121 



The phenomenon exhibited in the KCN flask is to be interpreted 

 by tiie fact that at the beginning of the experiment the KCN destioys 

 the vegetative forms of tiie protozoa and consecinenlly they are 

 prevented from clearing away the germs present in the water. The 

 cysts of the prolozoa are not killed by KCN. After a week so 

 mncli of the KCN has been decom|)osed throngh contingent chemical 

 processes, that the cysts again grow into vegetative protozoa, which 

 devour the Flexner bacilli, present in the water. 



CONCLUSIONS. 



When summarizing onr results it must be concluded that the 

 significance of the bacteriophage for the selfpnritication of water is 

 no doubt only small. I for one did not succeed in establishing the 

 slightest influence. 



The purification is effected in the absence of the bacteriophage, 

 whereas its presence does not accelerate the process, nor render 

 it more complete. 



The experiments again yield conclusi\e evidence for the prominent 

 role played by protozoa in the self-purification of water. 



When, under such circumstances as the laboratory enables us to 



establish, we eliminate the protozoa, the self-purification of water is 



entirely arrested even though bacteriophage be added to the water. 



{From the Laboratory for Dvpical Hygiene of the 



Ley den- University). 



