On the fifteenth day and again on the seventeenth
unmistakable responses to sound were observed; on
the eighteenth the responses were indefinite, and
on the nineteenth none were obtained. I continued
the tests up to the twenty-eighth day without further
indications of hearing.
Certain individuals in this litter reacted so vigorously
to the loud sound produced by striking the steel bar
a sharp blow and also to the Galton whistle, during
a period of five days, that I have no hesitation in
saying that they evidently heard during that period
of their lives. Other members of the litter seemed
to be less sensitive; their reactions were sometimes
so indefinite as to leave the experimenter in doubt
about the presence of hearing.
A third litter, which developed very slowly because
of lack of sufficient food, first showed unmistakable
reactions to sound on the twenty-first day. On
this day only two of the five individuals reacted.
The reactions were much more obvious on the twenty-second
day, but thereafter they became indefinite.
Still another litter, which consisted of one female
and four males, began to exhibit the quick, jerky
movements, already mentioned, on the fourteenth day.
On the morning of the fifteenth day three members of
the litter definitely reacted to the tone of the steel
bar, and also to the hammer blow when the bar was
held tightly in the hand of the experimenter.
My observations were verified by another experimenter.
Two individuals which appeared to be very sensitive
were selected for special tests. Their reactions
were obvious on the sixteenth, seventeenth, and eighteenth
days; on the nineteenth day they were indefinite,
and on the twentieth none could be detected.
Some individuals of this litter certainly had the
ability to hear for at least five days.
A sixth litter of four females and two males first
gave indications of the change in behavior which by
this time I had come to interpret as a sign of the
approach of the period of auditory sensitiveness, on
the seventeenth day. I had tested them almost
every day previous to this time without obtaining
evidence of hearing. The tests with the steel
bar and the Galton whistle were continued each day
until the end of the fourth week without positive
results. To all appearances the individuals of
this litter were unable to hear at any time during
the first month of life.
Practically the same results were obtained with another
litter of four females. The change in their behavior
was obvious on the eighteenth day, but at no time
during the first month did they give any satisfactory
indications of hearing.
In the accompanying table, I have presented in condensed
form the results of my auditory tests in the case
of twelve litters of young dancers.
PERIOD OF AUDITORY REACTION IN YOUNG DANCERS
PARENTS No. in Change in Ears Auditory
Reactions
Litter
Behavior Open Appear Disappear
