REVIEW OF RESPONSE OF ANISOTROPIC ORGANS 715 



abnormal or reversed response. Now, with regard to reversed 

 response in general I have shown it to be due to either of 

 two different conditions which hold good for all responding 

 tissues. These are in the first place sub-tonicity, and 

 secondly, fatigue. The abnormal response caused by the first 

 has been shown to be converted into normal, in the case of 

 the retina, by the action of an agent which enhanced the 

 excitability. 



Another phenomenon which I discovered in the response 

 ot retina was that of multiple response, induced by the 

 application of strong or of continuous stimulation. These 

 multiple responses have visual correspondences in the 

 multiple after-images seen in the retina, and in the visual 

 fluctuations which occur under the constant stimulus of 

 light. The latter of these facts was demonstrated by a 

 specially devised stereoscope (p. 432). In this connection 

 may be mentioned the interesting phenomenon of Binocular 

 Alternation of Vision. 



The various types of direct and after-effects observed in 

 vegetable tissues under light I find to have their close 

 correspondences in the responses of the retina. Just as in 

 the highly excitable lamina of Bryophyllum, constituting 

 Type I., we have the formula of ( + -), so also, in the 

 highly excitable retina of Ophiocephalus, the same sequences 

 of direct and after-effects is observed. In less highly 

 excitable vegetable tissues, such as the petiole of cauli- 

 flower, affording us Type III., the sequence was shown 

 to be (+...). In correspondence with this may be 

 mentioned the response of the isolated retina of fish, 

 observed by Kiihne and Steiner. In this case, as the effect 

 of isolation, the retina must have become sub-tonic, which 

 supposition is borne out by the fact that its response to the 

 immediate action of light was abnormal positive instead of 

 negative. I found a similar sequence to occur in an isolated 

 sub-tonic retina of Ophiocephalus (figs. 260, 261). 



Finally, in somewhat fatigued specimens, an intermediate 

 Type II. was found, in which the sequence was ( + ) 



