I 8 SAKYO KAXDA. 



and lowered the known density of the latter. Nevertheless, 

 there may exist some difference in the specific gravity of the 

 animals in different cultures, as seems to be indicated by the 

 experiments described. This must be borne in mind. 



Then the writer prepared a series of 10 tubes about 12.5 cm. 

 long and 0.4 cm. in diameter, in each of which was a definite 

 gum-arabic solution of known density from 1.034 to 1.044 

 thoroughly mixed with about two drops or slightly less of the 

 culture containing dense paramecia, filling each up to 12 cm. 

 Three drops of paraffine oil were placed on top of the solution 

 "to exclude oxygen and a possible consequent chemotropic 

 gathering." The writer's observations upon the paramecia so 

 treated agreed with Lyon's in all respects. His words may, 

 therefore, be quoted: "Invariably in all solutions, whether of 

 equal, greater, or less density than the animals, the latter slowly 

 rose and formed a dense ring near the top. The response was 

 slow, as the velocity of swimming in such viscous solutions is 

 extremely small. Two or three hours, or over night, was often 

 necessary. But often the rising ring of animals could be seen 

 in twenty minutes or less. It was typical geotropism very 

 much slowed" (17, p. 428). 



The animals so treated lived 5 days in all the solutions above 

 mentioned, though the number of the animals had noticeably 

 decreased at that time. A week after, all the animals in the 

 solutions of densities 1.044 to 1.037 na d died, though a few 

 animals in the solutions from 1.036 to 1.034 lived for 13 days. 

 It is rather interesting therefore to note that the animals in the 

 solutions of the greater densities than their own died earlier than 

 the animals in the solutions of the lesser densities. This may 

 not be simply due to density, but density may be at least one 

 of the causes of death of the animals. 



To avoid the criticism that the specific gravity of the animals 

 may have been increased by a prolonged stay in such solutions, 

 the writer carefully tested the matter, as Lyon did. After several 

 tests, he found that the animals had increased their density on 

 an average between 0.002 and 0.003 after 13 hours in the solu- 

 tions. This was determined by centrifuging tubes in which 

 the animals were suspended in solutions of known densities. 



