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struments kept under medical observation (see p. 173); and in critical cases it is advisable to use a combination of both the cap and a second method, preferably quinine, either in the form of ointment or of a quinine pessary. But with an intelligent, careful woman, properly fitted and instructed how to use the cap, the cap alone without any chemical is in most cases safe and sufficient, unless the woman is "incorrigibly fertile" (see p. 61). The reason for the safety of the cap is that it prevents the sperm entering the uterus (sperms, it should be remembered, may live even as long as seventeen days) and therefore confines the spermatozoa to the vagina where the naturally acid secretions of a normal woman should destroy their vitality.

One of the greatest advantages of the cap is a psychological one, namely, that it offers the very minimum of interference with the romantic side of the sex act. In this respect it is best used alone, because the quinine pessary may intrude on the consciousness, partly owing to its excessive greasiness and partly from the smell of the cocoa-butter, but the cap if used alone can be inserted some hours before bedtime, can be safely left undisturbed for twenty-four or forty-eight hours, and can be removed at