Volume 1 of 2. In the preparation of this work, the author has made use of all available, well attested facts to be found in the authoritative works on human nutrition, and has added thereto the results of nearly half a century's careful study of the subject, theoretically, clinically and experimentally. So far as the writer knows, this is the first work in which full recognition has been accorded and important discoveries of Bouchard, Metchnikoff, Tissier and others in relation to the influence of diet upon the intestinal flora through the effect upon the food residues which form the nutrient media for the various organisms, benign and pernicious, which by various means find their way into the human alimentary canal.