APPENDIX I 



THE ISOLATION AND IDENTIFICATION 

 OF METABOLIC PRODUCTS 



IN carrying out investigations into the metabolic 

 processes of micro-organisms it is obviously advan- 

 tageous to start with substances of laiown composition 

 only ; for this reason synthetic media should be employed 

 whenever possible for the growth of the organisms, 

 since the use of broth, meat extract and similar materials 

 introduces mixtures of substances of unknown nature and 

 amount. For ease in tracing the course of the metabolic 

 changes a single source of carbon, such as a sugar or 

 other suitable substance, and of nitrogen, such as an 

 ammonium salt, should be used. 



The fermented solution is usually an aqueous mixture 

 which will contain the organism, possibly calcium car- 

 bonate (which may have been added to maintain 

 neutrality) and insoluble organic calcium salts, volatile 

 neutral and basic substances, volatile acids, non- volatile 

 acids and non-volatile neutral or basic products. Gaseous 

 products are also often produced, the usual gases en- 

 countered being carbon dioxide, hydrogen and methane ; 

 these may be collected during the course of fermentation 

 in the usual way over water after removal of the carbon 

 dioxide by baryta or soda-lime. 



The course of fermentation can be followed by observ- 

 ing the disappearance of the carbon source ; glucose, for 

 instance, can be estimated by the optical rotatory power 

 of the solution or by the reducing power as determined 

 by the Shaffer-Hartmann method, for example, or by 



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