The embryo then which is to form the individual starts its career with a certain number of innate germinal characteristics which manifest themselves in the form of tendencies to grow in this direction or that. During the period of gestation a good many of these tendencies are well developed while a good many more only manifest their exact nature in later life. But it is upon the basis of these tendencies--and upon no other--that the making of the individual is possible. They represent the total assets available for the formation of character. Nothing of any new _kind_ can be added to them. All that can be done under the best conceivable circumstances is so to arrange the environment and surroundings of the embryo, and the subsequent individual, so that these tendencies are acted upon in such a way that the best are developed, and the worst eliminated. It must be remembered that it is under the constant action of everything that constitutes the environment of an embryo that the mass of body-cells gradually grows into a recognisable human personality. The question then arises, What are the factors external to the embryo which cause these germinal tendencies to become active and fully developed? These factors are those of (_a_) nourishment; (_b_) use, or exercise; and (_c_) injury. In the case of the human embryo by far the most important of these three factors is the first. A proper supply of nourishment and food, that is to say maternal nutrition of adequate quantity, is sufficient up to the time of birth to cause the inborn tendencies in all the body-cells gradually to assume the special characteristics of muscle, bone, gland, nerve, and so forth, which make the human embryo. After the period of embryonic life is over, the stimulus of nutrition is still sufficient for some of these body-cells. Thus we find that the hair, the teeth, the internal ears, and the organs of reproduction, all grow to their full development in the absence of any other factor or stimulus than that of nutrition. But, as we also know, this simple stimulus is not sufficient for most of the other body tissues to develop properly. They require the additional stimulus of exercise which, indeed, may be said to begin even in the life of the embryo. After that it is quite hopeless to expect a healthy embryo to develop into a fine child unless to the stimulus of nutrition there is added that of exercise. It is from the varying quantities and qualities of the three factors of nourishment, exercise, and injury, that part of the explanation is found for the variation in individuals of the same family. Starting with a good many of the same inborn tendencies none of them afterwards receive quite the same kind and amount of these stimuli, under the action of which they develop. And so we reach the second point, namely, that, in addition to innate characters certain others are subsequently acquired by the embryo of the individual in response to particular stimuli acting from without.