MECHANICS OF THE HEART-BEAT 



93 



base-line of atmospheric pressure the curve ascends, and how far below 

 the base-line it sinks. To exhaust the problem, we require to have 

 tracings of the exact form of the curve for each of the cavities of the 

 heart, and to know the time -relations of the curves so as to be able to 

 compare them with each other, and with the pressure-curves of the great 

 arteries and great veins. To obtain satisfactory tracings of the swiftly- 

 changing endocardiac pressure i 

 is a task of the highest techni- / 



cal difficulty, and it is only in vvwvzittAJ. 



very recent years that it has 

 been accomplished, with any ap- 

 proach to accuracy by the use 

 of elastic manometers, in which 

 the blood-pressure is counter- 

 balanced, not by the weight of 



a column of liquid aS K in . the Fig. 3 o.-DiagrL of Hurthle's Elastic ManoT 

 mercurial manometer, but by J^g, r> small chamber covered by mem . 

 the resistance to compression brane; /t tube communicating with interior 

 01 a small column of air or the O f heart; L, compound lever to magnify the 

 tension of an elastic disc or of movements of the membrane, 

 a spring. Modifications in the 



nature and dimensions of the elastic resistance of the recording apparatus 

 and of the size of the cavity have produced successive improvements, as, 

 e.g., in the manometers of Hiirthle (Fig. 30). 



The penetrating analysis of the principles of manometer construction 

 by Frank has recently stimulated renewed investigation of the whole 

 subject with the aid of instruments whose movements are optically re- 



Fig. 31. Diagram of Optical Manometer (Wiggers). 

 A is a vertical glass tube surmounted by a hollow 

 brass cylinder, B, which contains a stopcock, C, 

 whose lumen comes into apposition with a plate, 

 a, having a small opening in it. By opening the 

 stopcock more or less, the pulsations will be ' damped ' 

 to a smaller or greater extent. Above a the cylinder 

 ends in a segment capsule b (i.e., a capsule cut away 

 at one side) 3 mm. in diameter, covered with rubber 

 dam. Upon this a small piece of celluloid carrying 

 a little mirror, c, is fastened, so that it pivots on the 

 chord side of the capsule. Over the capsule and its 

 recording mirror is mounted a support bearing an 

 inclined reflecting mirror, E, adjustable about a 

 horizontal axis by a screw, so that the image of the 

 recording mirror appears within it. Upon this 

 image a strong light is focussed. The incident rays 

 are doubly reflected, as shown in the figure, and the 

 movements of the capsule are thus greatly magnified. 

 The beam of light is photographed on a moving 

 plate. 



c-- 



corded on a photographic plate, so as to eliminate all unnecessary fric- 

 tion. Fig. 31 is a diagram of the manometer devised by Wiggers on 

 this principle. 



Hurthle's spring manometer consists of a sn^all drum covered with 

 an indiarubber membrane, loosely arranged so as not to vibrate with 

 a period of its own. The drum is connected with the heart or with 

 a vessel, and the blood -pressure is transmitted to a steel spring by 

 means of a light metal disc fastened on the membrane. The spring 



