THE SKIN. 
339 
contain more than forty rows, and each row more than sixty 
pairs, making hi all about 5,000 individual papillae in a single 
square inch of skin. They are not, however, equally well de- 
veloped in all parts of the body, being' nearly absent on the 
back, where, however, the cutis is tolerably dense, for there is 
no relation between its thickness and the development of these 
papillae ; on the tongue, for instance, the cutis is extremely thin, 
and yet the papillae there are larger than in any other part of 
the body, and not that alone, but so thin also is the cuticle here 
that the individual papillae are seen, giving that peculiar rough- 
ness to the tongue which is found to a certain degree in man, 
and to a very high degree in some of the lower animals, as the 
ox and the cat tribe. 
Professor E. H. Weber instituted some delicate experiments 
on the sense of touch with the view of ascertaining its relative 
delicacy in different parts of the body, the method he adopted 
being to ascertain at what distance from each other two points 
of contact ceased to be perceived as one only, and were dis- 
tinctly recognised as two. For this purpose he slightly blunted 
the points of a pair of compasses -with sealing-wax and then 
applied them to different parts of the body. He then found 
that on the pulp or soft part of the tip of the fingers the 
points were perceived as two when separated only l-36th part 
of an inch, while on the middle of the arm and thigh they had 
to be separated as much as inches. He also found, as might 
be expected, that they were more readily perceived as two 
when placed across the direction of the branches of the nerves 
than when placed parallel to their branches. A well-known fact 
is that the sensations of heat and cold, which of course apper- 
tain to the sense of touch, are to a certain degree relative ; that 
is to say, that if we place one hand in warm water and the 
other in cold, and then plunge both into a vessel containing 
water at an intermediate temperature, this will appear hot to 
the hand which has been in the cold water and cold to the 
other. Weber has also shown a very curious fact, namely, 
that if both hands are plunged into water of the same tempera- 
ture without previous preparation it will seem warmer to the 
left hand than to the right. To obtain an accurate result this 
experiment ought to be performed with the eyes blinded, and 
in ignorance of the relative temperature of the water in the 
two vessels, so as to remove the influence of reason or imagi- 
nation. Some other curious phenomena regarding the sense 
of touch have also been found to exist, such as that' if two of 
the fingers be crossed^nd then a single small object, as a pea, 
be placed between them, the mind will appreciate it as two 
objects ; or, again, that if two points, as of a pair of compasses, 
be applied to the skin at a fixed distance, they will feel as if 
