An electron microscopic study on the red, white and inter­mediate muscle fibers of mouse

An electon microscopic study on the structural differences among the red, white and intermediate muscle fibers of mice was made and the following results were obtained. 1. The red fiber contained very numerous mitochondria, the white fiber a few and the intermediate fiber a moderate number. The distribution of mitochondria was different in each type of muscle fiber. The cristae of mitochondria of the red fiber was quite well developed, that of the white fiber poorly and that of the intermedtate fiber moderately. 2. Sarcoplasmic reticulum of the white fiber was considerably well developed but that of the red and intermediate fibers poorly developed. 3. Glycogen particles were abundant in the white fiber, less in the intermediate fiber and least in the red fiber.