316 Biological Chemistry. 



(F) METHOD OF ANALOGY FROM THE BIOCHEMICAL CHANGES 

 PRODUCED BY MICRO-ORGANISMS. 



Certain chemical transformations can be readily 

 brought about by micro-organisms which can be accom- 

 plished only with difficulty by the ordinary in vitro 

 chemical methods ; and it is highly probable that changes 

 similar to those due to micro-organisms take place within 

 the bodies of higher animals. A study of the intermediary 

 metabolism of micro-organisms is likely therefore to throw 

 considerable light on the intermediary metabolism of the 

 higher animals. The change which has perhaps been the 

 subject of the largest amount of study is the formation of 

 alcohol and carbon dioxide from dextrose by the action of 

 yeast. If the formulae are written 



CH 2 (OH) 



I CH 3 



CH(OH) | C0 a 



| CH 3 OH 



CH(OH) 



CH(OH) 



I CH 3 



CH(OH) | CO, 



I CH 2 (OH) 



it is not easy to conceive how two molecules of alcohol 

 and two of carbon dioxide can be derived from one mole- 

 cule of dextrose without the formation of a number of 

 intermediary products. 



Various complex changes of dextrose can also be 

 brought about in vitro which cannot be explained without 

 assuming the formation of a series of intermediary pro- 

 ducts ; thus, on treatment of dextrose with dilute alkalis 

 at 37, lactic acid in a yield up to 50 per cent, can be 

 obtained. There is evidence that this change can also be 



