472 PHYSIOLOGY. 



Effect of Muscular Work on Metabolism. 



The respiratory exchange is increased in all kinds of work. The 

 quantity of air breathed is also increased. Severe work causes the 

 gaseous exchange to increase during hard work about five to seven 

 times its amount during rest. 



When work is ended the gaseous exchange returns to normal 

 within four to nine minutes after medium work. Massage has no 

 marked effect upon metabolism, producing, however, a small increase. 

 The increase of utilization of oxygen in muscular work is in part due to 

 increased activity of the muscles of the cardiac and respiratory 

 apparatus. In muscular work the proteid is not used,, for urea is not 

 increased, but the carbohydrates and fats are made use of. The fats 

 are somewhat behind the carbohydrates in the formation of energy. 

 Atwater's results prove that fats and carbohydrates may be exchanged 

 for one another in a mixed diet and keep up the level of energy. The 

 question then arises, Does the muscle use the carbohydrates and fats 

 directly, or are they changed into glucose first before being utilized? 

 It is not decided whether glycogen and the fats are directly used or' 

 that they must first be changed into glucose. 



When the proteids are used in muscular work they probably have 

 in the liver their nitrogen part changed into urea, and the carbon 

 moiety is stored as glycogen or fat and directly oxidized in muscle 

 work. Fifty-eight per cent, by weight of the meat proteid metabolized 

 according to Lusk, can be converted into sugar in the body. About 

 fifty per cent, of the proteid taken becomes, by the exogenous metabo- 

 lism of the liver, converted into urea. The remainder goes to repair the 

 tissue or organized proteid of the body. The endogenous metabolism 

 of the organized proteid of the body is indicated not by the urea, but 

 by the creatinin and to a lesser degree by the uric acid. The question 

 now arises, Why not give carbohydrates and fats instead of proteids? 

 as the nitrogen moiety is removed by the liver and excreted by the 

 kidney. It is probable that in the splitting of proteid there are many 

 different kinds of amino-acids produced. These building stones must 

 be of various varieties to fit in the building up of the tissues or organ- 

 ized tissue proteid. 



Atwater and Benedict have shown that the total metabolism on 

 an alcohol diet was no greater than on a diet without alcohol ; in both 

 cases the same amount of work having been performed. In these 

 experiments 72 grammes of alcohol were taken in the course of the 

 day in place of an iso-caloric amount of fat. Here alcohol indirectly 



