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RESPIRATORY QUOTIENT. Ss7
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, hut also in part in the formation of water, sulphuric acid, and other
bodies. The volume of expired carbon dioxide is regularly less than the
CO
volume of the inspired oxygen, and the relation -rr11
, 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 j’ields 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 respirator}’ 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 bod}’, 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,
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