The science of life : fully illustrated in tone and line and including many diagrams
BOOK 1
ment is by no means despotic. Just as human governments may be swayed and controlled by small, active sections of the population, so here the brain is controlled by one of the abdominal organs. Further, it should be remembered that this influence is by no means restricted to pregnant individuals. The non-pregnant female experiences cyclical changes in her mental life, changes in her emotions, her desires, her intellectual liveliness, that synchronize with the rhythm in her reproductive organs. Moreover, it would seem that in animals with a periodic rut the males also have a rhythm that is caused by internal secretions. Even in some men there is said to be a monthly tide of sexual feeling. It is clear enough that the colour and efficiency—the tone, so to speak—of our minds may depend to a very considerable degree on the chemical substances poured into the blood by our organs of internal secretion, including our reproductive organs, and thus indirectly on the condition of those organs themselves. The corpus luteum acts as a chemical fairy godmother for the unborn child, taking all sorts of steps which ensure its being properly cared for both before and after birth. In particular we may note that the uterus is not a naturally hospitable organ ; its monthly habit is to clear itself out ; it receives and nourishes the embryo because the corpus luteum instructs it to, by means of its chemical messengers. As pregnancy advances the uterus begins to move and contract restlessly. Its muscular layer is affected by internal secretions from two sources. The substances made by the corpus luteum dispose it to keep quiet and nurse the embryo ; but there is an antagonistic substance, made by the monthly periodic activity of the pituitary gland, which stimulates the muscles of the uterus and urges it to contract. For nine months the substances of the former kind prevail, but at the end of this time the corpus luteum begins to degenerate and ultimately it ceases to turn its products into the blood. The uterus, relieved of this controlling influence, revolts at once, and contracts more and more forcibly, until its now unwelcome guest, the baby, is ejected. First the baby departs, and then the placenta and the investing membranes—the after-birth—are thrown out. In this process the uterus is not unassisted, for the diaphragm and the muscles of the abdominal wall participate heartily. It is as if the whole abdomen had been chafing at its burden, and as soon as the fairy godmother dies, rises to expel her protégé.
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THE SCIENCE OF LIFE
CHAPTER 4
In this fashion the baby finds itself flung into a new and larger world. As soon as this happens the muscles that move the tiny ribs begin to work, air rushes for the first time into the lungs, and the vocal cords are stirred, giving out the awkward, tentative cry with which the newcomer heralds his own appearance.
85 Childhood, Adolescence, and Maturity
At birth the whole economy of the child is suddenly changed. It has now to breathe air and collect its own oxygen, and it has to digest its own food. The lungs and bowels begin to work. As a matter of fact, the strain on the digestive organs is not very severe, for the baby receives in its mother’s milk a diet that requires hardly any chemical adjustment. Moreover, since it is no longer housed in a warm incubator, it has to regulate its own body-temperature.
Nevertheless, as far as development is concerned, birth is an incidental event that hardly affects a slow, continuous process. During the first few weeks of uterine life all the organs of the embryo are laid down in a more or less rudimentary way, and thereafter development consists in the elaboration and perfection of those rudiments. This is a process that goes on for some twenty-five years. Birth is an event for which the organs of the mother, not the baby, are responsible, and it does not correspond to any definite developmental change in the organism of the latter. As soon as the baby has adjusted itself to its new surroundings the processes of growth and differentiation go on in very much the same way as they did before.
One of the most striking changes that occurs during the first years of childhood is the mushroom-like expansion of the brain. By the end of the second year the child’s brain has attained more than half the adult size; by the end of the fourth year over eighty per cent. of its final bulk is already present. The adult cranium is a strong bony box that protects the brain, but at the same time prevents any further expansion of its precious contents; the brain has therefore to attain its full size early in lif while the skull-bones are still only partly formed and before they are solidly joined together. At the same time the human child needs a large brain, for it has to learn an enormous amount during the first few years of life.