The present book is the outcome of a course of eight lec tures delivered before the Lowell Institute of Boston in the early part of 1907. In this presentation of the subject the attempt has been made to give a systematic account of our knowledge regard ing some of the more important processes of nutrition, with special reference to the needs of the body for food. In doing this, the facts accumulated by painstaking Observations and experiments during recent years in our laboratory have been incorporated with data from other sources and brought into harmony, so far as possible, with the modern trend of physi ological thought.