Pregnancy and parturition offer an interesting field of observation, quite apart from purely obstetric considerations, because of the pronounced differences that occur in resistance to certain infectious diseases as well as other clinical conditions during the period of gestation and the puerperium. The change in the resistance to tuberculosis illustrates this very well.
That menstruation in itself is detrimental in tuberculosis is well known. The statement that the tuberculous woman "is killed by her menstruation" has often been repeated, and while mere repetition by no means carries conviction, there seems little doubt that careful clinical observation gives a firm basis for the belief. The biologic changes of the menstrual cycle, endocrine in origin, involve a profound alteration of the autonomic status of the organism and are associated, seemingly, with a definite ionic rearrangement. These metabolic changes are likewise associated with an increase in permeability of the vascular endothelium (observed in