REPORT OF MEDICAL SECTION. 155 
Second Report of the London Sub-Committee of the British 
Association Medical Section, on the Motions and Sounds of 
the Heart. 
Tue Committee appointed in London by the British Associa- 
tion for the Advancement of Science, to investigate the Motions 
and Sounds of the Heart, have the honor to lay before this meet- 
ing a short account of some investigations of the abnormal 
sounds of the heart and arteries in which they have been recent- 
ly occupied. 
Before describing these, the Committee would remark, that 
although their last inquiries have not been specially directed 
to that subject, yet they have had many opportunities of verify- 
ing the conclusions on the natural sounds as presented in their 
report of last year; and these conclusions not having been since 
shaken by any experiment or rational objection, it may be con- 
sidered as fairly established, that the first or systolic sound of 
the heart is essentially caused by the sudden and forcible tight- 
ening of the muscular fibres of the ventricles when they contract ; 
and that the second sound, which accompanies the diastole of 
the ventricles, depends solely on the reaction of the arterial 
columns of blood on the semilunar valves at the arterial orifices. 
It further appears that the first sound may be increased by an 
additional sound of impulsion against the walls of the chest, 
under certain circumstances of posture, of increased action of 
the heart, and of certain stages of the respiratory movements. 
It is also obvious that the character of the first sound may in 
some measure depend on the closure of the auriculo-ventricular 
valves, and on the quantity of blood ; inasmuch as these deter- 
mine the nature and time of the resistance against which the 
muscular fibres of the ventricles tighten. So, likewise, the vigour 
of the ventricular systole, the quantity of blood propelled by it, 
the sudden and complete character of the diastole, the fulness of 
the arterial trunks, as well as the perfect, mobile, and mem- 
branous condition of the semilunar valves,—will determine the 
character and loudness of the second sound. An experimental 
illustration of the effect of one of these conditions was observed 
by the Committee in the great diminution of the second sound 
by the free division of the carotid artery, which would greatly 
diminish the arterial tension. 
As additional illustrations of the production of a sound, like 
that of the heart, by muscular contraction, the Committee have 
noticed that which accompanies the action of the panniculus 
carnosus of the ass during life, and the quivering contraction 
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