552 ANIMAL PHYSIOLOGY. 
In man special forms of end-organs are found scattered over 
the skin, mucous and serous surfaces of the body, such as 
Pacinian corpuscles, touch-corpuscles, end-bulbs, etc.: while in 
lower forms of vertebrates many others are found in parts 
where sensibility is acute. There seems to be little doubt that 
these are all concerned with the various sensory impulses that 
originate in the parts where they are found, but it is not pos- 
sible at present to assign definitely to each form its specific 
function. 
It has been contended that the various specific sensations 
of taste, as bitter, sweet, etc., are the result of impulses con- 
veyed to the central nervous system by fibers that have this 
function, and no other; and a like view has been maintained 
for those different sensations that originate from the skin. 
For such a doctrine there is a certain amount of support from 
experiment as well as analogy; but the more closely the subject 
is investigated the more it appears that the complexity of our 
sensations is scarcely to be explained in so simple a way as 
many of these theories would lead us to believe. Whether 
there are nerve-fibers, with functions so specific, must be re- 
garded as at least not yet demonstrated. 
Let us now examine into the facts. What are the different 
sensations, the origin of which must be in the first instance 
sought in the skin, as the impulses aroused in some form of 
end-organ or nerve-termination ? 
Suppose that one blindfolded lays his left hand and arm 
on a table, and a piece of iron be placed on the palm of his 
hand, he may be said to be conscious of the nature of the sur- 
face, whether rough or smooth, of the form, of the size, of the 
weight, and of the temperature of the body; in other words, 
the subject of the experiment has sensations of pressure, of 
tactile sensibility, and of temperature at least, if not also to 
some extent of muscular sensibility. But if the right hand be 
used to feel the object its form and surface characters can be 
much better appreciated; while, if the body be poised in the 
hand, a judgment as to its weight can be formed with much 
greater accuracy. The reason of the former is to be sought in 
the fact that the finger-tips are relatively very sensitive in 
man, and that from experience the mind has the better learned 
to interpret the sensory impulses originating in this quarter; 
which again resolves itself into the particular condition of the 
central nerve-cells associated with the nerve-fibers that convey 
inward the impulses from those regions of the skin. Mani- 
