Chap, viii Fermentation 



429 



port of air to the cells of the interior and causing the 

 supply of oxygen to be considerably lessened. When the 

 temperature was maintained at 15 C, sufficient oxygen 

 was able to pass along the narrowed intercellular passages 

 to minister to the needs of the cells. When it was raised 

 to 30 C. this was not the case, and a sort of asphyxiation 

 set in. Fermentation supervened, a considerable additional 

 quantity of carbon dioxide was exhaled and alcohol was 

 produced. The ratio of oxygen to carbon dioxide changed 

 from 1 : 1-26 to 1 : 3-12. The increase of the latter gas 

 resulted from the fermentation of the sugar adding to the 

 quantity proceeding from the respiration of the cells, the 

 latter being the only factor when the lower ratio was 

 observed. This view of the cause of the increase was 

 supported by the observation that when air was admitted 

 more freely by subdividing the tissue into small pieces, 

 the ratio at once fell slightly, though as such subdivision 

 did not completely remedy the obstruction of the inter- 

 cellular passages, the difference was not very marked. 



The view that alcoholic and similar fermentation is 

 concerned in metabolic changes like those of aerobic re- 

 spiration, involving, that is, explosive decomposition of 

 the living substance, was called into question in con- 

 sequence of the discovery of Buchner in 1896 that the 

 yeast plant at least causes the production of alcohol by 

 means of the secretion of an enzyme, to which Buchner 

 gave the name zymase. The fact most easily ascertained 

 with respect to the action of yeast is that the pro- 

 duction of alcohol and the exhalation of carbon dioxide 

 are the result of a decomposition of a sugar which breaks 

 up entirely, though probably by several stages, into those 

 two compounds. 



It appears not improbable from Buchner's work that 

 the change in metabolism which diminution of oxygen 

 causes is the secretion of the enzyme, which then brings 



