The periodicity in the life of organic species may be compared to the wave-motions of light and heat as distinguished from those of water, the individual representing the single wave-length. The analogy is not, however, intended--to speak with Bacon--as one of nature, but merely as one of mind. And just here it may be questioned whether Fechner may not have been right, after all, in his assertion of the dependency of the organism upon periodicity of function, whether the periodic character of the individual life, dependent, as it must be supposed to be, on adaptation to a medium to some degree resisting, does not sacrifice its stability in so far as the increments of resistance lack uniformity. This is evidently the case in large relations; is it not logically necessary to suppose it so in minute relations, though the fact may not be so evident to the coarse measurement of the senses? Experience seems to prove that an approximate periodicity in larger relations, is most consistent with health; and it must be remembered that the non-periodic relations are subordinated to periodic ones, that not only in the case of waking and sleeping, working and eating, but also in those of rest and labor, a certain uniformity is necessary to the best mental and physical condition. A close observation will, I think, reveal a greater periodicity than was at first suspected; since much of it is of so-called "automatic," "unconscious," or "half-conscious" nature. It is to be noticed, here, that the termination of individual lives is often in the nature of a catastrophe, and a uniform periodicity of individual development and decay cannot be assigned, except in the form of an average that falls much below the figure attained by the thoroughly healthy individual. There is every reason to believe that if we could sleep, rise, eat, bathe, exercise, work, and rest with the regularity of a clock, we should be the better for it physically. But the irregularities outside the province of our will-power render it impossible for us to order our lives in this manner. Nor do we desire to do so. For these very irregularities, as representing greater or less change to which adaptation is necessary, are, in many cases and within certain lines, the conditions and signs of progress; though they may constitute in other cases and beyond these lines--that is, where they are of too great intensity or duration--conditions of retrogression, the imperfection in periodicity becoming catastrophe, which may extend beyond the individual to his offspring. We may thus infer that the final destruction of the individual organism is conditioned by its own progress and the progress of its species, but that on the other hand, when the destruction of the individual is too abrupt, it may mean catastrophe to the species also, or at least to a part of it, through heredity.