SILICA JELLY &7 



amination ig introduced and thoroughly mixed, before gelat- 

 inisation takes place ; or a ' streak ' culture may be made 

 on the surface after the medium has solidified. 



A large number of modifications and various combina- 

 tions of many of the culture media described in the fore- 

 going pages are employed by various workers in bacterio- 

 logical research. Amongst others may be mentioned : 

 mixtures of potato-paste with gelatine ; gelatine prepared 

 with milk ; mixtures of nutrient gelatine and agar ; and 

 solutions containing combinations of inorganic and organic 

 salts, such as alkaline phosphates and tartrates, etc. 



In addition to the above, various substances are added 

 to culture media to detect by qualitative reactions the 

 products of growth of the organisms under examination. 

 For instance, litmus, Congo-red, and iron salts are fre- 

 quent additions made to demonstrate the formation of 

 acids, alkalies, and sulphuretted hydrogen. 



