Swimming is a most valuable accomplishment, combining bathing and exercise.  Bathing of the feet should never be neglected.  Cleanliness of the hair is also another matter requiring strict attention, especially in children.

248.  Care of the Hair and Nails.  The hair brush should not be too stiff, as this increases the tendency towards scurfiness of the head.  If, however, the hair is brushed too long or too hard, the scalp is greatly stimulated, and an increased production of scurf may result.  If the head be washed too often with soap its natural secretion is checked, and the scalp becomes dry and scaly.  The various hair pomades are as a rule undesirable and unnecessary.

The nails should be kept in proper condition, else they are not only unsightly, but may serve as carriers of germs of disease.  The nails are often injured by too much interference, and should never be trimmed to the quick.  The upper surfaces should on no account be scraped.  The nail-brush is sufficient to cleanse them without impairing their smooth and polished surfaces.

[Illustration:  Fig. 107.—­Longitudinal Section of a Finger-Nail.

  A, last phalanx of the fingers;
  B, true skin on the dorsal surface of the finger;
  C, epidermis;
  D, true skin;
  E, bed of the nail;
  F, superficial layer of the nail;
  H, true skin of the pulp of the finger.
]

249.  Use of Clothing.  The chief use of clothing, from a hygienic point of view, is to assist in keeping the body at a uniform temperature.  It also serves for protection against injury, and for personal adornment.  The heat of the body, as we have learned, is normally about 98-1/2 degrees F. This varies but slightly in health.  A rise of temperature of more than one degree is a symptom of disturbance.  The normal temperature does not vary with the season.  In summer it is kept down by the perspiration and its rapid evaporation.  In winter it is maintained by more active oxidation, by extra clothing, and by artificial heat.

The whole matter of clothing is modified to a great extent by climatic conditions and local environments,—­topics which do not come within the scope of this book.

250.  Material Used for Clothing.  It is evident that if clothing is to do double duty in preventing the loss of heat by radiation, and in protecting us from the hot rays of the sun, some material must be used that will allow the passage of heat in either direction.  The ideal clothing should be both a bad conductor and a radiator of heat.  At the same time it must not interfere with the free evaporation of the perspiration, otherwise chills may result from the accumulation of moisture on the surface of the body.

Wool is a bad conductor, and should be worn next the skin, both in summer and winter, especially in variable climates.  It prevents, better than any other material, the loss of heat from the body, and allows free ventilation and evaporation.  Its fibers are so lightly woven that they make innumerable meshes enclosing air, which is one of the best of non-conductors.