THE GEOTROPISM OF PARAMOECIUM 997 
EFFECTS OF INGESTION OF SUBSTANCES HAVING A LOWER 
SPECIFIC GRAVITY 
Various substances were tried, but finally paraflinywas selected 
as best adapted for the purpose. Finely divided paraffin was 
obtained by melting and cooling in hot water several times till 
the paraffin was thoroughly washed. Then a small amount 
was melted in a flask of hot water and shaken and then suddenly 
cooled under the tap. The fine, suspended particles would soon 
rise to the top. For the control experiment paraffin in particles 
too large to be taken in was used. 
Experiment 4. Both Nos. 1 and 2 were shaken at the same 
time for several minutes and the tubes then allowed to stand. 
In No. 2 the animals at the end of fifteen minutes were aggre- 
gated densely at the bottom at rest. They remained so, under 
observation, for several hours. After twelve to twenty-four hours 
all would be found scattered through the tube. In the control 
no noticeable effect was produced by the paraffin. The dense 
ageregation at the bottom of No. 2 was obtained with cultures 
of the different types (fig. 5). 
The inference that the posterior end was buoyed up by the 
paraffin particles, so as to orient the animals downward, is the 
conclusion of the writer, for the present at least. * 
DISCUSSION OF RESULTS 
The above experiments seem to place the gravity orientations 
of Paramoecium on the same plane as the orientation of the axis 
of certain eggs by specific gravity. 
Lyon compares Paramoecium to a statocyst. It 1s not easy 
to see how an animal revolving continually on its axis could react 
to the localization of an internal stimulus. While such a stimu- 
lus might conceivably act effectively in an antero-posterior direc- 
tion, the explanation offered in this paper seems simpler, at least 
to the writer. 
Lyon centrifugated Paramoecia strongly into a tube ending in 
a capillary bore and found that the animals moved with the 
anterior end outward, and that certain heavier particles were 
driven into the anterior end. 
