Throughout history, and especially prior to the 20th century, there have been those who have held that sexual abstinence confers numerous health benefits. For males, lack of abstinence was thought to cause a reduction of vitality. In modern times, the argument has been phrased in biological terms, claiming that loss of semen through ejaculation results in a depletion of vital nutrients such as lecithin and phosphorus, which are also found at high levels in the brain. Conservation of the semen allegedly allows it to be reabsorbed back into the bloodstream and aid in the healthy development of the body. Along these lines, the noted German philosopher Friedrich Nietzsche spoke of the positive physiological effects of abstinence: "The reabsorption of semen by the blood ... perhaps prompts the stimulus of power, the unrest of all forces towards the overcoming of resistances ... The feeling of power has so far mounted highest in abstinent priests and hermits" (quoted by Walter Kaufman in his classic, "", p. 222). Before the "sexual revolution" of the 1960s, it was commonly believed by members of the medical profession that numerous mental and physical diseases in men were caused primarily by loss of nutrients through seminal discharge, and that the deliberate conservation of this substance would lead to increased health, vitality, and intellectual prowess. This also applied to masturbation, which was also thought to lead to bedwetting and hairy palms.