FACULTIES OF THE MIND. OT 
in the case of herbivorous animals, there are very marked 
differences in the species of the same genus, as between the 
ox and the buffalo,—the horse and the zebra. 
IV. On THE MUTUAL CoMMUNICATION OF FEELING. 
It is necessary, for the exercise of the various intellec- 
tual, but especially of the active powers, that animals should 
be able to make known to others, the impressions which 
they receive, or the propensities which they feel. In this 
kind of mutual communication, there are various ways in 
which the object is accomplished. The ear is subservient 
to the purpose in some cases, the eye, and even the touch, 
in others. The method of holding intercourse by means of 
sounds, being the most general, first merits our attention. 
a. The communication of Feeling by means of Sounds 
addressed to the Ear.—Among animals which employ 
sounds as the medium of expressing their thoughts, those 
only possess what is termed a voice, which breathe by means 
of lungs. The voice is generated, by the air expelled 
from the lungs passing through the wind-pipe and mouth, 
and exciting those vibrations in these parts which produce 
sound. ‘The variety of structure exhibited by the wind- 
pipe and mouth, on which the different conditions of the 
sounds depend, will afterwards come under our more par- 
ticular examination. We are at present considering the 
voice as an auxiliary power of the mind. Regarded in this 
light, the sounds which are uttered in the communication of 
feeling, are either natural or acquired. 
Every animal possessed of a voice, has the power of 
emitting those sounds which may be termed its Natural 
Language. These sounds, immediately after birth, are 
exclusively occupied in expressing the presence of pain, or 
the conditions of the instincts of food and temperature. 
