120 HYGIENE OF BREATHING. 



air that is in the lungs, which has lately entered the air tubes, 

 and part of which can only by diffusion reach the air vesicles, 

 where the exchanges are taking place between the air and the 

 blood. 



Hygiene of Breathing. If one had a barrel of water 

 with a lot of mud in the bottom, and something kept stirring 

 up the mud, of course the water would be muddiest near the 

 bottom. Now, suppose a cupful of the water from the top 

 were dipped out and thrown away, and a cup of pure water 

 were poured in. This method of renewing the water would 

 be like the renewal of the air in the lungs, in that the least 

 bad material is removed, while the addition of fresh supply 

 is made at the point where the material is least vitiated. We 

 see that here we might help matters by dipping faster, or by 

 using a larger cup. We cannot well breathe faster, unless we 

 are exercising, but we can take more air at a breath ; and this 

 we ought to do as often as we can, not only full inspirations, 

 but deep expirations as well. Frequently during our study 

 hours it will pay us to stand erect and take a number of full 

 breaths, with the window open (if the weather will permit), 

 so that the quality 9f the air may be as good as possible. 

 The position while sitting ought to receive careful attention, 

 for a cramped position will reduce the quantity of air taken 

 in at each breath. It is a good general rule to sit with the 

 lower part of the back against the lower part of the chair-back. 

 If one forms this habit, and resists the temptation to slide 

 down in the seat, thus curving the body and cramping the 

 lungs, it will be of great benefit. In walking, it is of great 

 value to the lungs to have an erect carriage, as well as greatly 

 improving the personal appearance. To hold the chest well 

 forward, and the chin well in, is of the utmost importance to 

 every one, and should not be left to the military cadets. It 

 will aid the health and appearance of other students as much 



