296 The Senses of the Lower Animals. [July, 
However this may be, enough has been advanced to show 
that the sense of sight even in animals whose eyes are per- 
fectly homologous with our own may supply them with 
information which to us is inaccessible. 
Very similar is the case with the sense of hearing. The 
human auditory nerves are sensitive to a certain range of 
sounds, and no further. Vibrations either more or less 
rapid do not to us break silence. But we have no right to 
infer that they may not be distinctly heard by other animals. 
That they actually are perceived has in many cases been 
shown by direCt experiment with the instrument known as 
“ Gabon’s whistle.” Upon this a line is marked indicating 
the usual upper limit of the sense of sound in the human 
species, and corresponding to from 41,000 to 42,000 vibra- 
tions per second. But when this limit is passed, and when 
the whistle no longer produces a sound appreciable to man, 
several animals still indicate by their movements that they 
hear. Cats, birds, and some inseCts seem decidedly more 
affeCted by high than low tones. In Sphinx Ligustri and 
Metopsilis Elpenor the reverse is said to hold good. In 
short, we may conclude that many living creatures recog- 
nise sounds which utterly escape our ears, and thus receive 
through the medium of the sense of hearing impressions 
perhaps more varied and numerous than, or at least different 
from, our own. A wonderful instance of combined delicacy 
and discrimination in the recognition of sounds is shown by 
deer in America. It has been repeatedly observed that if 
one of these animals is browsing in a forest in windy 
weather, when the trees are groaning and creaking to the 
blast, and branches are occasionally snapping, yet, if amidst 
all this uproar a rotten twig happens to crack beneath the 
foot of an approaching hunter, the animal at once stops 
feeding, gazes carefully around in every direction, and re- 
mains unusually suspicious often for hours. The ears 
which discriminate so nicely must be uncommonly sen- 
sitive. 
We come now to scent, which is to civilised man probably 
the vaguest of all the senses in its indications. It may 
yield us a certain amount of pleasure and a very palpable 
amount of annoyance. It may warn us against eating, 
touching, or approaching certain noisome or putrescent sub- 
stances ; but in this respeCt its warnings are not trustworthy. 
It is far from being proved, and indeed is highly doubtful, 
that the stage of animal or vegetable decomposition most 
offensive to our nostrils is the one which presents the greatest 
amount of danger. The most deadly atmosphere of the 
