94 MICROBIOLOGY 



Silicate Jelly (Winogradski). For the cultivation of 



nitrifying bacteria. 



1. Weigh out and mix, Ammonium sulphate 0.40 gram 



Magnesium sulphate 0.05 gram 



Calcium chloride 0.01 gram 



Distilled water 50 cc. 

 Label Solution A. 



"2. Weigh out and mix, Potassium phosphate 0.10 grams 

 Sodium carbonate 0.60 gram 



Dissolve in distilled water 50 cc. 



Label Solution B. 



3. Weigh out silicic acid 3.4 grams 



Dissolve in distilled water 100 cc. 



4. Pour the silicic solution into a large porcelain basin. 



5. Mix equal quantities of the solutions A and B ; then 

 add successively small quantities of the mixed salts to the 

 silicic acid solution, stirring continuously with a glass rod, 

 until a jelly of sufficiently firm consistency has been formed. 



6. Spread a layer of this jelly over the bottom of each 

 of several large capsules or "plates." 



7. Sterilize in the steamer for twenty minutes on each 

 of three consecutive days. 



Fermi's solution. For many purposes Fermi's solution 

 is a good one to add to the dialyzed jelly. This is made as 

 follows, for this purpose: Freshly-boiled distilled water, 

 100; magnesium sulphate, 0.2; monopotassium phosphate, 

 1.0; ammonium phosphate, 10.0. Dissolve. Then add glyc- 

 erin, 45.0. 



loopfuls, and from the second a third tube is inoculated. The test 

 tubes are then immediately cooled and solidified in a stream of water. 

 This mixture of serum and gelatin-agar remains transparent, and 

 permits accurate observation of the isolated developing colonies, as 

 well as the starting of fresh colonies from them. The solid medium 

 also serves very well for the preparation of stab cultures by means 

 of a glass needle. This medium was first employed by Bang and 

 Stribolt in the study of the organism of contagious abortion. 



