230 
They appear from these observations to dis- 
tinguish the difference between the tempera- 
ture of the water where they assume the 
normal forward course and the point where 
they give the avoiding reaction. This differ- 
ence within the range of temperatures com- 
patible with the life of the animal is probably 
some tenths of a degree, varying with the 
immediate antecedent experience of the in- 
dividual. 
The method of graphing has been found 
very useful in making accurate determinations 
of reaction where modification by environ- 
ment has been attempted and where accurate 
determination of sensibility is necessary. One 
has only to take readings from a graph like 
number 8, make statistical records, and com- 
pute percentages in the thirds, repeating the 
readings, at 4 min., 1-min. and 2-min., inter- 
vals, beginning after 4, 1, 2 minutes, etc., after 
the graph began to demonstrate that percent- 
age in the thirds, with short intervals at least, 
is a very unreliable method of making records, 
unless the reading is done with absolute pre- 
cision. 
The oceurrence of the rapid modifieation of 
behavior described in practically all the great 
‘groups of the animal kingdom leads one to 
attempt to explain the phenomenon on the 
basis of some physiological characteristic com- 
mon to all. In connection with the study of 
fishes the writer and Allen? suggested that in 
both the case of carbondioxide and lack of 
oxygen in water the increased irritability is 
due to increased acidity. In support of this 
we cited Waller who found that a small 
amount of carbondioxide increases irritability 
of nerves. 
A similar explanation of the shorter in- 
vasions of light in a light gradient in which 
the Daphnias turn back in a lower intensity 
as described by Davenport and Cannon, was 
offered by Loeb?® who anticipated our conclu- 
sion, independently derived, and cited Waller 
though he attributed the development of 
14 Shelford and Allee, Jour. An. Beh., Vol. IV., 
p. 7. Shelford, Jour. An. Beh., Vol. IV., p. 31. 
15 Loeb, ‘‘ Mechanistic Conception of Life,’’ p. 
222, 
SCIENCE 
[N. S. Vou, XLVIII. No. 1235 
acidity to the increased metabolism of the or- 
ganism due to the stimulation. 
Since the phenomenon of modification un- 
der consideration takes place in gradients of 
ammonia in alkaline water, and the fishes con- 
cerned are positive to the ammonia, and since 
such behavior has been noted in the avoidance 
of cold, darkness, etc., which depress metab- 
olism, thus the hypothesis of increased ir- 
ritability due to acidity can be maintained 
only on the assumption that all changes in the 
environment stimulate the metabolism tem- 
porarily. This is not out of accord with the 
effects of depressing drugs which nearly all 
stimulate first, for a short time, and then 
depress. : 
Whatever may be the correct physiological 
explanation of the phenomenon, we have noted 
that the process is similar in the mammal and 
in the Protozoan. The reactions of both are 
such as to suggest learning, that is, the pos- 
sible association of increasing stimulation with 
stronger stimulation farther on in the course 
being pursued, though it is hardly to be ex- 
pected in the Protozoan. If the most in- 
telligent animal behaves like the simplest 
Protozoan and if pleasure and pain are the 
basis for intelligence, an analysis of this type 
of modification may yield data showing that 
the modification is not essentially different 
from associative memory. The graphs appear 
to be but a general statement of the gagging 
of the chick at the sight of a distasteful 
species of caterpillar which it has tried on an 
earlier occasion. V. E. SHELFORD 
UNIVERSITY OF ILLINOIS 
SCIENCE 
A Weekly Journal devoted to the Advancement of 
Science, publishing the official notices and pro- 
ceedings of the American Association for 
the Advancement of Science 
Published every Friday by 
THE SCIENCE PRESS 
LANCASTER, PA. GARRISON, N. Y. 
NEW YORK, N. Y. ; 
Entered in the post-office at Lancaster, Pa., as second class matter 
