PROTEIN.—A food-stuff which is distinguished by the fact that it contains nitrogen and is a tissue builder.
PROTOPLASM.—The living substance in the cells which compose our bodies.
PUBERTY.—Sexual maturity in human beings.
PUBIC BONES.—The part of the pelvis which forms an arch in front of the bladder.
PUERPERIUM.—The same as the lying-in period.
RETINA.—The innermost coat of the eye-ball and the one which receives visual impressions.
RICKETS.—A disease of infancy characterized by softening of the bones.
SECRETION.—The product of the activity of a gland.
SEDIMENT.—The material which settles to the bottom of any liquid.
SPERMATOZOON (plural spermatozoa).—The microscopic cell contributed by the male parent, which stimulates the ovum to begin its development.