According to the duplicity theory the rods are colourblind sensory cells of low thresholds, whereas the cone system mediates colour sensation and operates a t higher stimulus intensities. Support for the conception of a duplex retina has also been obtained from investigations in which the eye has been stimulated with intermittent light. A low fusion frequency (upper limit roughly 25 fl/sec.) has thus always been found under conditions when the rod system is supposed to be operating: in retinae histologically dominated by rods, in man with peripheral fixation, a t low stimulus intensities, in cases of complete colourblindness. On the other hand a high fusion frequency (roughly about 50 I/sec.) has been the rule when according to the duplicity theory the cone system is responsible for sensation: in retinae histologically dominated by cones, in man with central fixation, a t high intensities, in hemeralopy. These well-known results are based chiefly on sensory and behaviourist data.Consistent results are obtained also when recording the flicker fusion frequency from the electroretinogram (ERG). I n the 'mixed' retina of man CREED and GRANIT (1933) and BERNHARD (1940) recorded fusion frequencies of 20-25 fl/sec. with weak stimuli, whilst DODT (1951) showed that it was possible to reach ERG fusion frequencies of about 60 fllsec. with strong stimuli. The retina of the cat is dominated by rods but contains a number of cones which according to GRANIT (1943) suffices to give a Purkinje shift in some elements. The aim of the present work is t o find out whether the cones present in the cat also can give cone flicker in 23-532758. Acta phys. Scandinao. V o l . 30. 376 EBERHARD DODT AND CHRISTINA ENROTH.the ERG and whether comparable fusion frequencies can be obtained by recording from single retinal ganglion cells, which represent the final common path destined for the higher cent,res. Meth o (1 8. Preparation:The experiments were performed either on decerebrate cats which in some experiments were given urethane solution (20 per cent), 2-5 ml/kg body weight, or on cats anaesthetized with urethanechloralose (0.05 g chloralose and 0 . 2 5 g urethane in 7 ml Ringer solution per kg body weight).In the experiments where only ERG was recorded this was led off between the cornea of the intact eye (atropinised) and either the nose or the decerebration wound. In those experiments where the retinal spikes also were recorded by the microelectrode technique, the eye was opened (see e. g. ENROTH 1952) and the ERG was then led off between the vitreous and nose or decerebration wound.Stimulation and recording. The light source was a tungsten ribbon lamp run at a colour temperature of 2,800"K. The variations in stimulus intensity were obtained by means of neutral filters and an iris diaphragm. Full intensity varied between 4,000 and 11,000 Lux. The light intensity was measured with a photoelectric luxmeter at the level of the cat's eye. A second lamp of about 1,000 Lux was used for light adaptation. It was kept on for half an hour or ...
SINCE Adrian and Matthews (1928) showed that the latent period of the optic nerve discharge can be influenced by the size of the area stimulated, the effect of area on the electroretinogram has been confirmed by a number of workers (Granit, 1933;Creed and Granit, 1933;Fry and Bartley, 1935;Boynton and Riggs, 1951).The size and shape of the electroretinogram can be influenced in the same way by increasing the stimulated area as by increasing the intensity ofthe stimulus. Fry and Bartley (1935) stated that the effect of areawas due almost entirely to stray light; they believed the effect of the focal area to be small. They performed the following experiment on the intact rabbit eye:Two adjacent bright areas were exposed alternately against a dark background. Since the amount of stray light was the same in each case and diffusely distributed over the retina, alteration could not affect it: each of the two retinal spots, however, should respond intermittently if the focal response were dominant. Actually, at fast rates of alternation, no response was obtained, and this finding was explained on the assumption that stray light, being constant and independent of the area stimulated, acted as a much more effective constant background than the alternating focal points, which were therefore believed to elicit only a negligible fraction of the b-wave. Granit, Rubinstein, and Therman (1935) disagreed with this generalization. To test it they produced,< on the retina of the excised and opened frog eye, two sharply focused spots, about 0 4 mm. in diameter and 0 3 mm. apart.Threshold stimuli were used to elicit a response of about 50 ,uV. In this case the two stimuli A and B together elicited a response only 10-15 per cent. less than the expected value of A+B. Stray light could thus account for only this percentage of the combined response. Nevertheless when one flash was made to succeed the other, the effect of the second was inhibited. They concluded that adjacent neurones also were influenced by some kind of physiological spread of the electrical response, while admitting of course the existence of stray light unless special precautions were taken to avoid it.More recently Boynton and liggs (1951) and Asher (1951) have emphasized that the retinal response is primarily aroused by stray light rather than
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