272 COMPARATIVE PHYSIOLOGY OF THE BRAIN 



recognise the objects, although it is not entirely blind. 

 What Munk mistook for psychic blindness is, in real- 

 ity, only hemiamblyopia or hemianopia (5, 6). 



6. One of the main arguments which Munk used 

 for his assumption of a psychic character of the visual 

 disturbances caused by the effects of a unilateral lesion 

 of a visual sphere was the fact that these disturbances 

 disappear in about six weeks. On the basis of this 

 fact he constructed the following hypothesis : The 

 visual images of memory are deposited each in a 

 single ganglion-cell or a group of cells in the region 

 A t of the opposite hemisphere. If this region be re- 

 moved, the dog loses all its images of memory. But 

 new images of memory can be deposited in the sur- 

 rounding parts A. This will be done after the loss of 

 the region Aj and the dog becomes normal again after 

 six weeks. If this hypothesis of Munk were correct, 

 visual disturbances of such a dog should not disap- 

 pear if it were kept in the dark, where it would have 

 no chance to acquire new visual images of memory. 

 I made that experiment. In dogs which possessed 

 only the right eye, the region Aj in the left cerebral 

 hemisphere was destroyed. In the majority of these 

 dogs, the operation produced no effect. In a few, 

 hemiamblyopia occurred. Of these several were put 

 in an absolutely dark room for the following six weeks. 

 As soon as they were taken out they were entirely 

 normal. This proves that their recovery was not due 

 to the acquisition of new visual images of memory, 

 but to the fact that a purely physiological effect upon 



