gradsky, who isolated them in pure culture. Of great im- 

 portance is the fact determined by Winogradsky that the 

 numerous species of the group of nitrifying bacteria may be 

 classified into two sharply divided sub-groups: Nitroso- 

 bacteria and Nitro-bacteria. The nitroso-bacteria oxidize 

 ammonia to nitrous acid, while the nitro-bacteria lack the 

 faculty of attacking ammonia, but perform the important 

 task of converting nitrous acid into nitric acid. 



We are indebted to E. Marchel for proving that the 

 faculty of eliminating ammonia from albuminoids is common 

 to many fungi. The potency of the different species was 

 found by him to vary, the largest quantity being produced by 

 Bacillus mycoides. 



The first researches along the line of denitrification were 

 undertaken by Jules Reiset in 1854 and 1855. He asserted 

 that free nitrogen was always evolved during the decomposi- 

 tion of manure. Denitrification in arable soil was first noticed 

 by Gappelsroder in 1862, and was long regarded as a purely 

 chemical process. The first reference to the agency of bacteria 

 in this decomposition was made by E. Mensel in 1875, and the 

 earliest pure cultures of such organisms were obtained by U. 

 Gay on and G. Dupetit in 1882. In succeeding years a large 

 number of species, all capable of reducing nitrates, was made 

 known. In 1888, P. Frankland was able to associate with the 

 group in question 17 out of 32 species, and R. Warington 16 

 out of 25 species examined. A. Maassen, in 1902, found that 

 out of 109 species, 85 were able to perform this function. 

 But few of the organisms which have been observed to reduce 

 nitrates to nitrites in pure culture, are able to continue the 

 reduction to the liberation of free nitrogen. 



For an inquiry into the various functions performed by soil 

 bacteria in general and with reference to the factors concerned in 

 the fixation of nitrogen by azotobacter, ammonification, reduc- 

 tion of nitrates and denitrification, in particular,seventy samples 

 of soil were taken. These soils comprise perhaps all of the various 

 types within our borders, with the possible exception of the alkali 

 tracts which are interspersed over the western half of our 

 state. Locations were made not with special reference to any 

 favored locality or type of soil, but rather that the samples 



