322 Mr F. J. Allen, On the nature of Heart-Sounds. [Nov. 9, 



There is no real similarity between the systolic sound and the 

 susurrus of muscles in tetanic contractions : the former is quite 

 smooth, the latter rough. A prevailing fundamental note may be 

 heard in each : but this is also heard in the second sound ; and is 

 therefore independent of muscle, and may be the fundamental note 

 of the observer's auditory mechanism. 



In the author's more delicate experiments a stethoscope of new 

 form was used. This was an ordinary binaural flexible stetho- 

 scope, fitted with a peculiar receiver which consisted of a small 

 dram with heads of thin caoutchouc membrane. This instru- 

 ment, called (in default of a better name) the tympanoid stetho- 

 scope, is very sensitive; since- the vibrations of a body can be 

 communicated to it by a very light contact with the outer drum- 

 membrane. 



Various kinds of muscle were examined both within and outside 

 the body. It was found that skeletal muscle, both of the frog 

 and of mammals, gave rise to an audible concussion or thud, when 

 contracting under the stimulus of single induction shocks. This 

 thud is louder when the muscle pulls on a weight ; but nevertheless 

 it appears to be independent of resistance : for it is still produced 

 when the muscle lies loose upon the membrane of the stethoscope, 

 and is even audible when a scrap of muscle no bigger than a pea 

 is used. Little or no sound is produced, however, when the 

 muscle is exhausted, even though its contraction remains visible 

 to the eye. 



The heart-muscle of warm-blooded animals, stimulated in the 

 same way, produces a similar concussion or thud ; which, however, 

 is much duller and weaker than that of the skeletal muscles. The 

 heart muscle-sound has not the character of a susurrus, but appears 

 to be merely the expression of a single contraction less sudden and 

 of longer duration than that of the skeletal muscle. 



The heart-muscle of cold-blooded animals (frog and crocodile) 

 gives rise to no sound audible with the tympanoid stethoscope. 

 This is apparently because the contraction, although of much 

 longer duration than those before mentioned, is not sudden enough 

 to produce an audible concussion. 



It appears that in the following kinds of muscles there is an 

 ascending scale of suddenness in contraction: — (1) Unstriped 

 muscle, (2) cold-blooded heart-muscle, (3) warm-blooded heart- 

 muscle, (4) cold-blooded skeletal muscle, (5) warm-blooded skeletal 

 muscle. The first two contract too slowly to give rise to an 

 audible concussion, and the last produces a very sharp concussion. 



Making experiments with the tension sounds produced by 

 suddenly stretching or jerking membranous substances, such as 

 tape and leather, I find that a sudden and weak jerk gives rise 

 to a short flapping sound, whilst a slower jerk with sustained 



