596 PHYSIOLOGY 



On making an opening into the cornea the fluid drains away and the eye- 

 ball becomes soft and collapsed, the cornea being folded, and the eye being 

 naturally useless as an optical instrument. The fluid which flows away, and 

 which forms the aqueous humour and also fills the interstices of the -gela- 

 tinous tissue of the vitreous, contains only a minute trace of protein, con- 

 sisting, in every 100 parts, of 98-7 parts water and 1-2 to 1-3 total solids, of 

 which only 0-08 to 0-12 part consists of protein. If a cannula be kept in the 

 anterior chamber this fluid rapidly alters its character, becoming coagulable, 

 and containing 3 to 4 per cent, of proteins. 



The intraocular fluid is continually being renewed. The eyeball receives 

 a rich vascular supply, which forms a close network of vessels and capillaries 



mm. Hg. 

 mm. Hg. 



Art. B.P. 



mm. Hg. 

 mm. Hg. 



10 sec. 



FIG. 309. Curve showing effects on the intraocular pressure (in the dog) of mechani 

 cal interference with the circulation. Blood-pressure measured in left carotid, 

 intraocular pressure in right eye. From p to s the descending thoracic aorta 

 was occluded. From Q to R the right vertebral and subclavian arteries were also 

 occluded. (HENDERSON and STARLING.) 



in the choroid coat, with its prolongations the ciliary processes and iris. 

 The chief seat of formation of the intraocular fluid is the ciliary processes. 

 Here there is a constant transudation of fluid from the blood-vessels into 

 the anterior part of the vitreous cavity, the amount of the transudation 

 varying with the pressure in the blood capillaries (Fig. 309), being increased 

 by any rise in the capillary blood pressure or by any fall in the intraocular 

 pressure. Of the fluid poured out by the ciliary processes a very small 

 proportion (perhaps one-fiftieth) passes backwards into the vitreous humour 

 and gradually drains out of the eyeball by the lymphatic spaces of the optic 

 nerve. By far the larger amount passes forward through the fibres of the 

 suspensory ligament into the posterior chamber (the annular cavity between 

 the iris in front and the lens and ciliary processes behind), and thence round 



