According to the observations of _Federns_, the blood-pressure undergoes a rhythmical change between one menstrual period and the next, the pressure curve being normally at its lowest at the time of the commencement of the flow, and at its highest at some time during the two days immediately preceding the flow. This rhythmical change of blood-pressure manifests itself also some time before the first onset of menstruation, when the approach of puberty is indicated only by the menstrual molimina.
Observations made by _Kretschy_ in a patient with a gastric fistula have proved the influence exercised on gastric digestion by the physiological processes occurring in the female reproductive organs. In this patient, his attention was especially directed to determining at what period of digestion the secretion of acid by the stomach attains its maximum, and how that secretion increases and diminishes. He observed that the digestion of breakfast was completed in four and one-half hours, the acid-maximum occurring in the fourth hour, and the reaction of the gastric contents becoming neutral one and one-half hours later. This apparently constant acid-curve began, however, to become irregular as soon as the first symptoms of the approach of menstruation became apparent. When the flow had actually begun, he found that the reaction of the gastric contents remained acid throughout the entire day. As soon as the flow was over, the normal acid-curve was immediately reëstablished.
These observations have been confirmed by _Fleischer_. This investigator carried out his researches in menstruating women with normal stomachs, and found that with the appearance of the catamenia the process of digestion was almost always notably retarded, but that with the diminution and cessation of the flow digestion returned to the normal.
By stimulation of the central segment of the divided hypogastric or great uterine plexus, _Cyon_ was able to provoke vomiting, a confirmation of the well-known physiological fact that irritative disturbances of the female reproductive organs have a reflex influence on the vomiting centre.
It is also clearly established that diverse stimulation of peripheral nerves, those for instance of the mammary gland, of the internal genitals, or of the epigastrium, is capable of affecting the motor centre of the uterus.