1896.] The Biologie Origin of Mental Variety. 967 
of neural activity for every psychic happening or sensation, 
and for every sense quality and shade of quality. That is, one 
sort for red, another for blue, and others for every sort of taste, 
smell, and so on. 
Next we may note that both propositions equally involve 
the fact that physical activities immediately underlying our 
psychic states are enormously complex. Demonstrably, by 
modern experimentation, they rest upon a chemical basis, in- 
tricate beyond all comparison ; each molecule comprising vari- 
ous atomic components which, in number, according to high- 
est authority, mount among the billions, and out-run all ade- 
quate comprehension.” 
Next we may observe that in proportion as these AR 
activities are complex, so will the molecular differences be 
great which correspondently lie between our different elemen- 
tary sensations, that is, which correspond to the psychic dif- 
ferences between sights, sounds, smells, tastes and our other 
major classifications of sensory elements; and between the 
reds, blues and greens, sweets, sours and bitters, and other 
minor differences observable in each subclassification, down to 
the limits of their infinity. 
Of course, the old doctrine of specific energies, banded down 
to us by Johannes Miiller, taught us to expect that every dif- 
ferent quality of sense must be paralleled by a different form 
of neural activity. But by emphasizing the enormous com- 
plexity of these neural forms, and the vast molecular differ- 
ences between them, which must be implied by the differences 
to be observed among our several senses, I wish to bring for- 
ward what appears to me to be one of the most important 
truths in mental science, and one which, in so far as I know, 
has never before been caught sight of, or taken into account 
in deciphering the great problem of mind and body 
For finally we may observe that, IJntrinsically and within 
themselves, these molecular differences, correspondent to the dif- 
ferences among our psychic elemeuts, must necessarily have con- 
stituted determining factors of animal evolution; and must have de- 
cided what peculiar psychic elements should be selected, and perman- 
2 See ‘* Man’s Glassy Essence,” by Charles Pearce, in The Monist, October, 1891. 
