It is a source of great satisfaction to us that a Second Edition of this treatise should be called for, especially because it has given us the opportunity to produce, we believe, a better book. Eighteen chapters, amounting to one-third of the whole, are new, and of these, 13 deal with subjects not covered at all in the First Edition. We have paid more attention to embryonic and fetal growth, with chapters on cell differentiation (Lehtonen and Saxen), embryonic growth (O'Rahilly and Muller), control of fetal size (Snow), regulation of fetal growth (D'Ercole and Underwood), and ultrasonic...