ADVANCED PHYSIOLOGICAL CHEMISTEY 479 



The same amount of oxygen will burn up 84*4 gr. of carbohydrate, 

 and yield thereby 346 calories, or 74-4 gr. proteid yielding 362 

 calories. It is therefore necessary, before employing the oxygen 

 absorbed as an index of the amount of energy liberated, to ascertain 

 that, when the determination is being made, the food stuffs under- 

 going oxidation are always the same. This can be ascertained by 

 estimating the respiratory quotient, the value of this being influenced 

 mainly by the nature of the food stuff undergoing combustion at the 

 time (see p. 145). So long as the R.Q. remains constant, any increase 

 or diminution in the amount of oxygen absorbed represents more 

 or less energy liberated. In order that we may be able to compare the 

 oxygen assimilation of different individuals under the same conditions, 

 Zuntz has suggested that the determination should be made the first 

 thing in the morning, immediately on awakening, and twelve hours 

 after the last diet (which should not contain much carbohydrate) has 

 been taken. The estimation should be made by Zuntz respiratory 

 apparatus. The amount of oxygen absorbed, and of carbon dioxide 

 exhaled, is then reckoned for each kilo, body weight, and for each 

 minute. The normal amounts for man are 3 to 4*5 c.c. 0, and 2*5 to 

 3-5 c.c. C0 2 . 



Example of a Metabolism Investigation. It is desired to know 

 whether a diet containing 125 grammes proteid, 50 grammes fat, and 

 500 grammes carbohydrate is sufficient for a man doing a moderate 

 amount of work. 



INTAKE. 



Carbon. Nitrogen. Calories. 



Proteid, 62 gr. 20 gr. 512-5 



Carbo., 200 2050'0 



Fat, 38 465-0 



Total, 300 gr. 20 gr. 3027-5 



OUTPUT. 



Carbon. Nitrogen. 



In urine, 11 gr. (16'5 x 0-67) 16-5 gr. 



In faeces, 5 1-0 



In the breath, 254 



Total, 270 gr. 17 -5 gr. 



Retained in Body. 30 grammes carbon and 2-5 grammes nitrogen. 

 This amount of nitrogen represents 2 '5 x 6 '25 = 15 -6 grammes proteid, 

 or 75 grammes muscle. Now, this amount of proteid will account for 



