. Eight lectures on the signs of life from their electrical aspect. Electrophysiology. I.] . RETINAL CURRENTS 11 "positive" the opposite direction from fundus to cornea. And I recognise in the deflection to the left that we have just witnessed what I am accustomed to regard as a reaction of the third stage, viz., a negative current, directed from before backwards in the eyeball. And I may just mention that a few hours ago, when I put up this eyeball for ex- periment (under difficulties inseparable from the pres- ence of belated workmen in a new laboratory), it gave a ,, , u T No
. Eight lectures on the signs of life from their electrical aspect. Electrophysiology. I.] . RETINAL CURRENTS 11 "positive" the opposite direction from fundus to cornea. And I recognise in the deflection to the left that we have just witnessed what I am accustomed to regard as a reaction of the third stage, viz., a negative current, directed from before backwards in the eyeball. And I may just mention that a few hours ago, when I put up this eyeball for ex- periment (under difficulties inseparable from the pres- ence of belated workmen in a new laboratory), it gave a ,, , u T NormaL response. positive deflection, such as 1 '^ have learned to be typical of a fresh and normal eyeball, and have chosen to characterise as a reaction of the first stage. These have been details of the laboratory, details that you have hardly followed as I had to do, to make plain to myself (and state to you) what was the direction of current in the eyeball indicated by the direction of movement of the spot of light. Those of you who are actual workers will appreciate the importance of attention to such details, and the hopeless confusion arising from doubtful determinations of direction of observed currents. Those of you who content themselves with the literature of the subject, will find it almost impossible to realise what writers mean by "positive" and "negative" effects. But the response we have just seen is not of the type that I wish to show in a first lecture; it is of what will be described later as a response of the third type, negative instead of positive; the eyeball may have been kept waiting too long, or have been accidentally compressed in the course of pre- paration. So I shall repeat the experiment on another eye- ball that has just been carefully prepared and set up for me by the assistant. \Experiinent.^ And now, as you see, the response to light is a normal response of the first type, viz., positive, for the spot has moved to your right
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