24 ‘PHYSIOLOGY AND ANATOMY. 
selves with a pin or needle, we draw blood, how slight soever 
the wound, because the two outer skins are so thin and deli- 
cate that the third feels the touch instantaneously, and the 
nerves of feeling being so numerous, pass off to the spinal 
marrow in the spine, and thence to the;,brain or mind, so 
that we feel every touch. There will frequently be white 
spots on the bodies of negroes, occasioned by a wound inthe — 
third skin, and the removal of some of the coloring matter 
on the second, which does not grow again. There are little ~ 
cells or pores-on the outer surface, which permits the sweats 
or perspiration to pass through ; and in this way many dis- 
eases which lurk about our bodies, are continually passing | 
off. This enables us to endure the very great heat of sum- 
mer ; for this constant perspiration produces a moisture which 
eotle the air. 
—_ eam isa a double organ, and hens in the middle of the 
