1914] Lipman-Burgess : Ammouification and Nitrification in Soils 129 



The only work with which the writers are acquainted which 

 allows of any direct comparison with our results is included in 

 the splendid series of investigations of Fred** on the effects of 

 small or limited quantities of various poisons on the higher as 

 well as the lower plant organisms. In addition to showing the 



stimulating powers of certain poisons like CS2 and p'-rr' ) 



on the bacterial count, nitrogen-fixing power, etc., of soils in direct 

 soil cultures, that investigator gives evidence also of work done 

 with the higher plants yielding similar results. Of a series of 

 metallic salts, further, with which Fred worked he was unable to 

 demonstrate stimulation to nitrification except perhaps one case 

 of slight stimulation through the use of FeS04 (100 mgs. per 100 

 grams of soil). The salts tested were MnS04, FeSO^, CUSO4, 

 and NaCl. The nitrifiable material employed was (NH4)oS04 

 and not the organic nitrogen of blood which we used. 



Aside from these investigations, only one or two of which 

 have any direct bearing on our subject, but little has been 

 accomplished of either direct or indirect applicability to our 

 results. Where any studies were carried out dealing with the 

 effects of the heavy metals on bacteria, such as those of Kellerman 

 and Beckwith" or Jackson," they were prosecuted in solutions 

 and therefore, as one of us has emphatically shown in other 

 publications,^- are scarcely comparable with results from soil cul- 

 tures such as are below discussed, or with results obtained with 

 plants in soil cultures. 



Since the experiments below described were completed there 

 has appeared from the pen of Greaves^^ a paper bearing on the 

 effects of arsenic on ammouification and nitrification in soils. This 

 work, because of the methods employed, is of pertinence here, 

 and interesting, because of the stimulating powers of considerable 

 quantities of arsenic in soils to ammonia and nitrate production 

 by the natural flora. While arsenic, chemically considered, is a 



9 Cent, fiir Bakt., 2'« Abt., vol. 31, p. 185. 



10 Bull. 100, Bur. PI. Ind., U. S. D. A. 



11 Jour. Am. Chem. Soc, vol. 27, II, p. 675. 



i2Bot. Gaz., vol. 55, p. 409 and literature there cited, 

 13 Cent, fiir Bakt., 2*"^ Abt., vol. 39, p. 542. 



