discover any such recession in eyes in which iridectomy had been performed. Thus the weight of

authority is rather against the occurrence of a diminution of the peripheral circumference of the lens in accommodation for near vision, and the above explanation remains a doubtful hypothesis.

Then with regard to the hypothesis of the supposed increased convexity of the crystalline lens being occasioned by the contraction of the ciliary muscle causing diminution of the tension of the elastic structures enveloping the lens, and thus allowing the lens to assume its normal form, which is alleged to be more convex than it is when these elastic envelopes are not relaxed by the action of the ciliary muscle: if this view is to be accepted we encounter this little difficulty, viz. that in advanced life distant accommodation remains perfect, while the faculty of near accommodation is diminished or lost. Hence we

must believe that the tension of the capsule with its connexions remains unimpaired or even increases in old age, while the muscular power of the ciliary muscle declines or is altogether lost. Does it not seem highly improbable that the supposed tension of these delicate structures should continue unimpaired or even increase with advancing years-for many presbyoptics require a convex lens even for distant vision?

Again, what reason is there for supposing that the muscular power of the ciliary muscle is so much impaired in old age when we find that the power of a neighbouring and analogous muscle, the circular fibres of the iris, is rather increased in old age, seeing that the pupil as a rule becomes more contracted as we grow older?

In normal or emmetropic eyes the limits of distinct vision vary much with age. Fellenberg says that at ten years of age the near point," that is, the minimum distance at which an object can be seen distinctly, is 2 inches distant from the front of the cornea; at twenty years, 35 inches; at thirty, 4 inches; at forty, 6 inches; at fifty, 12 inches; at sixty, 24 inches; and at seventy, 144 inches. The "far point" of distinct vision for normal eyes is infinite distance at all ages; but as before stated, many old persons require a convex lens for the distinct vision of even distant objects. The gradual increase of this "near point," as years increase, may, I think, be satisfactorily accounted for by the flattening of the eye lenses. That the cornea which gives its shape to the anterior aqueous lens becomes flatter in old age has been generally remarked, and I am convinced by

* Carpenter's Physiology,' 12th Edit., p. 801. These figures are probably averages, they are certainly not invariably correct.

repeated observations in old and young subjects of the catoptric appearances connected with the anterior surface of the crystalline, that the crystalline lens is also flatter in advanced age. Now we need not suppose that removal of the "near point" in advanced life is owing to a loss of power in the ciliary muscle, all we need say is that the action of the muscle cannot remedy the altered shape of the eye lenses.

72. Let us now consider the catoptric phenomena that have been observed in the change of accommodation from distant to near vision. When a candle is placed on one side of the eye and the observer looks at the eye on the level of the candle flame from the other side, three images of the candle flame are observed in the pupil : 1, a large, distinct, upright image of the flame on the side nearest the candle, the reflexion from the surface of the cornea; 2, a large indistinct, upright image of the candle flame near the centre of the pupil, the reflexion of the anterior surface of the crystalline lens; and 3, a small inverted image of the flame on the side most remote from the candle, the reflexion from the posterior surface of the crystalline lens. In the figures given by Cramer (Fig. 24) the large indistinct upright image of the flame is observed in accommodation from distant to near vision to move towards the bright upright corneal

image, its size being slightly diminished. In the figure given by Donders (Fig. 25) of the same phenomenon, the image reflected by the anterior surface of the lens moves more markedly towards the corneal image, while it undergoes an even greater diminution in size. In the figure given by Helmholtz (Fig. 26) no lateral movement is indicated, the image is only represented as diminished in size in accommodation for near vision, but he says it generally moves towards the centre of the pupil. Had he always observed this movement towards the centre of the pupil, he would doubtless have said so, but his language leads us to suppose that it sometimes did not appear to move in the indicated direction, and possibly that it was occasionally observed to move in the opposite direction.

73. In order to observe the changes that occur in the image of the candle flame reflected from the anterior surface of the crystalline lens I constructed an apparatus similar in principle to that used and devised by Cramer, but modified in such a way that I could at will observe the eye from either side, while the candle was placed at the opposite side. While the eye under observation was steadily fixed on an object right in front of it, the light of the candle impinged on the eye at a small angle on one side of the line of vision, and I looked at the eye through

a microscope of 1-inch focus placed at a similar angle to the line of vision on its other side. In this way I could see the three images of the candle as they were reflected respectively from the cornea, the anterior surface and the posterior surface of the crystalline lens (Fig. 29). Seen through the microscope the images are of course all reversed, but I represent them here in their true position. The large distinct upright image is the reflexion from the cornea; the small inverted image is the reflexion from the posterior surface of the crystalline lens; the dim large image between these two is the reflexion from the anterior surface of the lens. It is always extremely indistinct in normal eyes, and looks like the ghost of an image when contrasted with the clear, well-defined images reflected from the cornea and posterior surface of the lens. The cause of this indistinctness and want of definition is the very slight convexity of the central part of the anterior curvature of the lens. In some myopic eyes I have examined, where the myopia was evidently, in part at least, owing to the abnormal convexity of the anterior surface of the lens, the image of the candle flame is much more distinct and considerably smaller.

Fig. 29 represents the appearance of the reflected candle flame in the pupil of the right eye when the