170 



PRACTICAL PHYSIOLOGY 



pressure as 1 1 mm. Hg, the velocity of flow in the aorta as 320 mm. 

 per sec. Mercury 13*5 times heavier than blood 



The right heart is considered as doing one-third of the work of the 

 left heart. 



The total work of the human heart is estimated to be about 12,000 

 kilogramme-metres per day, or 500 kg.m. per hour. This equals 

 about 28 kilo-calories (425 kg.m. = 1 kilo-calorie). 



H Air Cushion, 



Recorder 

 FIG. 172. The Cardiometer. 



In the dog the output can be obtained by estimating the amount 

 of oxygen taken up by the blood from the inspired air in one 

 minute. This can be obtained by Fredericq's or Zuntz's method 

 (see p. 184). At the same time samples of arterial and venous blood 

 are obtained, and the oxygen difference between the two samples 

 estimated by the blood pump or Haldane's ferricyanide method (see 

 p. 190). The number of heart beats per minute is also counted. 

 Suppose 100 c.c. of oxygen are taken up per minute, the arterial 

 blood contains 5 c.c. per cent, more oxygen than the venous blood, 

 and the heart beats 80 times per minute. Then, as every 100 c.c. 

 of blood carries away 5 c.c. O 2 , 2000 c.c. of blood must have passed 

 through the heart in the minute. Thus the output 



2000 



80 



= 25 c.c. 



The output in mammals is reckoned to be about *0012 of the 

 body weight per sec. 



The Cardiometer. Demonstration of the method of recording the 

 volume of the output of the heart. The Cardiometer is made of 



