98 HIGH TEMPERATURE ORGAN'ISM OF FERMENTING TAX-BARK. 



In the stack there is a comparatively slow and prolonged evolution of carbon 

 dioxide which i?^ mainly, if not entirely, due to a bacteriological fermentation 

 while the speed of the fermentation seems to be regulated by the small amount 

 of nitrogenous matter in the bark. Were it to be mixed with some substance of 

 a nitrogenous nature, there is no doubt that the production of carbon dioxide 

 would he much more rapid. This was shown by the influence of asparagin in 

 one or two experiments. 



The organism is peculiar in some respects. It is capable of decomposing 

 sugar such as dextrose or saccharose when freshly isolated, but soon after it 

 requires the addition of alkali to enable it to act. There are some points yet 

 to be determined regarding its viability,. for the vegetative forms rapidly die off 

 under certain, as yet uninvestigated, conditions. The spores are very difficult 

 to destroy, especially when they are contained iu the por«s of the bark: tliey 

 were alive after an exposure to 186° to '205° for two and a half hours. 



While the bacteria can decompose tempered bark and stack-bark and also 

 raw tan-bark after it has been treated with alkali, we are not cjuite sure if they 

 are capable of fermenting cellulose such as disintegrated cotton-wool. When they 

 were tested with this there was not enough carbon dioxide given off to warrant 

 the conclusion that the cellulose had been attacked. 



There was no growth of the organism in media devoid of soluble sources of 

 carbon such as Uschinsky's solution. On the other hand there wa,s growth and 

 gas formation in similar solutions containing sugar. Thus the constituent of the 

 bark that is fermented is still unknown. 



SUMMAKV. 



The fermentation of spent wattle-bark in the corrosion of white lead is 

 caused by a stout rod-shaped bacterium having a terminal spore. Its optimum 

 laboratory temperature is 1)0° C., although in the corroding stacks the tempera- 

 ture may rise to 80°. 



Raw spent wattle-hark is difficult to ferment and requires a preliminary 

 treatment. As conditions which oxidise tannin substances favour the fermentation 

 of the raw bark, it is i)robable that the residual tannins inhil)it fermentation. 



I am indebted to Lewis Berger and Co., Ltd., for a supply of bark, and 

 to Mr. H. J. Sullivan, of the Company, tor notes upon the manufacturing pro- 

 cess. I am also indebted to Mr. W. W. L'Estrange for much kindly assistance. 



