2o6 



PHYSIOLOGY OF NUTRITION 



nomenon appears in the germination of seeds in darkness, where the loss in dry 

 weight is due to respiration in the absence of the photosynthetic process. 



Great interest is attached to the question of the role of oxygen in alcoholic 

 fermentation. Pasteur devised the apparatus shown in Fig. 89 for experi- 

 ments upon the development of yeast in the complete absence of oxygen. A 

 fermentable liquid is placed in the flask A , which has two glass necks (a and b) 

 with narrow openings. One of these is provided with a glass stop-cock and a 

 glass funnel while the other bends downward into a dish (c) filled with some 

 of the same liquid as is in the flask. Both masses of liquid are brought to boil- 

 ing, to expel air from the liquid. After cooling, the liquid in the dish is replaced 

 with mercury. Resting yeast cells are then introduced into the glass funnel and 

 admitted into the flask through the stop-cock. It was found that such resting 



yeast cells (called "old" cells 

 by Pasteur) produce no fer- 

 mentation when air is entirely 

 lacking. In another series of 

 experiments a small amount of 

 the fermentable liquid was in- 

 troduced into the funnel, in- 

 oculated with yeast, and fer- 

 mentation was allowed to take 

 place. A little of the ferment- 

 ing liquid, containing a very 

 few of the young, budding 

 cells was then allowed to pass 

 from the funnel into the flask, 

 the cock being immediately re- 

 closed. Vigorous fermenta- 

 tion occurred in the flask, more 

 than a gram of dry substance 

 being obtained from the very 

 slight amount of yeast that was introduced. It is clear, therefore, that oxygen 

 is essential to the development of resting yeast cells, while young cells can de- 

 velop when oxygen is entirely lacking, if nutrient materials are present. 



In connection with the relation of oxygen to fermentation, it is of great im- 

 portance to discover whether normal respiration occurs in yeast abundantly 

 supplied with oxygen. Ivanovskii, 1 who took up this question, grew a pure 

 culture of yeast upon a sterilized porous clay plate half immersed in sterilized 

 nutrient solution, the whole being in an air chamber formed by a bell-jar. 

 The yeast was thus abundantly supplied with oxygen, and the nutrient solu- 

 tion reached the cells only through the capillary passages of the clay plate. 

 After three days a gas analysis showed that the ratio between the amount of 



carbon dioxide eliminated and the amount of oxygen absorbed, \~f)~)' was 



1 Ivanovskii, D., On the influence of oxygen on alcoholic fermentation. [Russian. ] Works of the Botani- 

 cal Laboratory, Acad. Sci. St. Petersburg. No. 4. In Zapiski Acad. Sci. St. Petersburg 73 2 . 28 p. 1894. 

 Pagination of parts in vol. is separate.] 



Fig. 89.- 



-Apparatus for showing fermentation in the 

 absence of oxygen. 



