Advances in Biological and Medical Physics, Volume 12 covers the significant progress in various aspects of biology and medical physics. This volume is composed of 16 chapters. The opening chapters deal with the principles and application of freeze-etching technique and scanning electron microscopy. The succeeding chapters review the development rudimentary model of the chromosome, the mechanisms involving large number of steps to kinetic studies of multisubstrate enzyme systems, and some biophysical approaches to evaluate radiation effects and their repair. These topics are followed by discussions the origin of the observed fluorescence and phosphorescence spectra of DNA, as well as some aspects of energy transfer that apply to DNA and other polynucleotides. Other chapters explore the processes of cellular repair, cell's radiation sensivity, bacterial photoreactivation of mutation, and the genetic control of DNA repair and genetic recombination. The final chapters consider the mechanism of mutation suppression in yeast, the role of cytoplasm in radiobiology, and the different random factors governing the dose-effect relation. This book is of value to biologists, medical physicists, and medical practitioners.