A work has recently been published by M. ^ourens, the celebrated French physiologist, ita. which he asserts that the natural length of a man's life is five times as long as the period of growth, and assuming that the latter is twenty years, concludes that the destined pilgrimage of man on earth is one hundred years. From his own observations, and facts derived from the observations of Buff on, and from natural history, he believes that the proportionate length of life in animals to their periods of growth is established, and now claims to have discovered the peculiar physical change in the system of both animals and men which indicates the completion of growth. "It consists," says M. Flourens, "in the union of the bones to the epiphyses. As long as the bones are not united to their epiphyses, the animal grows. In man the same effect takes place at twenty, and consequently the duration of man's life is five times twenty. It is now fifteen years since I commenced researches into the physiological law of the duration of life, both in man and in some of our domestic animals, and I have arrived at the result that the normal duration of man's life is one century. Yes, a century's life is what Providence meant to give us." M. Flourens brings some striking and interesting facts forward, to prove the truth o*f this theory as applied to domestic animals, and claims that it has an exemplification in the relative duration of growth and life in the camel, horse, ox, dog, and other domestic animals. In dividing the several periods of man's life, M. Flourens prolongs the duration of infancy up to ten years, because it is from nine to ten that second dentition terminates ; adolescence up to twenty, because it is at that age the development of the bones ceases ; of youth, up to the age of forty, because it is only at that age that the increase of the body in bulk terminates. "After forty," he says, "the body does not grow, properly speaking ; the au^ -mentation of its volume which then takes place is not a veritable organic development, but a simple accumulation of fat. After the growth, or, more exactly speaking, the development in length and bulk has terminated, man enters into what may be termed the period of invigoration—that is, when all his parts become more complete and firm, and the whole organism more perfect. This period lasts to sixty-five or seventy years, and then begins old age, which lasts for thirty years." Although we cannot entirely agree with the theory of M. Flourens, that with corrected manners, passions, and habits, the life of man can be prolonged to the lengthened period he mentions, we yet think that with the good conduct he recommends, moderate labor, study, and a systematic course of living, it may not only be extended, but its evening may be sustained in beauty and vigor until night has entirely set in.