the latter is intact, sinking in this case to perhaps -11.2 millimeters.' What is striking in connection with the "quick-charging" of the ventricle is that the greatest and longest negative pressure in the auricle coincides, as we should expect, with the earlier part of its diastole, and therefore with the systole of the ventricle, when the auricle is cut off from it by the shut valve. By this suction within the auricle the flow from the veins into it probably is heightened, and the store of blood increased which accumulates in the reservoir to await the opening of the valve. The quick-charging mechanism itself is quickly charged. Nor should it be forgotten that the work of the ventricle contributes in some degree to this suction within the auricle. The heart is air-tight in the chest, which is a more or less rigid case. At each ventricular systole the heart pumps some blood out of this case, and shrinks as it does so, thus tending to produce a vacuum; in other words, to increase the amount of negative pressure within the chest, and thus help to expand the swelling auricles. Therefore for the suction which helps to charge the auricles during the systole of the ventricles, that systole itself is partly responsible.3

Is the Auricle Emptied by its Systole ?-Authorities differ still as to the extent to which the auricle is emptied by its systole; some holding the scarcely probable view that, during this time, its contents are all, or nearly all, transferred to the ventricle; and others taking the widely different view that the auricle actually continues to receive blood during its systole, which latter simply increases the discharge into the ventricle. According to this latter opinion the flow from the great veins into the auricle is absolutely unbroken. All are agreed, however, that the auricular appendix is the most completely emptied portion of the chamber.

Are the Venous Openings into the Auricle closed during its Systole? If not, does Blood then regurgitate, or enter ?—As to these questions differences of opinion are possible, because at the openings of the veins into the auricle no valves exist which are effective in the adult, except at the mouth of the coronary sinus. It is therefore a question, what happens at the mouths of the veins during the auricular systole. These mouths are surrounded by rings composed of the muscular fibres of the auricular wall; and for some distance from the heart the walls of some of the great veins are rich in circular fibres of muscle. We have seen already (p. 115) that a rhythmic contraction of the venæ cavæ and pulmonary veins occurs just before the systole of the auricles and must accelerate the flow into the latter. Their swiftly following systole is known to begin at the mouths of the great veins and from these to spread over the rest of each auricle. It is evident at once that the circular fibres must 1 Goltz und Gaule: op. cit., p. 109.

2 von Frey und Krehl: op. cit., p. 53; W. T. Porter: op. cit., p. 523.

* A. Mosso: Die Diagnostik des Pulses, etc. Zweiter Theil: Ueber den negativen Puls,

S. 42.

4

M. Foster: A Text-book of Physiology, New York, 1896, p. 182.

5 Skoda: "Ueber die Function der Vorkammern des Herzens,” Sitzungsberichte der mathem.naturu. Classe der kais. Akademie der Wissenschaften in Wien, 1852, Bd. ix. S. 788. L. Hermann: Lehrbuch der Physiologie, 1900, S. 66.

either narrow or obliterate, like sphincters, the mouths of the veins at the outset of the systole, and that these fibres thus take the place of valves. If the closure be complete, all the blood ejected by the systole must enter the ventricle, and a momentary standstill of blood and rise of pressure in the veins just without the auricle must accompany its brief systole. A recent observer believes the flow into the auricle to be interrupted even more than once during its cycle.1 If the venous openings be not closed but only narrowed during the systole of the auricles, the transfer of all or most of the ejected blood to the ventricle must depend upon the pressure being lower therein than at the venous openings. A slight regurgitation into the veins would, like the complete closing of their mouths, cause a momentary checking of their blood-flow just without the auricle, and a slight rise of pressure. Such a checking of the flow has in some cases been observed and ascribed to regurgitation. A systolic narrowing without closure of the venous mouths would leave room also for the view already given, that so far is regurgitation from taking place, that even during the systole of the auricles blood enters them incessantly, and the venous flow is never checked. In this case the systole of the auricle would still empty it partially into the ventricle, owing to the lowness of the pressure there.

The time has not arrived for a decision as to all these questions, which are surrounded by practical difficulties; but fortunately they do not throw doubt upon the functions of the auricle as a reservoir and pump which may be swiftly filled, and may swiftly complete the filling of the ventricle which it adjoins.

