1. 1. Spectroscopic analysis of intact larvae revealed the absorption bands in the approximate positions of cytochrome c, b, and a + a3. In addition the bands for hemoglobin and oxyhemoglobin were observed and appeared to be more intense in larvae which had been in the host muscle for at least 6 weeks. 2. 2. The catalytic activity of cytochrome oxidase and the cytochrome c reductases was determined spectrophotometrically in both larvae and adults. The enzymes appeared to be less active in the adult worms. Cytochrome oxidase was inhibited by cyanide, and by carbon monoxide in the dark. The latter inhibition was reversed by light. Succinic dehydrogenase activity was inhibited by malonate. 3. 3. The respiration of homogenates of the larvae is stimulated by succinic and α-ketoglutaric acids. Increased oxygen consumption in the presence of carbon monoxide was also observed. 4. 4. Enzymes of the tricarboxylic acid cycle, including aconitase, isocitric dehydrogenase, fumarase and malic dehydrogenase were measured in homogenates spectrophotometrically. Citrate formation from oxalacetic acid and acetate was demonstrated, utilizing paper partition chromatography. 5. 5. The evidence presented strongly indicates that the cytochrome system for electron transport and the tricarboxylic acid cycle for terminal oxidative processes occur in the tissues of the larvae of T. spiralis.
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