If circumstances are favorable for the performance of the sexual act satisfactorily, the constantly-increasing desire is complied with; if, however, conditions are unfavorable, inhibitory concepts occur, overcome the sexual longing, and prevent the sexual act. To civilized man cultivation of a readiness with ideas which inhibit sexual desire is necessary and distinctive. The moral freedom of the individual, and the decision whether, under certain circumstances, excess, and even crime, be committed or not, depend, on the one hand, upon the strength of the instinctive concepts and the accompanying organic sensations; on the other, upon the power of the inhibitory concepts. Constitution and, especially, organic influences have a marked effect upon the instinctive impulses; education and cultivation of self-control have a decisive influence on the opposing concepts. The exciting and inhibitory powers are variable quantities. Over-indulgence in alcohol in this respect is very fatal, since it awakens and increases libido sexualis, while at the same time it reduces moral resistance. THE ACT OF COHABITATION.[27] The essential condition for the man is sufficient erection. Anjel (_Arch. für Psych._, viii, H. 2) calls attention to the fact that in sexual excitement the erection centre is not alone influenced,—the nervous excitement is distributed to the entire vasomotor system of nerves. The proof of this is the turgescence of the organs in the sexual act, injection of the conjunctiva, prominence of the eyes, dilatation of the pupils, and cardiac palpitation (resulting from paralysis of the vasomotor nerves of the heart, which arise from the cervical sympathetic, and the consequent dilatation of the cardiac arteries, and the increased stimulation of the cardiac ganglia induced by the consequent hyperæmia of the cardiac walls). The sexual act is accompanied by a pleasurable feeling, which, in the male, is conditioned by the passage of semen through the _ductus ejaculatorii_ to the urethra, caused by sensory stimulation of the genitals. The pleasurable sensation occurs earlier in the male than in the female, grows rapidly in intensity until the moment of commencement of ejaculation, reaching its height in the instant of free emission, and disappears quickly _post ejaculationem_. In the female the pleasurable feeling occurs later and comes on more slowly, and generally outlasts the act of ejaculation.