BY R. GREIG SMITH. Ill 



been found in these experiments, but furthermore they were not 

 found in the disintegrating cement below the surface. This 

 points to the nitrifying organisms coming upon the scene at a late 

 period when disintegration is complete and when a considerable 

 amount of organic matter derived from algae, etc., is present in 

 the brown and black debris. 



The next line of investigation was the separation of organisms 

 that could multiply in the presence of an alkali such as sodium 

 carbonate. Taking the disintegrated cement obtained at a depth 

 of six inches into the canal face as being the sample most likely 

 to contain bacteria capable of causing disintegration, portions 

 were introduced into tubes containing 10 c.c. of bouillon and 

 quantities of alkali varying from 0-5 to 1*0 c.c. were added. 

 The tubes became turbid and orange-coloured colonies of one type 

 developed on plates inoculated with the growth of the tube con- 

 taining the highest amount of alkali. Subcultures of the organism 

 showed it to be Bact. croceuiin* a bacterium which had previously 

 been isolated from the Sydney water. It grows well at 37° C, 

 and this temperature was employed in subsequent trials with 

 further increasing amounts of alkali. These trials showed that a 

 turbidity, the evidence of growth, took place in the presence of 

 equal volumes of 10 % sodium carbonate solution and bouillon, 

 that is, the bacterium developed in the presence .of 5 % by weight 

 of sodium carbonate. A percentage greater than 5 prevented 

 the growth entirely. Plate cultures from the 5 % bouillon culture 

 showed the turbidity to have been caused by the growth of the 

 organism, while plates infected from the clear tubes containing 

 over 5 % remained sterile It is needless to say that the bacterium 

 grew in bouillon containing less than 5 % sodium carbonate 

 (Nao COg). With the exception of Bact. crocenmfi^ all the bacteria 

 in the deep cement were inhibited by 0-5 % sodium carbonate at 

 a temperature of 37° C. 



This organism is remarkable in being able to withstand so 

 much alkali. The records as to the limiting amount of sodium 



* These Proceedings, 1900, Part iii., p. 456. 



