1 88 The Story of the Bacteria 



town, so as to avoid the sewage of the town 

 itself, which, as a rule, is allowed to escape 

 directly into it. But in almost all cases, in 

 thickly settled countries, there are other 

 towns on these streams above the points at 

 which the water is taken, polluting it with 

 their sewage. Now so prevalent is typhoid 

 fever all over the civilized world that the 

 sewage of every large town is liable to contain 

 greater or less numbers of living typhoid 

 bacilli 



In older countries where the sanitary dan- 

 gers which always grow with the increase and 

 massing together of the people have been 

 longer observed and more definitely recog- 

 nized than in our own, legal enactments have 

 long been in force to prevent the pollution of 

 streams which might be sources of water sup- 

 ply of towns. But still large cities have found 

 it necessary to further protect themselves 

 against disease -producing organisms and 

 against filth, by the maintenance of filtering 

 systems on a large scale, by which the 

 dangerous elements of a contaminated water 

 may be largely or entirely removed. 



