The absorption of water is checked by the ingestion of extremely soluble salts, such as sulphate of magnesia, the heavy molecule of which diffuses with difficulty. We attribute the fact that sulphate of magnesia remains in the intestine, and prevents water from diffusing out of it, to its slowness in passing through a membrane, because this is what would happen in dialysis;[2] but we must remember that the living wall of the intestine is not a membrane. The cells which line the intestine take up substances far less easily diffusible than the sulphate of magnesia which they refuse. Nevertheless, speaking generally, it is the less diffusible salts which act as aperients, the more diffusible which are absorbed. The forward passage of the contents of the alimentary canal is hastened by castor-oil. The peristalsis of the intestines is stimulated by certain drugs, such as jalap or the burnt products of tobacco. Another class of drugs, of which aloes is an example, increases the secretion of the intestines, small or large. Certain purgatives, such as calomel, podophyllin, etc., used to be regarded as cholagogues. It was supposed that they increased the flow of bile. This is an error. Their action is complicated, but it affects chiefly the peristalsis of the intestine. The poor misunderstood liver still suffers from the libels of primitive medical science. It is the most innocent of organs, in no way responsible for derangements of digestion. It carries out its functions without haste and without delay. With the possible exception of salicylate of soda, no drug is known which can stimulate it to a more rapid output of bile. =Absorption.=—All the cells which line the alimentary canal are capable of absorbing food, if it is presented to them in a suitable form. In a suitable form means, speaking generally, in a diffusible condition, although it must not be supposed that the epithelial cells are incapable, under certain circumstances, of taking up non-diffusible substances, just as a unicellular organism—an amœba—can take in food. If soluble proteins, such as white of egg or acid-albumin, are injected into the large intestine, a very considerable proportion of the substance so injected is absorbed. It is possible, indeed, to supply in this way the whole of the nitrogenous food needed by the system, none entering by the mouth. If milk is injected, a certain amount of the fat also is retained. It can be shown that such absorption takes place when no digestion of the food occurs in the colon. The food is taken up by the epithelial cells in the form in which it is injected.