1 82 Clifford . — Notes on some Physiological 
rapidity x , thus creating a current as the water struck the 
wood, which was placed well to one side. Up to six revo- 
lutions per minute the plasmodium moved against the current, 
but if the number of revolutions was increased to seven it 
moved with the current, i. e. became negatively rheotropic. 
If the number was increased beyond seven, it crept up entirely 
out of the water, as if to protect itself from being swept away. 
There is in these movements a remarkable evidence of the 
extreme sensitiveness of naked protoplasm, exhibiting as it 
does positive rheotropism up to a certain point, beyond which 
it would, if continuing this habit, be in danger of being torn 
from its substratum, and just when the danger-point is 
reached, being possessed of sufficient sensitiveness to enable 
it to move out of harm’s way. But so unerringly did this 
power show itself, that there is no doubt of its existence. 
T I-IERMOTROPISM. 
In conducting the experiments upon thermotropism, the 
apparatus shown in Woodcut 4 was employed. It consists 
of a copper tank, 18 in. x 18 in., having upon each of its 
three sides niches, into which are fitted zinc boxes, so that 
three-fourths the length of a box projects beyond the tank. 
Each box is divided into compartments, the first partition 
passing along a line even with the side of the tank, the second 
at the same distance from the outer end. Each compartment 
is provided with openings in the lid, which can be closed 
by means of corks. The outer one has an opening on the 
front, near the top. The tank is filled with water, and heat 
applied by a gas-flame placed underneath. A stream of cold 
water is made to flow through the outer compartment of the 
box, the surplus being carried away through the opening upon 
the front. By means of this apparatus a uniform difference 
of temperature between the two ends of the middle com- 
partment can be maintained. 
1 This apparatus, as well as that employed in the experiments on thermotropism, 
was devised by Professor F. C. Newcombe of this laboratory. 
