NUTRIENT MEDIA 63 



solutions {a and h) are added, the solutions well mixed, and 

 at once poured into Petri dishes or flat-bottomed flasks. 

 The medium should gelatinise in from five to fifteen 

 minutes. The material containing the organisms for 

 examination is introduced and thoroughly mixed, before 

 gelatinisation takes place ; or a ' streak ' culture may be 

 made on the surface after the medium has solidified. 



(24) TTschinsky's Solution. — Uschinsky's solution, as 

 simplified by Voges and Frankel, has the following com- 

 position : 



Sodium chloride - - 5 grammes. 



Neutral sodium phosphate 2 ,, 



Ammonium lactate 6 ,, 



Asparagin - 4 ,, 



Distilled water 1000 ,, 



Many bacteria will grow very well in this simple non- 

 albuminous fluid. This and similar fluids have been 

 recently used in the study of the metabolic products of 

 several of the pathogenic organisms, notably diphtheria. 



A large number of modifications and various combina- 

 tions of many of the culture media described in the 

 foregoing pages are employed by various workers in 

 bacteriological research. Amongst others may be men- 

 tioned : 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 suphuretted hydrogen. 



