Page:Defensive Ferments of the Animal Organism (3rd edition).djvu/40

important stages in the nutrition of the young of the mammal. Right up to its birth, which is the first stage, the fœtus has received from the mother only food which is in harmony with her body, and it makes this harmonize with its own blood and its own cells. Its organism has never come into contact with entirely disharmonious substances, and thus its metabolic processes run on definitely balanced lines. But birth supervenes, and with it the first change in the mode of nourishment. The individual has become independent. Respiration begins, and the cells of the lungs immediately enter upon their duty of exchanging gases. With equal rapidity the cells and glands of the intestinal walls undertake their new functions, which are, with the help of ferments, to prepare new nourishment for the cells of the body. The mother facilitates this task by giving off a supply of milk that is adapted to the requirements of the infant. In the first place, the intestinal cells have their task simplified. They never come into contact with a continually changing mixture of ions, nor are they overwhelmed with all kinds of disintegrated organic by-products. In this way the as yet inexperienced being is gradually accustomed to its new functions, and finds itself at last well prepared when it has to deal with a new kind of food which requires it to exercise its functions in a more variable, and, consequently more difficult manner. From the moment of parting