CHAPTEE XVIII. 



Bacteriological study of water, air, and soil — Methods of counting 

 the colonies on the plates — Wolffhugel's counting apparatus — Sedg- 

 wick's method. 



The possible spread of infectious diseases by means 

 of water-supplies has formed a topic of discussion by 

 sanitarians for a long time. 



The school of Von Pettenkofer has always taken the 

 ground that the appearance and spread of epidemic 

 diseases, of which typhoid fever and Asiatic cholera are 

 types, is due more to alterations in the spil, resultitig 

 from fluctuations in the level of the soil-water, than 

 to any part that the drinking-water may play ; in op- 

 position to this Koch and his pupils hold that these 

 epidemics can, in most instances, be traced directly to the 

 influence of the water-supply. 



The weight of evidence as it now stands favors the 

 opinion that these diseases are frequently the result of 

 imperfections in the supply of water intended for do- 

 mestic purposes, and there exists sufficient proof of this 

 to necessitate our controlling all such supplies by careful 

 quantitative and qualitative bacteriological analyses. 



The Qualitative Bacteriological Analysis op 

 Water. — The qualitative bacteriological analysis of 

 water entails much labor, as it requires that not only 

 all the different species of organism found in the water 

 should be isolated, but that each representative should 

 be subjected to systematic study, and its pathogenic or 

 non-pathogenic properties determined. 



