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Effect Of Anoxia And Lowered Oxygen Tensions
The reactions of Vorticella microstoma to suddenly reduced oxygen tensions or complete oxygen lack are quite definite. The trophic ciliate forms a posterior ciliary wreath, detaches itself from its stalk and becomes a free-swimming non-trophic telotroch. The telotroch will not settle unless a trace of oxygen is present. The cysts are stimulated by suddenly decreased oxygen tensions and many will excyst. The following are typical experiments.
A hanging drop containing five trophic vorticellids and one dividing vorticellid was placed in the chamber and the air replaced with purified nitrogen. Within half an hour the first telotroch had formed and a second was being formed. Within four hours all seven ciliates had formed telotrochs. After twenty-four hours three telotroehs were still free-swimming while four were stationary and attempting to settle. After thiry hours all seven were attempting to settle and had ceased swimming freely in the hanging drop. After forty-eight hours only four viable telotrochs remained. These were still attempting to settle but no stalk or peristome was formed and there was no pulsation of the contractile vacuole. The drop was taken from the chamber after fifty hours and returned to air. Within an hour and a half one of the ciliates had formed a stalk and a peristome and was feeding.
Some difficulty was experienced in preserving the chamber free of oxygen If the flow of purified nitrogen was slowed or stopped, oxygen tended to diffuse back into the chamber. Consequently by leaving the drop in the chamber and turning the nitrogen flow on and off, the reactions of the ciliates to the presence or absence of oxygen could be observed.
A hanging drop of ten trophic vorticellids was placed in the chamber and the nitrogen flow turned on for forty minutes. The ciliates stopped feeding and one telotroch was formed. The flow of nitrogen was stopped, permitting oxygen to diffuse back into the chamber, and all recommenced feeding. The nitrogen flow was then turned on again and after an hour all the ciliates had formed telotrochs. The flow was stopped and the ciliates settled and recommenced feeding a id dividing as the oxygen diffused back into the chamber. After sixty-six hours there were about two hundred trophic ciliates in the hanging drop. The nitrogen flow was turned on once more and after three hours there were about one hundred and twenty telotrochs and after six and a half hours about one hundred and fifty. After twenty-four hours there were still about one hundred viable telotrochs and no trophic individuals. The nitrogen flow was stopped, and within two and a half hours all the telotrochs had settled and were normal trophic forms.
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Hanging drops of starved V. microstoma containing many cysts and a few trophic individuals were placed in the chamber. The drops also had cysts and a few trophic forms of Oxytricha pellionella. Unpurified nitrogen, still retaining a trace of oxygen, was passed through the chamber. The reactions of the ciliates are summarised in Table 1. Although the vorticellids react at first by forming telotrochs, they subsequently become adapted to the reduced oxygen tension and resettle.
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| Time | 0 | 30 mins. | 45 mins. | 18 hrs. 30 mins. |
|---|---|---|---|---|
| Vorticella | 9 trophic crliates many cysts | telotroch formation | 1 trophic 8 telotrochs | 100 trophic 2 telotiochs |
| 140 excysting | 30 cysts | |||
| Oxvtriha | 0 trophic many cysts | 45 trophic 11 excysting | ||
| Time | 0 | 30 mins. | 1 hr. | 5 hrs 30 mins. |
| Vorticella | 6 trophic many cysts | 1 telotroch | 30 telotrochs excystment | 50 telotrochs 200 trophic |
| Oxytricha | 4 trophic many cysts | 20 trophic |
The vorticellids showed the same reactions to the removal of oxygen if pure carbon dioxide was used to replace the air in the chamber. The following experiment shows the alternate effects caused by nitrogen with a trace of oxygen, pure carbon dioxide, and pure oxygen. Although the trophic ciliates initially form telotrochs, they ultimately settle again in a nitrogen atmosphere containing a trace of oxygen. They do not settle in an atmosphere of carbon dioxide.
A fresh drop of about twenty-eight trophic vorticellids was placed in the chamber and unpurified nitrogen passed through. Within twenty minutes posterior ciliary wreaths were being formed and within forty-five minutes there were about eighteen telotrochs. After an hour one had settled and the rest were still telotrochs. After two and a quarter hours, six had settled. Feeding and division took place. After twenty-one hours there were about fifty-five trophic and dividing ciliates and about eight telotrochs. The unpurified nitrogen flow was turned off and pure carbon dioxide turned on for quarter of an hour. Two hours later there were about sixty telotrochs and three forming. Pure oxygen was then passed through the chamber and, within an hour, sixty-six vorticellids were settled, one was settling and one was about to settle.
In one experiment using pure carbon dioxide, a thousand telotrochs, formed after passing pure carbon dioxide through the chamber, survived twenty hours in this atmosphere. After this time the chamber was flushed through with unpurified nitrogen and within an hour all but ten of the telotrochs had settled.