FIG. 1.

B, which fibers expand into the ped retina, C C. The unknown cates that the fibers of the are lost in the brain. This disof the percipient nerve-memin the bottom of the clear eye, the only instance in the body a nerve, which is essentially, part of the brain, is exposed to light, its natural stimulus, direct inspection by the aid of thalmoscope.

besides nerve fibers, there are lements in the thickness of the that exist nowhere else in the They are peculiar little transbodies, set in there for a specific se, and that purpose is the recog. of light, with its train of marconsequences. They are the ent elements, without which all rains and nerve-fibers in the would never perceive a ray of Their business is to receive imons from the contact of light, he nerve-fiber with which each s connected, and of which it the end, is charged with the f conducting or carying that imon to the brain, where consciousis enforced-and we see. But e specific endowment of these exe little bodies, which are simply nal expansions of the nerve-fibers lub-like ends, we would be withny means of knowing that such a as light exists, and the blackness

of darkness would be universal. No other texture or organ responds in the faintest degree to the stimulus of light. Hence the absurdity of all this crazy nonsense about clairvoyance, and people seeing with their toes, stomachs, or any other part not made to see with.

"But now hath God set the members, every one of them, in the body, as it hath pleased Him." It has pleased Him to charge the eye alone with the mysterious power of vision. The eye is the light of the body, and if that light be darkness, how great is that darkness? God, the all-seeing, and the totally blind, alone can give the answer.

The specific energies of the retina are better understood by comparison with the peculiarities of the other senses. There is a set of nerve-bodies

in which the nerve-fibers that supply the pulp of the fingers terminate. They are placed with exclusive referWe see with the eye, ence to touch. we feel with the fingers. But neither organ can usurp the place of the other; but they simply aid one another. Another order of nerve elements, enclosed in a hard, bony case filled with liquid to give them delicate lodgment, and exposed only to the direct vibrations of the air, are charged with hearing. The ear can never see, nor the eye hear, but each may verify or disprove the impressions received through Still other nerve bodies the other. are grouped in the tongue, and we enjoy taste. Then, again, that insinuating organ, the nose, must smell its way through the world in virtue of its peculiar gift. Each of these parts has its own God-appointed duties, and there is no vicarious performance of functions. They are the soul's sentinels, and can sleep only as they rest in the providence of Him who set them in their places.

Not only the eye, but every other organ of the organism, is connected by nerve-fibers (or conductors) with the great nervous center, the brain. They are linked together by a system of

eye. Of the multitude of pers forming the inner layer etina, each one turns suddenly , passes through the thickness membrane, and ends in this e enlargement that help to e outer layer. Examined unmicroscope these percipient ppear as an infinite number of icular rods standing on the surface of the retina, like the

FIG.1.

FIG. 2.

on pavement when the blocks ved from the trunks of small nd set on end. Detach the c and choroid coats from the

retina. It will be seen that R, the retina, has a considerable thickness; that the fibers of the optic nerve, N, bend outward into the inner layer of the retina and can be traced onward to where the nerve membrane terminates. Then on the outer surface of this inner layer of fibers, is seen the little rods and cones standing perpendicularly and forming the outer part or layer of the retina. The man

FIG.3.

F

ner in which each nerve-fiber ends in its corresponding rod, is most striking if the figure is viewed with a strong convex lens. It looks as though each fiber and rod form a mud pipe with the bowl of the pipe turned outward. Each rod has its own nerve-fiber to connect it with the brain, and may be considered as an individual microscopic organ. Fig. 2 shows some of the rods very much magnified, and Fig. 3 represents them in connection with their corresponding nerve-fibers or conductors.

It will be seen that the rods are absent on the end of the optic nerve, where it enters the eye. They are seen to terminate on either side of the section of the nerve-disc. Hence there is a blind spot in the bottom of the

all. Let the left eye be shut and the right one fixed steadily on the little cross at the left of Fig. 3; then by moving the book slowly to and from the eye, the white circle at the other end will completely disappear when the book is about five inches from the eye. To succeed in the experiment, it needs only close attention, keeping the right eye fixed immovably on the cross, and the left closed.

There are many other ways of verifying this fact, but this is sufficient. It proves at the same time, that the rods are the percipient elements, and not the nerve-fibers. The former are deficient here, but the latter are in the greatest abundance. If the rods could be taken out of the retina, leaving every thing else intact, not a ray of light could ever be known. The whole eye would be a blind spot, as is naturally the optic nerve. The ancients thought the retina could not be the instrument of vision because it is too thick for a defined, sharp image. Not knowing the existence of the layer of rods, on the exact inner ends of which the image must be formed, to be sharply appreciated, they supposed that the thin choroid coat was the visual membrane.

periments in the presence of King Charles the II, of England. This frivolous and dissolute king afterwards amused himself with his courtiers by making them appear to one another without heads. At a distance of a few feet the whole head can be blotted out by making its image fall on the blind spot-and the full moon can be eclipsed very easily in the same way. This important discovery of the blind spot led to a long discussion among philosophers, and at last culminated in the true theory of the retina being the visual membrane. Since then the question has been still further narrowed down to one layer of the retina— the layer of rods and bulbs. The absence of vision at the optic disc where the rods are deficient, and the fact that by a special arrangement we are able to see the shadows of the blood-vessels in our own retina, are sufficient to settle the question. Then the microscopie anatomy of the retina comes in to explain the phenomenon most admirably. The retina, possessing an appreciable thickness and being composed of different layers, the bloodvessels that ramify so beautifully in the retina are situated in the inner layer, next the vitreous humor. Now, as we can see shadows of those vessels, the vessels must of course be in front of the structures that appreciate the shadows. In other words, the percipient layer must be behind the vascular and nerve layer in order that the shadows of these vessels may be projected upon it. Indeed, the late H. Muller demonstrated by mathematical calculation that the distance of the layer of rods, as ascertained by measurement, behind the vessels, is just sufficient to account for certain phenomena in the movements of those shadows, as the source of the light is moved!!

The blind spot passed undiscovered till about the middle of the seventeenth century. E. Mariotte, a distinguished French academician, was the first to detect it. He instituted experiments in order to determine how vision was affected at the end of the optic nerve, He was a believer in the theory of the choroid being the visual membrane. As the choroid is deficient where the nerve penetrates the eye, he argued that sight ought to be also deficient at that point. And sure enough he discovered that it was a blind spot. The fact was established -the theory it was sought to confirm by it, was false. The discovery made such a sensation at the time that the

hor was invited to repeat the ex

Here we must leave the reader in the shade of his own retinal bloodvessels for another month.

I a banquet recently given at Jersey, to celebrate the opening Channel Islands Telegraph, M. "n de L'Huys, once the Premier -ance, now a refugee on the ls, was an invited guest. Offertoast to the success of the tele, with the vivacity of a Frenche said:

o you not admire, gentlemen, the gies achieved by Science in sethe domain of Man over the field of Nature? It is surely erful. Man says to the Thunder, thyself on the point that I indi

cate, and, following that thread, bury far beneath the earth thy powerless rage;' and the Thunder obeys, growling meanwhile like a caged and subdued monster. Man says to the Light, 'Take thy invisible pencil and produce my portrait;' and Light obeys. He says to the Air, 'Be illumined, become the sun of the night; in the darkness light up my labors and fetes.' He says to the Fire, 'Make friends with the water, thine old enemy, and I will yoke horses of steam to my chariots and my plows.' The Fire obeys. He says to the Lightning, 'Give me thy