, so here, too, the venous 

 pressure will also be equal to the intraocular pressure. This will not hold 

 for variations of intraocular pressure, as it does in the case of the brain, 

 because under these circumstances the eyeball is no longer a rigid case." 

 Yet Parsons* cites Koster's experiments, which prove that an increase 

 of intraocular pressure from 19 mm. Hg to 70 mm. Hg only increases the 

 radius of the globe - 027 mm., or the volume 45 cu. mm., or 7/1000 of 

 the original volume. (Koster's experiments were done on the freshly 

 excised eye.) 



E. E. Henderson and Starlingf sought to find evidence to prove that the 

 aqueous is a filtration produced by a higher capillary pressure in the ciliary 

 processes. They opened the anterior chamber and measured the outflow of 

 aqueous, and observed the effect of obstructing the aorta, and so raising the 

 arterial pressure in the eye. These conditions are wholly abnormal. Great 

 dilatation of the vessels of the ciliary processes and the iris results, because, 

 as we hold, the capillaries are no longer supported by the exactly equivalent 

 counter-pressure of the aqueous. The protein content of the aqueous rapidly 

 rises from the normal, less than 0*05, to 3, 4, and even 5 per cent., the 

 fluid becoming coagulable. If the drop in intraocular pressure is suddenly 

 made, red corpuscles may appear in the fluid on raising the arterial 

 pressure, the epithelium of the ciliary processes changes, and blisters may 

 form beneath it (Greeff). The operation actually converts the normal 

 conditions, which are quite otherwise, into those supposed to exist by 

 E. E. Henderson and Starling, and the result is to give a wholly different 

 fluid. To open the eyeball has the same result as abrading the skin. The 

 plasma escapes through the damaged and unsupported capillaries. After we 

 have freely opened and emptied the anterior chamber, we have observed the 

 effect of raising the arterial pressure by compressing the abdomen. The 

 iris and the ciliary body are congested, and with the lens bulge forwards, 

 coming into contact with the cornea. This is because the pressure of the 

 aqueous no longer balances the capillary venous pressure. Compressing the 

 abdomen after opening the anterior chamber causes blood to escape from 

 the iris. A convulsive movement of the animal may have the same 

 effect, hence the bleeding which occurs in lesions of the eyeball. Plasma 

 escapes from the anterior chamber under these conditions, just as it 

 does from the skin when abraded. Starling and E. E. Henderson felt the 



* Loc. tit, vol. 3, p. 1042. 

 t Loc. cit. 



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