



^V^*v . ■ 





Fig 6. — The Nitrate Org-anism of Winogradsky, 

 isolated from Quito earth. Converts nitrites into 

 nitrates — the second stag^e of nitrification. (After Wino- 

 gradsky : Ann. de 1' Institut Pasteur, 1891, Plate 

 XVIII. ) 



