THE BEHAVIOR OF INFUSORIA; PARAMECIUM 



69 





This is of course a result of their reaction to carbon dioxide produced 

 by themselves. In all experimental work on the reactions of these 

 organisms to stimuli it is 

 necessary to take these 

 facts into account. For 

 example, in order to get 

 clear results in. such 

 work, Paramecia must not 

 be taken with a pipette 

 directly from a dense 

 collection in a culture 

 jar, and at once mounted 

 on a slide. Such col- 

 lections contain carbon 

 dioxide, which may be- 

 come unequally distrib- 

 uted throughout the 

 preparation, as a result 

 of the fact that some of 

 the water outside the 



Collection is likelv tO be ^ IG- 53* Spontaneous collections of Paramecia, due to 

 . , , . COo. A, Collections formed in an upright tube, after Jensen, 



taken Up With the pi- B, Collection formed beneath a cover-glass, when water is 

 Dette at the Same time ta ^ en directly from a dense culture of Paramecia. C, Collec- 

 tion in the bottom of a watch-glass. 



The Paramecia quickly 



gather in the region containing most carbon dioxide, and their reac- 

 tions to other substances are inconstant and irregular, owing to the 

 interference due to the reaction to carbon dioxide (Fig. 53, B). For 

 experimental work it is always necessary before each experiment to 

 place a few drops of the .water containing the Paramecia in the bot- 

 tom of a shallow watch-glass, and to aerate it thoroughly by stirring it 

 and bringing it into contact with the air by means of the pipette. 

 Then this aerated water and its contained Paramecia must be used for 

 the experiments. This aeration must be repeated before each experi- 

 ment, and the test for the reaction to other chemicals must be made 

 immediately after the Paramecia are mounted, before they have had 

 time to produce an appreciable quantity of carbon dioxide. If these 

 precautions are neglected, the reactions of the Paramecia are incon- 

 stant, and the results of experiments are likely to be very misleading. 

 Paramecia in a solution of carbon dioxide react to other agents in a 

 manner entirely different from the reaction of individuals in water not 

 containing carbon dioxide. The account of their reactions given in 

 the present chapter assumes that the carbon dioxide has been in every 



