Purchase of this book includes free trial access to www.million-books.com where you can read more than a million books for free. This is an OCR edition with typos. Excerpt from book: CHAPTER III THE PHYSIOLOGY OF DIGESTION, ABSORPTION, AND NUTRITION By E. I. Spriggs, M.D., F.R.C.P. The energy needed for the various activities of the body is furnished by the processes of oxidation which take place in every living cell. The oxygen used is obtained from the atmosphere. The chemical substances oxidized are derived from materials taken into the body, which we call food. The constituents of the food are, however, seldom in a suitable condition for absorption into the blood, and before this can be effected they undergo a series of chemical and physical changes known as digestion. The products of digestion are then taken up by cells lining the alimentary canal, and passed into the blood in the process of absorption: this is not a simple transference of a given substance across the alimentary mucous membrane, but itself includes chemical change. Further, the materials absorbed from the intestines into the circulating blood are not even then in a form entirely suitable for oxidation in a cell, but have to suffer later transformations which are comprised in the term assimilation. The molecules finally presented to the living protoplasm may be oxidized rapidly for the sake of the energy thus set free, or may be built up for a longer period of time into the tissues of the cell. The term metabolism is used to designate all the chemical processes occurring in the tissues of the body ; it includes building up, assimilative, or anabolic processes, and breaking down, or katabolic processes, whether they take place in the essential protoplasmic structure or in the tissue fluids which bathe the cells. Since the body is continually oxidizing its own substance, the materials supplied to the cells must, besides being capable of oxidation, contain the elements neces...