New York Agricultural Experiment Station. 227 



for in a medium for this purpose; it should allow the greatest possible 

 number of soil bacteria to develop upon it, in order that the counts 

 obtained may be as nearly correct as possible; it should allow 

 the different kinds of bacteria to produce colonies as distinct as 

 possible in appearance, in order to facilitate classification; and it 

 should contain, as far as possible, no materials of unknown chemical 

 formula, in order that different batches of the medium may be of 

 the same chemical composition. In the past, these last two require- 

 ments have been almost overlooked. 



In the course of the present investigation it has not been found 

 possible to obtain a medium fulfilling all three of these require- 

 ments; but two new media have been tested out that are worth 

 recommending. Both of these media fulfill the first requirement as 

 well as any previously proposed medium. One of them, a soil- 

 extract gelatin, fulfills the second requirement better than any of 

 the other media proposed for soil work, and is therefore recom- 

 mended for qualitative work. The other, an agar containing sodium 

 asparaginate, fulfills the third requirement (except in so far as the 

 agar itself is of indefinite composition) and is therefore recommended 

 for quantitative work. 



The soil-extract gelatin consists of gelatin, soil-extract and dextrose 

 alone. This medium not only permits more ready classification of 

 the colonies than any other medium tested, but also allows a larger 

 number of colonies to develop than appear on the media ordinarily 

 recommended for soil work. The soil-extract is not absolutely 

 necessary, as practically as good results may be obtained when it is 

 replaced with tap-water, and only slightly inferior results when 

 distilled water is used in its stead. This gelatin medium is extremely 

 satisfactory for qualitative work; and might also be recommended 

 for quantitative work except for the indefinite composition of the 

 gelatin itself. 



The asparaginate agar contains no organic matter except the agar, 

 dextrose and sodium asparaginate. Besides these materials, it 

 contains several mineral salts. The formula given in this bulletin 

 is not to be considered the best combination possible, although 

 various proportions of the different chemicals have been tried without 

 better success. Nearly as good quantitative results may be obtained 

 by omitting the mineral salts and using tap-water instead of distilled 

 water; but the colonies then are so small that this simplification is 

 not to be recommended. The colonies developing on asparaginate 

 agar are not so readily classified as those on gelatin, and the count 

 obtained upon it is often lower, but its definite chemical composition 

 makes it seem worth recommending for general use in quantitative 

 work in soil bacteriology. 



The media that have been compared with these are: Fischer's 

 soil-extract agar; Temple's peptone agar; Lipman and Brown's 



