individuality further by clothing it in a particular color, or even personifying it outright as in the two cases given. Color audition and association of color with written characters are explained by many as due to physiological conditions, especially to the contiguity of the cortical center involved. Dr. Krohn, in a recent review of the subject in the American Journal of Psychology, adopts this explanation in part. It is doubtful whether this hypothesis is necessary to explain the comparatively rare cases of color associations; it certainly is not necessary for explaining number forms. In any case, physiological association would be due, either in its origin or as a justification of its survival, to useful psychic associations. Now, in the matter of number forms, suppose
that the child is required, as is very early the case in counting, to think of the numbers not separately, but in relation to each other. He has then the problem of arranging abstractions in a series, and, if he is naturally an ear-minded child, will arrange them as a mere series of associated sounds. If, however, he is eye-minded, he may consciously or unconsciously hit upon the device of a visual spatial image, and thus enable himself to comprehend and remember the numbers as he does other things by a mental picture. A number form thus becomes a little system of topical mnemonics. Its continuance, either in the individual or, in cases of inherited forms, in the family, is of course due to physiological conditions. In every case, however, its origin is probably to be traced to useful psychic associations.