SPRING-KYMOGRAPH. 121 



between two ligatures, or two spring clamps. With a pair of scissors make an oblique slit in 

 the artery, and into it tie a straight glass cannula, directing the pointed end of the cannula 

 towards the heart. Fill the cannula with a saturated solution of sodium carbonate, taking care 

 that no air-bubbles enter, and connect it with the lead tube which goes to the ascending limb 

 of the manometer. The tube which connects the artery with the manometer must be flexible 

 and yet inelastic, and a lead tube is best. It is usual to connect a pressure-bottle, containing 

 a saturated solution of sodium carbonate, by means of an elastic tube, with the tube attached to 

 the manometer. This bottle can be raised or lowered. Before beginning the experiment, raise 

 the pressure-bottle until there is a positive pressure of mercury in the manometer about equal to 

 the estimated blood-pressure, and then clamp the tube of the pressure-bottle where it joins the 

 lead tube. This positive pressure prevents the escape of blood from the artery into the solution 

 of sodium carbonate. When all is ready, the ligature on the cardiac side of the cannula is 

 removed, and immediately the float begins to oscillate and inscribe its movements upon the 

 recording surface. The fluid within the artery exerts pressure latterly upon the sodium 

 carbonate solution, and this in turn transmits it to the mercury. Peptones, or rather the 

 albumoses, when injected into the blood keep it from coagulating (p. 32). Roy finds that oil may 

 take the place of sodic carbonate.] 



[Precautions. In taking a blood-pressure tracing, after seeing that the apparatus is perfect, 

 care must be taken that the animal is perfectly quiescent, as every movement causes a rise of 

 blood-pressure. This may be secured by giving curara and keeping up artificial respiration, 

 or by the carefully regulated inhalation of ether. When a drug is to be injected to test its 

 action, if it be introduced into the jugular vein it is apt to affect the heart directly. This may 

 be avoided by injecting it into a vein of the leg, or under the skin. The solution of the drug 

 must not contain particles which will block up the capillaries. Care should also be taken that 

 the carbonate of soda does not flow back into the artery. ] 



[Continuous Tracing. When we have occasion to take a tracing for any length of time, it 

 must be written upon a strip of paper which is moved at a uniform rate in front of the writing- 

 style on the float (fig. 100). Various arrangements are employed for this purpose, but it is 

 usual to cause a cylinder to revolve, so as to unfold a roll or riband of paper placed on a 

 movable bobbin. As the cylinder revolves, it gradually winds off the strip of paper, which is 

 kept applied to the revolving surface by ivory friction-wheels. In Hering's complicated kymo- 

 graph a long strip of smoked paper is used. The writing-style may consist of a sable brush, or 

 a fine glass pen filled with aniline blue dissolved in water, to which a little alcohol and 

 glycerine are added.] 



[In order to measure the height of the pressure, we must know the position of the abscissa 

 or line of no pressure, and it may be recorded at the same time as the blood-pressure, or after- 

 wards. In fig. 102 - x is the zero-line or the abscissa, and the height of the vertical lines or 

 ordinates may be measured by the millimetre scale on the left of the figure. The height of the 

 blood-pressure is obtained by drawing ordinates from the curve to the abscissa, measuring their 

 length, and multiplying by two. ] 



(5) Spring-Kymograph. A. Fick (1864) uses a " hollow spring-kymograph " 

 on the principle of Bourdon's manometer (fig. 100, II). 



A hollow C -shaped metallic spring, F, is filled with alcohol. One end of the hollow spring 

 is closed, and the other end, covered by a membrane, is brought into connection with a blood- 

 vessel by a junction-piece filled with a solution of sodium carbonate. As soon as the com- 

 munication with the artery is opened, the pressure rises, and the spring, of course, tends to 

 straighten itself. To the closed end, b, there is fixed a vertical rod attached to a series of levers, 

 h, i, k, e, one of which writes its movements upon a surface moving at a uniform rate. The 

 blood-pressure and the periodic variations of the pulse are both recorded, although the latter is 

 not done with absolute accuracy. 



[Hering improved Fick's instrument (fig. 103). a, b, c, is the hollow spring filled with 

 alcohol, and communicating at a with the lead tube, d, passing to the cannula in the artery. 

 To c is attached a series of light wooden levers with a writing-style, s. The lower part of 4 

 dips into a vessel, e, filled with oil or glycerine, which serves to damp the vibrations of the 

 levers. At / is a syringe communicating with the tube, d, filled with solution of sodic 

 carbonate, and used for regulating the amount of fluid in the tube connecting the 

 manometer with the blood-vessel. The whole apparatus can be raised or lowered on the toothed 

 rod, h, by means of the millhead opposite, g, to which all the parts of the apparatus are 

 attached.] 



(6) Fick's Flat Spring-Kymograph. The narrow tube a, a (1 mm. diam.) is placed in con- 

 nection with a blood-vessel by means of the cannula, c, and over its vertical expanded end, A, 

 is fixed a caoutchouc membrane, with a projecting point, s, which presses against a horizontal 

 spring, F, joined to a writing-lever, H, by an intermediate piece, b. The whole is held in the 

 metallic frame, R R (fig. 104). In order to estimate the absolute pressure, the instrument must 

 be compared previously with a mercurial manometer. 



