158 THE CIRCULATION OF THE BLOOD 



the blood escapes past it under great pressure, and is ejected into a mass 

 of blood at low pressure, these being conditions which are well known 

 to create sounds or bruits. By examining the exact relationship of such 

 bruits to the normal heart sounds, deductions can be drawn concerning 

 the condition of the various valves. 



Record of Heart Sounds 



The heart sounds have been graphically recorded by transmitting them 

 through a stethoscope to a microphone placed in circuit with a string 

 galvanometer (electrophonograms,). Through this circuit passes a cur- 

 rent the strength of which depends on the resistance offered by the 

 microphone, and consequently to the number and amplitude of the 

 vibrations of the sounds transmitted to it through the stethoscope. 

 There are several objections to this method. One of these is depend- 

 ent on the varying distance of the heart from the chest wall, which 

 causes many of the sound vibrations to be lost before they reach the 

 stethoscope; another, on adventitious sounds arising from contracting 

 muscles, the impact of the heart against the chest wall, etc., and still 

 another on unequal resonation by the air in the neighboring portions of 

 lungs. To investigate the problem more thoroughly, Wiggers, 37 using 

 anesthetized animals, has recorded the sounds by carefully stitching to 

 the heart (exposed through a small opening in the pericardium) a lever, 

 the end of which was attached to a "transmitter" consisting of a 

 small capsule covered with rubber dam. The transmitter was connected 

 by rubber tubing to a * ' recorder ' ' consisting of another small capsule carry- 

 ing on its membrane (made of rubber cement) an eccentrically placed small 

 mirror, on to which a beam of light was thrown. The movements of the 

 beam of light reflected from the mirror, and caused by the sound vibra- 

 tions, were photographed. Mechanical vibrations set up in the apparatus 

 itself were largely eliminated by a side opening on the recorder, and the 

 effect of outside sounds minimized by surrounding the recorder by a 

 ventilated glass housing. 



Although this apparatus is not free from faults due to inherent vibra- 

 tion frequency and resonance, the records secured by it are valuable in 

 showing the exact relationship of the sounds to the events of the cardiac 

 cycle. The vibrations from the two ventricles are alike, but differ from 

 those taken from the aorta. The first ventricular sound consists of from 

 five to thirteen irregular vibrations, usually in three groups, the first 

 composed of two small vibrations, the middle one of several large vibra- 

 tions, and the third of a varying number of small vibrations. The 

 duration of the sound is from 0.05 to 0.152 seconds, and the periodicity 

 from 0.004 to 0.054 per second. When compared with an intraventricu- 



