119 



expecled if .a protozoal action had been assisted li\ ihe hacleiiophage 

 aiitidyseiiter'iae present in the water. 



In each flask the nimiliei (if protozoa inneased aireadv twodavs 

 after tlie iiiocuhition with llie mass of i)acleria. Their niiinlier was 

 greatest one dav before the contenis of the flasks became bicid, 

 whereas it decrease(i after the clarification had been completed; 

 some of them were transformed iiilo cysis. 



Again a ciilliii-e, equal to the one al the beginning of the experi- 

 ment was transplanted into ihe flasks in which the tTphiis-bacteria 

 and the cholera-vibriones had disappeared. The same was repeated 

 twice when, after about ten davs the contents had clarified again. 



After each new infection the number of |)rotozoa was augmented, 

 as with the first, reached its maximum shortly before the clarifica- 

 tion and decreased again aftei- it. Every time a portion of the pro- 

 tozoa were seen to turn into cysts. 



When the contents of the flasks had become ipiile clear agaui 

 after the fourth infection, another examination was performed for 

 bacteriophage aiitityphus abdomiiialis and anticliolera vibriones. The 

 result was absolutely negative. 



So these experiments go to show thai large crowds of iy|)lins- 

 bacleria and cholera-vibriones may disappear without any inter- 

 ference whatever of bacteriophages, from water into which they were 

 introduced fortuitously or intenlionally. Even in water containing a 

 bacteriophage anii-bacteria-dysenteriae the H. dysenteriae do not 

 disappear quicker than olher bacteria not attacked by bacteriophage. 



It was nevertheless of interest to examine especially the influence 

 of the presence or the abseiu-e of bacteriophage anti-shiga on the 

 rate of disappearance of B. dysenleriae from Ihe water. 



Two series of ex|)erimeiits were accordingly carried out. 



In the first sei'ies the faie o( B. dysenteriae in unliltered water 

 was compared with that of the same bacilli in filtered water. 



Protozoa cannot pass ilnough a filter impervious to bacteria, 

 whereas the bacteriophage is let ihrough. 



In the second series a comparison was made of the lapidity of 

 the self|iurificaiion process of bacteriophage containing watei' that 

 was or was not mixed wit KCN. 



The residls of these tests, winch were e\'ery lime the same, are 

 leported below. 



Vlietwaier, which contains bacteriophage, was used for llie iinpiiry. 

 Fart of it was filtered through a Berkefeld-filter. A ccnilrol-experi- 

 ment showed ihai this water is free from bacteria and protozoa. 



Part of the filtered, as well as the nnfiltered water was infected 



