352 APPENDIX 



microorganisms in soil, no one medium will suffice for the 

 cultivation of all species. Emphasis is therefore not laid 

 on any particular medium for plating soils. 



Omeliansky's medium for anaerobic cellulose fer- 

 mentation : 



Filter paper (in strips). Cotton, straw, or 



starch may be substituted for filter paper . 2.0 gms. 



CaC0 3 .. 20.0 gms. 



K 2 HPO 4 . . 1.0 gm. 



MgS0 4 0.5 gm. 



(NH 4 ) 2 SO 4 1 .0 gm. 



NaCl Trace 



Distilled water 1000.0 c.c. 



Method. 1. Introduce substances in order named 

 into 1000 c.c. distilled water. 



2. Stir to dissolve all soluble substances and tube while 

 insoluble substances are in homogeneous suspension, plac- 

 ing about 10 c.c. in each tube. 



3. Sterilize in autoclav. 



Media for studying urea decomposition: Urea broth, 

 gelatin and agar are generally prepared by adding 1% to 

 2% urea to the ordinary media. This medium favors the 

 growth of B. coli, B. proteus, B. erythrogenes, etc. 



Ordinary media to which 10% urea has been added favors 

 the growth of B. pasteurii, a spore-producing bacterium. 



Urea gelatin and agar may be prepared by adding 1 

 c.c. of a 15% aqueous solution of urea to each tube of the 

 ordinary media after sterilization, and then heating the 

 tubes again. This is the method preferred because the 

 addition of urea reduces the solidifying power of the gelatin. 

 A small amount of urea is converted into ammonia by 

 heating in the steam, but this has little influence on the 

 results obtained in the experiment. Heating in the auto- 

 clav is to be avoided! 



