3 o8 THE POPULAR SCIENCE MONTHLY. 



combined, which results from the prolonged exercise of it : and it is 

 especially in our inability to recollect something which we wish to call 

 to mind, that this failure of power shows itself. An interval of repose 

 completely restores the power, obviously (to the mind of the Physiolo- 

 gist) by the renovation of the worn-out Brain-tissue, and by the puri- 

 fication of the Blood that has become charged with the products of 

 its " waste." The impairment of the Memory in Old Age commonly 

 shows itself in regard to new impressions ; those of the earlier period 

 of life not only remaining in full distinctness, but even, it would seem, 

 increasing in vividness, from the fact that the Ego is not distracted 

 from attending to them by the continual influx of impressions jaro- 

 duced by passing events. The extraordinary persistence of early im- 

 pressions, when the Mind seems almost to have ceased to register new 

 ones, is in remarkable accordance with the Law of Nutrition referred 

 to in a previous paper. It is when the Brain is growing, that the 

 direction of its structure can be most strongly and persistently given 

 to it. Thus the Habits of Thought come to be formed, and those 

 Nerve-tracks laid down which (as the Physiologist believes) constitute 

 the Mechanism of Association, by the time that the Brain has reached 

 its maturity ; and the Nutrition of the organ continues to keep up the 

 same mechanism, in accordance with the demands upon its activity, 

 so long as it is being called into use. Further, during the entire pe- 

 riod of vigorous Manhood, the Brain, like the Muscles, may be taking 

 on some additional growth, either as a whole, or in special parts ; new 

 tissue being developed and kept up by the nutritive process, in accord- 

 ance with the modes of action to which the Organ is trained. And in 

 this manner a store of "impressions" or "traces" is accumulated, 

 which may be brought within the " sphere of consciousness " when- 

 ever the right suggesting-strings are touched. But, as the Nutritive 

 activity diminishes, the " waste " becomes more rapid than the reno- 

 vation ; and it would seem that, while (to use a Commercial analogy) 

 the "old-established houses" keep their ground, those later firms 

 whose basis is less secure, are the first to crumble away the Nutri- 

 tive activity, which yet suffices to maintain the original structure, not 

 being capable of keeping the subsequent additions to it in working 

 order. This earlier degeneration of fe^er-formed structures is a gen- 

 eral fact perfectly familiar to the Physiologist. 



The effects of Disease and Injury on the Memory are so marvellous 

 and diverse, that only a very general indication of them can be here 

 given. Cases are very common, in which the form of impairment just 

 spoken of as characteristic of Old Age shows itself to a yet greater 

 extent ; the Brain being so disordered by attacks of Apoplexy or Epi- 

 lepsy (for example), that it seems altogether incapable of retaining 

 any new impressions, so that the patient does not remember any thing 

 that passes from day to day ; while the impressions of events which 

 happened long before the commencement of his malady recur with 



