114 BACTERIA AND THE DISINTEGKATION OF CEMENT, 



The presence of a denitrifying organism deep in the cement is 

 neither an argument for nor against the action of the nitrite 

 organisms upon the cement. Vibrio denitrijicajis reduces nitrate, 

 but not nitrite, and in order to form the nitrate the lime of the 

 cement must first be converted into calcium nitrate. The 

 presence of Vibrio denitrificans, however, does not necessitate the 

 presence of nitrates. They are not essential to its existence. It 

 can grow freely in media devoid of them, so that the reduction 

 is purely an accessory phenomenon. Moreover no nitrification 

 was obtained on seeding solutions of ammonium sulphate with 

 portions of the deep cement where disintegration was in active 

 progress, and where the denitrifying organism was found. 



There are doubtless many bacteria in the decomposing cement 

 that can form acid from carbohydrates, but in the water and the 

 cement there are no carbohydrates, or if there are they are 

 present in such minute traces that they may be ignored. There is a 

 possibility that acid might be formed by bacteria in the absence 

 of carbohydrates, and to test this point neutralised asparagin- 

 cement-water was coloured with litmus and infected with the 

 samples. No change of colour became evident after two months' 

 culture, so that the possibility of acid formation by bacteria in 

 the interstices of the cement may be dismissed. 



On the whole there is considerable room for doubt regarding 

 the action of micro-organisms upon cement. There is more reason 

 to believe that the action is purely chemical, and brought about 

 by the decomposing and solvent action of the Avater alone upon 

 the cement which probably has not been adapted for resisting the 

 action. The debris had an alkaline reaction to litmus, and I 

 noted that in the bottles in which I endeavoured to obtain nitrifi- 

 cation of an ammonium sulphate solution there had formed upon 

 the glass a considerable incrustation of crystals of calcium 

 carbonate. It seemed peculiar that this should occur with a 

 sample which, to all appearance, was reddish-yellow sand and 

 grit. Curious to know the amount of free lime in the sample, I 

 added 5 grms. of saccharose to 500 c c. of boiled and cooled 

 distilled water, and after adding a few drops of phenolphthalein 



