Process of assimilation in the plant; in the animal—Digestive apparatus in the lower classes of animals; in the higher classes; in man—Digestive processes—Prehension, Mastication, Insalivation, Deglutition, Chymification, Chylification, Absorption, Fecation—Structure and action of the organs by which these operations are performed—Ultimate results—Powers by which those results are accomplished—Two kinds of digestion, a lower and a higher; the former preparatory to the latter Page 159 CHAPTER XI. OF THE FUNCTION OF SECRETION. Nature of the function—Why involved in obscurity—Basis of the apparatus consists of membrane—Arrangement of membrane into elementary secreting bodies—Cryptæ, follicles, cæca, and tubuli—Primary combinations of elementary bodies to form compound organs—Relation of the primary secreting organs to the blood-vessels and nerves—Glands, simple and compound—Their structure and office—Development of glands from their simplest form in the lowest animals to their most complex form in the highest animals—Development in the embryo—Number and distribution of the secreting organs—How secreting organs act upon the blood—Degree in which the products of secretion agree with, and differ from, the blood—Modes in which modifications of the secreting apparatus influence the products of secretion—Vital agent by which the function is controlled—Physical agent by which it is effected Page 279 CHAPTER XII. OF THE FUNCTION OF ABSORPTION. Evidence of the process in the plant, in the animal—Apparatus general and special—Experiments which prove the absorbing power of blood-vessels and membrane—Decomposing and analysing properties of membrane—Endosmose and exosmose—Absorbing surfaces, pulmonary, digestive, and cutaneous—Lacteal and lymphatic vessels—Absorbent glands—Motion of the fluid in the special absorbent vessels—Discovery of the lacteals and lymphatics—Specific office performed by the several parts of the apparatus of absorption—Condition of the system on which the activity of the process depends—Uses of the function Page 332 CHAPTER XIII. OF THE FUNCTION OF EXCRETION. In what excretion differs from secretion—Excretion in the plant—Quantity excreted by the plant compared with that excreted by the animal—Organs of excretion in the human body—Organization of the skin—Excretory processes performed by it—Excretory processes of the lungs—Analogous processes of the liver—Use of the deposition of fat—Function of the kidneys—Function of the large intestines—Compensating and vicarious actions—Reasons why excretory processes are necessary—Adjustments Page 369 CHAPTER XIV. OF THE FUNCTION OF NUTRITION.