150 APPLIED BACTERIOLOGY FOR NURSES 



of the colon-typhoid type. This method, therefore, affords 

 a simple means of protecting communities against water- 

 borne typhoid fever and other water-borne diseases. 



A modification of the chlorine method has been in- 

 troduced by Dakin for the emergency purification of 

 water. It consists in the addition to the water of a tablet 

 of halazone, a chloramine compound related to dichlor- 

 amine-T. (See page 42.) 



Purification by Distillation. — iVnother method of puri- 

 fying water is to distil it, i. e., to convert it into steam 

 and condense the steam in a vessel kept cold. Freshly 

 distilled water is absolutely pure, since not only all living 

 organisms are destroyed, but any chemicals in solution 

 are kept back. Such water is quite expensive and not 

 particularly palatable. Its continued use as a drinking- 

 water is thought by some to be harmful, owing to the ab- 

 sence of any salts and the likelihood to abstract salt from 

 the tissues. 



Purification by Boiling. — Probably the simplest, easiest, 

 and, at the same time, a very safe process of household 

 purification of water is to boil it for ten minutes. The 

 objectionable "flat" taste can be removed, for drinking- 

 water, by pouring from the vessel at a considerable height, 

 or by shaking it in an open vessel to aerate it. Of course, 

 water which has been boiled to sterilize it for surgical pur- 

 poses must be kept in a properly cotton-plugged vessel to 

 prevent air contamination. 



Bacteriologic Examination of Water. — Regular bac- 

 teriologic examinations of the water supply of a town 

 are made in order to keep informed on the purity of 

 the water and to enable one to locate contamination 

 at once. If tap-water is to be tested, it is necessary 



