GEOTROPISM OF PARAMECIUM AND SPIROSTOMUM. 



I.-! 



f Tube i. Density of gum-ar. sol. 

 Tube 2. Densitv of gum-ar. sol. 



I 



fTube i. 



II. i , 



Tube 2. 



Density of gum-ar. sol. 

 Density of gum-ar. sol. 



III. 



f Tube i. Density of gum-ar. sol. 

 Tube 2. Density of gum-ar. sol. 



Density of gum-ar. sol. 

 Density of gum-ar. sol. 



f Tube i. 

 I Tube 2. 



1.034, L300 revolutions; a few go to 



bottom. 



1.035, 1.300 revolutions; very few go to 



bottom. 



1.036, 1,300 revolutions; 2 or 3 go to 



bottom. 



1.037, 1.300 revolutions; none go to 



bottom. 



1.038, 1,300 revolutions; a few go to 



lower part than middle. 



1.039, 1.300 revolutions; some go to 



middle. 



1.030, 1,300 revolutions; many go to 



bottom. 

 1.043, 1.300 revolutions; many stay at 



top. 



The writer found thus that the density of the Paramecium 

 candatum is about 1.036 or 1.037. To make sure of the results, 

 three different series of the same experiments were made with 

 different cultures in each series. From two cultures, practically 

 the same results were obtained as the above, but it was found 

 in one culture that the animals when centrifuged were so weak 

 that they were all broken into pieces on the bottom. 



In comparison with Lyon's 1.048 or 1.049, we find a difference 

 of about 0.012. Although the difference does not seem very 

 great, it is great for such small organisms. Accordingly at the 

 suggestion of Dr. Knowlton and Dr. Lyon, the writer tested the 

 hydrometer which he used for the measurement of the density 

 of the gum-arabic solutions, by means of a density bottle with 

 Dr. Lyon's help. It was found that the weighing difference 

 between the hydrometer and the bottle was about 0.003. If the 

 test was correct, we may add this difference, 0.003, to 1.036 or 

 1.037, which makes the density 1.039 or 1.040. If so, the 

 difference between Lyon's 1.048 or 1.049 and the writer's 1.039 

 or 1.04 becomes a little less. 



The only possible source of error in Lyon's experiments is 

 that he may have placed too much "water containing para- 

 mecia" above "a little gum-arabic solution" in the "small" 

 and short tube which he adopted for the haematocrit attach- 

 ment. Under such circumstances, possibly the animals when 

 centrifuged carried some water with them into the gum solution 



