In continuing his investigations into this subject, Davis has confirmed his earlier result as to the marked influence of exercise on one side or the body in increasing power on the unexercised side, while bringing out many new results in matters or detail. The experiments were made with the dynamometer and the ergograph. The influence of the factors of length of hand, length of fore-arm, previous muscular development, and temperament are taken into account, and the sexual differences also noted. As regards temperament, Davis finds it most convenient, from this point of view, to recognise three temperaments: the nervous, the motor, and the phlegmatic. The influence of this factor of type is found to be very important. Persons of the nervous type tend to be quick in muscular and mental reaction, short as regards height, and light in weight. Persons of the phlegmatic temperament are found to be slow in muscular and mental reaction, tall as regards height, and heavy in weight. Persons of the motor type are in all respects medium. There are, of course, many cases of mixed type. On the whole, however, they require different degrees of exercise to produce the full effects of cross-education, the phlegmatic, as a rule, considerably more than the motor. Exercise that is too slight, or too severe and fatiguing for the individual, will fail to produce proper development. “If the work is just right in intensity and amount the anabolism provoked is greater than the katabolism, and there is development of the part used. An almost endless variation of conditions would be necessary to make the adjustment of exercise suitable to all individuals. Exercise must be prescribed per order just as a dress must be fitted to the individual.’’ Davis emphasises the conclusion to which his experiments point: that the mental factor is of much more importance than the muscular factor. Cross-education is mainly a matter of nervous centres and nervous channels. These researches are of considerable interest, both theoretical and practical.
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