252 THE PHYSIOLOGY OF MUSCULAR WORK 



the work be of an unusual kind the exchange is much greater the 

 first time that it is performed, but by practice it may be reduced 

 to two-thirds of its original value. This economical working of the 

 muscles is one of the most striking results of training. The well- 

 trained body is far more efficient than the best engine. 



INFLUENCE OF MUSCULAR WORK UPON THE GLANDULAR 



SYSTEMS 



It is impossible to consider this subject fully within the limits 

 fixed for this article, but attention may be directed to two im- 

 portant glands, the kidney and the sweat glands. 



The sweat glands are thrown into activity by muscular work, 

 and the evaporation of the sweat cools the body and removes waste 

 products. Figures l have been given to show how large an amount 

 of water and heat may be removed from the body in this way. 

 During work the production of heat is raised four or five times, 

 but the increased loss of heat due to the exposure of the blood 

 in the dilated vessels of the skin is insufficient to prevent the 

 temperature of the body from rising to a dangerous height. The 

 cooling of the body in such a case is effected by the evaporation 

 of sweat and moisture from the respiratory tract. A very striking 

 instance of the limitations and dangers incurred by a failure to 

 sweat has been .recorded by Zuntz and Tendlau ( 49 ). The man 

 upon whom they made observations had no sweat glands, and 

 directly his temperature rose to 39 on exposure to the sun or as 

 the result of moderate work he breathed double as much air as 

 during rest. His skin was flushed with blood, but these efforts of 

 compensation were insufficient to prevent his temperature rising. 

 He found that he could continua to work in summer only by 

 frequently soaking his shirt in water ; with this wet covering on 

 his body he was able to supply a substitute for sweat. 



The great loss of moisture during sweating reduces the amount 

 of water secreted by the kidneys, unless an adequate supply of 

 water be taken by the mouth. The urine is concentrated, and on 

 cooling throws down a ieposit of urates. After vigorous exercise 

 albumin is frequently found in the urine. This so-called " func- 

 tional albuminuria " needs further investigation on account of its 



Y Page 247. 



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