The fact of sexual need in man and animal is expressed in biology by the assumption of a "sexual impulse." This impulse is made analogous to the impulse of taking nourishment, and to hunger. The sexual expression corresponding to hunger not being found colloquilly, science uses the expression "libido."
Popular conception makes definite assumptions concerning the nature and qualities of this sexual impulse. It is supposed to be absent during childhood and to commence about the time of and in ...