RESPIRATORY QUOTIENT. 887 



of the expired air is less than that of the inspired air. This depends 

 upon the fact that not all of the oxygen appears again in the expired 

 air as carbon dioxide, because it is not only used in the oxidation of car- 

 bon, but also in part in the formation of water, sulphuric acid, and other 

 bodies. The volume of expired carbon dioxide is regularly less than the 



volume of the inspired oxygen, and the relation ^p, which is called the 



respiratory quotient, is generally less than 1. 



The magnitude of the respiratory quotient is dependent upon the kind 

 of substances destroyed in the body. In the combustion of pure carbon 

 one volume of oxygen yields one volume of carbon dioxide, and the 

 quotient is therefore equal to 1. The same is true in the burning of 

 carbohydrates, and in the exclusive decomposition of carbohydrates in 

 the animal body the respiratory quotient must be approximately 1. In 

 the exclusive metabolism of proteins it is close to 0.80, and with the decom- 

 position of fat it is 0.7. In starvation, as the animal draws on its own 

 flesh and fat, the respiratory quotient must be a close approach to the 

 latter figure. The respiratory quotient, which is calculated with exclusive 

 combustion of carbohydrate, fat and protein, as respectively, 1, 0.707 and 

 0.809 and with alcohol is 0.667, also gives important information as to 

 the quality of material decomposed in the body, especially with the 

 supposition that the carbon dioxide elimination is not influenced by some 

 special condition such as a change in the respiratory mechanism. Another 

 supposition is that no incomplete oxidation step in combustion is elimi- 

 nated. 



The respiratory quotient can also be strongly influenced by inter- 

 mediary processes in the animal body, as by the formation of glycogen 

 from protein, or from fat or by the formation of fat from carbohydrates. 

 In the first case the quotient may be lower than 0.7 and in the last case 

 it can be higher than 1. 



Knowledge as to the extent of oxygen consumption is of special 

 importance in the calculation of the energy metabolism from the extent 

 of gas exchange, and one can under some circumstances approximately 

 calculate the energy exchange from the calorific value of the oxygen 

 alone with regard to the respiratory quotient (ZUNTZ and co-workers). 

 The calorific value of oxygen must be different for each of the three men- 

 tioned foodstuffs, as they require different quantities of oxygen for their 

 combustion. For fat and carbohydrate this calorific value can be readily 

 calculated, as these bodies are completely burnt into carbon dioxide and 

 water. One gram of starch uses 828.8 cc. oxygen in its combustion 

 and produces 828.8 cc. carbon dioxide, and 4183 calories of heat are 

 developed. For one liter ( = 1.43 gram) oxygen, 5047 calories are pro- 

 duced, therefore for every liter ( = 1.966 gram) carbon dioxide formed, 



