An extensive study of the gaseous exchange of infants has been in progress for three years in connection with the Nutrition Laboratory and with the Massachusetts General Hospital. Pending the development of a method for determining the oxygen consumption directly — a factor that we deemed of very great importance — a preliminary communication was made in this journal1 in 1912. Since the appearance of this article, the apparatus and technic have been perfected so as to include direct determinations of the oxygen consumption. An apparatus has been constructed, tested and installed in a special room in the Massachusetts General Hospital, and except during the summer months, studies of the gaseous metabolism of infants have been made daily since January, 1913. Although the investigation is still in progress, sufficient data have been accumulated to justify the presentation of material in extenso in a publication of the Carnegie Institution of Washington.2