medical practitioners. As a means of diagnosis, however, the sphygmogram still leaves much to be desired. The same instrument, applied in immediate succession to different arteries of the same person, gives, as might be expected, pulse-traces of somewhat different forms. The same artery of the same person yields to the same instrument at different times different forms of trace, depending upon different physiological states of the circulation. But the same artery yields traces of different form to sphygmographs of different varieties applied to it in immediate succession; and even moderate changes in adjustment cause differences in the form of the successive traces which the same instrument obtains from the same artery. It is no wonder, therefore, that great care must be exercised in comparing sphygmographic observations, and in drawing general conclusions from the information which they impart.

The Details of the Sphygmogram.-Figure 26 is a fair example of the sphygmograms commonly obtained from the healthy human radial pulse. When this trace was taken, the subject's heart was beating from 58 to 60 times

FIG. 26.-Sphygmogram from a normal human radial pulse beating from 58 to 60 times a minute. To be read from left to right (Burdon-Sanderson).

a minute. The trace records the effects upon the lever of five successive complete pulsations of the artery, which all agree in the general character of their details, while differing in minor respects. By the tracing of each pulsation the up-stroke is shown to be sudden, brief, and steady, while the down-stroke is gradual, protracted, and oscillating. The commencing recoil of the arterial wall succeeds its expansion with some suddenness. In many sphygmograms this is exaggerated by the inertia of the instrument. As shown by the trace represented in the figure, and by most such traces, the recoil soon changes from rapid to gradual, and, in the trace, its protracted line becomes wavy, indicating that the slow diminution of calibre varies its rate, or even is interrupted by one or more slight expansions, before it reaches its lowest, and is succeeded by the up-stroke of the next pulsation. In each of the five successive pulsations the traces of which are shown in Figure 26, the line which represents the more gradual portion of the down-stroke of the pulse is made up of three waves, of which the first is the shortest, the last the longest and lowest, and the middle one intermediate in length, but by far the highest. This middle wave is, in fact, the only one of the three to produce which an actual rise of pressure occurs; in each of the other two, no rise, but only a diminished rate of decline, is exhibited. The changes of pressure which produce the first and third of the waves just spoken of, in the pulse-trace under consideration, are very obscure in their origin, and are inconstant in their occurrence, sometimes being more numerous than in the trace shown in Fig. 26, and sometimes failing altogether to appear.

The Dicrotic Wave.-The oscillation of pressure, however, which pro

duces the middle wave of each of the pulsations of Figure 26, is so constant in its occurrence that it is undoubtedly a normal and important phenomenon, although, in different sphygmograms, the height, and position in the trace, of the wave inscribed by this oscillation may vary. Occasionally this oscillation is morbidly exaggerated, so that it may be not only recorded by the sphygmograph, but even felt by the finger, as a second usually smaller up-stroke of the pulse. In such a case the artery is felt to beat twice at each single beat of the ventricle, and is said, technically, to show a "dicrotic" pulse. Where a dicrotic pulse can be detected by the finger, it is apt to accompany a markedly low mean tension of the arterial wall. The dicrotic pulse was known, and named, long before the sphygmograph revealed the fact that the pulse is always dicrotic, although to a degree normally too slight for the finger to appreciate. The sphygmographic wave which records the slight "dicrotism" of the normal pulse is called the "dicrotic wave." Where dicrotism can be felt by the finger, the sphygmogram naturally exhibits a very conspicuous dicrotic wave.

The origin of the dicrotic oscillation has been much discussed, and is not yet thoroughly settled, important as a complete settlement of it would be to the true interpretation and clinical usefulness of the sphygmogram. It is believed by some that this fluctuation of pressure is produced at the smaller arterial branches, as a reflection of the main pulse-wave, and that the dicrotic wave, thus reflected, travels toward the heart, and, naturally, reaches a given artery after the main wave of the pulse has passed over it, travelling in the opposite direction. The weight of probability, however, is in favor of the view that the dicrotic wave essentially depends upon a slight rise of the arterial pressure, or slackening of its decline, due to the closing of the semilunar valve; and that, therefore, this wave follows the main wave of arterial expansion outward from the heart, instead of being reflected inward from the periphery. If the dicrotic wave be caused solely by reflection from the periphery, it ought, in a sphygmogram from a peripheral artery, to begin at a point nearer to the highest point of each pulsation than in the case of an artery near the heart, in which latter vessel, naturally, a reflected wave would undergo postponement. On the other hand, if the dicrotic wave be transmitted toward the periphery, and caused solely by the closure of the aortic valve, it ought, in a sphygmogram from a peripheral artery, to occupy very nearly the same relative position as in a sphygmogram taken from an artery near the heart. But a wave running toward the periphery may be modified by a reflected wave in the same vessel, and a reflected wave may undergo a second reflection at the closed aortic valve, or even elsewhere, and thus give rise to an oscillation which will be transmitted toward the periphery. These statements show with what technical difficulties the subject is beset, whether the sphygmograph be employed, or, in the case of animals, the elastic manometer, the traces recorded by which also exhibit the dicrotic wave. As

