The Effect of Increased and Decreased Oxygen Pressure upon the Intestinal Protozoa of Macacus rhesus

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Abstract
In his experiments upon the toxicity of oxygen for protozoa Cleveland (1925, a, b, c) was able to kill the intestinal protozoa of Termites, without injuring the host, by increasing the pressure of oxygen for varying lengths of time. He found that at one atmosphere pressure of oxygen the intestinal protozoa of Leucotermes were killed in 24 hours; those of Termopsis in 72 hours; whilst those of Reticulitermes and Cryptotermes were not all killed in ten days. At 3·5 atmospheres of oxygen he found that the intestinal protozoa of all four species were killed in less than an hour. At this pressure the intestinal protozoa of cockroach and frog were killed in 3½ hours and 28 hours respectively, whereas it took 90 hours to kill the cockroaches and 65 hours to kill some of the frogs. He also experimented upon warm-blooded vertebrates (rats), but he found that these animals survived only 5–6 hours at 3·5 atmospheres of oxygen and their intestinal protozoa were not killed in that time. Trichomonas, grown in cultures, however, from frog, rat, and man, were killed in 6, 10, and 11 hours respectively when subjected to 3·5 atmospheres of oxygen.