THE HUMAN HAND ; A SCHOOL LESSON 31 



be more accurately ascertained in the following way. 

 Take a hair-pin, or a pair of blunt-pointed compasses, and 

 open the points until they can just be distinguished as 

 separate by the finger-tip. Read off the distance of the 

 points on a scale, and then make the same trial with the 

 back of the hand. I have just tried this, and find that 

 the back of the hand, in order to distinguish the points 

 as separate, requires them to be distant more than fourteen 

 times as far as is requisite in the case of the finger-tip. 

 There are parts of the skin (on the back, for instance) 

 which are less sensitive than any part of the hand. 



The finger-tip has a special structure, which is known 

 to be closely connected with the sense of touch. The old 

 naturalist and anatomist, Malpighi, made this discovery, 

 and he tells us how he was led to it. Examination of the 

 tongue of the ox showed him that the upper surface, 

 which comes in contact with the food, is beset with 

 numerous papillae. Some of these (for he was able to 

 distinguish three kinds) had a special nervous supply, and 

 these, he thought, were particularly concerned with the 

 sense of taste. The lips, being employed by the ox to 

 investigate its food, might be expected to show papillae 

 too. Malpighi stripped off the epiderm ot the lip, and 

 found the deep layer of the skin crowded with them. The 

 human hand next suggested itself for inquiry. Examining 

 the tip of the finger with a lens, he made out the ridges, 

 and what he rightly took to be the sweat-pores on them. 

 Here again he satisfied himself by microscopic examina- 

 tion that the deep layer abounded in minute papillae, and 

 now he felt convinced that the sense of touch resides in 

 the papillae of the skin. You can form a fair notion of 

 these papillae, if you can persuade some companion to 

 allow you to look at the surface of his tongue with a 

 magnifying glass. On the tongue the papillae are covered 

 with a very delicate skin, which does not conceal their 

 shape, but on the finger-tip the epiderm is comparatively 

 thick, and fills up the depressions between the papillae. 



