the First Sound of the Heart is produced. 



nature — a matter of the deepest interest to the biologist — the 

 mechanism of the comparatively modern rifle. 



The resistance to the stream of blood issuing from the ventricle is 

 offered by the block formed by the column of blood resting on the 

 aortic valves. These in their action are described by Dr. Pettigrew 

 as " closed by a spiral movement, by which these valves are wedged, 

 and, as it were, screwed, more and more tightly into each other"; 

 the movement here — the spiral movement — being caused by " the 

 direction of the sinuses of Valsalva, which curve towards each other 

 and direct the blood in spiral waves upon the mesial line of each 

 segment." * 



We find that various estimates have been given of the absolute pro- 

 pelling power of the ventricles and of the resistance of the column 

 in the pulmonary artery and in the aorta respectively. For example, 

 Professor Michael Foster says : — " If we take 180 grams as the 

 quantity in man ejected at each stroke at a pressure of 3*21 metres 

 of blood, this means that the left ventricle is capable at its systole of 

 lifting 180 grams 3*21 metres high, i.e., it does 578 gram-metres of 

 work at each beat." t 



Different estimates of the propelling force are given by physio- 

 logists, and the estimates of the resistance vary more even than the 

 estimates of the propelling power. It will therefore suffice to say 

 that authorities are substantially agreed that the driving power and 

 the resistance are in the proportion of 4 to 3, the really important 

 point for our present purpose being the relation they bear to each 

 other. 



In the motion thus described and the resistance we have all the 

 elements for the production of a sound ; and a sound being produced, 

 we ask what it is. The reply must be : the first sound of the heart, 

 the cause of which we now seek. 



If it be admitted that sound is a result of resisted motion, we have 

 in this instance a remarkable illustration of movement and resistance. 

 The movement of the blood with all the force, precision, and velocity 

 of a rifle or spiral movement, is directed against a fixed and definite 

 resistance, the moving power and the resistance being capable of 

 definite measurement and found to be quite sufficient themselves to 

 explain the source of the sound of which we are in search. This 



* ' Transactions of the Eoyal Society of Edinburgh,' vol. 23. 



f As an illustration of the great mechanical force exercised by the muscular 

 walls of the heart, Professor Michael Foster 3ays that " the work of the whole heart 

 during the day would amount to 75,000 kilogram metres, which is just about the 

 amount of work done in the ascent of Snowdon by a tolerably healthy heavy man " 

 ('Text-book of Physiology,' by M. Foster, M.A., M.D., London, 1893). 



Professor Haughton, F.B.S., in his learned and most interesting work on ' The 

 Principles of Animal Mechanics,' says that " the daily work of the left ventricle 

 is equivalent to lifting 89*7 tons through 1 foot " (Longmans, London, 1893). 



