PRELIMINARY REPORT ON SYNTHETIC MEDIA 143 



PREPARATION OP MEDIA 



Conditions 



All water used was double distilled from glass retorts and 

 condensers. All chemicals used were the purest the market 

 afforded. Each chemical was tested for impurities before use. 

 All measures of growth were macroscopic. 



Tests with liquid solutions were made in test tubes. Tests 

 with solid media were made in Petri dishes. The incubator 

 temperature adopted was 28°C. All media used were made 

 neutral to phenolphthalein. The influence of sterilization by- 

 heat on composition and structure may be eliminated in most 

 instances where an acid is used as a source of energy by pre- 

 paring a medium in such a manner that it automatically steril- 

 izes itself. This will be explained under preparation of media. 

 Whenever this has not been possible the compound whose 

 structure is liable to be influenced by high temperatures, has 

 been sterilized by itself in neutral aqueous solution and added 

 to the other sterile constituents, in correct proportion, by means 

 of a sterile pipette. All transfers were made from cultures 

 48 to 96 hours old grown on standard agar. 



Solid synthetic media 



It will be necessary to describe the solid media first in order 

 to explain the reason for the concentration of the liquid media. 

 After numerous trials with starch, cellulose, aluminum hydroxide, 

 iron hydroxide and washed agar as agglutinants, it was finally 

 demonstrated that silica jelly was the most suitable solid medium. 

 The silica jelly was made by a modified "Stevens Temple Meth- 

 od." (Centbl. Bakt., etc., II abt., vol. 21, 1908, p. 84.) 



The method consisted essentially of dissolving c. p. KgSiOs 

 and c.p. Na2Si03 in water in sufficient amounts to give a con- 

 centration of 34.2732 grams of H2Si03 per liter. One half this 

 concentration of H2Si03 per liter gives a medium which will 

 solidify in approximately five minutes, thus making a medium 

 suitable for plating. The mixture of sodium and potassium sili- 



