Reverting again to a discussion of the lower organisms--we have yet to consider the character and extent of the compensation which these organisms, which are unconscious of sacrifice, receive. The conscious sacrifice of higher animals receives a conscious compensation; similarly the unconscious sacrifice of lower organisms receives an unconscious compensation. It will be remembered that the amoeba did not die, but that it was _rejuvenated in its offspring_. In the next and every succeeding generation there is no death, but a rejuvenation. It thus transpires that these lowly organisms enjoy immortality; or perhaps it may be better stated, that the protoplasm of these organisms enjoys immortality and this immortality is the compensation for the sacrifice which each successive individual makes unconsciously in the division of its protoplasm. This principle of biology was first discovered and formulated by the great German Biologist, Weissmann. Summary of Principles. a. The propagation of offspring and the protection and support of the young and defenseless always involve sacrifice on the part of the parents and the stronger members of the race. b. Sacrifice made consciously for the race is, in the natural order of things, compensated. CHAPTER II ADOLESCENCE IN THE MALE ADOLESCENCE IN THE MALE. The period of a young man's life from about fifteen to twenty-five years, when he is growing from boyhood to mature adult life, is called the period of _adolescence_. The period of adolescence is ushered in by a series of physical and psychical changes which make a well defined initial period called _puberty_. The period of puberty is about two years in length, and in the average case among American boys, covers the period between the fifteenth and seventeenth years, and is completed when the youth can produce fertile semen capable of fertilizing the human ovum. It is now universally recognized, however, that when the youth reaches this point in his development, while he may be called a man, he represents manhood in its lowest terms. He has not reached either a physical or mental development or maturity which justifies him in undertaking the responsibilities incident to procreating his kind. It requires in the average case a period of eight more years to develop the young man to the full stature of adult manhood, possessing his full physical and mental powers and the strength required of one who should assume the responsibilities of parenthood, so that at the age of twenty-five in the average case the young man may be said to have reached this period of complete development and to have finished the adolescent period. We may profitably now consider more in detail some of the changes incident to this most important period. 1. PHYSICAL CHANGES. General Changes in the Body.