ELIMINATION OF SPORING BACTERIA 81 



of various kinds yeasts, fungi, possibly flagellates 

 (such as Bodos), paramecia, and other ciliates, and 

 any of the numerous organisms which may infect 

 ordinary tap water, or which float about in the 

 dust of a room. There is little trouble, by 

 selecting suitable areas of a culture, in freeing 

 amoeba cysts from everything but bacteria, 

 although small moulds and minute flagellates will 

 persistently appear in cultures which are not made 

 with strict sterile precautions. A point of the 

 greatest importance is the necessity for the 

 removal of spore-bearing bacteria, which were 

 constantly present in every culture we examined, 

 and which have proved to be by far the greatest 

 difficulty we have had to contend with. We 

 know of no germicide which will certainly destroy 

 spores without killing amoeba cysts, and the 

 separation must be carried out entirely by 

 mechanical means. After many failures, through 

 the employment of methods which have already 

 been described, we undertook the preparation 

 independently by two different methods, one of 

 which has been successful and the other partially 

 so. 



METHOD 1. RESULT : PURE MIXED CULTURES OF 

 AMOEBA WITH B. fiuorescens non-liquefaciens 

 AND WITH B. brunneum 



Beginning with the most impure culture 

 we could obtain, several subcultures were made 

 on 2-per-cent. agar jelly in small Petri dishes 

 inverted over water. By this method of cultiva- 

 tion a more rapid development of the amoeba is 

 nr 6 



