he other hand, all stimulations (whether
mediate or immediate) which are selected without especial regard to
the anatomy or physiology of the horse, and bear no inseparable
relation to the thing to be done but are associated with it at the
will of the trainer. The rider's use of reins, and control by means
of leg-pressure and manner of sitting in the saddle, and the
driver's use of the lines,----all these, then are aids. A simple
pull at the reins, however, is not an aid, but a sign. The whip may
be used for giving signs as well as aids,----the latter, when it
does the work of the spur or of the pressure with the knees, as is
the case with ladies' riding-horses and in lunging. All calls and
all movements of the hand or head merely, on the part of the
trainer, are to be regarded as signs.]

Such unequivocal results, however, were only obtained after we had
provided blinders of sufficient size (15 x 15 centimeters). Mr. von
Osten believing that the horse would not suffer these to be applied, had
at first proposed other measures. He held a slate before his face. Some
of the horse's responses were right, others wrong. The tests were
repeated and were successful as long as I, myself, held the slate before
my face, but not a single one of the responses was correct when another
would attempt to hold the slate before me. Mr. von Osten then brought
forth a kind of bolster which he fastened on the right side of the
horse's face,--the side which was turned toward the questioner. But this
also gave uncertain results. Finally he agreed to apply blinders. But
these were much too small and projected at a great angle from the head
(Mr. von Osten had cut the straps, for he thought they worried the
animal). The result was that only the posterior part of the horse's
normal field of vision was obstructed. Therefore, one could never be
quite sure whether Hans, who--it will be borne in mind--made every
attempt to see the questioner, had not perhaps after all been able to
peer over the edge of the blinder. The number of "undecided" tests,
therefore, became very great. Of 108 tests, only 25 could be placed in
the category of "not seen", 44 in the "seen", and 39, i. e., a third of
the total, in the "undecided." The percentage of correct answers for
these three categories were, respectively: 24%, 82% and 72%. Here we
have once more approximately the same ratio between the categories of
"seen" and "