| Show fluid that continually spreads over retina gives Us the ability to see the elaborate mechanism for vi vision would fail to give ability to see it if it were not for a fluid that continually spreads over the retina the viewing plate in the back of the eyeball on which the objects seen are projected as a picture according to a writer in the new york herald d tribune this plate is covered with a structure of rods and cones which appear to be the elements from which the picture is transmitted to the sight center in the brain these rods and cones would be unable to transmit their picture unless they were covered with a fluid called visual purple the chemical nature of this substance has been unknown dr selig hecht of columbia university has ascertained that it is a protein by establishing its size by passing it through a porous porcelain filter this test showed it has a molecular weight of about which indicates it is a highly complex molecule and a protein since no other class of substances possess such high molecular weights visual purple has been extracted from animals eyes and has been found sensitive to light in its natural state it is a pinkish color but when it has been exposed to light it changes to a yellow and finally becomes colorless by leaving it in J the dark it will return to its original pink color and regain its sensitivity to light when the eye looks at too strong a light the visual purple is changed to its inactive state and when the eye is plunged into a dark are area from one too strongly illuminated it is unable to see well until the visual purple has been regenerated or a new supply spread on the retina carotene a parent substance from which the body makes vitamin A seems to be necessary for the body when it is manufacturing visual purple lack of vitamin A leads to blindness |
