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did it before me, [1]and those that have mention'd the same experiment since (without taking notice hereof) have mistook my intent in it. For the putting the Retina in water is not to wash off the mucous Substance, which is its proper Substance, but 'tis to expand the Fibres by the playing it up and down in warm water, and to magnifie the Image of it by a double refraction of the lucid raies, which pass through that and the Glass that contains it.
That there is a little white slimy matter comes off upon washing the Retina is true, and this serves to fill up the interstices of the Fibres and thicken the Coat, whereby the Raies terminate the better, and pass not through to the Choroeides, (which takes off in some measure Monsr. Mariotte's objection of which more anon) and this may be part of the succus Nutritius of the Nerve; tho however the Coat may be as well said sistere species (as they call it), or to terminate the Raies, as the Oil'd Paper does the turning Images in the Lantern, notwithstanding it be in some measure diaphanous. Besides toward the bottom of the Eye the Fibres of this Coat converge very much or come closer together, and 'tis here that is the most lively representation or exquisitest sense of the object, for wch reason partly, as also partly from it's figure, I formerly took the liberty of calling it a Pupilla inverted. This lies in Men diametrically opposite[2] to the Pupill, as the Optic Nerve is plac'd in the forementioned figure: but in Brutes more obliquely by reason of the insertion of the Optic Nerve more toward the inner Canthus; so that sometimes (as we may see in Horses upon starting} they are forc't to turn their Eye accordingly, to distinguish clearly objects that surprize them.
7. But next of all I would have it observ'd, that whereas I say the intermediate Fibres gradually differ in tension as they are nigher or further from the top of the Thalami Optici, it may be easily suppos'd that they do it by so Mi-
nute
