relations, that is, the difference between them, which is the pulsepressure, and the relation of this pulse-pressure to the pressure scale.

The pulse-pressure tells us the fall in pressure between the heart and arterioles, and is analogous to what is termed a "head" of water in hydrostatics. But this "fall," as an index to efficiency of the circulation, is conditioned to a considerable extent by its place in the pressure scale. A given pulse-pressure in one part of the pressure scale may not have the same value as a factor in the circulation as the same pulse-pressure in another part. For example, a pulse-pressure of 40 mm. Hg produced by a systolic blood-pressure of 200 mm. Hg, and a diastolic pressure of 140 mm. Hg will not, naturally, be attended with as efficient a circulation as the same pulse-pressure produced by a systolic pressure of 120 and a diastolic pressure of 80. A theoretic conclusion, which receives practical support, is that there is a particular place in the pressure scale for each individual and each particular condition, where a given pulse-pressure, other things being equal, will produce the fullest circulation and will at the same time be attended with the greatest circulatory flexibility and reserve power; and that pulse-pressures, placed above or below this ideal place in the pressure scale, in order to produce an adequate circulation, must ordinarily increase in magnitude, and that such increase means diminution in the flexibility of the circulation and encroachment on the reserve power of the heart. If the diastolic pressure fails to fall in just correspondence with a falling systolic pressure and thereby permits the pulse-pressure to become unduly small, clinical symptoms of circulatory insufficiency may arise; and if the systolic pressure fails to rise in just correspondence with a rising diastolic pressure and thereby permits the pulse-pressure to become unduly small, the same lessening of circulatory efficiency may be brought about. By the term "just correspondence," used in connection with the rising and falling in reference to each other of the systolic and diastolic pressures, is meant an increase of the pulse-pressure at least adequate to the bare needs of the circulation.

The pacemaker for the pulse pressure, at least in conditions of disease, seems to be the diastolic pressure more often than the systolic. Movements of the diastolic pressure for any considerable distance in either direction from its normal place in the pressure scale regularly cause the pulse pressure to increase in size if the circulatory balance

is to be preserved. In cases where the systolic pressure rises while the diastolic falls it is difficult to determine which is chiefly responsible for the increase in the pulse-pressure. This phenomenon is observed with apparently healthy hearts responding to a transient de mand, and also sometimes in cases with pathologic conditions which counterbalance each other. A normal pulse-pressure, as well as normal systolic and diastolic pressures, may be observed in cases which show signs and symptoms of cardiac insufficiency.

Before proceeding to discuss the clinical significance of specific variations of the three phases of blood-pressure, it is desirable to state what we consider the normal character of those phases to be, and what their ranges in conditions of apparent health. That we are reluctant to do, because there are no definite standards; blood-pressure conditions in health and disease overlap widely; pressures which are without pathologic significance in some conditions may possess such significance if found in others; and a considerable allowance must always be made for individual peculiarities. Only approximations are possible at the best, and the following figures are offered with the caution that they are subject to many exceptions.

The systolic pressure may range in healthy young adults between 100 and 130, being mostly between 110 and 125. In people of middle age it usually ranges nearly ten points higher, and in elderly people about twenty points higher. In young and middle-aged people a systolic pressure of 140 is often observed without apparently indicating serious disease, at least for a time, and elderly people who appear to be in good health often show a systolic pressure no higher than do young or middle-aged adults. In young adults a systolic pressure below 100 may be considered low, as may one of 110 for a middleaged person or one of 120 for an elderly person.

The diastolic pressure in young adults may range between 65 and 85, in the middle-aged between 75 and 90, and in the aged between 80 and 100.

The pulse-pressure in health is usually not far from 40, and it may vary between 30 and 50 without necessarily possessing pathologic significance. A pulse-pressure as low as 20 or as high as 60, if persistent, suggests a pathologic condition.

For short periods, as a result of transient functional causes, wide variations of the above figures are observed.

With these few general remarks, we will now proceed to discuss specific variations in the blood-pressures observed in different diseases and morbid conditions. This we can do most conveniently, perhaps, in view of our imperfect knowledge of the subject, if we approach the subject from the side of the diseases themselves.

Chronic nephritis regularly produces changes in the blood-pressure, which, however, other conditions may modify or counteract. The conditions which most often modify the blood-pressure in chronic nephritis are arteriosclerosis, myocarditis, and chronic toxæmia. In some cases one or other of these coexisting conditions may be a more prominent element in the pathologic complex than the nephritis, but in a large and fairly definite group of cases the nephritis is the predominating condition, and in that group the following changes in blood-pressure may be observed.

The diastolic pressure is regularly raised, and the degree of its elevation is roughly proportionate to the severity of the kidney lesion. This seems to be the most characteristic blood-pressure change in chronic nephritis. The diastolic pressure may rise to only 100 in mild cases, but in severe ones it may rise to 120, 140, 160, and even higher. Along with the rise of the diastolic pressure there is regularly a rise of the systolic pressure and increase in the pulse-pressure to meet the changed requirements of the circulation. The systolic pressure may rise to 175, 200, 250, 300, and even higher. In order to maintain this high systolic pressure the left ventricle regularly hypertrophies. When this hypertrophy has reached its limit and myocardial degeneration has developed to a notable degree, so that there is no more reserve power in the heart, the systolic pressure ceases to rise, and as the case progresses it declines. Then there may be some fall in the diastolic pressure, but not enough to produce a pulse-pressure large enough to compensate for the myocardial weakness: the diastolic pressure falls considerably only in the later stages of the disease, when symptoms of cardiac exhaustion have appeared. The pulse-pressure is regularly large while there is circulatory compensation of the kidney insufficiency. It increases more or less in a geometric ratio with the increase in the diastolic pressure, being in mild cases about 60, which is nearly within normal limits, and in severer cases 80, 100, and even more. With a diastolic pressure of 140, a

pulse-pressure adequate to maintain circulatory compensation of the kidney insufficiency will usually be found not far from 100.

