224 BACTERIA, YEASTS, AND MOLDS 



running streams, or those that pour their sewage into a lake 

 and then pump the water out for drinking purposes. The 

 housewife in the city cannot control her water supply. 

 This must be left to health boards and water commissions. 

 But she should learn whether the water is from a source 

 liable to be contaminated with sewage. If so, she must 

 regard it as dangerous and bestir herself to treat it in 

 some way that will make it safe for drinking. This can 

 be easily done by simply boiling the water, since even a 

 brief boiling destroys typhoid bacteria. This is the only 

 satisfactory method of rendering such water harmless. 

 After boiling, the water may be cooled with ice and used 

 for drinking. 



Many households are supplied with various kinds of fil- 

 ters attached to their faucets for the purpose of purifying 

 the water. The ordinary filters are worse than useless. 

 They may make the water look clear and may remove 

 some of the solid material ; but, while it looks pure, such 

 water is no safer after filtering than before. Filters in 

 ordinary use have no value whatsoever in removing typhoid 

 germs. They do remove large particles of dirt, but bac- 

 teria pass through them as easily as dust through mos- 

 quito netting ; and though they make the water clear they 

 do not make it a whit less dangerous. 



One type of water filter (the Pasteur, the Berkefeld, and 

 the Chamberland) is able to remove bacteria from water 

 and thus remove all danger. Such a filter is shown -in 

 Fig. 76. The actual filter is a cylinder (Fig. 76, a) made 

 of unbaked porcelain which is placed inside of a metal 

 covering. The water enters the metal tube and is filtered 

 through into the inside of the filter. These filters have 



