80 PULSE that muscular exertion increases the frequency of the pulse. The effect of posture has thus been expressed by Dr. Guy : Average temti per minute In Standing. Sitting. Lying. 81 71 66 91 84 79 According to this, the difference between stand- ing and lying in the former is one fifth of the whole, in the latter one eighth ; when this change is effected by muscular effort the vari- ation is greater, accounting for many cases of sudden death in persons with disease of the heart or in very weak conditions on quickly assuming an erect position. Mental excite- ment, the digestive process, alcoholic drinks, and elevation above the sea level, accelerate the pulse ; as a general rule, though with nu- merous exceptions, it is more frequent in the morning than in the evening, and in sanguine than in lymphatic temperaments. The pulse is slower during sleep, and from the effect of rest, diet, cold, venesection, and the action of many drugs, especially digitalis, aconite, and hellebore. The pulse may be counted in any artery, and in a manner familiar to all, but most conveniently in the radial at the wrist, in the carotids, temporals, brachial, or femoral. The average numerical proportion of the arte- rial pulsations to the respiratory movements is 4 or 5 to 1 ; when this proportion is widely departed from, there is either some general diseased condition of the system accompanied with fever, some obstruction to the proper lUTHtion of the blood, or some disorder in the nervous system ; in inflammatory or acute diseases, the pulse may rise to 120 and 160 in the adult, and so that it cannot be counted in the child; in pneumonia, with the quick- ened pulse the number of respirations in- creases more rapidly, the above proportion becoming as 3 or even 2 to 1 ; in hysteria a similar increase may occur in both without any serious cause. The exact form of the ar- terial pulse has been determined by means of a contrivance termed the " sphygmograph," which consists of a small metallic or ivory plate, held in contact with the integument im- mediately over the vessel by means of a deli- cate spring, and lifted from its bed by each pulsation of the artery. The plate carries an upright rod, which in its turn moves a long but light index, the end of which traces an alter- nately ascending and descending line upon the surface of a strip of paper moving with uni- form velocity. Thus the extent of the verti- cal motion measures the width of the arterial expansion ; and its greater or less obliquity, as traced upon the paper, indicates its rapidity or slowness, as compared with the horizontal movement of the paper itself. Such a trace is very useful, first by showing minute peculiari- ties of the arterial pulsation, too small to be distinctly perceptible by the touch; and sec- ondly, by leaving them in the form of a perma- nent record, suitable for subsequent study and comparison. The ordinary trace of the radial pulse, taken in this way, consists of a nearly vertical ascending line, which indicates the sudden and rapid expansion of the artery, fol- lowed by an oblique and somewhat undula- ting descent, showing the comparatively slow- er and more irregular collapse of the vessel. These two ascending and descending lines are repeated for every pulsation of the artory. FIG. 1. Trace of the Radial Pulse, taken by the Sphygmograph. Sometimes the undulations of the descending line become more perceptible, owing to an in- crease of temperature or some other cause which diminishes the resistance of the arterial walls to the heart's impulse ; and under these circumstances the expansion of the vessel is more sudden and vertical, while its collapse ia indicated by one or two well marked oscilla- tions, in the trace of the descending line. In FIG. 2. Trace of the Radial Pulse under the influence of Increased Temperature. certain cases of disease this oscillation of the artery at the period of collapse becomes so marked that a sort of secondary beat, or redu- plication of the pulse, is perceptible even to the touch ; and this constitutes what is known as the double or dicrotic pulse, in which there are two perceptible pulsations of the artery for every contraction of the heart. Of these two FIG. 8. Trace of a Dicrotic Pulae, in Typhoid Fever. pulsations, only the first is directly caused by the impulse of the heart ; the second is due to the oscillation of the blood in the relaxed ar- terial tube. Dr. E. R. Hun, who at that time was special pathologist to the New York state lunatic asylum at Utica, published in the " American Journal of Insanity" for January, 1870, the results of a series of investigations, in which he found that the pulse of the insane " always tends toward the dicrotic or mono- FIG. 4. Trace of Pulse In Dementia. erotic type, being never tricrotic in uncompli- cated cases. It becomes more characteristic as the mental condition degenerates, and assumes
