Nutrients 103 



sidered typical. The nutrient used in this labora- 

 tory for all routine cultures at present (1942) has 

 the following constitution: 



Salts Mg. /liter Mols. 



Osmotic value n - 1.8 atm. 



Since this nutrient is used in great quantity and 

 must be made up at frequent intervals, it is not 

 efficient to weigh out the separate constituents for 

 each new set of nutrient. In practice only the 

 sucrose and the iron are weighed each time, the 

 first because any stock solution containing sucrose 

 would ferment unless sterilized and kept sterile, 

 the second because in solution Fe 2 (S0 4 ) 3 rapidly 

 oxidizes and precipitates. All the other constitu- 

 ents are taken from concentrated stock solutions 

 which will keep indefinitely. 



The inorganic stock solution is made up as fol- 



