Advances in Biological and Medical Physics, Volume IV, provides an overview of the state of knowledge in biological and medical physics. The book contains eight chapters and opens with a discussion of the application of X-ray diffraction to crystalline proteins. This is followed by separate chapters on the relationship between the chemical information which can be stored in the nucleic acid molecule and the sequence of amino acids found in polypeptides and proteins; materials for the biophysical and biochemical study of cell division; and the action of high and low temperatures in the destruction of unicellular organisms. Subsequent chapters deal with infrared spectrometry; the kinetics of iron metabolism; the gross composition of the body; and an argument for a theory of aging, which states that the tendency toward further disease experience is at a metabolic rate determined by accumulated disease experience of the past.