CONDITIONS INFLUENCING METABOLISM 1/9 



are the more important. They not only furnish energy 

 which is immediately used up in running the machinery of 

 the body, but they deposit, or attempt to deposit, a reserve 

 supply to protect the proteid portions of the organism 

 against accidents to temporary deprivation of food, demands 

 for an unusual amount of energy, malnutrition from vari- 

 ous causes, etc. savings laid by for the proverbial rainy day. 

 This reserve supply takes the form first of glycogen, which 

 is soon used up, meeting as it were only the demands of the 

 hour, and second of fat, which begins to be drawn upon when 

 the glycogen is exhausted, and which lasts for a length of 

 time depending upon its amount. 



Conditions Influencing Metabolism. Regular exercise is 

 undoubtedly favorable to the nutrition of any part, as e. g., 

 the muscles, the brain, etc. Exercise may mean increased dis- 

 assimilation, but if so it also means increased assimilation. 

 With regard to muscular exercise of average severity and 

 reasonable duration, the results of cellular activity seem at 

 first a little surprising, but are really to be expected if the 

 concluding remarks of the previous paragraph are true. The 

 amount of urea under such exercise is not appreciably in- 

 creased which means that disassimilation in the protoplasm 

 of the muscle cells is not increased. This remark holds good 

 however, only when the supply of sugars, starches and fats 

 is abundant ; if they are not present in sufficient quantity to 

 meet the increased demand for energy-supplying materials, 

 then the proteids must be oxidized to furnish it, and the urea 

 discharged is increased. In striking contrast to the constant 

 output of urea is the largely increased output of CO2, repre- 

 senting oxidation of the carbohydrates and fats. 



During sleep the nitrogenous output is not materially di- 

 minished, while that of CO2 is markedly less. This is ex- 

 plained by the fact that there is less energy needed and cor- 

 respondingly less oxidation of the energy-producing mate- 

 rials. Proteid metabolism is undisturbed. 

 f A low external temperature does not increase the output 



