BY R. OIIEIG SMITH. 



.339 



taking 1 c.c. of glacial acetic acid and diluting it to 50 c.c. This 

 was found to be equivalent to ^=. It was diluted progressively 

 from 5 to 500 times, and tested with B. coli communis in the 

 usual manner. All the tests were positive with exposures from 

 one to four hours. Acetic acid is, therefore, inactive in dilutions 

 ranging from zero up to ^, that is, up to 72° of acidity. It 

 follows that any assistance given by the acid in the dilutions of 

 the oils cannot be due to the acid directly, but to a condition 

 that the acid brings about. 



The next experiment was made with cineol which was acidified 

 with acetic acid so that it contained 92-5° of acidity. This is 

 close to the acidity of the specimen of the rectified oil of E. 

 cinerea which had been previously tested (Table iv.). 



The acidified oil was a little more toxic, but the differences 

 were comparatively slight, due possibly to the fact that, when 

 the oil is diluted 300 or 350 times, the original acidity is reduced 

 to 0-26" ( = a quarter of a c.c. of normal acid per litre) which is 

 a comparatively slight acidity. 



The effect of using acidified water in place of neutral distilled 

 water was then investigated. A supply of recently distilled oil 

 of E. polybractea with a natural acidity of 10° was used. Dilu- 

 tions were made with water acidified with acetic acid and con- 

 taining varying degrees of acidity. 



Table xix. B. coli communis. 



* = or weaker. 

 The results are somewhat irregular, but as a whole they show 

 that an acid condition increases the potency of the oil in aqueous 



