For more than ten years I have been studying the glands of internal secretion with increasing interest, and in explanation of the work of a laboratory of applied endocrinology now known as The Harrower Laboratory which was established in the foot-hill city of Glendale, eight miles north of Los Angeles, California, in February, 1918, I must preface this book with a few remarks. My interest in the endocrine glands grew out of some work which I did in 1908-9 on metabolism, acidemia and, especially, the urinary acidity. I wrote a number of papers during that period, some of which appeared in prominent medical journals in America and Europe. In asking myself why faulty metabolism and deficient cell chemistry was brought about I could not but consider the regulators of metabolism, as Noel Paton calls them — the hormones of the glands of internal secretion.