I. THE THEORY OF MEMORY 341 



tein molecules. The renewal of the protein in the brain cells may be 

 tedious as compared with that of other cells, but it seems little doubt 

 that even the brain cells have to change occasionally the old protein 

 molecules with new ones. If the pattern of the memory was not 

 transferred to the newly synthesized protein, the memory of the cells 

 would be lost on every renewal of the protein. Thus, the protein 

 holding a memory must involve a specific structural pattern cor- 

 responding to the memory. In other words, the transmissible pattern 

 of memory must be a structure produced in the protoplasm protein 

 by the "impression". 



Now, if we assume that structural factors which may prevent the 

 change of a protein from A to -B-structure are removed when the pro- 

 tein achieves the change A— >-B, it may be expected that the protein 

 having recovered the original .4-structure, will achieve the change 

 more readily than before, and since the repetition of the change may 

 result in the more complete removal of the preventing factors, the 

 repetition of the change will facilitate the reaction the more. The 

 protein structure resulting from the removal of such factors can be 

 considered as the pattern of the memory. This may be comparable to 

 a path beaten across a wilderness overrun with grass. If a man 

 traverses the pathless wilds for the first time, he must have a hard 

 walk, but on repeating the traverse the grass will be gradually re- 

 moved until at last an easy path will be made. The above cited in- 

 stance that the rubber tube is easily bent at a certain part on the 

 repetition of the bending at that part, may also depend upon the re- 

 moval of the structural factors which prevent the bending. 



The path beaten across the wilds by repeated walk will be lost 

 by being overgrown with weeds if the walk is given up for a long 

 time. In a similar way, oblivion may occur in the brain by the reap- 

 pearance of the preventing structural factors which were once removed. 

 Thus it can be said that oblivion of the memorj^ is also a result of 

 the structural return to the original form. 



The concept thus far formed of the memory phenomenon is illus- 

 trated in Fig. 32. Protein-I which is folded in the form-A under a 

 certain environmental condition is converted to the form-B when the 

 environment is changed in favour of the establishement of B-form. 

 During this change the protein is temporarily to be unfolded into the 

 polypeptide chain; the side chains represented by © and is assumed 

 to prevent the change, A ->• B. The repetition of this change leads to 

 the removal of these preventing side chains, and as a result protein-I 

 is changed in its structure into II. 



When such a change is once established, the conversion to B-form 

 will occur with facility, training effect being thus attained. Since the 



