374 BACTERIOLOGY. 



ing organisms remain. These are to be seen as an 

 almost transparent film attached to the clumps and 

 granules of magnesium carbonate on the bottom of the 



For their cultivation upon a solid medium he em- 

 ploys a mineral gelatin, the gelatinizing principle of 

 which is silicic acid. A solution of from 3 to 4 per 

 cent, of silicic acid in distilled water, and having a 

 specific gravity of 1.02, remains fluid and can be pre- 

 served in flasks in this condition (Kuhne). By the 

 addition of certain salts to such a solution gelatiniza- 

 tion occurs and will be more or less complete, according 

 to the proportion of salts, added. The salts that have 

 given the best results, and the method of mixing them 

 are as follows : 



f Ammonium sulphate . 0.4 gramme, 



o < Magnesium sulphate . 0.05 " 



•■Calcium chloride . trace. 



/Potassium phosphate . O.i gramme. 



& -I Sodium carbonate . . 0.6 to 0.9 " 



( Distilled water ... . 100 c.c. 



The sulphates and chloride (a) are mixed in 50 c.c. 

 of the distilled water, and the phosphate and carbonate 

 (6) in the remaining 50 c.c. in separate flasks. 



Each flask with its contents is then sterilized and 

 after cooling are mixed together. This represents the 

 solution of mineral salts that is to be added to the 

 silicic acid, little by little, until the proper degree of 

 consistence is obtained (that of ordinary nutrient gela- 

 tin). This part of the process is best conducted in the 

 culture dish. If it is desired to separate the colonies, 

 as in an ordinary plate, the inoculation and mixing of 

 the material introduced must be done before gelatiniza- 

 tion is complete ; if the material is to be distributed 



