50 SULPHUR BACTERIA 



in the change from the nitrate to free nitrogen there is a total 

 gain in energy of 



74-6 + (i| X 112) + 6-8 == 249-4 calories. 



The sulphur denitrifying bacteria are peculiar in that they 

 utilize the oxygen derived from the nitrate reduction to oxidize 

 sulphur compounds in place of the carbohydrate oxidized by 

 the ordinary denitrifying bacteria. The sulphur compounds 

 (sulphuretted hydrogen, sulphur, etc.) must be regarded as 

 fermentable substances and their oxidation as exothermic 

 processes (or fermentation processes), which have as their 

 biological purpose the supply of energy to the organisms. 

 The sulphur compounds must thus be regarded not as them- 

 selves the suppliers of energy but rather as the vehicles 

 that arc made use of in the transformation of energy. As in 

 the true sulphur bacteria they are parts of the respiratory 

 machinery of these bacteria. It is interesting to note that 

 Cranston and Lloyd find that the denitrifying organism 

 examined by them often converted 100 per cent, of the nitrate 

 supplied to it into free nitrogen, and that if this is universally 

 true for such organisms the whole of the nitrate is used for 

 respiratory purposes and none is used to build up the protein 

 molecule. 



Physico-chemical Speculations in regard to Organic 

 Matter in Sulphur Waters. 



There are both biological and chemical methods for the 

 direct estimation of organic matter in water. Indirect methods 

 must therefore be regarded as of subsidiary importance. 

 Consideration is given to the following speculative treatment 

 of the subject by Baas-Becking, on account of its interesting 

 physico-chemical deductions. He attempted to prove the 

 smallness of the organic content of the sulphur waters, rich 

 in sulphur organisms, which are found in the neighbourhood 

 of Stanford University, California. He bases his deductions 

 upon the facts that the CO2 of the atmosphere is in equilibrium 

 with the CO2 in the water and that the pW value of sulphur 

 waters varies from pW 7-6 to pH 8-6. 



