TOXICITY OF OXYGEN FOR PROTOZOA. 465 



These experiments, as well as those on free-living protozoa, 

 show thai en i- directly toxic for protozoa, that it acts on 



them directly and not through any tissues of their hosts. In 

 other words, the tissues of the hosts are not stimulated by the 

 oxygen in give off products which kill the protozoa. 



8. Free-living Protozoa. 



h -i- uied highly desirable to compare the toxirity of 0x3 

 fur free-li\ in;; |ruiu/ua with that for parasitic or entu/uic proto- 

 zoa; i <in-e(|uently, several genera of flagellates and ciliates were 

 -elei ltd .iinl enated in the same manner as were the cul- 



ture- ( it' p.ira^itic protozoa. 



TABLI-: III. 



Ari , MI-.IMI M TIME REQCIRED AT AN OXYGEN PRESSURE OF 3.5 AT 



KIM. Aii INDIVID I'ERTAIN FKI-:I:-I.I\ i >\. 





5 



4 



6o 



50 



Flagellate* 



Euglena. . . . 

 Htteroncma . 



65 

 50 



Ilie re-ul i- "I these experiments are given in Table III. The 

 fart tli.it /' mi is killed in 5 hours, Chilodon in 4, ll!\tica 



in 50. and /': in 60 shows conclusively that oxygen i> ju>t 



toxic l'n -nine free-living ciliates as it is for some parasitic 

 ciliaie- and ll.r^ellate-. It is actually even more toxic for Para- 

 iid Chilodon than for Trichomonas of frog, rat, and man 

 in cult tire; the t. Miner are killed in 5 and 4 hours respectively. 

 \\hileit rei|iiin-d (i. 10 and ii hours respectively to kill the lat ter. 

 And \\e ha\ e -i-en that the frog Trichomonas in culture is killed in 

 about half the time required to kill it in the frog, yet it is killed 

 much >OOIHT than the ciliates, Opalina and Nyctotherns. It has 

 not been p<>--ible to cultivate Xyctotherus and Opnlina from frogs, 

 but, riM-oniiiL: from the time required to kill Trichomonas in vivo 

 and in vitro, it would take IO to 12 hours to kill them in culture, 

 or more than t \\ice the time required to kill Parania-ciiini and 

 Chilodon. I cannot explain why oxygen is less toxic for Diophrys 

 and llolosticu than for Paramcecinm and Chilodon. Perhaps a 

 combined -tndy of the metabolism, habitat, and oxygen toxicity 



