They may also cause other trouble; for instance, if your collar chafes the back of your neck, and to relieve the itching you rub it a little too hard with your finger, your nail may scratch the skin; and if it be blackened with infectious dirt, this may get into the little scratch and give rise to a boil, or a festering sore.
How to Clean the Nails.

This cleaning of the nails, however, must be done carefully and gently; for, if too harsh methods are used, the delicate skin on the under surface of the nail will be torn, the nail will be roughened or split, the dirt will work in just that much deeper next time, and the germs in it may set up inflammations under the nail.
For this reason it is best not to use a sharp-pointed knife in cleaning the nails, but a blunt-pointed nail cleaner, such as can be bought for a few cents at any drug store, or such as many pocket-knives are now provided with.

It is also best to trim the nails with a file or with scissors, instead of a knife, as the latter may split or tear the nail, or cut down to the quick.

Before any of these are used, the nails should be thoroughly softened in warm water, and scrubbed with a moderately stiff nailbrush, such as should be kept on every washstand.
It is also best not to push back the fold of skin at the base of the nails, with instruments of any sort; or indeed, with anything harder than the ball of the thumb or finger.

This fold protects the delicate growing part, or root, of the nail; and if it is shoved back too vigorously, the root may become exposed, or even inflamed and infected, and cause one of those extremely irritating little sores known as a "hangnail." DISEASES AND DISTURBANCES OF THE SKIN Their Chief Causes.