Certain definite hygienic rules must now be prescribed. First of all, the strictest cleanliness must be observed, not only in the intervals, but also during menstruation. The prejudice against changing the under linen during the flow must be overcome, and care must be taken that at this time the external genitals are washed twice daily with water at a temperature of 26° C. to 28° C. (about 80° F.), and a wad of absorbent cotton-wool or a piece of clean linen (sponges are not to be used for this purpose); any article of underclothing that becomes soiled with blood must be changed. Most useful are the so-called “sanitary towels,” made of sterilized absorbent cotton-wool, fastened to a linen band which surrounds the waist, or simple pads of absorbent material may be used, kept in place by means of a bandage. During menstruation, full baths, warm or cold, are to be avoided, likewise long walks, riding, long journeys by rail, gymnastics, with or without apparatus, skating, lawn tennis, and bicycling; dancing, above all, must be prohibited, since it involves a combination of several noxious influences—the very active movement, which produces hyperæmia of the genital organs, sexual excitement, loss of sleep, long hours spent in close rooms, prolonged voluntary retention of urine, and the risk of a chill. Singing, also, must be discontinued during menstruation, since otherwise an injury to the voice is very likely to result. A certain limitation in respect of physical and mental activity is indicated as a general precautionary measure during menstruation, but this measure must not be pushed to excess, so that the habit is acquired of resting completely during the period, passing the days on a sofa. The favorite practice, in cases of scanty menstruation, of taking hot foot-baths is to be rejected. At the conclusion of each menstrual period, however, a tepid bath should be taken. The knowledge we have now acquired of the rhythmical “menstrual wave” process (see p. 19 _et seq._) points to the practical conclusion that the physician should not direct his attention to the actual menstrual period only, but also, and more than has hitherto been customary, to the premenstrual period, in which temperature, blood-pressure, and excretion of urea attain their acme; especially should this be done, with the aim of prescribing suitable hygienic precautions, in cases in which the menstrual discharge is very profuse or in which nervous manifestations accompany menstruation. Important is it also for the physician to take precautions against the practice by young girls of unduly prolonged voluntary retention of the urine, resulting in over-distension of the bladder; also against the performance of very active movements and against powerful muscular efforts when the bladder is in a distended state. All of these are liable to result in displacements of the uterus.