The problems of constitution in its relation to medical problems have expanded greatly since the first edition of this monograph appeared. It was the original purpose of the author to correlate information touching on problems of biology and medicine, and the book was enthusiastically received by the profession. The style and purpose of the first edition have been maintained in this revision. The only change has been in bringing the material down to the present. Itis concise and practical, and the reader is not confused by a mass of conflicting data. Becauseof the author's background in biology and clinical medicine he is able to present this subject tothe physician in an authoritative manner. Some readers, especially those primarily interestedinbiology, may deplore the paucity of bibliographic references or discussion of the work of other investigators in the field. This, however, has undoubtedly been a purposeful omission to conform with simplicity in presentation.