If the reader will observe the analogy between the decomposition of substances in vessels or pools, and the decomposition of food in the reservoir called the stomach; and its further decomposition in a long canal (the small intestine), connecting the stomach with other receptacles called the colon and sigmoid flexure; and then the decomposition of _their_ contents; he will readily comprehend the chemical putrefactive or fermentative changes or bacterial action that take place in the organism, if for any reason the contents be confined. Of the four chief elements that enter into the composition of living bodies three are gaseous, or convertible into gas. In the physical man water constitutes three-fourths of the weight of the body. This being so we realize why, notwithstanding our sense of solidity and weight, chemical changes occur quite as readily in our organism as in the substances we see about us. There are no waterproof walls in the body of man to impede the percolation of liquids freighted with promiscuous Passengers from the alimentary canal; Passengers designed to nourish the organs for which they have an affinity. But there are those that have no organic affinity, and these are tramps, vagabonds, and even murderers, disturbing and destroying the normal functions of the system. Through extravasation, that is, through fluid infiltration of tissues, these Passengers come to be one with us, and we make them part of our tissue; but some of the Passengers are the demolishers of the living temple. Water is universally present in all the tissues of the body, and it is indispensable for introducing new substances into the system and for eliminating the worn-out tissues and foreign substances. It is indeed important to emphasize the fact that properly to eliminate the foreign and waste products from the system requires, in a healthy person, at least five pints of water during twenty-four hours. The amount of gastric juice secreted in twenty-four hours is from six to fourteen pints; of pancreatic juice, one pint; of bile there are two to three pints, and of saliva one to three pints. It is estimated that the juices secreted during digestion in a man weighing 140 pounds amount to twenty-three pounds in twenty-four hours. These fluids are poured back and forth in the process of transforming food into flesh and eliminating waste material.