ANATOMICAL AND PSYCHIC LOCALISATION 271 



sees nothing in the right half of his visual field. If 

 the same operation be performed in a dog, it causes 

 not a complete hemianopia but a hemiamblyopia (5). 

 The dog is not blind for the right half of its visual 

 field, but has only a reduced power of vision. It be- 

 haves like an animal that pays less attention to that 

 half of its visual field, or whose threshold for this half 

 is reduced. If we stand before such a dog and hold 

 two pieces of meat in front of it, simultaneously, one 

 piece in each hand, the dog invariably chooses the 

 piece at its left. It almost seems as though it did 

 not see the piece at the right. Now we know that a 

 moving object acts as a stronger optical stimulus than 

 a stationary object. If the two pieces of meat are 

 again held before the dog in the manner described 

 above, only with the difference that the piece that is 

 in the right half of the field of vision is moved, the clog 

 jumps at the latter (6). This proves that in the dog 

 the threshold of stimulation for optical stimuli has 

 been raised in the right half of the field of vision. 

 But how could Munk mistake the hemiamblyopia for 

 a psychic disturbance? In a dog, the divergence of 

 the optical axes is greater than in man. Hence the 

 right half of the visual field is controlled more by the 

 right eye than by the left. If we produce the hemi- 

 amblyopia or the hemianopia in a dog, the eye oppo- 

 site the injured hemisphere is blind or injured for 

 considerably more than one half of its retina. If the 

 other eye of such a dog be closed, its field of vision is 

 reduced to a very small area, and the dog does not 



