724 . EXPERIMENT STATION RECH)RD. 



No. 1-3, pp. 65-l.'i). — The author claims that tho temporal lire of the surface 

 layers of the soil in tho Tropics is sutticioutly hijih during much of the day to 

 promiit(> the growth of thoruiophiUms bacteria in great numbers and of many 

 species. Several subspecies of Bucilhis tlicnnopluluH are isolated and described. 



Some remarks on aerobic nitrogen-fixing bacteria in the Tropics, E. de 

 Kruijff {Bid. Df-pt. Agr. Indes Neerland., 1909, No. 30, pp. 18-21; Ccntbl Bakt. 

 [etc.], 2. Abt., 26 (1910), No. 1-3, pp. 5.'/-56).— In a genera! examination of 

 tropical soils for nitrogon-tixing bacteria, three si)ecies, a Micrococcus and two 

 Bacterium forms, were found and described, and the amount of free nitrogen 

 they wore able to fix is given. 



The formation and utilization of nitrous oxid by bacteria, .M. W. Bi;i- 

 JERINCK and I). V. J. Minkman (Ccutbl. Bakt. [cfr.\, 2. Abt., 25 {1909), No. 

 1-^h PP- 30-63, pi. 1, figs. Jfj abs. in Jour. Chcm. »S'oc. [London], 96 {1909), No. 

 566, II, pp. 10Ji3, lOJfJt). — The formation of nitrous oxid in different media and 

 with A-arious infection materials is given with much detail as to apparatus and 

 methods used, and results obtained. 



It was found that when earth was used as infection material in bouillon 

 with from 5 to 12 per cent of nitrates at from 20 to 37° C, it gave a gas 

 volume with more than SO per cent of nitrous oxid. When the nitrate content 

 was lowered, relatively less nitrous oxid and more free nitrogen was liberated. 

 The most active denitrifying agent in these soil experiments was the polymor- 

 phic spore former, Bacillus nitroxtis and its subspecies. Pure cultures of B. 

 pyocyaneus, B. Htutzeri, and Micrococcus dcnitrificans, in bouillon with a 1 per 

 cent nitrate at 37° gave gas volumes containing from 65 to 75 per cent, 10 

 per cent, and 20 per cent nitrous oxid, respectively. The nitrate used for the 

 last two was ammonium nitrate and in tho case of M. dcnitrificans there was 

 also liberated 42 per cent of free nitrogen. Denitrification by the spore-form- 

 ing bacteria was more intense in the crude than in the pure cultures. 



The experiments relative to the utilization of the nitrous oxid showed that 

 , when denitrifying bacteria decompose nitrous oxid under favorable conditions, 

 the nitrogen is liberated and the oxygen appears combined with carbon in 

 the form of carbon dioxid. B. stutzcri possesses this characteristic to a high 

 degree. Nitrous oxid can become a source of oxygen to some bacteria, as 

 Spirillum, and prevent the growth of Azotobacter. The bacteria which do not 

 directly denitrify the nitrate can, after other species have decomposed it. brealc 

 up the resulting nitrous oxid. A new formula as to the chemical reactions 

 occurring in denitrifying processes is proposed. 



Two new methods for growing Azotobacter, C. Hoffmann and B. W. Ham- 

 mer (Gentbl. Bakt. [etc.], 2. Abt., 2Jf {1909), No. 5-7, pp. 181-183).— To obtain 

 a large amount of pure Azotobacter, the authors use S or 11 inch Petri dishes 

 with a i in. layer of agar medium in the bottom. The plates are then inocu- 

 lated with a heavy suspension of Azotobacter, there being used 10 cc. per 

 plate distributed evenly over the agar and incubated. An abundant growth 

 consisting entirely of Azotobacter is thus obtained which can be scraped off 

 the surface of the agar and used for chemical analysis. 



To study the influence of different chemical compounds upon the nitrogen- 

 fixing properties of Azotobacter, a " sand-slope " culture was devised, consist- 

 ing of from 10 to 15 gm. of sand in a 150 cc. flask, to which is added 20 cc. of 

 the liquid culture medium, and then inoculating with a 1 cc. heavy suspension 

 of Azotobacter. After inoculation the sand is so sloped that considerable of 

 it is above tho surface of the liquid culture. 



Ammonia and nitrate as a nitrogen source for molds, (4. Ritter {Bcr. 

 Dent. Bot. Grscll., 27 {1909), No. 10, pp. 582-588 ) .—The results of exi)erimouts 

 with various ammonium salts and nitrates as a source of nitrogen for species 



