224 Royal Society .— 



" On the Adaptation of the Human Y.ya to varyhig Distances." 

 By Charles Archer, Esq., Surgeon, Bengal Army. 



The following is a summary of the author'sviews on the question : — 

 \. The eye is adapted to varying distances principally by an alter- 

 ation in the fibrous arrangement of the lens itself. Moreover, that 

 when the lens is removed after an operation for cataract, the power 

 of adaptation is nearly lost, and can only be exerted within very 

 confined distances. 



2. That the purpose of focalizing light at short distances is doubt- 

 less assisted, as suggested by Bowman, by the contractions of the 

 ciliary muscle, in its antero-posterior dii'ection, bringing forward the 

 ciliary processes. 



3. That as the posterior hemisphere of the capsule is firmly united 

 to the hyaloid membrane, this portion must always remain quiescent, 

 and therefore the antero-posterior contractions of the ciliary muscle 

 must be very limited as regards the lens. 



4 . That the ciliary muscle, being placed around the eye, and its 

 fibres being of a somewhat plexiform character, the contractions of 

 the muscle will relax those yielding portions of the eye placed within 

 its circumference. 



5. That the relaxations of the ciliary processes will deprive the 

 capsule of its firm support. It will be pressed forward by the lens, 

 which will meet with no further resistance to the expansion of its 

 short axis. 



6. That the lens itself, as microscopically described by Bowman 

 and Kolliker, is admirably adapted to the varying changes which 

 take place in the capsule. 



7. That the posterior capsule being firmly united to the hyaloid 

 membrane, the alteration in the diameters of the cavity of the cap- 

 sule must take place from the periphery of the lens to its centre, 

 and from behind forwards, but not from before backwards, on account 

 of the close union of the posterior capsule to the hyaloid membrane. 



8. That to allow such alteration to take place without endanger- 

 ing the achromatism of the lens, the alterations in the plane of its 

 long diameter must be synchronous with the alterations in the plane 

 of its short diameter. To allow of this, the margin of the lens is free 

 in the canal of Petit ; were it not the case, chromatic aberration 

 would result. 



9. That the elasticity of the capsule of the lens and the ciliary 

 muscle are antagonistic ; that on the ciliary muscle becoming relaxed, 

 the capsule of the lens is free to exert that elasticity. 



10. That, by the pressure exerted by the anterior hemisphere of 

 the capsule by means of the polygonal cells of Virchow on the ante- 

 rior face of the lens, the organ is able to fulfil all the requirements 

 for adapting it to receive focalized light from long distances. 



1 1 . That the polygonal cells of Virchow are placed on the pos- 

 terior surface of the anterior hemisphere of the capsule with the 

 view before mentioned, and that they are arranged with their long 

 diameters in an antero-posterior direction, that pressure may not 

 injure their transparency, which would be the case if placed laterally, 



12. That these cells are not found in other parts of the capsule. 



