The luminescence phenomenon underlies many investigative methods in the most diverse disciplines: analytical chemistry, geology, fault detection, paleontology, forensic medicine, and other. It comprises two types of emission: fluorescence and phosphorecence. In medical and biological research, fluorescence analysis has no equal in terms of availability of equipment, simplicity of procedure, reproducibility of results, and sensitivity to minute quantities of the biological sample. This popular science book describes the application of fluorescence analysis to investigations of physiological processes and also to the diagnosis of diseases, assessment of its severity, and control of its course. Separate sections of the book are devoted to the use of this method in public health and pollution control. This book is intended for the general reader and those who are interested in problems of public health.