316 L. R. CLEVELAND. 



longing to the genus Trichomonas (Figs. 5, 6) were killed within 

 24 hours and had disappeared from the termites' intestines, while 

 Trichonympha and Leidyopsis, the two largest genera, and Streblo- 

 mastix, the smallest genus, remained practically unaffected. Of 

 course a few others were probably killed, but not many. The 

 termites were not affected in the least by the oxygen. However, 

 we should not expect them to be for many animals can live in an 

 oxygen atmosphere at this pressure for a much longer period. 

 The surprising thing is that the oxygen kills the protozoa so 

 quickly and removes one genus completely long before the others. 

 When the termites were confined to the oxygen atmosphere 

 for more than 24 hours, Trichonympha, Leidyopsis and Streblo- 

 mastix began to die, though not all individuals of these genera 

 were dead until about 72 hours. Sometimes they were dead a 

 little earlier than this and sometimes a few hours later, the 

 variation probably depending on the percentage of oxygen in 

 the particular flask or vial containing them. The oxygen which 

 was used was obtained by heating C. P. K 2 Mn. 4 O 8 and was 

 washed in NaOH before being run into the flasks and vials where 

 it displaced most of the air. No effort was made to determine 

 the percentage of oxygen in such an atmosphere, which must 

 have varied considerably at times. Known percentages of 

 oxygen at one and at more than one atmosphere pressure are 

 now being used in the work on toxicity of oxygen for intestinal 

 protozoa. The significant fact is that in all of more than 75 

 experiments which were carried out the protozoa were all removed 

 in approximately 72 hours. In these 75 experiments, more than 

 1 200 termites were used and none of them, in so far as could 

 be determined by careful observation, ever suffered any ill effects 

 from the oxygen. They easily live eight to ten days in an 

 oxygen atmosphere which kills their intestinal protozoa in three 

 days. No effort was made to determine just how long they 

 would live, for after their intestinal protozoa have been taken 

 from them, they cannot live more than three to four weeks in air. 



c. Oxygenation and Starvation. 



It was noticed in the starvation experiments that Tricho- 

 nympha disappeared entirely after the termites were starved 

 six days and that Leidyopsis had disappeared entirely by the 



