THE ACTION OF SOME DENITRIFYING BACTERIA. 153 



Calcium succinate is soluble in these proportions, and the medium 

 is quite clear. Free growth was manifested by the cloudiness of the 

 medium forty-eight hours after inoculation, and nitrite formation was 

 apparent. After ninety-six hours the medium appeared quite milky, 

 and this milkiness was due to the presence of exceedingly fine particles 

 of a substance which was soluble in dilute hydrochloric acid with 

 evolution of gas, and was presumably Calcium carbonate. These 

 particles were so minute tliat they remained in suspension in the 

 liquid, and could only be satisfactorily separated from it by centre- 

 fugalizing. The addition to this culture of very fine particles of 

 hydrated Calcium sulpliate, or of larger particles of sand, resulted in 

 the aggregation around them of the particles of Calcium carbonate, 

 forming a concentrically laminated concretion around a central 

 nucleus. These concretions were hard, and of almost crystalline 

 appearance under the microscope, and were soluble in dilute Hydro- 

 chloric acid with evolution of bubbles of a gas which when the 

 operation was performed on a microscopic slide, could be completely 

 absorbed by running in a solution of Sodium hydrate under the cover 

 slip. Once this process of concretion has been initiated, it appears to 

 progress independently of the presence of particles which act as 

 nuclei, and a large concretion may often be found having a number 

 of smaller concretions around it, or continued into a chain of small 

 spheres, the whole presenting somewhat the arrangement shown by 

 freely budding yeast cells. The deposition of this form of Calcium 

 carbonate also takes place on the sides of the flask, and more especially 

 over any area where the glass is scratched or roughened. 



It would seem a reasonable suggestion that similar bacterial agency 

 may have played a part in the formation of oolitic limestones, which 

 are composed of concretions of Calcium carbonate around central 

 nuclei often consisting of particles of sand or shells. In the same 

 way bacterial action may have been of great importance in the pre- 

 cipitation of the various chalk strata, and indeed in the formation of 

 many rocks largely composed of Calcium carbonate. 



If this view as to chalk and oolitic limestone formation is correct, 

 it would seem probable that the precipitation of these rocks must 

 have occurred in comparatively shallow seas, which received the drain- 

 age from a country in wliich extensive weathering of rocks containing 

 Calcium salts was progressing, and where there was a considerable 

 amount of vegetation from the decay of which the organic matter 

 necessary for bacterial L;rowth would be derived. 



-NEW SKlilKS. — VUI,. IX. NO. 2. OCTOUEi;, 1911. 



