. Eight lectures on the signs of life from their electrical aspect. Electrophysiology. 44 THE SIGNS OF LIFE [LECT. | 24. The effects of tetanisation upon the effects of light. Experiment II.—Our next experiment is to show that the electrical response to light is modified by tetanising cur- rents. I had to use very weak currents for the first ex- periment, I shall use much stronger currents for this one, because I want to show an unmistakable modification of the electrical response to light, and I may use strong currents if while they are passing they are short-circuited from the gal- vanometer
. Eight lectures on the signs of life from their electrical aspect. Electrophysiology. 44 THE SIGNS OF LIFE [LECT. | 24. The effects of tetanisation upon the effects of light. Experiment II.—Our next experiment is to show that the electrical response to light is modified by tetanising cur- rents. I had to use very weak currents for the first ex- periment, I shall use much stronger currents for this one, because I want to show an unmistakable modification of the electrical response to light, and I may use strong currents if while they are passing they are short-circuited from the gal- vanometer. First notice the response to light, it is about + 14 degrees of scale. Now, I plug out the galvanometer and tetanise the eyeball for half a minute. I then unplug, and the spot has flown off scale to your right. That has been what on first witnessing it I called a blaze-current; it has been provoked by the tetanisation to which the eyeball has just been subjected. But for the present it is not our principal concern. I bring the spot back on to scale by means of a compensating current, and as soon as the spot has come to comparative rest—it has been gradually falling off to the left by reason of the gradual subsidence of the blaze-current—we again take a reading of the electrical response to light ; it is now 30 as compared with 14, its value before tetanisation, , the normal response to light has been more than doubled in consequence of tetanisation. 1] (5,000). O 5 |_ L5 L \L° L /5L \_20mins. Before Afber FlG. 20.—Frog's eyeball. Influence of tetanisation upon the normal retinal response to light. Ordinary arrangement of induction coil, fed by two Leclanche cells. Secondary coil at 9 centims. (5000 units on Berne scale). After tetanisation the positive response is considerably augmented, and falls during illumination. The terminal positive deflection at break of light is almost completely abolished. This marked augmenta
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