168 TECHNOLOGY OF BACTERIA. 



the albumen of animal or vegetable origin which 

 remains in solution in the above-mentioned cul- 

 ture-media. But this element can also be appro- 

 priated when present in the form of ammonia, or 

 of one of the salts of ammonia in combination 

 with a vegetable acid. 



Culture -fluids may therefore be made which are 

 suitable for the development of numerous species 

 of bacteria, by adding to distilled water a small 

 quantity of a salt of ammonia, together with cer- 

 tain mineral salts, as in the formula of Mayer, 

 given on page 113. Pasteur's solution contains 

 ten per cent, of sugar candy and a fraction of one 

 per cent, of ashes of yeast. (See p. 112.) 



Sterilization of Culture-Fluids. Heat is the agent 

 most available for the sterilization of culture-fluids, 

 as chemical reagents which would accomplish the 

 same result would also, by their presence in the 

 fluid, prevent the development of organisms intro- 

 duced for the purpose of cultivation. It would 

 doubtless be possible to sterilize a fluid by means 

 of a chemical reagent a mineral acid for exam- 

 ple and subsequently to neutralize the germicide 

 agent e. g. by lime or magnesia. But in prac- 

 tice it will be found that no other method is likely 

 to give as satisfactory results as that commonly 

 employed ; which consists in subjecting the fluid, 

 enclosed in a germ-proof receptacle, to a tempera- 

 ture which insures the destruction of the vitality 

 of contained organisms. 