1 From diкpoтos, double-beating.

already stated, however, the probabilities are in favor of the valvular origin of the dicrotic wave.

If it be true that the closure of the aortic valve causes the dicrotic wave, the instant marked by the commencement of this wave, in the manometric trace inscribed by the pressure within the first part of the arch of the aorta itself, practically marks the instant of closure of the aortic valve. We have seen (p. 130) that this doctrine has been made use of in the elucidation of the curve of the pressure within the ventricle.

The Diagnostic Limitations of the Sphygmogram.-The feeling of the pulse, imperfect as is the most skilled touch, cannot be replaced by the use of the sphygmograph. The presence, between the cavity of the artery and the surface of the body, of a quantity of tissue the amount and elasticity of which differ in different people, and even differ over neighboring points of the same artery, renders it impossible so to adjust the spring of the sphygmograph as to be able to obtain a reliable base-line corresponding to the abscissa, or line of atmospheric pressure, in the case of the manometric curve of bloodpressure. The effects produced by slight differences in the placing of the instrument tend to the same result. By the absence of such a base-line the sphygmographic curve is shorn of quantitative value as a curve of bloodpressure, and cannot give information as to whether, in clinical language, the pulse be hard or soft, large or small. Nor can a long or short pulse be identified from the appearance of the sphygmogram. The pulse-trace still requires much elucidation; but when further study shall have rendered clearer the true extent, the normal variations, and the causes of the complex and incessant oscillations of the walls of the arteries, it may well be believed that both physiology and practical medicine will have gained an important insight into the laws of the circulation of the blood.

P. THE MOVEMENT OF THE LYMPH.

The Lymphatic System.-The lymph is contained within the so-called lymphatic system, the nature of which may be summarized as follows:

The lymph appears first in innumerable minute irregular gaps in the tissues, which gaps communicate in various ways with one another, and with minute lymphatic vessels, which latter, when traced onward from their beginnings, presently assume a structure comparable to that of narrow veins with very delicate walls and extremely numerous valves. These valves open away from the gaps of the tissues, as the valves of the veins open away from the capillaries. The lymphatic vessels unite to form somewhat larger ones, each of which, however, is of small calibre as compared with a vein of medium size, until at length the entire system of vessels ends, by numerous openings, in two main trunks of very unequal importance, the thoracic duct and the right lymphatic duct. The latter is exceedingly short, and receives the terminations of the lymphatics of a very limited portion of the body; the terminations of all the rest, including the lymphatics of the alimentary canal, are 1 M. von Frey: Die Untersuchung des Pulses, 1892, S. 35.

VOL. I.-10

duces the middle wave of each of the pulsations of Figure 26, is so constant in its occurrence that it is undoubtedly a normal and important phenomenon, although, in different sphygmograms, the height, and position in the trace, of the wave inscribed by this oscillation may vary. Occasionally this oscillation is morbidly exaggerated, so that it may be not only recorded by the sphygmograph, but even felt by the finger, as a second usually smaller up-stroke of the pulse. In such a case the artery is felt to beat twice at each single beat of the ventricle, and is said, technically, to show a "dicrotic" pulse. Where a dicrotic pulse can be detected by the finger, it is apt to accompany a markedly low mean tension of the arterial wall. The dicrotic pulse was known, and named, long before the sphygmograph revealed the fact that the pulse is always dicrotic, although to a degree normally too slight for the finger to appreciate. The sphygmographic wave which records the slight "dicrotism" of the normal pulse is called the "dicrotic wave." Where dicrotism can be felt by the finger, the sphygmogram naturally exhibits a very conspicuous dicrotic-wave.

