BIOLOGY AND HEALTH 429 



8. Proper care of the teeth is necessary if food is to be thoroughly 

 chewed. It is sufficient to remember that tooth decay is a bac- 

 terial process, that the warmth and moisture of the mouth make 

 ideal conditions for bacterial growth, and that perfect cleanliness is 

 our only means of protection. This suggests frequent careful 

 brushing, use of antiseptic tooth washes, and a visit to a dentist 

 at least twice a year " whether you need it or not." 



9. Violent exercise, severe study, worry, or any mental or 

 physical activity, at or near meal-times interferes with proper 

 digestion. 



10. Regular attention must be given to the removal of waste 

 from the intestine, as a long series of illnesses can be traced to 

 lack of care in this regard. 



Hygiene of Respiration. We have learned the use which the body 

 makes of oxygen in releasing the energy in our foods and keeping 

 us alive and active. Naturally, proper breathing is required if this 

 process is to go on in a healthful way. 



We need to train our breathing muscles, because few of us know 

 how to breathe, even though we use the expression " natural as 

 breathing." 



Deep breathing means using more lung tissue, getting more 

 oxygen, and developing the diaphragm and rib muscles, 

 properly. 



We cannot use all our lung capacity at once, but should use all 

 we can. We train the other muscles for less important uses; why 

 not train our breathing muscles for the race of life? 



Erect position and comfortable clothing are necessary if we are 

 to breathe properly. 



The nose was made for breathing, not the mouth (see Chap. 39) 

 and any disease or growth which interferes with nose breathing 

 should be removed. 



Ventilation. Deep breathing will do little good if the air breathed 

 is bad: this means attention to ventilation. Proper ventilation 

 should secure 



1. A sufficient amount of air in proportion to the number 

 concerned 



