Ultraviolet Radiation

another in the animal body. The full demonstration of the importance of transmethylation and of its relationship to the metabolism of choline, betaine, creatine, sarcosine, and a number of other methylated substances involved research that extended over a number of years. The discussion forms the subject matter of three of the chapters and requires considerably more than one-half of the book. In the last chapter, the author describes briefly the most recent investigations of the complex polypeptide pressor hormones of the posterior pituitary, studies in which modern techniques are applied to the problem of the determination of amino acids and in which the trail of research has led in full circle back to a problem similar to that with which it started, the determination of cystine in insulin. Taken together, this discussion of the work of the author and his numerous collaborators is an outstanding example of what is best in American biochemistry. It illustrates the application of rigid and relentless chemical logic to the solution of biological problems, some of which were relatively simple but most of which were extremely complex. Inevitably the book will become required reading for all graduate students in biochemistry and it will indeed serve as an encouragement to them, for it shows how the wellplanned experimental attack in which nothing is left to chance and no loose ends remain for others to toy with leads in the end to unequivocal advance in knowledge.