jSTew York Agricultural Experiment Station. 201 



such as beef-extract-peptone gelatin, as used by Hiltnerand Stormer, 4 

 or Heyden agar as used by Engberding. 8 None of these were 

 very satisfactory and it was soon concluded that special media must 

 be used in soil work. The simplest modification (e. g. that of 

 Hoffman 6 ) differed from the ordinary beef-extract-peptone formulae 

 only in the substitution of soil-extract for pure water. A slight 

 improvement was claimed for this modified formula, but it has not 

 been generally regarded as sufficient to warrant its continued use. 

 The recent modifications have all been of a different sort. The 

 best results have been obtained on media low in organic matter. 

 The low organic content of these media undoubtedly holds in check 

 certain rapidly growing organisms that would otherwise prevent the 

 growth of the more numerous but more slowly growing bacteria. 

 Fisher 7 in 1909 described several media of this nature. Early in the 

 following year 8 Fischer recommended another medium, still simpler 

 in composition, which allowed even more soil bacteria to produce 

 colonies. This last medium was an agar to which nothing was added 

 but soil-extract (prepared by extracting with a 0.1 per ct. solution 

 of Na2C0 3 ) and potassium phosphate. The advantage of reducing 

 the amount of organic matter was discovered contemporaneously by 

 Lipman and Brown 9 who recommended an agar which contained 

 no nitrogen beyond that furnished in 0.05 gram of peptone per litre. 

 In 1911 Temple 10 recommended a culture medium for soil work 

 which was also low in organic content, although it contained one 

 gram of peptone per litre. Temple states that he could obtain 

 better results with this medium than with Lipman and Brown's 

 formula. In 1913 Brown 11 published a modification of Lipman and 

 Brown's formula, replacing the .05 gram of peptone with one gram 

 of albumin. (For the complete formulae of the last four media see 

 Table I.) Brown gives the results of six comparative tests that 



4 See footnote 2. 



6 Engberding, D. Vergleichende Untersuchungen iiber die Bakterienzahl im 

 Ackerboden in ihrer Abhangigkeit von ausseren Einflussen. Centbl. Bakt. Abt. II, 

 23:569-642, 1909. 



6 Hoffman, C. Relation of Soil Bacteria to Nitrogenous Decomposition. Wis. 

 Agr. Exp. Sta., 23 Ann. Rpt., pp. 120-134, 1906. 



7 Fischer, H. Bakteriologisch-chemische Untersuchungen. Bakteriologischer Teil. 

 Landw. Jahrb. 38:355-364, 1909. 



8 Fischer, H. Zur. Methodik der Bakterienzahlung. Cenbtl. Bakt., Abt. II, 25: 457- 

 459,1910. Although similar soil-extract media have been used by other bacteriologists, 

 the directions given by Fischer for preparing this medium are so explicit that it is 

 denoted in the present publication as Fischer's soil-extract agar. 



9 Lipman, J. G., and Brown, P. E. Media for the Quantitative Estimation of Soil 

 Bacteria. Centbl. Bakt., Abt. II, 25:447-454, 1910. 



10 Temple, J. C. The Influence of Stall Manure upon the Bacterial Flora of Soil. 

 Centbl. Bakt., Abt. II, 34:206-223,1911. Also Ga. Agr. Exp. Sta., Bui. 95:1-34, 

 1911. (See p. 9 of the latter reference.) 



"Brown, P. E. Media for the Quantitative Determination of Bacteria in Soils. 

 Centbl. Bakt. Abt. II, 38:497-506, 1913. Also la. Agr. Exp. Sta. Research Bui. 

 11:396-407, 1913. 



