Eight lectures on the signs Eight lectures on the signs of life from their electrical aspect eightlectureson00wall Year: 1903 44 THE SIGNS OF LIFE [LECt. § 24. The effects of tetanisation upojt 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 ar
Eight lectures on the signs Eight lectures on the signs of life from their electrical aspect eightlectureson00wall Year: 1903 44 THE SIGNS OF LIFE [LECt. § 24. The effects of tetanisation upojt 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. / ipoo T, (3,000) [Ia^-^ 1_ 20mins. O 5 lOmins. 0 \_ L-^ L \!P L '-^ L Before bet, After bebanisd-Uon. Fig. 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 lig
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