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poses. Today we know what constitutes dangerous pollution, and the 

 bacteriologist tells us precisely Avhat the processes of boiling and filtering 

 do to this pollution in the water. He can very readily detect a polluted 

 water by analysis, and aside from showing the presence of pathogenic 

 bacteria, he can show the presence as Avell of those bacteria which come 

 only from sewage. Along this same line bacteriology is indispensable 

 to the sanitary scientist in testing the efficiency of water filters, both 

 large and small. In the matter of sewage disposal, he has shown the 

 effects of the soil bacteria in destroying the infectious material in filth 

 which is spread over the surface of the ground, or upon filter beds; 

 and again, in the putrefying action in the septic tank, he has shown 

 an efficient purification. 



It is now known through the researches of the bacteriologists that 

 the ti'phoid bacillus and other pathogenic bacteria can and do resist 

 the freezing temperatures for many weeks. Hence the freezing of water 

 does not necessarily purify it of all of its disease-producing agencies. 



It has been shown that the changes which occur in milk are wholly 

 due to bacteria. Hence the bacteriologist has pointed out the necessity 

 of bacteriological cleanliness in and about the dairies. Oftentimes dis- 

 ease germs may be found in the milk, pointing to the need of inspection 

 of daii'ies and the careful supervision of our public milk supplies. 



Putrefactive changes in meat and oth(?r foods, due to bacterial 

 growths, result oftentimes in the production of ptomaines. Therefore 

 care should be exercised in the sale of meat and other foods. Fruits 

 and vegetables are known to harbor germs on their outer skins, and, 

 when handled by infected persons, may result in spreading disease. 

 Undoubtedly this is the source of many so-called sporadic cases of 

 disease. Experiments have shown that the typhoid bacillus may remain 

 alive in the stomach of the living oyster for several weeks. Serious 

 epidemics of typhoid fever have been spread through the agency of 

 oysters which were fattened in sewage polluted waters. 



The masterly researches of Pasteur, Tyndall and Lister resulted 

 in the protection of wounds from infection, and made it possible to 

 undertake previously impossible surgical operations. They simply proved 

 the presence of germs in the dust of the air, and showed the necessity 

 of keeping this germ-bearing dust away from the vicinity of the oper- 

 ating table. 



