If we make a graphic representation of the mean differences in temperature commonly observed throughout the various stages of an entire menstrual cycle, we see that the curve does in fact take the form of a wave. That drawn by _Reinl_ is shown in the following figure: (FIG. 5.) [Illustration: FIG. 5. ] The rising portion of the wave, the beginning of the tidal flow, corresponds to the second half of the interval; the height of the tidal flow, the crest of the wave, corresponds to the premenstrual epoch. As the flow gives place to the ebb, as the wave begins to decline, we come to the actual period of the catamenial discharge; later in the ebb is the post-menstrual epoch, and the lowest portion of the declining wave corresponds to the first half of the interval. Rhythmic changes corresponding to those observed in the temperature have been recorded—at least in isolated stages of the menstrual cycle—affecting the blood-pressure by _Jacobi_ and by _von Ott_, affecting the excretion of urea by _Jacobi_ and by _Rabuteau_, and affecting the pulse by _Hennig_. It is evident that the vital activity of the organism attains its maximum shortly before menstruation; and that with or immediately before the appearance of the catamenial discharge, a decline of that activity commences. _Schrader_, through his researches on metabolism during menstruation in relation to the condition of the bodily functions during this process, has established that immediately before menstruation the elimination of nitrogen in the fæces and the urine is at its lowest, a fact which indicates that at this period of the menstrual cycle the disintegration of albumen in the body is notably diminished. _Von Ott_ found in thirteen cases out of fourteen that at the beginning of the catamenial discharge or just before a considerable fall in blood-pressure occurred, and that throughout the flow the pressure almost always remained below the mean, no rise taking place till menstruation was finished; this fall in blood-pressure during menstruation was more considerable than could be accounted for by the moderate hæmorrhage. The same author, in conjunction with _Schichareff_, examined fifty-seven healthy women in respect of heat-radiation, muscular power, respiratory capacity, expiratory and inspiratory power, and tendon-reflexes. He found that the energy of the functions of the female body increased before the beginning of menstruation, but declined with or immediately before the appearance of the catamenial discharge. He exhibited this rhythmical variation in the vital processes by means of the following curve, in which the line _A B_ represents these physiological variations, whilst on the abscissa line _c e_, the days of observation are recorded, and the interval _m n_ represents the menstrual period. The degree of intensity of the united functions is indicated by the numbers 0–100 on the ordinate. [Illustration: FIG. 6. ]