THE GEOTROPISM OF PARAMECIUM CAUDATUM. Ill 



In comparison with the writer's previous results, that is, 1.037 

 or 1.037 0.003, the difference is not great. In his previous 

 experiments, however, he was not critical enough to test the 

 lowering of the specific gravity of the gum-arabic solution after 

 one or two drops of water containing Paramecia were added to 

 the tubes. The writer, therefore, considers that the present 

 result is more correct than the previous one. 



A more accurate estimation could possibly be made by having 

 the animals before adding them to the centrifuge tube in gum 

 solution of a density only a little less than that of the animals. 

 The lowering of specific gravity by mixturewould thus be lessened. 

 Nevertheless, the writer believes that the assumption of 1.039 

 as the specific gravity of Paramecium caudatum is close enough 

 for biological purposes. 



2. The Effects of Centrifugal Force on the Protoplasm of Parame- 

 cium caudatum. 



The specific gravity of the animal being known as about 1.039, 

 a gum-arabic solution of higher specific gravity, that is, about 

 i.i, was prepared. If Paramecia are strongly centrifuged in 

 such a solution, they all should be suspended in the solution. 

 And the heavier end of the animals should, also, be passively 

 thrown away from the axis of the centrifuge. Now the writer 

 put a certain number of drops of the gum-arabic solution in a 

 pair of heematocrit tubes already described, and on the top of 

 each, one drop of water containing dense Paramecia was added. 

 The solution and the water in the tubes were well mixed by means 

 of a fine glass needle. The tubes were centrifuged for fifteen 

 minutes at a velocity of 108.3 revolutions per second and with 

 radius of 2.5 cm. to 7 cm. 



The paramecia with some of the gum-arabic solution, after 

 being centrifuged, were sucked out in a capillary tube and were 

 killed in I per cent, chromic acid, being left in the solution for 

 about one minute. Then they were stained by McClendon's 

 method, "in Biondi's methyl green, orange G and acid fuchsin 

 mixture with a little less fuchsin and of about one fourth saturated 

 strength" 1 for about four minutes, dehydrated and mounted. 



1 McClendon, J. F., loc. cit. 



