METABOLISM. 473 



serves as a source of energy for muscular work, but only by taking the 

 place of fats and carbohydrates as a generator of heat. Alcohol in 

 this amount does not lower the energy produced by the other food- 

 stuffs. 



Frenzel found that sugar increased the activity of muscle when 

 exhausted, but he also found that protein in iso-dynamic quantities 

 was much more effective, and whilst the saccharose lost its effect at 

 the end of the third hour, the effect of proteid continued until the 

 seventh hour. 



Action of Various Agencies upon Metabolism. 



Mental activity has no direct effect upon metabolism. The 

 glands especially are, next to the muscles, generators of heat. Sun- 

 shine acts upon metabolism by increasing the activity of the nervous 

 system and thus the movements of the muscular system, which pro- 

 duces more energy. Sunshine has no direct action on metabolism. 

 Cold increases the generation of heat, the consumption of oxygen and 

 the exhalation of carbon dioxide. With a rise of external temperature 

 the increase in metabolism in warm-blooded animals is less than when 

 the temperature falls. Cold baths or douches may increase the oxygen 

 and carbon dioxide exchange from 50 to 200 per cent.; hot baths 

 increase them from 50 to 100 per cent. At the seashore gaseous 

 exchanges were increased in two individuals, but not in a third one. 



Alterations of pressure in air chambers, whether a decrease of 450 

 millimeters or an increase of 1,500 millimeters, do not affect the con- 

 sumption of oxygen in the dog or man. This is true in rest and in 

 work. In high altitudes the respiratory gaseous exchange is primarily 

 increased 10 to 20 per cent, compared with persons living on the low 

 lands and not used to climbing mountains. This result is neither due 

 to a diminution of pressure nor only due to increase of work by the 

 muscles of respiration. It is a result of some climatic influence to 

 which the body must adapt itself. 



Effect of Age and Size. In the infant and the child the taking in 

 of and taking out of C0 2 is greater than in the adult, due to the 

 relation between skin surface and mass, for the larger the animal is the 

 smaller the ratio between the surface and its mass, for surface increases 

 as its square and weight as its cube. In old people the respiratory 

 exchange is smaller than in the adult, due to quietude and loss of tone 

 in the muscles. 



The smaller' animal has a greater exchange of and C0 2 than 

 a larger animal. 



