WHERE AND HOW WE REMEMBER. 61 1 



may be, he no longer looks for his food and water in their usual places, 

 and when they are put before him he does not seem to know them as 

 food and water until his nose is put into them, when he recognizes 

 them by other senses than sight. The sight of the whip, which used to 

 make him run into a corner, does not frighten him any more, though he 

 jumps when he hears it snap. He used to give his paw when the hand 

 was held out for it. Now he will not do so until the word paw is 

 spoken, when he holds it up as before. The dog is not blind, but he 

 has lost the power of recognizing objects formerly recognized by sight. 

 He has been deprived, by the operation, of his sight-memory pictures, 

 or sight-imaging power. He has been put back, as far as one sense is 

 concerned, into the condition in which he was when bom — that is, des- 

 titute of knowledge acquired by sight-perception. He acts just like a 

 puppy ; for he soon begins to smell and lick objects in an inquiring 

 way, and to run to and examine curiously things with which he was 

 formerly familiar. He sees these things, he learns again to know them; 

 in a word, he begins at once to lay in a new store of memory-pictures. 

 It is only necessary to put his nose into water a few times ; after that 

 he looks for and finds it when he is thirsty. Then he begins to know 

 his master. The whip soon becomes again a dreaded object. And in 

 the course of two or three months he has gained a new set of mem- 

 ories and recognizes objects just as before the operation. 



In the first dog, the entire posterior part .of the brain was removed, 

 and the dog was made permanently blind. In the second dog, a por- 

 tion of this part of the brain was cut out, and the dog was deprived of 

 his sight-memory. He was, however, able to recover. And, if by suc- 

 cessive operations the experiment be repeated on the same dog, it will 

 be found that recovery is always possible until the entire posterior 

 part of the brain is removed, when, like the first dog, he becomes per- 

 manently blind. The recovery then was possible because around the 

 area cut out there was left a ring of gi*ay matter which was in connec- 

 tion with the eye ; and in this ring of gray matter, which formerly 

 contained no memory-pictures, the new memory-pictures were stored. 

 All the posterior part of the brain in the dog is, therefore, a potential 

 area for sight-memories. The actual area of sight-memories occupies 

 only a part of the potential area. If the actual area is cat out, but a 

 part of the potential area remains, the dog is temporarily deprived of 

 sight-memory, but can recover. If the potential area is entirely ex- 

 tirpated, the dog remains blind, and can never regain his memories. 

 The distinction between actual and potential memory is important, as 

 we shall see when we come to similar phenomena in man. 



The experiments just described were first made by Hermann Munk, 

 Professor of Physiology in the University of Berlin, and they have 

 been confirmed by many other experimenters. What has thus been 

 proved of the location of perception by sight, and of sight-memories 

 in the posterior part of the brain, has also been proved of other senses 



