ABSTRACT
In general, as daily life abundantly shows, the disuse of a mental function weakens it, and the amount of weakening increases, the longer the lack of exercise. There have been, however, a few unfortunate statements made by psychologists to the effect that bonds perfect themselves after exercise has ceased by a process of mere inner growth or organization. So Coover and Angell ['07, p. 336] say that "the common belief in beneficial effects of incubation periods on bodily activity has been amply confirmed by numerous investigations of practice and fatigue," but give neither any evidence, nor any reference to any evidence, of the confirmation. Book, who does not himself assent to this doctrine of learning to skate in the summer and to swim in the winter, describes it as the assumption "that the associations previously formed had been slowly perfecting themselves unconsciously by some sort of neural growth process which completed itself during the interval of no practice." ['08, p. 80]
This doctrine of continuance of improvement after the cessation of practice seems to contradict the general rule announced above, and would do so if the doctrine were made general and consistent. But the advocates of learning to skate in summer and swim in the winter would in concrete
cases always demand that improvement should have a certain large impetus in order to continue without further exercise, aud would always admit that after a certain length of time disuse does not improve, but injures, a function's efficiency.
