The Experimental Method 9 
plays in the result unless he study the effects of each under 
different conditions that can be controlled. Little by little, in 
this way we can hope to gain a clearer insight into the condi- 
tions that, taken all together, produce the result. 
So much for the experimental method. It is pertinent to ask 
what is an experiment? If I cut an earthworm in two to see 
what will happen, have I performed an experiment? Perhaps 
not, for the actual performance of cutting the worm in two is 
not the essential point. The essence of an experiment is a trial 
or test, and the conditions are so arranged that an answer is ex- 
pected. If the worm is cut in two in order to study the physio- 
logical behavior of the two ends, as has been done in fact, with 
some interesting results, or in order to see what regenerates at 
the two cut ends, we have a distinct purpose in view, although no 
formulated problem. If we proceed farther and remove a 
definite number of segments in order to see how many come 
back, and then try to determine what conditions are involved 
in the results, we are clearly carrying out an experiment with a 
more definite aim. This illustration will serve to show that the 
most essential feature of an experiment is the anticipation of 
the results of a test. The operation may be so simple, and the 
conditions so little known, that to call the performance an 
experiment may easily expose one to the ridicule of those un- 
favorably inclined to the claims of experimental work. If the 
process is carried out with scarcely a thought as to its purpose, 
and in complete ignorance of all the conditions entering into 
the problem, it can scarcely be called an experiment at all. At 
most it is only a preliminary testing of possibilities. Much of 
the pioneer work in experimental zodlogy has necessarily been 
of this kind, and crude as such preliminary work must be, it 
should be looked upon only as the first step toward a further 
and more critical analysis. 
The carrying out of an experiment implies the formulation of 
a working hypothesis, and this usually presupposes some knowl- 
edge of the possible conditions that control the phenomena. 
The experimental work becomes more explicit and accurate the 
