Avausr 30, 1913] 
air where the worm was placed, are not shown. 
After entering the moist air the worm turned 
back im progressively higher moisture con- 
tents, until the end of fifteen minutes of the 
seale; another somewhat longer invasion is 
followed by the same repeated decrease in in- 
vasion between 16 and 26 minutes and between 
29 and 36 minutes. 
A series of preliminary experiments were 
performed on Paramecium. After a number 
of trials in which chambers of different sizes 
were used, a chamber was cut out of a large 
drop of beeswax darkened with graphite, on a 
slide. This chamber was 2 mm. wide, 9 mm. 
long, and 1 mm. deep. The slide was laid 
over the edges of two Petri dishes. Water at 
36° C. was run into one of these and water at 
16° C. into the other. The optimum of the 
culture was 23° C. as shown by the point of 
aggregation of the greatest number of in- 
dividuals in a box 5 mm. deep, 20 mm. wide, 
and 170 mm. long. The apparatus at hand 
did not permit measurements of temperature 
in the 2mm. x 9 mm. chamber. The position 
of the slide over the hot and cold water was so 
adjusted with a considerable number of indi- 
viduals in the cell, that they aggregated at the 
cold end rather than at any point in the long 
axis of the cell. Movements were observed 
with a binocular. A single individual was 
then introduced from a diluted infusion. 
It is not possible for one person to observe 
and graph the movements. The writer ac- 
cordingly observed the animals and stated 
their position according to a scale, ete., while 
another person with watch at hand drew the 
graphs. Graph 10 is typical of what was ob- 
served repeatedly. Several invasions of the 
high temperature occurred before the graph 
began. This is due to the fact that when 
water was removed from the cell and another 
drop added it was necessary to allow two or 
three minutes for the drop to attain the tem- 
perature which accorded with the temperature 
of the slide beneath it. After the graphing 
began, an invasion of the high temperature 
at the end of the first minute was followed by 
turning in lower temperature. An invasion 
which did not reach the highest temperature 
SCIENCE 
229 
at the end of the third minute was followed 
by two turnings in much lower temperature. 
An inspection of the rest of the graph shows 
that each invasion of the high temperature is 
followed by two or three turnings in lower 
temperature; this was the rule in the un- 
graphed observations. 
Graph 11 shows the reaction of an individual, 
beginning within five to ten seconds after the 
drop was introduced into the chamber. No 
time was allowed for the temperature of the 
drop of water to become adjusted. Accord- 
ingly the temperature at the warm end rose 
while the observations were going on. The 
slide has also been shifted too far over the hot 
water. When the graph began the animal was 
in the hot end; it moved to the cool end and 
on its return, turned back twice in lower tem- 
peratures. Then one long invasion of high 
temperature was followed by a very short one; 
three long ones, by a period of rest. During 
this period avoiding reactions had increased in 
violence until they began to dominate over 
other movements and the temperature had 
risen to a point where normal reaction did 
not occur. The animal darted rapidly, giving 
the avoiding reaction in the higher tempera- 
tures, so violently that none of the courses * 
were followed up and after a number of rather 
long stays in the high temperature it died. 
One striking feature of the behavior is the 
orientation of the individuals in the long axis 
of the gradient. This is however apparently 
trial and error and, as Jennings has noted, 
when headed toward the optimum temperature 
they swim ahead without giving the avoiding 
reaction. The graphs bring out the fact that 
they give the avoiding reaction at different 
temperatures in accord with their preceding 
experience. It is however evidently not cor- 
rect to assume that the Paramecium disting- 
uishes the difference between the temperature 
of the water in contact with the two ends of 
the body as shown by dividing the total dis- 
tance necessary to give a degree difference by 
the length of the animal. On this basis 
Mendelssohn?* decided that they can disting- 
uish one one hundredth of a degree centigrade. 
18 Davenport, loc. cit. 
