THE RESPIRATORY EXCHANGE 489 



The formula for the fat is a hypothetical one to represent the 

 mean composition of fats, oleostearopalmitin, but a similar equa- 

 tion can be given for olein or stearin. According to this equation 

 100 grm. of glucose would during its transformation into fat 

 yield 21-8 litres of carbon dioxide. 



In the marmot the deposition of fat is extremely marked in 

 the autumn ; during the winter this store undergoes combustion 

 during the animal's very prolonged, but perfectly natural, fast. 

 On general biological grounds it is improbable that the processes 

 of metabolism in this animal differ fundamentally from those 

 in non-hibernating mammals ; the difference is probably only 

 quantitative and not qualitative. In fact, there is evidence to 

 show that this view is correct. Respiratory quotients greater 

 than unity have been found by various observers both in the case 

 of men and animals after the ingestion of a meal rich in carbo- 

 hydrates. 



It is probable that the respiratory quotient represents the 

 resultant of various processes of combustion, in some of which 

 oxygen is absorbed without a corresponding output of carbon 

 dioxide, in others carbon dioxide is discharged in excess of the 

 oxygen absorbed, the extra quantity of oxygen contained in the 

 carbon dioxide being derived from the intramolecular oxygen 

 of the food. Fasting and feeding accentuate these procesess 

 respectively, and since it is probable that the liver is most 

 actively engaged, the results obtained from determinations of the 

 gases of the blood flowing through any particular organ may 

 appear to be out of harmony with the character of the total 

 respiratory exchange. The one is a local respiratory exchange, 

 the other the resultant of the respiration of all the tissues of 

 the body. 



Stress has been laid upon these points, for there has been a 

 tendency to deny, or at least ignore, the existence of respiratory 

 quotients above unity ; it is also necessary to enforce the fact 

 that an analysis of one of two samples of the air expired during 

 a short period may give an inaccurate idea of the total respiratory 

 exchange of an animal or man. 



Total Respiratory Exchange. The following table (see p. 490) 

 shows the value of the total 1 respiratory exchange of man and 

 various animals during a condition of rest. 



