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occur and pathology would furnish instances of mistakes.

Second. Certain forms of congenital blindness, such as cataracts and complete closure of the pupil, can be remedied by operation. These children learn by touch the correct (erect) position of objects, and their first impression when sight is restored would be an inversion of the object, according to the current theory. As far as the author knows no case of this kind has ever been recorded.

Dr. J. L. Minor, Memphis, Tenn., reported to the writer in November, 1898, two cases of congenital cataracts. The patients were brothers between thirty and forty years of age, and had never seen. After removing the cataracts the doctor kept these men under observation for a month, and assures us there was never even a suggestion of inverted images."

The case of Rev. Mr. Hanna, reported by Sidis, who after falling from his carriage lost all memory of his former life experience, is a unique bit of evidence. He was as a newly born infant opening his eyes for the first time on the world. So totally obliterated from memory were the experiences of his past life that even the simplest mental processes, like the appreciation of distance, form, size, and magnitude, were effaced from his mind, but objects were seen erect.

Mr. Hanna's subsequent statement is as follows: "The eyes suddenly opened quite involuntarily,

and here indeed was a new world of wonder and study. Objects were all alike as to distance, shape, and thickness, but the variety of color was the feature of interest. The room was a great beautiful picture, absolutely without movement or distance beyond the eye." I

Furthermore, this is a misconception, based on the old theory of special immediate creation of perfected organisms, and finds no place in the scientific thought of to-day. It is inconsistent with the facts of evolution, which means a regular progression from the simple to the relatively complex; and the explanation of the phenomena of sight must cover the primitive eye, as well as the perfected organ.

The function of the primitive eye must have been limited to simple sensitiveness to light, and the implication of the law of natural selection, that every minute change which was continued was of greater advantage to its possessor than a preceding stage, absolutely excludes the tactile reinversion theory. The specialization of a sense organ in such a way that its evidence of the outer world was misleading (inverted) until corrected (reinverted) by some other sense organ (touch), could not have been of more advantage to its possessor than a less highly developed organ which could be trusted; and natural selection would have carefully avoided propagating any such variation.

The inversion is an accomplished fact as soon as * Sidis: Multiple Personality.

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the primitive eye is able to locate an external point in space, for it can never see the point till it can tell its direction.

The subsequent changes are all along this line of so perfecting the mechanism that a luminous point in space shall produce an irritant point on the retina. Thus there is no break in the contemporaneous development of the organ of seeing and the psychical act of seeing. They advance with equal step. There is no catastrophe; no period when the optical apparatus gives wrong impressions to the sensory.

It is indeed strange that ophthalmologists have so universally neglected to elucidate this puzzling phenomenon, and in what follows the author is borrowing from Le Conte, whose explanation is the only satisfactory one which has come to his notice.

A cone of light emitted by a radiant point falling on a convex refracting surface is again converged to a point behind the refracting surface. These two points are called conjugate foci (literally yoked together), because if the radiant be placed at either focus the light will be brought to a point at the other focus. (Fig. 1.)

FOCUS

FOCUS

FIG. 1. CONJUGATE FOCI.

In the normal eye, at rest, a luminous point twenty feet or more distant is focused as a point on the

retina. (Fig. 2.) If the luminous point be nearer than twenty feet, the refracting or bending effect of the eye must be increased (accommodated) so that

FIG. 2.- NORMAL EYE AT REST, FOCUSED FOR DISTANCE. the conjugate focus shall still be at the retina. (Fig. 3.) This is accomplished by increasing the thickness of the crystalline lens, shown by the dotted line, Fig.

FIG. 3. ACCOMMODATION FOR NEAR VISION BY INCREASED THICKENING OF THE LENS.

3. As before stated, when the eye is able to reproduce a luminous point in space as an irritant point on the retina, the optical requirements for perfect vision are secured.

Now "outward projection " means that the retina is touched at this mathematical point, and, like all other senses, it refers the sensation back to the source; in this case along the central line of the pencil of rays. The size of the image on the retina of the largest object that can be seen at all clearly at one time with

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out moving the eye or the object is probably not greater than three millimeters.

Conversely, the field of vision of clear visionwith an immovable eye is extremely limited. At the length of the arm a circle the size of the thumbnail represents all that can be seen clearly, and it is only by rapid excursions that the eye sees in detail those portions that were only outlined before. The field of vision has been compared to a painting which is hazy and indistinct except a circle one-half inch in diameter, in which the most minute details are worked out. This small area may be any portion of the picture which is desired, by turning the eye toward that spot, but no two places at once. It is hard to believe this, for the eye, by rapid excursions, so quickly covers a large field that the separate sensations are fused into one.

Now, the analogy and bearing of this is important when it is understood that we do not see even this one-half inch object as a whole. Each mathematical point of which the object is composed sends out its bundle of rays, which are again converged to a point upon the retina, and from this irritation conveyed to

1 According to Suter: "Refraction and Motility of the Eye," page 142. "The fovea centralis, upon which falls the image of every object attracting mental attention, does not exceed 0.4 mm. in diameter." Taking the distance of the nodal point in front of the retina to be 15 mm. (Dennett), by a very simple problem of similar triangles, it is demonstrable that, at a distance of one-half meter, an object to be discerned with normal acuity cannot exceed 13.5+ mm. in diameter.