204 W. L. COURTNEY, M.A., LL.D., 
seems extremely probable. But that we can thus explain the 
whole operation of memory is a very different question. We 
must here distinguish the two forms of memory mentioned 
above, the passive or retentive function and the active or 
reproductive. With-regard to the first of these the physical 
basis is obvious. For it is probable that every action of a 
stimulus or an end-organ of sense, and every transmission of 
energy through nervous fibres and cells, considerably, and 
perhaps permanently, affect the general nervous mechanism, 
just as in photography a plate of dry collodion, after a brief 
exposure to the sun’s rays, retains for weeks in the darkness 
the effects of those delicate changes which it has undergone. 
We can get at this result by several commonplace experi- 
ments. We are jolted all day m a train, and for the next day 
and sometimes for succeeding days the same jolting motion 
continues in our consciousness, as a sort of abiding companion 
of all our other mental states. In the case of vision, there is 
an after image impressed, as it were, on the retina which we 
ean cal] up into consciousness for some time whenever we 
will. Or again, it is difficult to explaim how certain actions 
become habitual without supposing some permanent altera- 
tion in our nervous energies. Thus knitting, or playing on 
the piano, which at first involve a series of acts of will, finally 
proceed with such regularity that we become unconscious of 
the accompanyig nervous processes. There can be no 
doubt that there is every kind of interaction between the 
cells and fibres of our sensory and muscular system. Every 
activity leaves its mark or trace in an altered capacity or 
acquired tendency. And the many freaks of memory of 
which we have daily experience seem themselves to argue a 
physical and material explanation in the relative position of 
certain neural processes. That all this proves a physical 
basis for memory, so far as it is a retentive function, seems 
certain. Still it must be remarked that while such explana- 
tions show why we remember one thing rather than another, 
granted that we can remember at all, they hardly render clear 
and precise the possibility of memory itself. For the reten- 
tive function, so far as it is unconscious, is not what we mean 
by 1nemory. Conscious memory doubtless presupposes all 
the range and sphere of retentive capacity. Still, unless it is 
conscious, it forms no more a part of what we include in our 
mental life than that vague phantasmagoria of dreams which 
we leave behind us when we rise from our beds, 
What can we say, however, of active, reproductive 
memory ? Can we give any physical explanation of this? 
