USE OF HYDROCHLORIC ACID 93 



(3) Hydrochloric Acid (2 per cent, of B.P. pure 

 31'8-per-cent. HC1). As described before, this is 

 the most useful germicide for separating amoeba 

 cysts from living bacteria provided that the bacteria 

 are found by actual experiment to be killed by it. 

 It has been of no use when applied directly to 

 impure cultures in which the nature of the bacteria 

 was unknown. We first employed it on a culture 

 of P. f. liq. and B. brunneum, both of which were 

 totally destroyed on jelly media, and in solution by 

 2-per-cent. HC1 in twenty-four hours. The acid 

 was originally washed away eight times with sterile 

 water, but this is unnecessary, for amoebae will 

 excyst on media containing at least 0'2 per 

 cent. HC1. 



(4) Among numerous other substances employed 

 by different authors we need only mention alkalies, 

 to which there seems to be no objection, as cysts 

 will stand exposure to 5-per-cent. caustic soda for 

 at least a week. Sodium bicarbonate has been 

 used, and if spores are absent we think it might be 

 adequate. 



SUMMARY 



By means of various mechanical devices and 

 the use of germicides, cultures of amoebae with 

 a limited variety of bacteria were obtained, and 

 these, when subjected to the action of 2-per- 

 cent, hydrochloric acid for twenty-four hours, or 

 to thorough drying for six weeks, were found 

 to be free from living bacteria, while the cysts 

 were still alive and have been employed in 

 making pure mixed cultures, the results bein 

 tabulated briefly as follows : 



