100 PHYSIOLOGY OF YEASTS 



pounds which were accessible to them. By decomposing these, they 

 are able to get this oxygen. Alcoholic fermentation would then be a 

 method for resisting suffocation. The yeast, not finding oxygen avail- 

 able and not being able to live without this element, will be obliged 

 to take it from some of its combinations in sugar which they find in 

 the medium. 



The same thing takes place in other living beings. The yeasts 

 possess, then, the property in common with other organisms, but they 

 are better adapted than the others to produce fermentation and thus 

 resist suffocation. 



In short, states Pasteur, nearly all known beings without excep- 

 tion are only able to respire and sustain themselves by assimilating 

 free gaseous oxgyen; there is a class, however, in which respiration 

 will be quite active in order that they may live away from air by tak- 

 ing their oxygen from certain combinations, from which results a slow 

 and progressive decomposition. This last class of organized beings 

 will be made up of the ferments entirely similar to the beings of the 

 first class, living with them, assimilating carbon, nitrogen and phos- 

 phates, having like them a need for oxygen, but differing from them in 

 that they are able to respire with oxygen taken from compounds, 

 when free oxygen is not available. 



Pasteur's theory has precipitated numerous objections among 

 which is this, that the classic formula of Gay-Lussac accepted by 

 Pasteur does not leave a place for the setting free of oxygen. 



This theory of Pasteur's has been modified. Alcoholic fermenta- 

 tion has always been considered as a phenomenon of resistance to 

 suffocation and that it has for its purpose the securing of energy 

 for the life of the yeast. The fermentation will be, then, from the 

 viewpoint of energy, the equivalent of respiration. The yeast, during 

 fermentation, continues to develop, making new tissue and retaining 

 its usual functions. The yeast carries on a slow deliberate decomposi- 

 tion in quest of its energy and it is alcoholic fermentation which fur- 

 nishes it. The yeasts are constructed to live in contact with or away 

 from air. In the first case, they burn carbohydrates; in the other, 

 they cause a breaking up or shifting of parts of a complex molecule. 

 But the sources of cellular life are the same in each case. 



Theory of Wortmann and Delbriick 



Wortmann and later Delbriick have regarded alcoholic fermenta- 

 tion as a phenomenon comparable to the secretion of a toxin. In 

 this case the alcohol serves the role of a poison with which the yeast 

 is able to compete with other organisms with which it comes in con- 



