In an attempt to pursue the relationship of the fine structure of a cell to the biochemical function, the author at first tried to demonstrate cytochemically the actual sites of activity of enzymes in the terminal electron transport system involved in energy production with the use of the electron microscope. Namely, cytochemical reactions were performed by using potassium tellurite, a heavy metal salt, and then the author succeeded in the electron microscopic detection of the enzymes by freezing-drying method and by means of formalin fixation, strong reducing agents and osmium tetroxide fixation. As the results the author has been able to verify that the reactions of the enzymes belonging to the terminal electron transport system are found localizing in the mitochondria being arranged fairly densely and continuously on the critae and partially on the membrane, although some differences in the grade of the activity are
found in each mitochondria even in one cell and a marked difference between the mitocndria belonging to the different kinds of cells. Furthermore, it has been clarified that the activity of the endogenous dehydrogenase
system (mainly DPNH- or TPNH-dehydrogenase and others) is
chiefly strong in cristae, and that the succinoxidase system exists both in cristae and membrane.</p
