ONE of the most remarkable recent additions to the modern equipment for clinical diagnosis are the so-called heart stations now in operation at the Presbyterian and Mt. Sinai hospitals, in New York, and at 1lhe Johns Hopkins Hospital in Baltimore. The new apparatus represents the most refined diagnostic instrument at the service of the heart specialist, and not only enables him to follow with great certainty and c1earness the specific features upon which his judgment of the case must be based, but it furthermore is capable of yielding data which would be quite unattainable either by the unaided human sense organs or with the aid of the ordinary instruments hitherto employed to extend somewhat the sensibilities of the organs of touch, sight and hearing. The principle upon which the new method and apparatus are designed consists in the observation of certain electrical currents which accompany and are intimately related to the characteristic phases of the hearts action. The chief credit for the development of this method must be given to Waller, an Englishman, and especially to Eint hoven, the noted Dutch physiologist. The latter it is who, in 1903, in his laboratory at Leyden, devised the so-called “string galvanometer the most eBsential feature of the new apparatus. In most galvanometers the magnet is the movable part and the current to ,be measured passes through a stationary coil. In Einthoven's instrument this arrangement has been reversed; the magnet is stationary and the current passes through.an extremely fine wire, measuring 0.001 to 0.003 millimeter in thickness.- The filament may be or quartz covered with a fine silver coating to render it conducting, or it may consist of platinum. A very serviceable platinum thread would measure 35 millimeters in length, and from 2 to 4 micromes in diameter. This is about one-third to one,half the diameter of a red blood corpuscle. So delicate is the thread that it can be seen with the naked eye only when powerfully illuminated against a dark background. Such a thread is too light to be weighed upon even an extremely sensitive balance. Its weight has, however, been calculated by Einthoven to be about 3 to 7 thousandths of a milIigramme. The ends of the thread are fixed, so that the thread is stretched and free to vibrate very much like the string of a musical instrument. This is the feature that has ¦given the name “string galvanometer” to the device. The Istring is suspended midway between the pole pieces of a magnet, which is preferably an electromagnet. It operates on the principle that When an electric current is passed through a magnetic field, the conductor, if free to move, suffers a deflection perpendicular to the lines of force which pass between the poles of the magnet; thus when a current passes through the string of the Einthoven galvanometer this string is deflected to one side or the other, according to the direction in which the current passes. In order to obtain an accurate indication and record of the oscillations produced by the passage through the galvanometer of the feeble currents originating in the heart, a magnifying and photographically recording apparatus is provided. The cores and poles of the magnet are pierced through their centers, and two microscOpe tubes are inserted in the openings. One of these tubes is fitted with a lens for focusilg a strong electric light upon the string; the other is a pJojection microscope which throws an enlarged image of the illuminated string upon the slit of the photographing apparatus, or else upon a white !creen on which the movements of the thread can be observed directly by eye. Incidentally, it is interesting to note that a filament can be made from quartz ¦dust by a speeial process. The threads BO ohtained are probably thf fnest ever made, measuring about 1/1,250 of an inch in diameter. By the aid of this remarkable instrument the phy- sician can see and record the oscillations which the string undergoes as the result of the electric -urrents generated in the human heart during its muscular excitation which precedes every beat. The rapidity of the string movements, their extent, and the regularity or irregularity of their rhythm reveal significant information regarding the condition Of the heart muscle. And the remarkable thing about the method is that the diagnosis may be performed with the vatient in a distant room or building, the necessary connection being established through a line of electric wiring. While the coarser features of the characteristic movement of the galvanometer string can be followed by eye, for purposes of obtaining an exact record of all the finer features it is necessary to resort to photographic registration. The magnified image of . the string is projected by means of a powerful electric light upon a slit in a dark box containing a moving photographic film. Ordinarily a film of half the length of an ordinary Kodak film is sufficient for one observation. Occasionally, however, much longer photographic films may be employed. A lever connected with a chronometer marking fifths or tenths of a second oscillates before one end of the slit, so that a series of marks appears upon the film and clearly indicates tha lapse of time corresponding to the several motions recorded upon the film. The record thUB obtained is called “electrocardiogram." One can, if desired, also record simultaneously on the same film a sphyg-mographic curve of the carotid pulse by placing before the slit a lever connected with a drum and receiver. But another expedient for this purpose is registration of the carotid pulse by means of a telephone and a second sma'ler galvanometer, the string of which is projected on the same slit. J,f desired, a third galvanometer may be used in connection with a microphone, and an electrophonographic record (or “cardiophonogram") of the heart sounds be made simultaneously with the electrocardiogram and carotid sphygmogram upon the film. This means that by the aid of the galvanometer and its auxiliaries, the conditions of the heart and arteries can be investigated simultaneously in at least three different ways: (1) As regards the electrIcal changes in the heart mUscle, (2) as regards the pressure changes in the carotid artery, and (3) as regards the sounds produced in the heart during activity or while it is at rest. Yet, as stated, the patient, while the examination is being made, may be at a considerable distance from the heart station. Thus the electricity in the body oif a patient in the hospital in Leyden, one and a half miles away, has revealed important facts regarding the condition of his heart to the physicians working in Einthoven's laboratory of physiology. The apparatus in the heart station includes a whole series of different instruments, and is employed for the observation and recording of heart excitation and pulsation, heart sounds, pulse waves, blood-pressure, etc., with a view of determining if the heart is healthy or diseased; and the station is remarkable for the delicacy and compactness of the apparatus which is accomplishing such results in the aid o,f medical science. In operation the connection of the patient with the station is naturally of much importance, so that the current generated by the heart may be transmitted without loss if possible. The patient places left arm, left foot and right arm in three electrodes, which consist of zinc pans filled with normal salt solution of a strength of 8 grammes to the liter, or they may be made of German silver plates covered with felt and soaked in salt solution. From each of these, wires are conducted to three switches, by means of whlch any two of the electrodes can be connected to (Continued on page 9U.)