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gentlemen. In a few of these experiments the Count zu Castell, Count R.
von Matuschka and Mr. Schillings undertook the role of questioner. Where
these are not mentioned in the results here published, I myself did the
questioning.

With regard to the number of experiments and their performance, the
following precautions were observed. A sufficiently large number of
tests was made in each series in order to obviate the possibility of the
contention that the horse's errors were due to chance. The conditions of
experimentation were such that the further contention that he happened
to be tired or otherwise indisposed, whenever the reactions seemed to be
inadequate, could not be offered. The possibility of confusing the horse
by means of unwonted conditions also had to be avoided. For this reason
it was necessary to alternate the trial in which procedure was with the
knowledge of the answer on the part of the questioner, with the trial in
which the procedure was without such knowledge. Such precautions had
hitherto been neglected, and therefore those negative results which had
been occasionally obtained in single trials, could not claim objective
validity, even though the persons making the tests were subjectively
convinced.

The course of the experiments was determined by the nature of the
problem itself. By means of a very simple test it was possible to
discover whether or not Hans was able to think independently. He was
confronted with problems in which the procedure was without knowledge of
the answer on the part of the questioner. If under these conditions he
could respond with the correct answer--which could be the result of a
rational process only--then the conclusion that he could think
independently, was warranted. The examination would be closed and Mr.
von Osten would be justified in all he claimed for the horse. If,
however, Hans should fail in this test, then the conclusion that he
could think was by no means warranted, but rather the inference that he
was dependent upon certain stimuli received from the questioner or the
environment. Further investigation would be for the purpose of
discovering the nature of these stimuli.

To ascertain by means of which sense organ or organs the horse might
receive these necessary stimuli, the method of elimination was employed.
We began by excluding visual stimuli by means of a pair of very large
blinders. Should this investigation be without results, then we would
proce