BIOLOGY IN HUMAN AFFAIRS 



With the heart remaining in situ in the intact animal, 

 two methods have been extensively used to estimate the 

 volume of blood pumped out. In one of these an ingenious 

 apparatus, called a stromuhr, which is inserted into the 

 aorta — or large artery leaving the heart — measures the 

 amount of fluid flowing through it. In the other method, 

 the heart is completely enclosed in an apparatus called a 

 cardiometer, which can be easily constructed from an 

 ordinary tennis ball and a piece of rubber, and is arranged 

 to measure the volume changes of the heart. The change 

 from its maximal volume to the minimal represents the 

 amount of blood discharged at each beat; and since, there- 

 fore, the number of beats per minute is known, the amount 

 discharged per minute can be easily calculated. The use 

 of both of these methods has led to valuable knowledge 

 concerning the activity of the heart, but, since extensive 

 operative procedures are necessary, the question has been 

 raised as to how far the values can be applied to the heart 

 in the normal animal. 



Over half a century ago, the German physicist and phys- 

 iologist, Fick, announced a principle upon which many 

 recent methods have been based. He did not attempt to 

 try out a method based upon his idea, probably owing to 

 the lack of suitable analytical methods for gas analysis 

 in blood. The Fick principle, as it has come to be called, 

 consists in determining the total quantities of oxygen or 

 carbon dioxide in the blood of the right and left sides of 

 the heart, respectively, and simultaneously estimating the 

 quantity of oxygen absorbed or carbon dioxide given 

 off" by the animal through the lungs. Now, if M.V. repre- 

 sents the volume of blood in liters per minute discharged 

 by one side of the heart, Ao the quantity of oxygen and Ac 

 the quantity of carbon dioxide in the arterial blood, Vo the 

 amount of oxygen and Vc the amount of carbon dioxide 

 in the mixed venous blood of the right heart, the oxygen 



[280] 