The origin of the dicrotic oscillation has been much discussed, and is not yet thoroughly settled, important as a complete settlement of it would be to the true interpretation and clinical usefulness of the sphygmogram. It is believed by some that this fluctuation of pressure is produced at the smaller arterial branches, as a reflection of the main pulse-wave, and that the dicrotic wave, thus reflected, travels toward the heart, and, naturally, reaches a given artery after the main wave of the pulse has passed over it, travelling in the opposite direction. The weight of probability, however, is in favor of the view that the dicrotic wave essentially depends upon a slight rise of the arterial pressure, or slackening of its decline, due to the closing of the semilunar valve; and that, therefore, this wave follows the main wave of arterial expansion outward from the heart, instead of being reflected inward from the periphery. If the diçrotic wave be caused solely by reflection from the periphery, it ought, in a sphygmogram from a peripheral artery, to begin at a point nearer to the highest point of each pulsation than in the case of an artery near the heart, in which latter vessel, naturally, a reflected wave would undergo postponement. On the other hand, if the dicrotic wave be transmitted toward the periphery, and caused solely by the closure of the aortic valve, it ought, in a sphygmogram from a peripheral artery, to occupy very nearly the same relative position as in a sphygmogram taken from an artery near the heart. But a wave running toward the periphery may be modified by a reflected wave in the same vessel, and a reflected wave may undergo a second reflection at the closed aortic valve, or even elsewhere, and thus give rise to an oscillation which will be transmitted toward the periphery. These statements show with what technical difficulties the subject is beset, whether the sphygmograph be employed, or, in the case of animals, the elastic manometer, the traces recorded by which also exhibit the dicrotic wave. As 1 From diκpoтoç, double-beating.

already stated, however, the probabilities are in favor of the valvular origin of the dicrotic wave.

If it be true that the closure of the aortic valve causes the dicrotic wave, the instant marked by the commencement of this wave, in the manometric trace inscribed by the pressure within the first part of the arch of the aorta itself, practically marks the instant of closure of the aortic valve. We have seen (p. 130) that this doctrine has been made use of in the elucidation of the curve of the pressure within the ventricle.

The Diagnostic Limitations of the Sphygmogram.-The feeling of the pulse, imperfect as is the most skilled touch, cannot be replaced by the use of the sphygmograph. The presence, between the cavity of the artery and the surface of the body, of a quantity of tissue the amount and elasticity of which differ in different people, and even differ over neighboring points of the same artery, renders it impossible so to adjust the spring of the sphygmograph as to be able to obtain a reliable base-line corresponding to the abscissa, or line of atmospheric pressure, in the case of the manometric curve of bloodpressure. The effects produced by slight differences in the placing of the instrument tend to the same result. By the absence of such a base-line the sphygmographic curve is shorn of quantitative value as a curve of bloodpressure, and cannot give information as to whether, in clinical language, the pulse be hard or soft, large or small. Nor can a long or short pulse be identified from the appearance of the sphygmogram. The pulse-trace still requires much elucidation; but when further study shall have rendered clearer the true extent, the normal variations, and the causes of the complex and incessant oscillations of the walls of the arteries, it may well be believed that both physiology and practical medicine will have gained an important insight into the laws of the circulation of the blood.

P. THE MOVEMENT OF THE LYMPH.

The Lymphatic System.-The lymph is contained within the so-called lymphatic system, the nature of which may be summarized as follows:

The lymph appears first in innumerable minute irregular gaps in the tissues, which gaps communicate in various ways with one another, and with minute lymphatic vessels, which latter, when traced onward from their beginnings, presently assume a structure comparable to that of narrow veins with very delicate walls and extremely numerous valves. These valves open away from the gaps of the tissues, as the valves of the veins open away from the capillaries. The lymphatic vessels unite to form somewhat larger ones, each of which, however, is of small calibre as compared with a vein of medium size, until at length the entire system of vessels ends, by numerous openings, in two main trunks of very unequal importance, the thoracic duct and the right lymphatic duct. The latter is exceedingly short, and receives the terminations of the lymphatics of a very limited portion of the body; the terminations of all the rest, including the lymphatics of the alimentary canal, are 1 M. von Frey: Die Untersuchung des Pulses, 1892, S. 35.

VOL. I.-10