Abstract
The claim of Lund 1 that Paramecium is insensitive to KCN though questioned by Hyman 2 has been confirmed by Gerard and Hyman. 3 A similar insensitivity of an alga, Chlorella, was described by Warburg and by Emerson, 4 and an even more striking resistance to cyanide by a bacterium, Sarcina lutea, has been reported by Gerard. 5 It seemed desirable to extend observations as to cyanide sensitivity to other protozoa, The present work is limited to the Protozoan, Colpidium campylum.
Methods. Pure cultures of colpidia were obtained from a single individual, and cultured on a spring water rye infusion seeded with the coccus Achromobacter candicans grown on agar slants for 2 days at 350°C. The colpidia were added 24 hours after the bacteria and grown for 48 hours before use. The cultures were prepared for respiration studies by gentle centrifuging, removing the bacterial layer, washing the lower sediment of protozoa and bacteria with spring water and recentrifuging, repeated 5 to 7 times. At the end the colpidia were practically bacteria free, and any of the latter still present could not have affected the respiration perceptibly. Oxygen consumption was determined by the Warburg method and the results are expressed in terms of Qo2, the cmm. of oxygen used per million animals per hour. The colpidia were enumerated with an hæmocytometer after killing with formalin. Before mounting in the manometers, the heavy protozoan suspension was diluted with a fresh phosphate buffer at pH 7.4, made by adding 5 cc. of Sorensen's phosphate to 95 cc. of spring water. The cyanide was also made fresh every day, neutralized to phenol red and dissolved in the same buffer solution.
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