PROTOPLASM OF PROTOZOA 79 



was that of Jensen (1893), who attempted to determine the energy rela- 

 tions of the movement of P. aurelia. He obtained the value of 1.25 by 

 suspending the organisms in solutions of potassium carbonate, a proce- 

 dure which gave too high values because of excessive shrinkage, due to 

 osmotic pressure. Later Piatt (1899) suspended killed or anaesthetized 

 Paramecium and Spirostomum in solutions of gum arable and found 

 their specific gravity to be 1.017. Lyon (1905) centrifuged living Para- 

 mec'ium in solutions of gum arable and obtained 1.048 or 1.049. This 

 was repeated by Kanda (1914, 1918), who finally arrived at a value of 

 1.0382 to 1.0393 for Paramecium and 1.028 for Spirostomum. Fetter 

 (1926) utilized approximately the same value, 1.038, which she ob- 

 tained by centrifuging Paramecium in sugar solutions, in calculating 

 the protoplasmic viscosity of that form. 



Leontjew (1927) has determined the density of various Protozoa 

 {Fuligo, Stemonitis, slime molds; NaegJeria, an amoeba; and Dunaliella, 

 a flagellate) to be 1.020 to 1.065. Some of his readings on Fuligo varians, 

 obtained with a micropyknometer, are interesting enough to be men- 

 tioned in detail: in moist weather the density was 1.01 6; in dry, 1.040, 

 and 11 hours before spore formation, 1.065. 



Heilbrunn (1929a, 1929b) used 1.03 as the specific gravity of the 

 protoplasm in his studies on viscosity of A. dubia. Motile amoebae 

 {Naegleria) have a density of 1.043, according to Leontjew (1926a), 

 and cysts I.O6O to 1.070 (Joschida, 1920, cited by Leontjew, 1927); 

 cysts of Hartmanella hyalina, a soil amoeba, have a specific gravity of 

 1.084 (Allison, 1924). 



It is, of course, generally recognized that the protoplasm of encysted 

 Protozoa contains less water than that of active forms. Allison (1924) 

 determined the specific gravity of cysts of Colpoda by the time required 

 to fall through water. He finds that four-day cysts averaging 40.1 microns 

 in diameter, have a density of 1.042; while twenty-day cysts, averaging 

 25.1 microns, have a density of I.06I. Similar results were found for 

 cysts of Gonostomum. The decrease in size and increase in specific grav- 

 ity are apparently caused by water loss. 



The specific gravity of protoplasm other than that of Protozoa has 

 been found to vary from about 1.02 to 1.08, with average values about 

 1.045. The publication of Pfeiffer (1934) gives a resume of the meth- 

 ods and results of such studies. 



