Page:Personal Beauty and Racial Betterment.djvu/49

Rh goes with the full bloom of sexual vigor, when the human organism is at its perfect development for the perpetuation of the species. This is so obvious that it would be superfluous to discuss it further.

7. Muscular tonicity. The voluntary muscles of the body, i. e., the muscles of the face, scalp, trunk, arms and legs, are kept in a condition of tonus, by nerve currents constantly supplied to them by the motor nerves. Tonus is a state of partial contraction, which constitutes the readiness for action of the muscle. If the motor nerve trunk which supplies any voluntary muscle be severed, the muscle at once becomes flabby. The tonus does not depend entirely on the nerves which stimulate the muscle. In order to be stimulated, the muscle must be in the appropriate chemical condition to receive the stimulus, and this chemical condition is dependent not only on the general metabolic conditions of nutrition, fatigue and rest, but also on the specific actions of hormones produced by several of the internally secreting glands, notably the adrenalin produced by the adrenal glands.

In case of injury or disease affecting certain parts of the nervous system, certain muscles become flabby. In case of general flabbiness, it is of course not evident immediately whether the primary defect is in the nervous system, or in the metabolism of the body. In any case,