The Intimate Causes of Old Age. 203 



such earthy salts, to some extent and in some tissues, at 

 certain stages of life, do accumulate in a way to embar- 

 rass the cell life and to weaken the tissue. But this con- 

 dition is far from being constant, or continuous, or 

 secularly progressive. It is incidental and often associated 

 with microbic invasions. As to the undue wasting of the 

 cellular protoplasm by oxygen, that is largely a mj'th ; a 

 far greater difficulty in old organisms is to get oxygen to 

 the cells at all ; they smother for want of it. An hypoth- 

 esis of the old-aging of the nervous system and cerebral 

 tissue of man has also been advanced from the progressive 

 effects of continuous or oft-repeated mnemonic^ and sensory 

 impressions in the protoplasmic substance of the brain and 

 minor nerve centers. 



Memory, experience, and the growth of the intellect 

 depend on impressions from the external world which 

 come to the brain through the organs of special sense and 

 the general sensibility, and remain there as pictures. Such 

 impressions, or pictures, are believed to be physically in- 

 wrought in the sentient substance by something akin to 

 dynamic action, and, as is well known, will remain there, 

 mentally recognizable, for many decades. From such 

 portraiture of the external world, physically impressed in 

 the material substance of the brain, we have what is com- 

 monly termed, experience. This experience, however, is 

 something more than an accumulation of impressions or 

 pictures; for it is accompanied by the formation of 



