TOXICITY OF OXYGEN FOR PROTOZOA. 459 



interesting result occurred, Streblomastix was killed before Tricho- 

 monas in many hosts. At a pressure of 2.5 atmospheres. Tricho- 

 nwnas and Streblomastix are both killed at or about the same time. 



trdle-- of the- amount of pressure, the- hirers t protozoa of 

 '1'rrmopsis, with the- exception of one very -mall form (Tritrypano- 

 plusniui not pre-ent in all hosts and abundant in only a fe\\ , are 

 in\ ari.ihly the la-t ones to be killed, but in Cryptoternit^ and 

 rmes this is not always the case. In Cryptotermes. for 

 m-tance. -ometirnes all individuals of the la- I^iph- 



nymph killed when many Decescovina are kit alixr. 



:ty indi\ iilu.ils of Tertnopsis were confined in oxygen at 3.5 

 atmo-phen 3. \t the end of forty hours, every individual had 



me immoliik'. The experiment was stopped alter fort y-ti\e 

 hour-, \\lu-n it appeared that every individual was dead, although 



A h<. ut- Liter two individuals became feebly motile, and v 



two days later. Forty-five hours at 3.5 aim..-- 

 phete- uiii-i be about the time required to kill this termite, \\hich 



7.5 linn - as long as it takes to kill its proto/oa. In other 

 \\ord-. MI at this pressure is 67.5 times as toxic for the 



. rmites as for the termites themselves. 



1 'he time required to kill the protoxoa of these termite- at ; V 5 

 .it in. .-pin it - of oxygen certainly does not injure the termite- in 

 the KM Deflation at this pressure is surely a very rapid 



me. in- 1. 1 t termites of their protozoa. It is very much more 



.sati-lat ioi \ in many ways than incubation (Cleveland, '-4 1 , and 

 luini-lie- .1 very ready means of determining whether or not all 

 protozoa-harboring termites are dependent on their pr<.t<>/<.a to 



-t their t 1 for them. 



In order to determine what effect, if any, partial pr. ..t' 



oth. particularly nitrogen, had on o\\_e:i toxicity, ter- 



mii ich ot the four genera that were oxygenated \\i-re con- 



Imed in ti\e at m.'-pheres of air (the partial oxygen pnure ot" 

 ti\e atmo-jiheie- ..1 air approximates the total oxygen piv--ure of 

 OIH- atm.>-plnie ..!' oxygen) for the same time that they \\ere 

 (on lined in one atmo-plu-re of oxygen. Fi\e atmo-plierc- of air, 

 in e\ cry instance, gave exactly the same re>ult as one atmo-jihere 

 of oxygen. Tim-, the toxicity of oxygen is unal'tected b\- the 

 presence of nitrogen and the rare gases of the air. In another 

 experiment ,v5 alnx .-phei e- of air \\ere u>ed with the re-ult th.it 



