908. _Why have we nails at our fingers' ends?_
Because they give _firmness to the touch_, and enable us to apply the extremities of the fingers to many useful purposes for which they would otherwise be unfitted. They enable us to _press the tips of the fingers_, where the highest degree of sensitiveness prevails, so as to bring _the largest amount of nervous perception_ into the sense of touch.
909. _Why do white spots occur upon the nails?_
Because the vascular surface underneath is attached to the horny texture of the nail; but by knocks and other causes, the nail sometimes _separates in small patches from the membrane_ below, and becomes _dry and opaque_.
910. _Why is there a circular line of whitish colour at the root of the nail?_
Because there the nail is _newly formed_ by the vascular substance out of which it grows, and has not yet assumed its proper horny and transparent nature.
Because the blood-vessels that supply its surface are so very fine that they do not admit the _red corpuscles_ of the blood.
912. _Why does the eyeball sometimes become blood-shot?_
Because, under exciting causes of inflammation, the _blood-vessels become distended_, and the red corpuscles enter, producing a net-work of red blood-vessels across the white surface of the eye.
Because the lips are formed of the _mucous membrane_ that lines the body internally, and covers the surface of most of the internal parts. This membrane contains a great number of minute red vessels, which give softness and moisture to the surface. A very beautiful illustration of the softness, moisture, and delicate colour of the mucous membrane is afforded by turning up and examining the under surface of the upper eyelid.
[Verse: "Hast thou not known, hast thou not heard, that the everlasting God, the Lord, the Creator of the ends of the earth, fainteth not, neither is weary? there is no searching of his understanding"--ISAIAH XL.]
914. _Why do delicate persons look pale and languid?_
Because, generally from the want of exercise and fresh air, their blood is deficient of the healthy proportion of _red corpuscles_.
915. _Why does exercise and fresh air impart to healthy persons a red and fresh appearance?_
Because the redness of the blood is due to the _amount of oxygen_ which it contains, and air and exercise _oxygenise_ the blood, and diffuse it throughout the system.
