WATER SUPPLY AND SEWAGE DISPOSAL 155 



has been sterilized. If these bacteria are of the kinds that 

 produce disease, serious results may follow when the water 

 is used for drinking and for other domestic purposes. 



The most important disease bacterium found in water is the 

 typhoid bacillus. For that reason the death rate from typhoid 

 fever is often taken as a sort of index to the condition of the 

 water supply. There is given here a graphic representation of 



WESTERN EUROPE 



Munich 1 



Leipsic ! 



Berlin wm2 



London mmmt'J 



UNITED STATES 



Cleveland 1 



Boston i 



Chicago 1 



Philadelphia- 12 



St Louis mmmm~*i^~,\->, 



Baltimore mm^^^^^^mmmmmm 22 



EASTERN EUROPE 

 Moscow. ^^^fmmmmtm^^l:! 



St. Petersburg ^^m^m~*u^^^^^^^m^i^m^=^mB, 50 



FIG. 79. Death rate from typhoid 



The figures show the number of deaths per hundred thousand population, 



based upon data for 1912. The dark line indicates the proportionate number 



of deaths in each city 



the typhoid death rates in a number of cities (fig. 79). You 

 will be able to draw your own conclusions as to the safety 

 of the different sources of supply. 



At one time Chicago had a typhoid death rate of 173 per 

 100,000 population, and at that time this was the highest 

 death rate from typhoid in the civilized world. The rate was 

 only 13. 7 per 100,000 in 1910 and 7.5 in 1912. The manner in 

 which such changes are brought about will be an important 

 subject of discussion in this chapter. 



173. Kinds of impurities. There are many kinds of impuri- 

 ties found in water. Some of these are highly objectionable, 



