THE GEOTROPISM OF PARAMECIUM CAUDATUM. IIQ 



magnesium chloride, cane sugar, ethyl alcohol and chloroform in 

 appropriate strength were tried but no better results were ob- 

 tained. 



IV. SUMMARY AND CONCLUSIONS. 



1. The specific gravity of living Paramecium caudatum is 

 between 1.0382 and 1.0393. 



2. Paramecium caudatum contains protoplasmic materials of 

 different gravities. 



3. Paramecium caudatum, when strongly centrifuged, assumes 

 a position with its anterior end directed away from the axis of the 

 centrifuge. In so doing, it must be passively thrown by the 

 centrifugal force, because the centrifugal force used was alto- 

 gether too strong to be resisted by the animal. For this reason, 

 its anterior end must be heavier than its posterior end. The 

 negatively geotropic orientation, therefore, is an active process 

 and the mechanical theory is not correct. 



4. The whole organism seems to be a "statocyst," since the 

 recovery of negative geotropism after centrifugalizing is syn- 

 chronous with the reestablishment of normal relations of sub- 

 stances in the cell. 



5. So-called reversibility of the negative geotropism of Para- 

 mecium caudatum by temperature and by chemicals is extremely 

 doubtful. Mechanical "shock" or agitation is chiefly responsible 

 for the reversal one sees in such cases. 



In conclusion the writer wishes to acknowledge his indebted- 

 ness to Professor E. P. Lyon, under whose direction this work was 

 completed, and who gave valuable suggestions and criticism of 

 the work and manuscript. His thanks are due also to Dr. J. F. 

 McClendon, who gave his generous help and suggestions during 

 the experiments. 



