clxxiv Journal of Comparative Neurology. 



5. In total color blindness the optic purple is the only light-per- 

 ceiving substance. The optic yellow arising from it is here, however, 

 not capable of further decomposition. 



6. The hitherto observed exceptions to Newton's law of color 

 mixture and Purkinje's phenomena can be explained by the fact that 

 with increasing intensity of the light the spectral subdivision alters its 

 stimulus value for the sensation called forth by the decomposition of 

 the optic purple and the optic yellow. 



7. The physiological process associated with the sensation of 

 white is not an intensifying of that associated with gray (the threshold 

 of the stimulus.) 



Recurrent Images following Visual impressions. 1 



This paper details some carefully planned and very instructive 

 experiments bearing on the oscillatory character of visual impressions. 

 We can give only the author's summary. Those interested in the 

 physiology of vision or of nerve transmission should consult the origi- 

 nal paper. 



It appears that when the retina is exposed to the action of light 

 for a limited time, the complete order of visual phenomena is as fol- 

 lows : 



(1). Immediately upon the impact of light there is experienced a 

 sensation of luminosity, the intensity of which increases for about one- 

 sixtieth of a second; more rapidly towards the end of that period than 

 at first. 



(2). Then ensues a sudden reaction, lasting for about one-sixtieth 

 of a second, in virtue of which the retina becomes partially insensible 

 to renewed or continued luminous impressions. These two effects 

 may be repeated in a diminished degree, as often as three or four 

 times. 



(3). The stage of fluctuation is succeeded by a sensation of steady 

 luminosity, the intensity of which is, however, considerably below 

 the mean of that experienced during the first one-sixtieth of a second. 



(4) . After the external light has been shut off, a sensation of di- 

 minishing luminosity continues for a short time, and is succeeded by 

 a brief interval of darkness. 



(5). Then follows a sudden and clearly-defined sensation of what 

 may be called abnormal darkness — darker than common darkness — 



'Bidwell, Shelford. On the Recurrent Images following Visual Impres- 

 sions. Proc. Roy. Soc, LVI, 337, Sept., 1894. 