O. THE ARTERIAL PULSE.

Nature and Importance.-The expression "arterial pulse" is restricted commonly to those incessant fluctuations of the arterial pressure which correspond with the incessant beatings of the ventricles of the heart. These rhythmic fluctuations of the arterial pressure have been explained already (p. 92) to depend upon the rhythmic intermittent injections of blood from the ventricles; upon the resistance to these injections produced by the friction within the blood-vessels; and upon the elasticity of the arterial walls. It has also been explained that the interaction of these three factors is such that the blood, in traversing the capillaries, comes to exert a continuous pressure, free from rhythmic fluctuations; in other words, that the pulse undergoes extinction at the confines of the arterial system. It is at once apparent that the pulse may be affected by an abnormal change, either in the heart's beat, in the elasticity of the arteries, or in the peripheral resistance, or by a combination of such changes; and that, therefore, the characters of the pulse possess an importance in medical diagnosis which justifies a brief further discus

sion of them.

A pulsating artery not only expands, but is lengthened. The sudden 1 W. T. Porter: op. cit., p. 534.

2 François-Franck: "Variations de la vitesse du sang dans les veines sous l'influence de la systole de l'oreillette droite," Archives de physiologie normale et pathologique, 1890, p. 347.

increase in the contents of an artery which causes the pulse therein, is accommodated not merely by the increase of calibre which produces the "up-stroke: of the arterial wall against the finger, but also by an increase in the length of the elastic vessel. If the artery be sinuous in its course, this increase in length suddenly exaggerates the curves of the vessel, and thus produces a slight wriggling movement. This is sometimes very clearly visible in the temporal arteries of emaciated persons. On the other hand, the increase in the calibre of the artery is relatively so slight that it is invisible at the profile even of a large artery, dissected clean for a short distance for the purpose of tying it. Such a vessel appears pulseless to the eye, although its pulse is easily felt by the finger, which slightly flattens the artery and thus gains a larger surface of contact.

66

Transmission of the Pulse.-If an observer feel his own pulse, placing the finger of one hand upon the common carotid artery, and that of the other upon the dorsal artery of the foot at the instep, he will perceive that the pulse corresponding to a given heart-beat occurs later in the foot than in the neck. This phenomenon is readily comprehended by considering that room for the pulse-volume" injected by the heart is made in the root of the arterial system both by local expansion and by a more rapid displacement of blood into the next arterial segment. This next segment, in turn, accommodates its increased charge by local expansion and by a more rapid displacement; and this same process involves segment after segment in succession, onward toward the capillaries. The expansion of the arterial system, then, is a progressive one, and, as the phrase is, spreads as a wave from the aorta onward to the arterioles. The rate of transmission of the "pulse-wave" from a point near the heart to one remote from it, may be calculated. This is done by comparing the time which elapses between the occurrence of the up-stroke of the pulse in the nearer and in the farther artery with the distance along the arterial system which separates the two points of observation. In one case, for example, that of an adult, the absolute amount of the postponement of the pulsethat is, the time required for the transmission of the pulse-wave from the heart itself to the arteria dorsalis pedis, was 0.193 second. The time of transmission of the pulse-wave from the heart to the dorsalis pedis is often longer than in this case, amounting to 0.2 second or a little more. If we reckon the duration of the ventricular systole at about 0.3 second, it is evident that the fact of the postponement of the pulse in the arteries distant from the heart does not invalidate the general statement that the arterial pulse is synchronous with the systole of the ventricles.

The general estimates of the rate, as opposed to the absolute time, of transmission of the pulse-wave vary, in different cases, from more than 3 meters to more than 9 meters per second. As the blood in the arteries does not pass onward at a swifter rate than about 0.5 meter per second, it is clear that the wave of expansion moves along the artery many times faster than the blood does; and that to confound the travelling of the wave with the travelling of

1 J. N. Czermak: Gesammelte Schriften, 1879, Bd. i. Abth. 2, S. 711.

the blood would be a very serious error, easily avoided by bearing in mind the causes of the pulse-wave as already given.

Investigation by the Finger.-The feeling of the pulse has been a valuable and constantly used means of diagnosis since ancient times. Indeed, the ancient medicine attached to it more importance than does the practice of to-day. But it is still advisable to warn the beginner that he may not look to the pulse for "pathognomonic" information; that is to say, he may not expect to diagnosticate a disease solely by touching an artery of the patient under examination. The pulse is most commonly felt in the radial artery, which is convenient, superficial, and well supported against an examining finger by the underlying bone. Many other arteries, however, may be utilized.

