THE HEART 



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ness depends solely upon the pressure in the aortic and 

 pulmonary systems. Increased loudness of this sound, 

 therefore, always indicates an increased arterial or 

 pulmonic blood-pressure. The sound produced in the 

 left ventricle is always louder than that of the right, 

 and both attain their maximum intensity between the 

 ages of twenty and forty. The pulmonary second sound 

 is louder than the aortic up to the age of puberty ; there- 

 after the aortic second becomes progressively the louder. 



First Opening 

 sound of 



semilunar 

 valves 



Second 

 sound 



The Work of the Heart.* 



The total work of the heart is the sum of that done 

 by its different chambers. The work of the ventricles 

 consists chiefly in overcoming the pressure in the aorta 

 and pulmonary artery, and, to a much less extent, in 

 imparting to the expelled blood the necessary velocity. 



* Benno Lewy, ' Die Arbeit des Gesunden und des Krankeu 

 Herzens,' Zeit. f. Klvn. Med., 1897, xxxi. 321. 



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