Just as each of our individual sense-organs selects from the multitude of ether vibrations constantly beating upon the surface of the body only those waves to the velocity of which it is attuned, so each one of us as an integral personality selects from the stream of sensory experiences only those particular objects of attention that are in some way related to the present or habitual trend of thought. [Sidenote: _The Man on Broadway_] Just consider for a moment the countless number and variety of impressions that assail the eye and ear of the New Yorker who walks down Broadway in a busy hour of the day. Yet to how few of these does he pay the slightest attention. He is in the midst of a cataclysm of sound almost equal to the roar of Niagara and he does not know it. Observe how many objects are right now in the corner of your mind's eye as being within the scope of your vision while your entire attention is apparently absorbed in these lines. You see these other things, and you can look back and realize that you have seen them, but you were not aware of them at the time. Let two individuals of contrary tastes take a day's outing together. Both may have during the day practically identical sensory images; but each one will come back with an entirely different tale to tell of the day's adventures. [Sidenote: _Waxen Tablets_] _All sensory impressions, somehow or other, leave their faint impress on the waxen tablets of the mind. Few are or can be voluntarily recalled._ Just where and how memories are retained is a mystery. There are theories that represent sensory experiences as actual physiological "impressions" on the cells of the brain. They are, however, nothing but theories, and the manner in which the brain, as the organ of the mind, keeps its record of sensory experiences has never been discovered. Microscopic anatomy has never reached the point where it could identify a particular "idea" with any one "cell" or other part of the brain. [Sidenote: _Not How, but How Much_] For us, the important question is not _how_, but _how much_; _not the manner in which, but the extent to which_, sensory impressions are preserved. Now, all the evidences indicate that _absolutely every impression received upon the sensorium is indelibly recorded in the mind's substance_. A few instances will serve to illustrate the remarkable power of retention of the human mind.