170 PHILOSOPHY OF ZOOLOGY. 
effects produced on their skin by the air. These may arise 
from the resistance of that fluid, or other causes with which 
we are but imperfectly acquainted. Bats appear to possess 
this exquisite sensibility of touch, independent of habit or 
experience. SpaLLANZAN1 has observed these animals, 
even after their eyes had been destroyed, and ears and _nos- 
trils shut up, fly through intricate passages without strik- 
ing against the walls, and dexterously avoid cords and lines 
placed in their way. The expanded membrane of their 
wings is probably the organ which, in such cases, receives 
the impressions produced by a change im the resistance, mo- 
tion, or perhaps temperature of the air. The susceptibility 
of being acted upon by these agents, which exercise a feeble 
influence over us, is a condition natural to these animals, 
and necessary to enable them to find their way in the dark 
caverns in which they dwell. It cannot therefore be re- 
garded as one of those resources employed in time of need, 
in the case of bats, although it appears to be such in 
blind people. Man naturally moves but little in the dark, 
so that he does not require such susceptibility. It is, how- 
ever, fortunate that his body is susceptible of acquiring it 
in the time of need. 
The sense of touch appears, in man, to be able to obtain 
nearly all the information, with regard to external objects, 
which it is capable of receiving. In a few instances, the 
Jower animals surpass us in the delicacy of this sense, as the 
bat, which is warned, indirectly, by its aid, of the presence 
of bodies, previous to coming in contact with them. The 
feelers of insects are likewise better adapted for exploring 
the condition of the surface of bodies, than any organ 
which we possess. But, in all these cases, the sensibility of 
touch is limited to particular qualities, or confined within 
narrow bounds. The human hand, on the contrary, by its 
