CHAPTER XVIII 



PRINCIPLES OF BIOLOGY APPLIED TO HEALTHFUL 



LIVING 



I. PERSONAL HYGIENE 



448. Hygiene. In this chapter it will be shown that 

 very many of the facts and principles of biology are of great 

 value when applied to making the human body freer from 

 disease and a more efficient mechanism for carrying on a use- 

 ful and happy life. 



That department of biological science which deals with the 

 established principles of human health is commonly known 

 as hygiene. It is simply a phase of applied biology. When- 

 ever hygiene deals with the health of individuals, how to take 

 care of oneself, as in rules for eating, breathing, sleeping, etc., 

 it is called personal hygiene. This is chiefly the principles 

 of biology, particularly of physiology, applied with a good 

 proportion of common sense. By this we mean, for example, 

 that one who has studied the structure and working of the 

 lungs will need only common sense to enable 'him to see that 

 tight clothing will interfere with the natural movements, and 

 then the hygienic rule " do not wear tight clothing " is seen 

 to be a scientific application of the biological principles re- 

 lating to human breathing. The same is true with regard 

 to every organ; and we do well to examine every proposed 

 new rule of hygiene from the standpoint of applied biology. 

 Thousands of foolish rules of hygiene have been published, 

 but it is usually possible to select the good ones because they 

 are obviously based upon the principles of biology. For 

 example, if some one advised prolonged mastication of fat 



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