Saint Francis de Sales Seminary

1. In 10–5 M KCN respiration in Pelomyxa carolinensis is inhibited by 63 per cent. In much higher concentrations of KCN, up to 10–2 M, only slightly greater inhibition occurs.2. Pelomyxae which have been exposed to potassium cyanide (10–5 to 10–2 M), for 12 to 24 hours, show many changes in protoplasmic structure.3. In 5 x 10–3 M potassium arsenite the maximum inhibition of respiration in Pelomyxa carolinensis is 35 per cent; this effect, however, is only temporary.4. In 0.17 M (1.5 per cent) ethyl urethane the respiration of Pelomyxa carolinensis is inhibited by 65 per cent.5. Respiration in Pelomyxa carolinensis appears to occur chiefly through a cytochrome-cytochrome oxidase system, and partly through a mechanism involving glutathione.6. The respiratory mechanism of Pelomyxa carolinensis, a rhizopod, differs considerably from that of a number of the ciliates.