370 



PEACTICAL PHYSIOLOGY 



the amount of oxygen absorbed by the tissues as an index of the amount of energy 

 liberated in them. In order to do this, however, it is necessary to remember that 

 the amount of energy liberated, when different food-stuffs are burnt, is not the 

 same ; thus 100 gr. of oxygen are necessary for the combustion of 35 gr. of fat, 

 the amount of energy hereby liberated amounting to 325 calories. The same 

 amount of oxygen will burn up 84 '4 grm. of carbohydrate, and yield thereby 

 346 calories, or 74 '4 grm. protein 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 

 undergoing 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. 185). 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. 

 oxygen, and 2 '5 to 3 '5 c.c. carbon dioxide. 



Example Of a Metabolism Investigation. It is desired to know whether 

 a diet containing 125 grammes protein, 50 grammes fat, and 500 grammes carbo- 

 hydrate is sufficient for a man doing a moderate amount of work. 



Protein, - 

 Carbohydrate, - 

 Fat, - 



Total, 



In urine, - 

 In faeces. - 

 In the breath, - 



Total, 



INTAKE. 



Carbon. 



62 grm. 

 200 



38 



300 grm. 



OUTPUT. 



Carbon. 

 11 grm. 



5 

 - 254 



Nitrogen. 

 20 grm. 



20 grm. 



(16-5x0-67) 



Calories. 



512-5 

 2050-0 



465-0 



3027-5 



Nitrogen. 

 16-5 grm. 

 1-0 



- 270 grm. 



17'5 grm. 



Retained in body = 30 grammes carbon and 2'5 grammes nitrogen. This 

 amount of nitrogen represents 2'5 x 6*25 = 15*6 grammes protein, or 75 grammes 

 muscle. Now, this amount of protein will account for 8 "25 grammes carbon ; so 

 that 30-8-25 = 21-75 grammes carbon represent 21'75 x 1-3 = 28*3 grammes fat. 

 On this diet, therefore, the subject retains in his tissues 15 '6 gr. protein and 

 28'3 gr. fat per diem. 



To express this result in terms of energy liberated, we know that 3027 "5 C. 

 were supplied and that all these have been used except 15*6 x 4 "1 = 64 retained as 

 protein, and 28 '3 x 9 '3 = 263 '2 retained as fat, or in toto 327 '2 C. We find, there- 

 fore, that 3027-5-327-2=2,7000. have been required. 



