70 PHYSIOLOGY OF THE HUMAN BODY. 
blood-vessels in the chest, abdomen, and pelvis. This system of ganglia, 
which seems to regulate, almost independently of the will, the processes 
of digestion, circulation, and respiration, its influence being little, if at all, 
dependent on the brain, has therefore been called the nervous system of 
organic life, or the sympathetic system. 
When an impression is made on any of the nerves of the body, it 
carries this impression to the brain, and causes a sensation. The impres- 
sions made on the nerves are not all the same, however ; the different 
kinds of sensations thus caused in the brain are classed into those of 
‘Touch, Taste, Smell, Hearing, and Sight. 
Touch. 
The special seat of the sense of touch is the surface of the skin. The 
epidermis, it will be remembered, is not sensitive ; the parts really sensi- 
tive are the papille, on the outside of the cutis, or true skin. It is to 
these papille that the nerves are distributed on which the impressions are 
made by the various objects touched, and by which these impressions 
are conveyed to the brain. They are largest and most numerous on the 
palms of the hands and the soles of the feet ; on the back and outside of 
the limbs they are much less numerous. ‘They are small elevations, 
usually conical or club-shaped. Where the sense is acute, however, they 
have several points, from which they are called compound papilla. The 
epidermis is also particularly thin on those parts where the sense of touch 
is acute, as, for example, on the tips of the fingers and lips. The papille 
are arranged in rows, and it is these rows that cause the fine ridges in 
the epidermis seen on the palm and fingers. 
The simplest idea conveyed to our minds on touching any object is 
resistance ; by the degrees of resistance we meet on touching a hody, we 
judge whether it be hard or soft; and on moving the fingers over the 
surface, the impression made on the papille informs us whether it be 
smooth or rough. Were it not for our faculty of moving the hands over 
bodies, indeed, the sense of touch would have been of far less value than 
it is; for without that faculty we could not have formed our ideas of 
form and ‘size. 
The seat of the sense of taste is principally, though not exclusively, on 
the surface of the tongue, and the arrangement is very similar to that 
described for Touch. The nerves of taste, like those of touch, are dis- 
tributed to papille, in the outer membrane of the tongue. One remark- 
able difference in the arrangement of the papille of the tongue is that, 
instead of being concealed in its skin, they project and form the rough- 
ness of the tongue, being covered of course by the outer coat. There are 
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