Eight lectures on the signs Eight lectures on the signs of life from their electrical aspect eightlecturesons00wall Year: 1903 26 THE SIGNS OF LIFE [ behaves itself with a more prolonged exposure of the eye. So I adjust the shutter for such prolonged exposure to light —a minute will be a convenient time—expecting to obtain, if the eyeball is quite normal, a larger and increasing posi- tive deflection during exposure. And now watch the spot rather closely for what will happen when I cut off the light by closing the shutter; as you hear the click of closure, you see that the spot makes a
Eight lectures on the signs Eight lectures on the signs of life from their electrical aspect eightlecturesons00wall Year: 1903 26 THE SIGNS OF LIFE [ behaves itself with a more prolonged exposure of the eye. So I adjust the shutter for such prolonged exposure to light —a minute will be a convenient time—expecting to obtain, if the eyeball is quite normal, a larger and increasing posi- tive deflection during exposure. And now watch the spot rather closely for what will happen when I cut off the light by closing the shutter; as you hear the click of closure, you see that the spot makes a short positive excursion to your right before falling back to its original starting position. All these features will be best realised from a photographic record of the travelling spot; here is such a record, on which you readily distinguish the large positive and increasing response to a prolonged exposure, ending by the small positive response er- as we familiarly call it in the laboratory—the ' parting bow ' o mins. !0 FlG. 10.—Frog's eyeball. Galvanometric record of five successive normal responses to light; each illumination lasts for one minute. at the cessation of illumination, after which the current gradually falls to its original level. This has been no excep- tional result, but the typical and regular mode of response of a normal carefully prepared eyeball; the photographic record of five such responses taken on a more slowly travelling plate will be sufficient evidence of this. In each case there is deflection in the positive direction at ' make ' of light, during light, and at ' break ' of light. 15. Further points.—There are several subordinate points
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