PART III 

 BACTERIA AND SEWAGE 



CHAPTER XII 

 THE PROBLEM OF SEWAGE- DISPOSAL 



EARLY in his history man learned to know that the 

 committal to earth of his waste products was quite 

 effective in rendering them harmless and inoffensive. 

 As long as he. retained his nomadic existence, and kept 

 moving from place to place, the problem of refuse- 

 disposal was not a vital one. The time came, however, 

 when he established himself more or less permanently 

 in camps and villages. It then became necessary for 

 him to protect himself against being poisoned by his 

 own excreta. Trenches and pits were therefore located 

 outside of the habitations to receive the waste and offal 

 capable of undergoing putrefaction. 



But the tent and the hut were finally replaced by 

 the more permanent home. Human life itself became 

 more complex. Man's mind developed and his wants, 

 straightway, became more numerous. He began to 

 cook his food, to wear garments, to wash them, and to 

 use considerable quantities of water for purposes other 

 than drinking. The shallow trench being no longer suf- 



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