254 THE WORK DONE. [BOOK i. 



each stroke at a pressure of 250 mm. 1 of mercury, which is equiva- 

 lent to 3'21 metres of blood, this means that the left ventricle is 

 capable at its systole of lifting 180 grms. 3 '21 m. high, i.e. it does 

 578 gram-meters of work at each beat. Supposing the heart to 

 beat 72 times a minute, this would give for the day's work of the 

 left ventricle nearly 60,000 kilogram-meters. Calculating the 

 work of the right ventricle at one-fourth that of the left, the work 

 of the whole heart would amount to 75,000 kilogram-meters, which 

 is just about the amount of work done in the ascent of Snowdon 

 by a tolerably heavy man. 



A calculation of more practical value is the following. Taking 

 the quantity of blood as -^ of the body weight, the blood of a 

 man weighing 75 kilos would be about 5,760 grms. If 180 grms. 

 left the ventricle at each beat, a quantity equivalent to the whole 

 blood would pass through the heart in 32 beats, i.e. in less than 

 half a minute. 



1 A high estimate is purposely taken here. 



