[Illustration: Fig. 56.--Showing method of using blood pressure instrument during operation without interfering with the operator or assistants. Sheet thrown back to show cuff on arm of patient. Anesthetist has chart on table beside him, dial pinned to pad in full view, bulb near hand. Extra tubing must be put on the blood pressure instrument.] A sudden drop in the pressure picture may mean a large hemorrhage. The gradual return of the pressure picture means that the vasomotor mechanism has acted to keep up the pulse pressure. Should the diastolic pressure continually fall, it may mean that the hemorrhage is still taking place (Wiggers). =Blood Pressure in Obstetrics= One might affirm almost without fear of contradiction that the constant determination of blood pressure during pregnancy is more important than the examination of the urine. Within recent years a number of observers having access to a large material, have given the results of their findings. There is a striking unanimity of opinion, although now and then a difference in minor details. The blood pressure should be taken frequently during pregnancy. The usual and highly essential precautions in taking pressure in general apply most particularly in these cases. Towards the end of pregnancy the pressure should if possible be taken daily and oftener if necessary. Pressure in women is usually below 120 mm. Many patients have a temporary rise in blood pressure during pregnancy, due oftenest to constipation, without developing other symptoms. This is common to all conditions and has no significance. Some think that an abnormally low pressure, that is, a systolic below 90 mm., suggests that the patient is likely to react unduly to the strain of labor. This is denied by others. Among 1000 cases (Irving) the pressure was below 90 in only one case. A gradually rising pressure precedes albuminuria, as a rule. If there is albumin without change in pressure the albumin may usually be disregarded. Some think that a pressure over 130 mm. systolic should be carefully watched. The danger limit is set by some at 150 mm. If the blood pressure from the very first is high, it may mean only that that was the patient's normal pressure. This calls for increased watchfulness. It is held by some that high blood pressure favors hemorrhage and probably explains the hemorrhagic lesions in the placenta and some viscera in eclampsia and albuminuria. All are agreed that the most significant change is the gradual but sure rise from a low pressure. When this is combined with albuminuria the danger of toxemia is imminent. The high blood pressure in those under thirty years of age seems to be a more certain sign of approaching toxemia than the same pressure in those older. The pressure falls within a few days to its normal after delivery in the toxic cases. Although the emesis gravidarum is held to be a sign of a toxemia of some unknown nature, the blood pressure is never raised even in the pernicious form.