THE PREPARATION OF CULTURE MEDIA 27 



phenomena of nitrification 1 and for the nutrition of 

 the nitrous organism we have employed the following 

 solution : 



Ammonium chloride . . . . *5 gram \ 



Potassium phosphate (K 3 P0 4 ) . '1 Jn ^ 000 c c of ^ 



Magnesium sulphate (MgS0 4 , 7H..O) . -02 L ' ,, , ' ' 



Calcium chloride (CaCl 2 ) ^. . . '01 



Calcium carbonate . ... .5-0 grams / 



On the other hand, for the special nutrition of the 

 nitric organism War ing ton 2 has employed 



Potassium nitrite *3 gram 



Potassium phosphate . . . *1 



Magnesium sulphate . . . . '05 

 Calcium carbonate ..... son 



In 1,000 c.c. of dis- 

 tilled water. 



In order to ascertain whether a micro-organism has 

 the power of reducing nitrates, the authors 3 have used 

 a solution of the following composition : 



Potassium phosphate .... '1 gram 

 Magnesium sulphate (cryst.) . . . -02 



In 1,000 c.c. of dis- 

 tilled water with 

 4 grains of pure 

 calcium carbonate 

 in suspension. 



Calcium chloride (fused) . . . -01 

 Nitrogen combined in the form of potas- 

 sium or calcium nitrate . . . '168 

 Invert sugar or dextrose . . . '3 ,, 

 Peptone '25 



On no account must the precaution be neglected of 

 testing the solution for nitrites before use. 



In the case of bacteria requiring a more nutritive 

 medium for their growth an addition 4 of potassium 

 nitrate (5 grms. per litre) may be made to broth- 

 peptone and similar culture liquids, but the results 

 obtained are in general not so decisive for diagnostic 

 purposes as when the above weaker solution is employed, 

 whilst the fate of the nitrogen in its various forms is 

 far more difficult to trace. 



1 Phil. Trans, clxxxi. (1890) 107. 

 * Chem. Soc. Journ. 1891, 519. 



3 Ibid. 1888, 374. 



4 Warington, Chem. Soc. Journ. 1888, 745. 



