ed to test the sense of hearing. The elimination of auditory
stimulations would be more difficult, because ear-caps or the closing of
the passage by means of cotton would not give sufficient assurance that
the sound-waves were being interrupted, even if the horse were docile
enough to suffer these appliances. Thereupon would follow the testing of
the sense of smell and of the skin-senses. And finally there might be
involved another still unknown sense, such as seems to exist in the
lower animal-forms. The reader therefore can readily see that the
investigation might possibly have become very complex, and that the
investigator had to be prepared for all of these possibilities.

The results of the experiments and the essential circumstances under
which they were conducted, were in every case recorded immediately.

It goes without saying that in the final formulation of the results, all
values--including those which were not consonant with the majority--were
to be used.

B. EXPERIMENTAL RESULTS

During the course of these experiments Hans wore his accustomed
trappings, i. e., a girdle, light headgear and snaffle, and he either
stood alone, untied, or was held loosely by the bridle either by the
questioner or (though only in a few instances) by his attendant. The
questioner always stood to the right of the horse, as Mr. von Osten had
been accustomed to do. As reward for correct responses Hans received
from the questioner[G]--and from him only--a bit of bread or carrot, and
at times also a square of sugar. Never was a whip applied. From time to
time the horse was led about the courtyard or was allowed to run loose
in order to secure the needful respite. Besides myself there was usually
present Prof. Stumpf and Dr. von Hornbostel, who kept the records, and
frequently also Mr. von Osten. Several times I worked alone with the
horse. The results obtained in the horse's stall were in no respect
different from those got in the course of the experiments carried on in
the courtyard. Whenever a doubt arose as to the number of taps made by
the horse (though this did not frequently occur), then the series in
question was immediately repeated.

[Footnote G: The expressions _questioner_ and _experimenter_ are used
interchangeably in this treatise.]

In this report of the results of our experiments, the reader must bear
in mind that it was impossible to adhere to that order and distribution
of tests which we are wont to re