CHAPTER III

PRELIMINARY REMARKS ON IMMUNITY IN THE ANIMAL KINGDOM 40 Examples of natural immunity among the Invertebrates.—Immunity against micro-organisms and insusceptibility to microbial poisons are two distinct properties.—The refractory organism does not eliminate micro-organisms by the excretory channels.—It destroys them by a process of resorption.—The fate of foreign bodies in the organism.—The resorption of cells.—Intracellular digestion.—This digestion effected by the aid of soluble ferments.—Digestion in Planarians and Actinians.—Actinodiastase.—Transition from intracellular digestion to digestion by secreted juices.—Digestion in the higher animals.—Enterokynase and the part it plays in digestion.—The psychical and nervous elements in digestion.—Adaptation of the pancreatic secretion to the kind of food.—Excretion of pepsin in the blood and in the urine.