The Volume of the Pulse.-This is determined partly by the actual size of the artery, partly by the quantity of blood sent into the artery at each beat of the heart. If much blood is sent in, the pulse is full or large; if but little blood, the pulse is small.

Hardness of the Pulse: Arterial Tension.-If the finger be placed upon the radial artery, and pressed upon it with increasing force the flow of blood is at length stopped; and this arrest of the blood-flow can be more easily effected in some pulses than in others. Those in which slight pressure is sufficient are called soft or compressible pulses; those in which much pressure is required are called hard or incompressible pulses. If when the pulse has been stopped by compression the finger be slowly lifted, the blood will be felt to pass under the finger with much greater force in the case of the hard than in the case of the soft pulse; and the estimation of the hardness of the pulse is generally much helped in this way. A hard pulse is not necessarily very small or very large. It feels like a cord, but it is important to distinguish from a purely hard pulse that kind of rigidity which is due to atheromatous and calcareous changes in the wall of the artery. The wall then feels rough and irregular, and the vessel has often a tortuous course. The two conditions, rigidity of arterial wall and hardness of pulse, may coexist. A pulse is hard in proportion to (1) the quantity of blood thrown into the arterial system, (2) the difficulty of egress through the capillaries and veins (capillary resistance), and (3) the degree of contraction of the arterial coats upon their contents. It is soft under the opposite conditions. Thus, hardness is favored by a powerfully-acting heart, a normal amount of blood, contraction of the peripheral arterioles-as, for instance, by cold, which stimulates the muscular coat of the arteries (vasomotor stimulation). Softness of pulse is favored by a feeble heart, by valvular imperfections interfering with the supply of the blood to the arterial system, by a free flow through capillary area, and by dilatation of the arteries and arterioles as a result of vasomotor paralysis. The hard pulse is indicative of high arterial tension; the soft pulse of low arterial tension. The former is often accompanied by an accentuated aortic second sound, heard at the inner end of the second right intercostal space, and sometimes by a reduplication of the first sound, heard over the septum ventriculorum (see p. 440).

Dicrotism.-Especially in febrile conditions, but also in the soft varieties of healthy pulses, a peculiar doubling of each pulse-beat can be felt, which is known as dicrotism. As a rule, the main beat is followed by a much slighter elevation of the artery-wall. In most pulses there is no difficulty in distinguishing this from a true pulse-beat, because it takes place in the course of the elevation due to the ventricular contraction, and auscultation proves that there is no ventricular systole corresponding to it. It is due to a wave reflected from the closed aortic valves and the aortic walls, and transmitted peripherally to the wrist. It is favored by the conditions producing softness

of pulse, and is most marked in highly febrile states; it is diminished by conditions leading to hard pulse, such as Bright's disease, and by aortic regurgitation, in which case the reflexion of a wave takes place imperfectly.

The Sphygmograph.-The accurate estimation of the pulse is much aided by the sphygmograph, which, at the same time, furnishes a permanent record for future comparison.

The needle of the sphygmograph makes a tracing on blackened paper, and each beat of the heart is shown by the needle rising above the base line, and again falling. The frequency or regularity of the pulse can thus be seen at a glance; but the special features of each beat are of more importance. In the tracing of each beat of the arterial pulse there is an upstroke, which is uninterrupted and almost vertical; and a downstroke which is oblique, and is interrupted by one of two elevations with intervening depressions.

The upstroke represents the contraction of the ventricle, driving blood into the aorta and thereby causing a wave which is rapidly transmitted to the peripheral arteries. The apex of this upstroke has been known as the percussion-wave. Its height is proportionate to the force of the ventricular contraction, and the quickness or suddenness of the contraction is indicated by the vertical course of the stroke.* The height is also greater when the arterial wall is yielding, less when it is tense and resistant. Compare Figs. 12 A and 13 A, B with Figs. 12 B and 14 A, B, C.

Of the elevations in the course of the downstroke, the most constant is the dicrotic wave (Fig. 12 A, c, Fig. 13 A, c, Fig. 14 A, c). This is the same as can be felt with the finger in pulses that are called "dicrotic;" it is shown

With a Marey's sphygmograph a long and quick upstroke is curved backward, in consequence of the needle being at the end of a long lever, which works on a fulcrum, with an axis transverse to the line of movement of the paper.

by the sphygmograph to be present in the majority of pulses, even when not perceptible to the finger. As already stated, it is due to a reflected wave from the closed aortic valves or from the walls of the aorta. It is immediately preceded by a depression, the aortic notch, the depth of which is proportionate to the size of the dicrotic wave. In Figs. 12 and 14 they are both slight, in Fig. 13 they are both well marked. When the aortic notch reaches the base line (Fig. 13 A) the pulse is called fully dicrotic; it sometimes falls below the base line, and is then called hyperdicrotic (Fig. 13 B). In this case the percussion wave of the next beat appears to come before the dicrotic wave has completely passed. Dicrotism is best marked in soft pulses, with yielding and elastic walls; it is a common result of vasomotor

B. HYPER-DICROTIC PULSE IN PYREXIA (ENTERIC FEVER). TEMP. 1030.

paralysis as seen in highly febrile conditions (Fig. 13), and can be at once produced by the administration of amyl nitrite. The aortic notch corresponds to the termination of the systole of the ventricle-that is, it marks the closure of the aortic valves.

