10 Mr. T. Smith on the Muscular Structure and Functions 



of tissue the capsular belt and radii surrounding it belonged, 

 I removed the lens from the capsule, and immersed the cap- 

 sule attached to the radiated zone, along with the whole vi- 

 treous humour, in boiling water. The belt contracted both 

 in length and breadth, and became white ; the anterior part 

 within the belt became white, but did not contract ; the pos- 

 terior part within the belt remained transparent. The radii of 

 the hyaloid zone contracted, and became white. These radii, 

 therefore, and the belt around the capsule exhibit the pro- 

 perties of muscular tissue. 



Assuming the muscularity of the capsule and hyaloid zone 

 as declared by the test, it remains to try whether such a struc- 

 ture in action is capable of performing the function of adjust- 

 ment, as it is found to be performed, in the perfect eye. 



The function of the muscular belt around the capsule is 

 made sufficiently evident by its effects on the figure of the lens 

 when plunged in boiling water; but the function of the radii 

 of the zone around the capsule can only be understood by 

 attending to the fixed points towards which their contraction 

 must carry their extremities. 1 have stated above, that these 

 fixed points correspond to the position of the ciliary ligament. 

 Hence the contraction of that part of each of the radii that 

 lies between the capsule and the ligament must draw the cir- 

 cumference of the capsule towards the ligament, and increase 

 the diameter of the lens. The function of the radii, therefore, 

 is antagonist to that of the belt. 



As a sense of straining or effort is experienced when the 

 eye is adapted for a considerable length of time, either to very 

 near or very distant objects, followed by a sense of fatigue, it 

 would appear that there is a middle point, to which the con- 

 vexity of the lens is naturally adapted, and that the adjustment 

 of the eye to nearer or more distant objects is made by a func- 

 tional exertion. If the adjustment to near objects is made by 

 contraction of the capsule, and to distant objects by contrac- 

 tion of the radii, I find by a calculation founded on optical 

 principles, that the changes of curvature of both surfaces of the 

 lens, easily made by these means, fully account for a range of 

 distinct vision equal to that which the young and healthy eye 

 actually commands. What increases the probability that the 

 adjustment of the eye to different distances is really effected 

 by these means, is, that the accommodation made in this way 

 is attended with no change of the optical centre of the eye ; 

 whereas it can be demonstrated that by every other method 

 that has been proposed, a change in the position of the opti- 

 cal centre, and consequently an apparent motion of stationary 

 objects, must occur during the act of adjustment to different 



