372 
quently necessary to prove that the response 
is due to “constant intensity,” 7. e., that the 
orienting stimulus acts continuously and is 
not due to changes of intensity. This I have 
been unable to do in any case whatsoever in 
spite of persistent efforts, and as far as | am 
aware it has never been done. It was owing 
to this that I made the statement that the 
orienting reactions in Ameba do not support 
the idea connected with the theories of Loeb 
and Verworn that “a constant intensity pro- 
duces a constant directive stimulation” 
quoted by Holmes. His failure to “ under- 
stand the pertinency of this criticism,” as he 
says, indicates that he did not understand 
these theories. 
The second case which Holmes cites in sup- 
port of his contention that my investigations 
lend support to Loeb’s theories shows even 
more clearly than the first that he did not 
understand these theories. After admitting 
that in case of the orientation in Arenicola 
larve “the question remains open whether 
the stimulus is produced by the direct action 
of light on the sensitive surface of the animal 
or by changes in intensity of the stimulus 
caused by the lateral movements of the body ” 
he maintains that orientation in these ani- 
mals is in accord with “the well-known 
theory of Loeb” because it is “ apparently 
automatically . . . regulated” (italics mine). 
Thus admitting that it can not be proved that 
orientation is due to continuous stimulation, 
he would make automaticity the criterion of 
Loeb’s theories, ignoring all other distinguish- 
ing characteristics found in them. 
It is true that Loeb often uses the term 
automatic in discussing reactions which he 
calls tropisms, but what does it mean? Auto- 
matic means mechanically self-acting, that is, 
involuntary. In accord with this definition 
are there any reactions whatsoever in Arent- 
cola or in any other organism below man 
which are not automatic? Investigations and 
speculations without end have been directed 
toward the solution of this very problem and 
yet there are few bold enough to say that it 
has been solved for even a single case. Of 
what possible value then can automaticity be 
SCIENCE 
[N.S. Von. XXXV. No. 897 
as a distinguishing characteristic of a group 
of reactions supposed to be specific, and what 
bearing can the statement that the orienting 
reactions of Arenicola larve are apparently 
automatic have on the mechanics of orienta- 
tion (tropisms) of this or any other organ- 
isms ? 
It is precisely such loose and uncritical 
statements as Holmes has made regarding 
Loeb’s theories with the suggestion of such 
impossible criteria as automaticity that have 
brought the discussion centering around the 
term “tropism” to the chaotic condition in 
which it is found at present. To show that a 
reaction is in accord with any one of Loeb’s 
three theories it must of course be demon- 
strated that it is in harmony with all of its 
characteristics, not merely with one of them, 
as my critic seems to imply. It must be 
proved, among other things, as demonstrated 
above, that the external stimulating agent acts 
continuously in the process of orientation. 
Until this is done Loeb’s statement that 
orientation is a function of the constant. in- 
tensity must be classified as anthropomorphic 
speculation. And if the statement of my 
critic is true, that my investigations afford 
about as good support as has been furnished 
for Loeb’s theories, it is evident that they rest 
on extremely nebulous foundations. If 
Holmes can produce a single case in which he 
can prove that orientation occurs in accord 
with any of these theories I trust that he will 
do so in answer to my reply to his criticism. 
My discussion concerning certain theoretical 
views held by Jennings brings out the most 
caustic criticism that Holmes has to offer. 
He quotes the following paragraph from my 
book: 
Every step in the development of the theory 
[Jennings] is supported by numerous experimental 
facts and all seems to fit what is known concerning 
the reactions of organisms. Reactions, according 
to this theory, are, as stated above, primarily due 
to physiological states. External agents ordinarily 
produce reactions through the effect they have on 
these states. By the application of this idea all 
the different phenomena connected with reactions 
to light as summarized at the beginning of this 
chapter can be accounted for. 
