468 L. R. CLI-: \TI.A\D. 



is certainly just as toxic for some free-living ciliates as it is for 

 parasitic ciliates; for others, it is not. For Puramarinni and 

 Clrilodon, it is really more toxic; for Diophrys and Holostica, it is 

 considerably les, toxic. It is not very toxic for two plant-like 

 flagellates, Eitglena and Heteroneina. hut would probably be found 

 to be just as toxic for some animal-like free-living flagellates as 

 for some parasitic species. 



Oxygen in excessive amounts is toxic for all animals, but proto- 

 zoa possibly take up a correspondingly larger amount of it as 

 the tension or pressure is increased than do higher animals and 

 for this reason are affected more adversely than termites, cock- 

 roaches, earthworms and frogs. During oxygenation the proto- 

 plasm of the protozoa sometimes becomes very much vacuolated, 1 

 which may indicate that it is being consumed, perhaps actually 

 burned up, by increased metabolism. However, the metabolism 

 of higher vertebrates is said to be slowed down by increased 

 oxygen pressure. But Amberson, Mayerson, and Scott ('24) 

 were "able to show that the metabolic rate in some of the higher 

 marine invertebrates, with well developed respiratory mecha- 

 nisms, is closely dependent upon the oxygen tension in the water 

 over a wide range." 



REFERENCES CITED. 



Amberson, W. R. ( Mayerson, H. S., and Scott, W. J. 



'24 The Influence of Oxygen Tension upon Metabolic Rate in Invertebrates. 



Journ. Gen. Physiol., 7, 171-76. 

 Bert, Paul M. 



'74 Rerherches Experimentales sur 1' Influence que les Modifications dans la 

 Pression Barometrique Exercent sur les Phenomenes de la Vie. Paris 

 167 pp. 

 Cleveland, L. R. 



'24 The Physiological and Symbiotic Relation-hips between the Intestinal 

 Protozoa of Termites and their Host, with Special Reference to Rcliculi- 

 termes flavipes Kollar. BIOL. BULL., 46, 177-225. 



'25, '2sb The Effects of Oxygenation and St.n \ ,n ion on the Symbiosis between 

 the Termite, Termopsis, and its Intestinal Flagellates. BIOL. BULL., 

 48.309-27. 

 Haldane, J. S. 



"22 Respiration. Yale University Press, 427 pp. 

 Putter, A. 



'05 Die Atmung der Protozoen. Zeitschr. f. Allgem. Physiol., 5, 566-612. 



1 It is also true that many dying protozoa, regardless of the cause of death, 

 sometimes become vacuolated. 



