While it is difficult to give an entirely satisfactory definition as to what constitutes food, the following extracts from standard works will serve as guides. Hermann[1] says: "The compound must be fit for absorption into the blood or chyle, either directly, or after preparation by the processes of digestion, i.e., it must be digestible. It must replace directly some inorganic or organic constituent of the body; or it must undergo conversion into such a constituent, while in the body; or it must serve as an ingredient in the construction of such a constituent." He further says that water, chlorides, and phosphates are the most indispensable articles of diet. Watts[2] states that "whatever is commonly absorbed in a state of health is perhaps the best, or rather the truest, definition of food." [Footnote 1: Elements of Human Physiology, by L. Hermann. Translated by Gamgee.] [Footnote 2: Dictionary of Chemistry, vol. iv., pages 147-8.] Chemical analysis shows that the most important and widely applicable foods contain carbon, hydrogen, oxygen, nitrogen, and mineral matter, the latter containing phosphates and chlorides. Other things being equal, it may be considered that the comparative nutrient value of two articles is in proportion to the amounts of carbon, nitrogen, and phosphoric acid they contain. "The food of man also contains certain substances known under the name of condiments. Since these bodies perform their functions outside the real body, though within the alimentary canal, they have no better reason to be considered as food than has hunger, _optimum condimentum_."[1] Such is the positively expressed opinion of Foster, the author of the article on nutrition in Watts' Dictionary of Chemistry. With a view of determining how far the common condiments deserve this summary dismissal, a number of analyses have been made in the laboratory of the Philadelphia Polyclinic. My examinations were especially directed to the mineral matter, phosphoric acid, and nitrogen. The following table shows the result of the analyses: Percent. Percent. of ash. of P_{2}O_{5}.