498 THE RESPIRATORY EXCHANGE 



in the absorption of oxygen and the discharge of carbon dioxide, 

 such a widespread effect upon the exchange of material in the 

 body. Man in a primitive condition is forced to muscular exercise 

 in order that he may obtain food or protect himself from wild 

 animals, or more often from his fellow-man. Civilisation cannot 

 override in a generation or two the characteristics impressed 

 through countless ages, and the need for exercise becomes im- 

 perative and finds satisfaction in sport, when, owing to the process 

 of division of labour, some classes become differentiated for work 

 necessitating but little muscular activity. An agricultural popula- 

 tion find the requisite exercise in their daily toil, which is sufficiently 

 diversified to exercise all the muscles ; in a manufacturing com- 

 munity the specialisation is so great that muscular activity is in 

 some forms of work very slight or directed into some narrow 

 channel, and outdoor sport becomes a necessary pleasure to the 

 fit. One of the marked characteristics of life is oxidation ; but the 

 benefits of muscular work are not to be attributed to that alone. 

 Muscular activity is not a simple increase of oxidation ; the body 

 is not a machine from which more work can be obtained simply 

 at the expense of more fuel and increased wear and tear. The 

 co-ordination of all the systems of the body is necessary, and all 

 parts are affected ; the growth and vitality of the body is favoured 

 by the work performed. In these respects muscular exercise is of 

 the utmost importance, and one may see in the training for war- 

 fare among the highly civilised, and especially the manufacturing, 

 nations a blessing in disguise. Should the danger of war ever be 

 entirely removed the only safeguard against degeneration would 

 be outdoor sport. 



The effect of muscular exercise can be best shown by a contrast 

 of the respiratory exchange during rest and exercise. The most 

 marked rest is sleep ; the respiratory exchange is then at its daily 

 minimum. When, however, a man is awake but lying down, the 

 relaxation of the muscles is incomplete and the respiration is 

 greater ; it is only by the exercise of great care that the subject 

 of the experiment can more completely relax his muscles, and thus 

 imitate the condition during sleep. Loewy and Johansson took 

 such precautions in some of their observations, and then obtained 

 an output of carbon dioxide and an intake of oxygen which were 

 but little above the quantities found during sleep ; from their 

 results an average figure O3 grm. may be given for the discharge 



