The Supply and Uses of Water 217 



coarse parts of the sediment are broken up and in time liquefied 

 unless they are unusually resistant material. Such substances 

 as paper, cotton cloth or similar vegetable fiber, wood, and 

 certain kinds of wool fiber are dissolved in the course of a few 

 months. The third division effects a continuous removal of 

 the purified liquid without disturbing the main body. 



Disease-causing bacteria. The third group of bacteria 

 found in sewage and due to human waste is the disease-causing 

 or pathogenic kind. This group forms a real danger to the 

 health of all members of the family and community. One 

 variety of the pathogenic bacteria is that known as the typhoid 

 fever bacillus or germ. This may come from two sources : 

 first, from the discharges of patients suffering with the disease ; 

 second, from individuals who are typhoid carriers. Some of 

 these may never have had the disease, and be immune to it, 

 yet carry the germs and distribute them unknowingly where 

 much harm may result. Other individuals who have suffered 

 with typhoid fever may continue to harbor the germs after 

 recovery and throw them off in such ways as to endanger the 

 health of others. There are, moreover, other diseases, such as 

 dysentery, cholera, diarrheal disorders, and hookworm, which 

 are distributed through the careless and imperfect disposal of 

 human waste products. The germs of such diseases may be 

 transferred accidentally to places where food and water may 

 be contaminated. It often happens that vegetables like lettuce 

 and celery, which are eaten without cooking and upon which 

 dangerous microorganisms thus escape destruction by heat, are 

 fertilized or otherwise polluted with unpurified sewage. Water 

 which appears to be pure may be swarming with deadly micro- 

 organisms transferred to it through carelessly distributed 

 human waste matter. Thus such germs find their way from 

 the ill, or those who have been ill with such diseases, to those 

 persons who are healthy. 



These facts, which have been demonstrated repeatedly, 

 should make clear the necessity and obligation of every one to 



