146 PATHOGENIC BACTERIA, 



metically-sealed pre-sterilized glass bulb, and must be 

 examined as soon as possible, as the bacteria multiply 

 rapidly in water which is allowed to stand for a short 

 time. In determining the species of bacteria found in 

 the water reference must be made to the numerous mono- 

 graphs upon the subject, and to tables such as those 

 compiled by Eisenberg. 



The discovery of certain important pathogenic bacteria, 

 as those of cholera and typhoid, will be considered under 

 the specific headings. 



Unfortunately, the bacteriologic examination of waters 

 does not throw satisfactory light upon their exact hygi- 

 enic usefulness. Of course, if cholera or typhoid-fever 

 bacteria are present, the water is harmful, but the quality 

 of the water cannot be gauged by the number of bacteria 

 it contains. 



Filtration with sand, etc. diminishes the number of 

 bacteria for a time, but, as the organisms multiply in 

 the filter, the benefit is not permanent. The filters must 

 frequently be renewed. Porcelain filters seem to be the 

 only positive safeguard, and even these, the best of which 

 seems to be the Pasteur-Chamberland, allow the bacteria 

 to pass through if used too long without renewal or with- 

 out firing. 



