Histo-chemical and cytochemical studies on the succinic dehydroge-nase system with three ditetrazolium salts, NT, Nitro-NT, and Nitro-Bt

1. Histochemical and cytochemical studies with respect to the sites of reaction were made on the succinic dehydrogenase system activity of human and animal tissues using ditetrazolium salts, namely, neotetrazolium chloride, nitro-neotetrazolium chloride, and nitra-blue tetrazolium chloride. 2. The advantages and disadvantages of each ditetrazolium salt for histochemical and cytochemical purposes and the reaction taking place in frozen tissue sections and that in fresh tissue blocks were compared, and the method of procedure suitable for each condition was established with some modification. 3. Selecting conditions suitable for cytochemical purpose, it was shown that the reaction took place at the sites coinciding with mitochondria, and the distribution of the enzyme reaction was also examined. In addition, several new findings in the brains and other tissues cytochemically made clear were pointed out.