METABOLISM OF PROTEIN 



189 



Underwood and Underwood 



The amounts of human energy expended in various types of work can be measured by a calor- 

 imeter. This is done by devices which measure the amount of oxygen absorbed and the amount 

 of carbon dioxide given off by the subject doing a particular kind of work. 



ing new cells and for repairing any wastage. If there is a surplus 

 of protein materials it is thought that a portion is held as a sort 

 of storage supply in the liquids or tissues of the body. This sur- 

 plus is then utilized when the loss of protein from the cell is 

 greater than the supply needed by the body for repair, as in time 

 of illness. 



If there are more proteins (in the form of amino-acids) than 

 the cells can utilize, some of the excess is eliminated by the 

 kidneys, while others are taken care of by cells in the liver. 

 These cells in the liver are capable of separating the amino-acids 

 into ammonia and non-nitrogenous products (oxygen, hydrogen, 

 carbon, sulphur, and phosphorus). The ammonia combines with 

 other elements to form urea which is eliminated by the kidneys as 



