STUDIES ON FERMENTATION. 257 



Such is the large volume of oxygen necessary for the develop- 

 ment of one gramme of yeast when the plant can assimilate 

 this gas after the manner of an ordinary fungus. 



Let us now return to the first experiment described in this 

 paragraph (page 238), in which a flask of three litres capacity 

 was filled with fermentable liquid, which, when caused to fer- 

 ment, yielded 2 '25 grammes of yeast, under circumstances where 

 it could not obtain a greater supply of free oxygen than 16*5 c.c. 

 (about one cubic inch). According to what we have just stated, 

 if this 2"25 grammes (34 grains) of yeast had not been able to 

 live without oxygen, in other words, if the original cells had 

 been unable to multiply otherwise than by absorbing free 

 oxygen, the amount of that gas required could not have been 

 less than 2*25 x 414 c.c, that is, 931'5 c.c. (56'85 cubic inches). 

 The greater part of the 2-25 grammes, therefore, had evidently 

 been produced as the growth of an anaerobian plant. 



Ordinary fungi likewise require large quantities of oxygen 

 for their development, as we may easily prove by cultivating 

 any mould in a closed vessel full of air, and then taking the 

 weight of plant formed and measuring the volume of oxygen 

 absorbed. To do this, we take a flask of the shape shown in 

 Fig. 66, capable of holding about 300 c.c. (lOJ fluid ounces), 

 and containing a liquid adapted to the life of moulds. We 

 boil this liquid and seal the drawn-out point, after the steam 

 has expelled the air wholly or in part ; we then open the flask 

 in a garden or in a room. Should a fungus- spore enter the flask, 

 as will invariably be the case in a certain number of flasks out 

 of several used in the experiment, except under special circum- 

 stances, it will develop there and gradually absorb all the 

 oxygen contained in the air of the flask. Measuring the 



the experiment described, was not to some extent at least due to oxida- 

 tion apart from free oxygen, inasmuch as some of the cells were covered 

 by others. The increased weight of the yeast is always due to the action 

 of two distinct modes of vital energy — activity, namely, in presence and 

 activity in absence of air. We might endeavour to shorten the duration 

 of the experiment still further, in which case we woiild still more assimi- 

 late the Life of the yeast to that of ordinary moulds. 



S 



