New York Agricultural Experiment Station. 



203 



tains agar and peptone. The term " synthetic " is justified only 

 on the assumption that variations in these materials do not affect 

 the growth of bacteria; but Brown states 17 that the form of nitrogen, 

 even when used in such minute quantities, is of great importance 

 in determining the value of the medium. The agar medium tested 

 out in the present work, concerning which a preliminary note has 

 already been published 18 , is furnished no organic nitrogen except that 

 contained in sodium asparaginate, and is apparently the first medium 

 ever used for making poured plates from soil that does not contain 

 nitrogen in the form of some indefinite chemical compound. 



Table I gives the formulae of the media preferred respectively 

 by Fischer, by Lipman and Brown, by Temple, and by Brown in 

 the publications already mentioned. It also gives the formulae of 

 the soil-extract gelatin and asparaginate agar recommended by the 

 writer. The present work is an investigation of these six media. 



Table I.- — Composition of Various Culture Media for Soil Bacteriological 



Work 



* Prepared by heating soil for half an hour at 15 pounds pressure with an equal weight 

 of a 0.1 per ct. solution of Na 2 C0 3 . 



t Prepared by boiling soil half an hour with an equal weight of distilled water (see 

 P-ID- 



17 See footnote 11. la. Bui. p. 397. Centbl. p. 498. 



18 Conn, H. J. A New Medium for the Quantitative Determination of Bacteria 

 in Soil. Science, N. S., 39:764, 1914. 



