THE RESPIRATION 305 



2. Food. The taking of food at once sets up active changes 

 in the digestive apparatus. The muscular mechanism is 

 set in action, and the various glands secrete. As a result 

 of these processes the respiratory interchange is at once 

 increased. That the increase is dependent upon the in- 

 creased activity is shown by the fact that it is produced 

 by the taking of substances which cannot be absorbed and 

 used in the metabolic processes of the body. 



But while the immediate increase in the respiratory inter- 

 change following the taking of food is due to the increased 

 activity of the digestive structures, there is also an increase 

 due to the utilisation in the body of the food taken. 

 Whether proteids, fats, or carbohydrates, or all of these form 

 the diet, more oxygen is consumed and more carbon dioxide 

 given off than during starvation. The proportion between 

 the oxygen taken and the carbon dioxide excreted is not, 

 however, the same with all these food-stuffs. If the food 

 is rich in carbon and poor in oxygen, a greater quantity of 

 oxygen must be taken to oxidise it than if it is rich in 

 oxygen. Thus while the carbohydrates contain about 40 per 

 cent, of C and 53 per cent, of O, the fats contain about 76 

 per cent, of C and only 12 per cent, of 0, and the proteids 

 contain 52 per cent, of C and 22 per cent, of 0. 



Hence on a carbohydrate diet the respiratory quotient 



(p. 299) * is hi g h > about ' 9 to 1* wnil e on a fatty or 

 proteid diet it is low, 0-7 to 0-8. 



3. Temperature. If the temperature of the body is in- 

 creased, the metabolic processes become more active and 

 the respiratory interchanges are increased. But if the tem- 

 perature of the air round the body is elevated, the metabolic 

 processes may be diminished in activity, and the respiratory 

 exchange decreased. 



4. Light. It has been shown that light increases the 

 metabolic changes and therefore the respiratory activity. 



5. Sleep. Since in sleep the animal is in a condition of 

 muscular rest, since light is excluded from the eyes, and 

 since food is not taken, the respiratory exchanges are less 

 active during sleep than during the waking hours. Simi- 

 larly, in the long winter sleep of certain animals (hiber- 

 nation), these factors as well as the diminished temperature 



20 



