These contain some starch, sugar, dextrin, salts, and minute quantities of proteid, and are of small nutritive value.
Potatoes contain very little proteid, but a considerable quantity of starch, upon which their nutritive value almost entirely depends.
Carbohydrates, . . .
The most striking points are the very large proportion of pro-teid in the leguminous fruits, and the comparative richness of all vegetables in starchy food stuffs.
Water is the great medium by which food is dissolved and made capable of ingestion. Spring water always has a certain quantity of lime and other salts in solution, and in proportion to the amount of salts is said to be "soft" or "hard." Water is tasteless, inodorous and colorless when pure. Soft water, such as rain water, is pure, but not so agreeable to taste as spring water, and is very liable to contamination in passing through gutters, etc., previous to collection. Standing water should be avoided for drinking, owing to the probability of its containing organic matter.
Since water is known to be a common means of communicating disease, care must be taken as to the source of drinking water, and we should be able to form an opinion as to its purity when its source is not known. It is, perhaps, impossible to detect in it the specific impurity which causes any disease, but there are some, characters, supposed to be commonly associated with its pathogenic properties, which can be easily recognized, and should be familiar to a student of Physiology. The want of brilliant limpidity must be regarded with suspicion. Any kind of smell, disagreeable or not, indicates impurity. The reduction (loss of color) of permanganate of potash, when added in small quantity to acidified water, indicates the probable presence of organic matter. A high percentage of chlorides is often associated with sewage contamination.