INDESTRUCTIBILITY OF CEREBRAL IMPRESSIONS. 65 



mory of all sensations may be improved by means of 

 proper discipline. 



' If it is asked, How can the brain be the organ of 

 memory, when you suppose its substance to be ever 

 changing ? or, How. is it that your assumed nutritive 

 change of all the particles of the brain is not as destruc- 

 tive of all memory and all knowledge of sensuous things 

 as their sudden destruction by some great injury is ? the 

 answer is, because of the exactness of assimilation accom- 

 plished in the formative process ; the effect once produced 

 by an impression upon the brain, whether in perception or 

 intellectual act, is fixed and there retained ; because the 

 part, be it what it may, which has been thereby changed, 

 is exactly represented in the part which, in the course of 

 nutrition, succeeds to it.' l 



The persistency of ideas in memory, like that of 

 forms in vegetables and animals, &c., is probably a conse- 

 quence, and one of the numerous forms of manifestation, 

 of the great principle of persistency of force. Persistency 

 of form depends upon repetition of similar causes. A 

 body in a state of motion, tends, under a continuance of 

 the same conditions, to continue in that state of motion 

 until something arises to prevent it, and thus gives rise to 

 a continued series of similar effects, as in the reproduction 

 of similar forms or impressions. 



The power of receiving impressions which may after- 

 wards be revived or recalled, is not confined to living 

 cerebral matter, but exists also in inanimate substances, 

 and even in metals ; for instance, in all latent photo- 

 graphic impressions before they are developed ; also in 

 what is known as Moser's pictures, and in Chinese mirrors, 

 &c., the latent images of which may be developed at any 



1 Paget, Lectures on Surgical Pathology, vol. i. p. 52. 

 F 



