WHERE AND HOW WE REMEMBER. 611 



may be, he no longer looks for bis food and water in tbeir usual places, 

 and wben tbey are put before bim be does not seem to know them as 

 food and water until bis nose is put into tbem, when be recognizes 

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

 make bim run into a corner, does not frighten bim any more, though be 

 jumps when be hears it snap. He used to give bis paw when the hand 

 was held out for it. Now be 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 bis 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 born — that is, des- 

 titute of knowledge acquired by sigbt-i^erception. He acts just like a 

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

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

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

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

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

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

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

 the course of two or three months be 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, be becomes per- 

 manently blind. The recovery then was possible because around the 

 area cut out there was left a ring of gray 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 2^otential 

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

 only a part of the potential area. If the actual area is cut 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 bis 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 



