CHAPTER XII 



CLEANLINESS AND SANITATION— WATER SUPPLY 

 AND SEWAGE 



Filth and disease have gone hand in hand 

 from the beginning of the world; but only dur- 

 ing the last quarter- century have we known the 

 true cause of infection, and why it is so closely 

 associated with dirt. The danger of uncleanli- 

 ness lies in the existence of certain microscopic 

 organisms belonging to the vegetable kingdom, 

 known popularly as microbes or germs, but more 

 properly as bacteria. Bacteria, like the plants 

 with which we are more familiar, thrive in mois- 

 ture and moderate heat, but differ from them in 

 many respects. Some of the more striking 

 differences are structure and method of repro- 

 duction, many of them possessing the faculty of 

 growing without sunlight. Bacteria are com- 

 posed of minute masses of vegetable matter 

 which vary from one ten -thousandth to one- 

 thirty thousandth of an inch in length, and they 

 reproduce by simple .division. This process of 

 multiplication may occur as often as once in 

 half an hour ; thus immense numbers may de- 



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