RESPIRATORY CHAMBERS 145 



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of the pulmonary fan separate, and as they separate the 



air chambers in their forks expand and air rushes into 



them. But that only happens if all three walls of the 



thoracic bellows are set in motion — its front and side 



walls and its floor or diaphragmatic piston. If we breathe 



lazily we may move only one part of the chest wall, and 



then it is only one part of the pulmonary fan that is 



fully expanded. Hence the importance of setting the 



human machine in full motion for some minutes each 



day. If we set the machine thus going combustion takes 



place in the body ; the nerve centres which control the 



movements of the respiratory bellows are at once flooded 



with impure blood and automatically stimulated. They 



are stimulated so that more oxygen may be taken in 



and more carbon dioxide discharged. A child needs no 



teaching how to breathe ; set it running, playing, climbing 



trees or stairs, and it cannot help using its lungs fully and 



rightly. There is no more need to teach a child how to 



breathe than how to suck — Nature has seen to that. 



But every child has to be taught, and we have all to 



learn, that under modern conditions of life there are 



temptations to abuse Nature's contrivances by neglecting 



them, by failing to set them fully and frequently in 



motion. 



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