PRELIMINARY REPORT ON SYNTHETIC MEDIA 139 



compounds containing both energy and nitrogen. For such 

 organisms as are not able to develop upon a medium contain- 

 ing one of the simplest nitrogen salts, and a non-nitrogenous com- 

 pound as a source of energy, we may develop a suitable medium 

 by using a solution containing the essential mineral salts to 

 different portions of which we add a different nitrogenous com- 

 pound until we find a nitrogenous compound upon which it 

 will develop. However, we must exercise caution here, particu- 

 larly in the employment of complex compounds for mixed floras, 

 because as a general rule the more complex the compound the 

 greater the number of species which can utilize the compound 

 or its degradation products. It is by simplicity of compounds 

 that we may hope to control the growth of the great mass of 

 saprophytes. 



Possible media may be grouped according to their energy 

 requirements as follows: 



THE AMMONIA GROUP 



Ammonia as a source of energy, no other form of nitrogen. 



THE NITRITE GROUP 



Nitrite as a source of energy, no other form of nitrogen. 



THE SULPHUR GROUP 



Sulphur as a source of energy, + ammonia. 



THE IRON GROUP 



Iron as a source of energy, + ammonia. 



THE CYANIDE GROUP 



Cyanide as a source of energy (no other form of nitrogen). 

 Cyanide as a source of energy, + ammonia nitrogen. 



NITROGEN FIXING GROUP (Oligonitrophilic) 

 Compounds of carbon with hydrogen and oxygen as sources of energy, no 

 nitrogen added. 



THE ALIPHATIC ACID GROUP 



The Aliphatic acids as a source of energy, + ammonia nitrogen. 



Monobasic Monobasic hydroxy Monobasic keionic 



Formic Glycolic Pyruvic 



Acetic d-lactic Acetoacetic 



Propionic 1-lactic Levulinic 



Butyric Hydracrylic 

 Isobutyric 

 Isovaleric 

 Normal Valeric 



