Great varieties of salts are taken into the system, of which chloride of sodium forms the largest proportion. These have, no doubt, very important functions to perform, in entering into combination with the various tissues, and also, probably, in aiding the chemical changes of parts of which they do not form a normal constituent. They help to render certain substances soluble, and stimulate the cells of certain glands to more active secretion, e.g., the kidney excretes more urea when there is an abundant supply of common salt in the food.

Fig. 44. Section of Pea, showing starch and aleurone granules imbedded in the protoplasm of the cells. {After Sachs.) a. Aleurone granules. st. Starch granules. i. Intercellular spaces.