Physiology of reproduction in relation to nutrition.

In the infantile animal the reproductive organs gradually develop but do not begin to function as organs of reproduction until the age of puberty, although their internal secretions begin before this time. In the female the cause for their functioning lies outside the ovary itself, for immature ovaries transplanted into adults begin to function immediately, whereas adult ovaries transplanted into immature animals do not function until the age of puberty is reached (Foa, 1901). It is now generally recognized that the functioning of the ovary depends on gonadotrophic hormones coming from the anterior-pituitary gland (Smith & Engle, 1927; Zondek & Aschheim, I927), the two main hormones being the follicle-stimulating hormone (F.s.H.) and the luteinizing hormone (L.H.). The anterior-pituitary gland also produces growth hormones (Evans, Meyer & Simpson, 1933). Normally the onset of puberty occurs as the adult weight is approached and the rate of growth declines. Injection of gonadotrophic hormones into the infantile animal immediately causes functioning of the ovary and the onset of puberty, and so one must suppose that the time of onset of puberty depends on a change in the balance of output between the gonadotrophic and the growth hormones of the anterior-pituitary gland. With animals that have a breeding season (such as the sheep) the age and size of the animal when puberty begins vary according to the time of year at which it is born, for in such species the gonadotrophic hormone output of the anterior-pituitary gland is seasonal and is dependent on the ratio of hours of darkness to hours of daylight. Thus a definite age and size are not necessarily associated with puberty. How far then is the age of puberty affected by the plane of nutrition on which the animal is reared? Experiments by Prentice, Basket & Robertson (1930) (Table I) on fowls have shown that increased rate of growth due to good nutrition lowers the age