28 THE ROYAL SOCIETY OF CANADA 



isolated on Medium A was also accompanied by a granular precipita- 

 tion in the medium. This has already been referred to in connection 

 with the direct cultural examination of the water samples. 



The precipitates in the liquid cultures settled after a few days 

 on the walls of the flasks and gradually increased in thickness as 

 growth progressed, particularly at the surface of the cultures where 

 growth was most active. The deposits were scraped off the flasks and 

 examined microscopically and chemically and were found to consist of 

 spherular crystalline nodules of calcium carbonate containing traces of 

 magnesium carbonate. The deposits in the solid medium were sepa- 

 rated by dissolving the latter in boiling water and centrifugalizing the 

 solution whilst still hot. They seemed to consist of the same material. 



Specimens of the precipitates obtained by these means were 

 submitted to Dr. Edwin T. Hodge of the Geological Department of the 

 University of British Columbia for mineralogical examination. From 

 a consideration of the optical properties of the precipitates Dr. Hodge 

 considered that they consisted of calcite. He found perfect rhombs 

 scattered throughout all the precipitates from liquid media, but only 

 spherules in the preparation from the agar medium. In the former 

 case the cleavages are related to each other at angles which are a 

 little small for calcite which Dr. Hodge suggests may be due to the 

 presence of the dolomite molecule. The precipitates agree therefore 

 in the main in mineralogical properties with those obtained by Drew 

 by the action of marine denitrifying organisms. 



This precipitation of calcium carbonate does not seem to depend 

 entirely on the production of nitrite or of ammonia in the cultures. 

 It occurred quite as strongly in the cases of the cultures inoculated 

 with the 100 fathom sample, in neither of which nitrite was formed 

 and in only one of which ammonia developed, as in the others. In 

 the cases in which ammonia was formed, either by reduction of the 

 nitrite or by the break down of peptone, the calcium carbonate clearly 

 resulted in part from the direct interaction of the CO2 produced by 

 bacterial action, on the calcium salts in solution. Granted the 

 presence of a base to combine with the acid radicle set free from the 

 calcium salt this reaction is bound to occur in neutral solutions and it is 

 clear that ammonia when present will so function. In cases where 

 denitrification occurs (as in those studied by Drew) the base liberated 

 by the complete elimination of the acidic group from the nitrate will 

 also perform the function,^ but in cases where neither ammonia forma- 



^ It is interesting to note in this connection that precipitation of calcite takes 

 place in media containing the same constituents as those dealt with here, but made 

 up with distilled water, under the influence of organisms isolated from soil. 



