Muscle tissue is by far the most abundant cellular tissue in the body, and is relatively uniform as to cellular composition. Profound biochemical changes in muscle are known to accompany electrolyte disorders, circulatory disturbances, nutritional deficiences, and physical exercise. In addition, morphological changes occur in some muscle disorders and in generalized diseases. Biochemical and morphological 148studies of muscle tissue in man, under various physiological and pathological conditions, have proved to be of great value in clinical research and diagnosis of various diseases.