Frequency and Regularity.—The most conspicuous qualities of the pulse are frequency and regularity. Usually these can be appreciated not merely by a physician but by any intelligent person.. The physiological variations in the frequency of the heart's beats have been referred to already (p. 121). In an intermittent pulse the rhythm is usually regular, but, at longer or shorter intervals, the ventricle omits a systole, and therefore, the pulse omits an upstroke. Either intermittence or irregularity of the cardiac beats may be caused by transient disorder as well as by serious disease.

Tension.—When unusual force is required in order to extinguish the pulse by compressing the artery against the bone, the arterial wall, and hence the pulse, is said to possess high tension, or the pulse is called incompressible, or hard. Conversely, the pulse is said to be of low tension, compressible, or soft, when its obliteration is unusually easy. A very hard pulse is sometimes called "wiry;" a very soft one, "gaseous." High tension, hardness, incompressibility, obviously are directly indicative of a high blood-pressure in the artery; and the converse qualities of a low pressure. It follows from what has gone before that the causes of changes in the arterial pressure, and hence in the tension, may be found in changes either in the heart's action, or in the peripheral resistance, or, as is very common, in both. An instrument called a sphygmomanometer' or sphygmometer is sometimes applied to the skin over the artery, in order to obtain a better measurement of its hardness or softness, and hence of the blood-pressure within it, than the finger can make. Such instruments are not free from sources of error.

Size. When the artery is unusually increased in calibre at each up-stroke of the pulse, the pulse is said to be large. When, at the up-stroke, the calibre changes but little, the pulse is said to be small. A very large pulse is sometimes called "bounding;" a very small one, "thready." Largeness of the pulse must be distinguished carefully from largeness of the artery. The former phrase means that the fluctuating part of the arterial pressure is large in proportion to the mean pressure. But if the mean pressure be great while the fluctuating part of the pressure is relatively small, the artery, even at the end of the down-stroke, will be of large calibre, while the pulse will be small.

1 From oovyμóc, pulse.

It has been seen that the increased charge of blood which an artery receives at the ventricular systole is accommodated partly by increased displacement of blood toward the capillaries, and partly by that increase in the capacity of the artery which is accompanied by the up-stroke of the pulse. The less the contents of the artery the less is the arterial pressure, the less the tension of the wall, and the more yielding is that wall. The more yielding the wall, the more of the increased charge of blood does the artery accommodate by an increase of capacity and the less by an increase of displacement. Therefore, a large pulse often accompanies a low mean pressure in the arteries, and hence may appear as a symptom after large losses of blood. In former days, when bloodletting was practised as a remedial measure, imperfect knowledge of the mechanics. of the circulation sometimes caused life to be endangered; for a "throbbing" paise in a patient who had been bled already was liable to be taken as an “indiation" for the letting of more blood. If this were done, an effect was combated by repeating its cause.

Celerity of Stroke.-When each up-stroke of the pulse appears to be slowly accomplished, requiring a relatively long interval of time, the pulse is called slow, or long. When each up-stroke appears to be quickly accomplished, requiring a relatively short time, the pulse is called quick or short. These contrasted qualities are among the most obscure of those which the skilled touch is called upon to appreciate.

The Pulse-trace.-The rise and fall of a pulsating human artery, if near enough to the skin, may be made to raise and lower the recording lever of a somewhat complicated instrument called a sphygmograph. Of this instrument a number of varieties are in use. If the fine point of the lever be kept in contact with a piece of smoked paper which is in uniform motion, a “pulsetrace" or "pul-e-curve" is inscribed, which shows successive fluctuations, larger and smaller, which tend to be rhythmically repeated, and which depend upon the movements of the arterial wall produced by the fluctuations of bloodpressure. In an animal, a manometer may be connected with the interior of an artery, and thus the fluctuations of the blood-pressure may be observed more directly. It has been explained (p. 90) that the mercurial manometer is of no value for the study of the finer characters of the pulse, owing to the inertia of the mercury. On the other hand, the best forms of elastic manometer give pulse-traces which are more reliable than those of the sphygmograph. This is because the sphygmographic trace is subject to unavoidable errors dependent upon the physical qualities of the skin and other parts which intervene between the instrument and the cavity of the artery. Nevertheless, the sphygmographic pulse-trace, or "sphygmogram," is the only pulse-trace which can be obtained from the human subject; and, when obtained from an animal, it has so much in common with the trace recorded by the elastic manometer, that the sphygmograph has been much used for the study of the human pulse, in health and disease, both by physiologists and by 1 Marshall Hall: Researches principally relative to the Morbid and Curative Effects of Loss of Blood, London, 1830. From couuos, pulse, and yoãoɛir, to record.