WHAT IS PHYSICAL LIFE 



there is no such thing as vitality or vital 

 force. The trained physician feels then 

 like bidding these mere theorists to hold 

 their peace, for the principles of his great 

 science of Hygiene are as well settled as 

 those of any science whatever. Those 

 principles, in short, are to help life fight 

 life, that is, so to promote, on the one 

 hand, the vitality of the individual by 

 every means possible, that he can success- 

 fully resist invading micro-organisms, and, 

 on the other hand, to make his victory 

 easier by weakening the vitality of the 

 unicellular enemies. Vitality, therefore, 

 is doubly enlisted. The physician strives 

 to increase the general health of the in- 

 dividual by good food, fresh air, sunlight, 

 cleanliness or washing, and exercise. 

 Meantime if he enters the dark, close 

 rooms of a crowded tenement, he knows 

 that pernicious micro-organisms are there 

 in countless millions. But fresh air makes 

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