METABOLISM. OF DENITRIFYING ORGANISMS 243 



presence of. arabinose; B. subtilis, 2.41 in the presence of glucose, 

 6.55 per cent, in the presence of levulose, and 6.22 per cent, in the 

 presence of galactose; Clostridium gelatinosin, 45.55 per cent, in the 

 presence of arabinose, and 9.68 per cent, in the presence of xylose; 

 and B. prcdigiosus, 2.58 per cent, in the presence of xylose. The 

 reaction was in all cases relatively slow and was not alike for all the 

 sugars. 



Of the organisms which reduced nitrates to free nitrogen, B', 

 hartlebii set free 93.97 per cent, of the nitric nitrogen in the presence 

 of glucose, 87.59 per cent, in the presence of levulose, 84.66 per cent, 

 in the presence of galactose, 66.38 per cent, in the presence of arab- 

 inose, 83.38 per cent, in the presence of xylose, 84.48 per cent, 

 in the presence of sucrose, and 77.15 per cent, in the presence of 

 lactose; B. centropunctatum, 5.17 per cent, in the presence of glucose. 

 B. flitrowrum, 5.17 per cent, in the presence of levulose; B. coli 

 communis, 5.34 per cent, in the presence of galactose; and Bad. 

 fluorescens liquefaciens , 7.08 per cent, in the presence of arabinose. 

 The reaction was as a rule very intense both with the sugars and 

 with the salts of organic acids, especially of lactic acid, and was 

 accomplished by a gradual breaking up into carbon dioxid and 

 hydrogen or into carbon dioxid and water. The hydrogen produced 

 was thought to play a very important reducing role. 



Xylan and araban, the most abundant and widely distributed 

 carbohydrate materials in soils and manures, yields on hydrolysis 

 xylose and arabinose which are very poor sources ot carbon and 

 energy for denitrifying organisms. However, Stoklasa and Vitek 

 found that the typical denitrifying organism, B. hartlebii, assimilated 

 33.6 per cent, of the total nitrate nitrogen in a nutritive solution 

 containing arabinose and converted it into protein compounds. 



Sodium citrate, sodium acetate or glycerin added to a soil greatly 

 increase denitrification, and it is generally considered that the addi- 

 tion of starch, straw, rape cake, compost, etc., to a soil favors deni- 

 trification, whereas well-rotted manures, rape cake, and composts 

 are much less apt to have this effect. 



Metabolism of Denitrifying Organisms. Deherain found that 

 reduction was more rapid in closed flasks than in the open air, the 

 nitrogen escaping mainly in the form of protoxid. From this he 

 argued that the organisms, being deprived of the necessary oxygen 

 of the air, were forced to appropriate that contained in the nitrates 

 and thus accomplish their reduction, but we now know that the 

 denitrifiers do not necessarily require anaerobic conditions for deni- 

 trification, but do require a readily oxidizable carbohydrate. More- 

 over, as pointed out by Stoklasa, there are two classes of denitrifiers 

 one which reduces nitrates to elementary nitrogen, the other 

 which reduces it only to ammonia. Probably in both groups of 

 organisms the first steps in the process are the same. The carbo- 

 hydrates are broken down under the influence of the microorganism 