In the following cases, cited to illustrate blood-pressure variations in chronic nephritis, the kidney lesion seems to be a prominent or the predominating factor in producing the blood-pressure picture. Nearly all of the blood-pressure records mentioned were taken by the auscultatory method.

CASE 1.-Man, 53; albumin and hyaline and granular casts in urine; heart moderately enlarged, systolic murmur over aortic valve, sounds impure; bloodpressure, 220 systolic, 120 diastolic. Eight months later (patient had a severe attack of erysipelas in the meantime): Blood-pressure, 175 systolic, 120 diastolic; marked signs and pronounced symptoms of myocardial insufficiency present.

CASE 2.-Woman, 39; trace of albumin and granular casts in urine and diminished urea; blood-pressure, 290 systolic, 170 diastolic. During following two months systolic pressure, when observed, was about 300, being twice found 325. She died two months later, beyond the writer's observation. This patient, when first seen by the writer, two years before her death, had a systolic pressure of 290, which came down under treatment to 220.

CASE 3.-Woman, 28; trace of albumin and hyaline and granular casts in urine and diminished urea; blood-pressure, 215 systolic, 145 diastolic. Nine months later, after treatment, blood-pressure was 155 systolic, 110 diastolic; trace of albumin, but no casts, found in urine, and urea normal.

CASE 4.-Woman, 60; seen in mild attack of uræmia; blood-pressure, 260 systolic, 50 diastolic. Improved under treatment, but blood-pressure did not become much lower.

CASE 5.-Woman, 31; had chronic nephritis since birth of child, two years ago; suffers from headache, shortness of breath on exertion, and general weakness; blood-pressure, 240 systolic, 140 diastolic.

CASE 6.-Woman, 59; suffers from dizziness on rising in morning; examination of urine negative; heart sounds impure and faint systolic murmur over aortic valve; blood-pressure, 270 systolic, 120 diastolic.

CASE 7.-Woman, 35; very obese; suffers from shortness of breath on exertion and headaches; trace of albumin, granular casts, and trace of sugar in urine and diminished urea; blood-pressure, 200 systolic, 140 diastolic. Treatment failed to produce much reduction of blood-pressure.

CASE 8.-Man, 43; suffers from vomiting, apparently uræmic; blood-pressure, 275 systolic, 140 diastolic.

CASE 9.-Man, 41; complains of no particular symptoms; blood-pressure, 220 systolic, 115 diastolic. One month later, after treatment, blood-pressure was 170 systolic, 112 diastolic.

CASE 10.-Man, 21; "gets tired easily and often wakes up with a start"; has been told that he has chronic nephritis; albumin and hyaline and granular casts in urine, quantity in 24 hours 6 pints, urea in 24 hours 58 grammes; bloodpressure, 115 systolic, 75 diastolic. Three days later, after treatment, albumin and casts in urine, quantity 4 pints, urea 34 grammes. Ten days later, few casts in urine, but no albumin, quantity 4 pints, urea 26 grammes. Seventeen days

still later, trace of albumin in urine, but no casts, quantity 3 pints, urea 19 grammes. Patient went to Jamaica for winter, and report from there three months later showed no albumin or casts. This seems to have been a case of the so-called azoturic diabetes.

In arteriosclerosis the blood-pressure changes seem to be less regular and uniform, less obstinately persistent, and less definitely characteristic than in chronic nephritis, and they seem to be more sus ceptible to modification by other conditions than in the latter disease. It is often difficult to disentangle the elements in the blood-pressure picture which are due to the arteriosclerosis from those due to the other conditions. Moreover, the lesions of arteriosclerosis differ widely in their intrinsic influence on the blood-pressure according to their character and distribution: some have very little influence, while others, notably lesions affecting the aorta, the coronary arteries, and the arteries in the brain, may have a great influence. The diastolic pressure in arteriosclerosis may or may not be raised. It is usually raised when the arterial supply of vital regions is involved, but the elevation does not seem to be so high, as a rule, as in chronic nephritis. The systolic pressure may be raised to produce an adequate pulsepressure. When myocarditis complicates, the enlargement of the pulse-pressure seems often in part to be produced by lowering of the diastolic pressure, thus securing a relief which does not seem to be available in advanced chronic nephritis.

In the following cases, cited to illustrate blood-pressure variations in arteriosclerosis, the arterial lesions seem to be a prominent or the predominating factor in producing the blood-pressure picture:

CASE 1.-Woman, 75; suffers from shortness of breath on exertion and general weakness; left ventricle of heart slightly enlarged, systolic murmur over aortic valve transmitted upwards, late systolic murmur at apex; examination of urine negative; blood-pressure, 175 systolic, 100 diastolic.

CASE 2.—Man, 50; suffers from shortness of breath on exertion, vertigo, palpitation, and insomnia, heart slightly dilated, faint systolic murmur in aortic region, pulse becomes slower by 15 to 20 beats on going upstairs; blood-pressure, 100 systolic, 80 diastolic. Four weeks later, after treatment, blood-pressure was 115 systolic, 80 diastolic, showing an increase in the pulse-pressure of from 20 to 35. In this case myocarditis is evidently a prominent complication.

CASE 3.-Woman, 62; suffers from shortness of breath on exertion and a tendency to deflect to the right when walking; examination of urine negative; blood-pressure, 160 systolic, 70 diastolic.

CASE 4.-Man, 66; suffers from dizziness and shortness of breath on exertion; trace of albumin and hyaline casts in urine; blood-pressure, 180 systolic, 120