ENERGY SUPPLY OF THE CELL 41 



gas fermentations of the colon group are also well stud- 

 ied. Data upon other sugar fermentations are rather 

 incomplete. 



One single equation to cover the entire action of any 

 species of bacterium upon the entire available food is 

 evidently impossible. It is even impossible to cover the 

 decomposition of just the sugar by yeast in one formula 

 because Pasteur found that about 5% of the sugar is 

 used for the construction of new yeast cells, and we could 

 not possibly write this in a chemical equation. 



It seemed possible for a while to describe, in one 

 equation, that part of sugar dissimilation which is not 

 used for constructive purposes, but even that is inac- 

 curate and incomplete, as a number of old and new 

 experiments have shown. Most organisms have the 

 ability to decompose sugar in more than one way, and 

 this is due to the fact that all sugar fermentations are 

 the result of a number of interlinking reactions. By a 

 change of environment, the one or other of these reac- 

 tions might be prevented, or changed, and the result is a 

 different product, or a different proportion of the prod- 

 ucts obtained. Besides, interreactions between sugar 

 and nitrogenous material are always possible, so that 

 any equation that does not consider the nitrogenous 

 material may not show the real facts (see p. 62). 



A type of fermentation may be described by one 

 general equation with the reservation that the formula 

 holds true only for the conditions of the one experiment, 

 and that even then, it accounts only for about 90% of 

 the sugar decomposed. If a niore accurate understand- 

 ing of the process is wanted, the different successive 

 stages of the change from sugar to the final product 

 must be worked out, and their interrelations must be 

 studied. 



