BACTERIA AND SANITATION 163 



trary to the usual belief). They are most abundant in 

 rivers that flow through populous regions. They are com- 

 paratively scarce in dry, sandy soils, and very numerous in 

 moist, loamy soils. The water of cities should never be 

 taken from a stream or lake into which sewerage flows 

 unless it is thoroughly filtered. Filters are constructed 

 thus : first a layer of small stones, next a layer of coarse 

 sand, lastly a layer of very fine sand on top, the total thick- 

 ness being four or five feet. Beneficial microbes live upon 

 the grains of sand and destroy all, or nearly all, of the 

 dangerous microbes as the water slowly soaks through. 

 The construction of such waterworks is left to sanitary 

 engineers, of course, and the average citizen does not need 

 to know the details. 



The department of street cleaning should receive the 

 willing cooperation of all citizens. Banana peelings, paper, 

 etc., should not be thrown upon the street or school 

 grounds. Garbage, ashes, and rubbish should be placed in 

 separate cans, as the rules provide. Garbage cans, if not 

 thoroughly cleaned, acquire unpleasant odors and breed 

 flies and bacteria. They should be thoroughly washed 

 with very hot water and sal soda and scalded with boiling 

 water and scrubbed with an old broom. 1 



The chief duties of the Health Department are: quar- 

 antine isolation and disinfection, with the purpose of pre- 

 venting or controlling contagious and infectious diseases ; 



1 The chief Disinfectants are : fresh air, sunshine, heat, formaldehyde, etc. 

 Airing and sunning will destroy some germs in bedding and clothing as effec- 

 tually as chemicals. Boiling and steaming are the best ways of applying heat. 

 Formaldehyde is a volatile liquid. After room is sealed and strips of paper 

 pasted all over cracks, a specially constructed generator is applied to keyhole, 

 and room kept closed for 1 2 hours. Mercuric chloride (corrosive sublimate) 

 is used I part to 1000 parts of water for disinfecting soiled clothing, towels, 

 utensils, surgeon's instruments, and wounds. In place of this, carbolic acid\ 

 5 per cent solution, may be used, but it is not so good a germicide. 



