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Every one acquainted with the field of digestion knows of the important contributions of Northrop. This book summarizes for the student of digestion and enzymes nearly all that is worth knowing on the isolation and chemistry of pepsin, trypsin and bacteriophage. Every investigator in this field will have occasion to use the book. The author points out that "bacteriophage has not been crystallized and may not be an enzyme, but the results of the experiments with bacteriophage are essentially similar to those obtained with the enzymes and are, therefore, included in the present volume." In the appendix are described methods for the estimation of pepsin and trypsin, with use of hemoglobin as a substrate. In my experience these methods are the best available and may be used with facility in the clinical laboratory. This book should be studied by all pediatricians interested in the chemistry of the digestion and the
Crystalline Enzymes: The Chemistry of Pepsin, Trypsin, and Bacteriophage. Columbia Biological Series, no. 12.. Am J Dis Child. 1939;57(6):1477. doi:10.1001/archpedi.1939.01990060257027