It is sufficient that we find in the sexual impulse two very well marked constituents, so intimately connected as to seem but one; and yet so easily, separable as to make, as a writer says, "two distinct stages in the same process:"* a first Btage, in which, under simultaneous external and internal stimuli, images of a voluptuous character are formed in the mind, the impulses of desire, love, expectancy, awakened, and the sexual apparatus engorged with blood; and a second Btage, in which the sexual explosion occurs as the culmination of sexual excitement, being succeeded by exhaustion, and a more or less deep sense of organic relief.' The Erst stage may exist without the second; but the second cannot exist without the first.