Between the percussion wave and the dicrotic wave- that is, preceding the aortic notch, and therefore corresponding to the period of systole of the ventricle-there is often a wave which has been attributed to the outward flow of the current of blood following the percussion wave. It is called the tidal or predicrotic wave (Fig. 12 A, b, Fig. 14 A, b, B, C). It is best seen in hard pulses (Fig. 14)-that is, in conditions of high arterial tension, when be supposed that the undulation of the blood would be unusually well

it

may

transmitted. On the other hand, in very soft pulses, the tidal wave is lost in the percussion wave (Fig. 13 A, B). A pulse, in which the tidal wave rises higher than the percussion wave, has been called anacrotic, because the percussion wave forms an elevation in the ascending limb between the base and the highest point.

One or two slight undulations are occasionally seen after the dicrotic wave (Fig. 14 A, d). These were formerly attributed to defects in the instrument employed. But they only occur in tracings of pulses of high tension, and not in those of low tension.

Landois, in explaining a sphygmographic tracing, describes only two primary waves, namely, (1) that which we have called the percussion wave, and (2) the dicrotic wave. Both the tidal wave and the undulations which follow the dicrotic wave are called by him elastic elevations, and are considered by

A. ACUTE BRIGHT'S DISEASE. PRESSURE, FOUR OUNCES.

B. ACUTE BRIGHT'S DISEASE; FIVE WEEKS' DURATION. PRESSURE, SEVEN OUNCES.

C. CHRONIC BRIGHT'S DISEASE. PRESSURE, SIX OUNCES.

him to be secondary results of the percussion and dicrotic waves, as a consequence of the high condition of tension in the vessels.

Whatever be the explanation, it remains the fact that conditions of high arterial tension are indicated by a high tidal wave, and by moderate dicrotism; whereas in low tension the dicrotism is considerable, and the tidal wave is small or absent.

It has been already said that the pulse of high tension is hard, and resists compression by the finger. The amount of this resistance can be accurately estimated by a properly-constructed sphygmograph, in which a graduated pressure can be applied to the spring, which lies upon the artery. It will then be ascertained that some very hard pulses require a pressure of twelve or fourteen ounces to stop the flow of blood in them; while in others the current can be arrested by a pressure of five or six. Similarly, in the former kind of pulse a pressure of five, six, or seven ounces is necessary in order to

get a correct tracing, whereas in soft pulses a pressure of one, two, or three ounces is sufficient. (Compare Fig. 14 with Fig. 12 A.)

Certain valvular diseases and some alterations in the walls of the vessels impart special features to the pulse, which will be treated of in future chapters. The pulses which result from mitral disease, from aortic regurgitation, from arterial obstruction, from aneurism, and from atheroma, are the most characteristic (Figs. 19, 20 and 21).

When the heart's action is very feeble, the pulse is affected by the act of respiration, and the base line of the tracing is undulating instead of straight (respiratory wave).

THE VENOUS PULSE.

As a result of tricuspid regurgitation, pulsation occurs in the internal jugular and other veins of the neck, and in the hepatic veins in the liver; the rise is synchronous with the ventricular systole. A tracing shows an elevation in the ascending limb, and an unbroken line of descent.

DISEASES OF THE HEART.

ENDOCARDITIS.

Endocarditis, or inflammation of the lining membrane of the heart, occurs in two forms-simple and malignant.

SIMPLE ENDOCARDITIS.

This is commonly described as acute or chronic; but the term chronic endocarditis is often applied to the permanent deformities and alterations in the valves, which result from acute endocarditis, as well as to a separate inflammatory process of slow development.

Etiology.-Endocarditis, like pericarditis, is, in the great majority of cases, caused by rheumatic fever; it also occurs, during the progress of chorea, and in scarlet fever, diphtheria, typhoid, and some other infectious diseases. Bright's disease, syphilis, and other chronic dyscrasiæ, are said occasionally to cause it. It may be brought on by local injuries, such as the rupture of a sigmoid valve, or of the chorda tendineæ, and the unnatural friction of one part of the heart with another; or the passage of currents of blood through abnormal apertures may cause the local inflammation of the endocardium.

It is always in limited patches, and never affects the whole interior of the heart. In rheumatism and other general diseases it affects the valves first or

alone.