554 



SCIENCE 



[N. S. Vol. XXXI. No. 797 



higher percentage of colon colonies than either 

 the standard litmus lactose agar or the esculin 

 medium, and is a very favorable medium for 

 colon isolation, the malic acid agar gives a still 

 higher percentage of colon colonies, combined with 

 a very low total count, and is a very satisfactory 

 medium for colon isolation when only the active 

 forms indicative of recent pollution are desired. 

 Studies in Soil Bacteriology, IV.: The Inhibition 



of Nitrification by Organic Matter, Compared 



in Soils and in Solutions: F. L. Stevens and 



W. A. WiTHEKS, assisted by P. L. Gainet, J. K. 



Plummeb and F. W. Shebwood, North Carolina 



Collie of Agriculture and Mechanic Arts. 



In experiments regarding nitrification it was 

 demonstrated that: 

 In Liquid Medium 



Peptone 0.8 per cent, inhibited at 4 weeks. 



Cottonseed meal, nitrogen equivalent, 0.1 per 

 cent, inhibited at 4 weeks. 



Cottonseed meal, nitrogen equivalent, 0.1 per 

 cent, inhibited at 16 weeks. 



Peptone 0.8 per cent, inhibited at 16 weeks. 

 In Liquid Medium absorbed by Soil 



Peptone 1.25 per cent, retarded at 4 weeks. 



Peptone 5 per cent, inhibited at 4 weeks. 



Peptone 5 per cent, did not retard at 16 weeks. 



Cottonseed meal, nitrogen equivalent, 0.4 per 

 cent, retarded at 4 weeks. 



Cottonseed meal, nitrogen equivalent, 0.5 per 

 cent, retarded at 16 weeks. 



Cottonseed meal, nitrogen equivalent, 0.1 per 

 cent, did not retard at 4 weeks. 



Cow manure in quantities equivalent to 1, 5, 

 10, 20, 30, 40, 80, 160 tons per acre in 2-week, 

 8-week and 12-week periods, did not retard nitri- 

 fication in soil at 8 weeks but rather favored it. 



Nitrification occurred in pure cow manure at 

 8 weeks and at 12 weeks. 

 A Simple Low-temperature Incubator: Kael F. 



KEiiEBMAN, Bureau of Plant Industry, Wash- 

 ington, D. C. 



During the winter of 1905 the writer found it 

 necessary to improvise a low-temperature incu- 

 bator, and since that time has had similar ones 

 in almost constant operation. The incubator is 

 fundamentally a four-compartment refrigerator 

 carrying ice in the upper right-hand compartment 

 and a heater, consisting of a single incandescent 

 electric-light globe and a thermo-regulator, in the 

 lower left-hand compartment. The thermo-regu- 

 lator may be operated on a separate circuit using 

 a storage battery or Edison-Leland cell, or from a 



shunt circuit from the main feed wire. Such in- 

 cubators may be installed readily and may be used 

 for either temporary or permanent purposes. 

 Plagella Staining of Pseudomonas radidcola 



(B.) Moore: Karl F. Kellebman, Bureau of 



Plant Industry, Washington, D. C. 



Staining unfixed smears of Pseudomonas radi- 

 dcola with saturated alcoholic stains according 

 to the method of Edwards and Barlow has occa- 

 sionally given the figures described by these 

 authors as indicating the polar flagella or " giant 

 whips." I have been able to duplicate these ap- 

 pearances almost exactly by mixing bacteria 

 which had no polar flagella with artificial slime 

 or gum and preparing and staining the slides 

 according to the method of Edwards and Barlow. 

 Therefore, while this method of staining may have 

 a diagnostic value for the peculiar slime secreted 

 by Pseudomonas radidcola, I do not believe that 

 the flagella themselves are indicated. 

 Nitrification Studies in Nevada and, Utah: Kabl 



F. EIellerman, Bureau of Plant Industry, 



Washington, D. C. 



In the arid and semi-arid regions of the west 

 there are two areas which in many ways should 

 be comparable; these areas are the beds of the 

 prehistoric Lake Bonneville in Utah and Lake 

 La Hontan in Nevada. The former, containing 

 the Mormon settlements, has long been famous 

 for the crop-producing power of its soil; the 

 latter has furnished some valuable farms to early 

 ranchers, and recently considerable areas have 

 been brought under irrigation as the Truckee- 

 Carson project. 



During the past year nitrification studies have 

 been carried on in Utah by Mr. I. G. McBeth and 

 in Nevada by Mr. E. R. Allen. These studies have 

 indicated that nitrification proceeds in Utah soils 

 following the same general rates of activity in 

 the different layers that occur in eastern soils, 

 nitrate formation decreasing very rapidly below 

 the surface, although it persists to much greater 

 depth than has usually been described. Azoto- 

 baoter is very frequent and occurs in appreciable 

 numbers even as far below the surface as the 

 tenth foot. In the Nevada soils nitrification is 

 very erratic, the surface layers in many cases 

 nitrifying much less rapidly than deeper layers, 

 while some regions seem to lack the nitrifying 

 flora almost completely. The deficiency in nitri- 

 fying bacteria seems correlated with poor crop 

 production in many cases, although the prevalence 

 of alkali is also a source of crop injury. When 

 not present in excessive quantities the white 



