THEORY OF FERMENTATION 309 



of 14.5 cc. (0.88 cub. in.) of oxygen.' The weight of the 

 yeast, in a state of dry ness, was 0.035 gramme. 



It follows that in the production of 35 milligrammes 

 (0.524 grain) of yeast there was an absorption of 14 or 

 15 cc. (about J cub. in.) of oxygen, even supposing that 

 the yeast was formed entirely under the influence of 

 that gas: this is equivalent to not less than 414 cc. for 

 i gramme of yeast (or about 33 cubic inches for every 20 

 grains). 10 



Such is the large volume of oxygen necessary for the 

 development 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 

 the paragraph on page 292 in which a flask of three litres 

 capacity was filled with fermentable liquid, which, when 

 caused to ferment, yielded 2.25 grammes of yeast, under 

 circumstances where it could not obtain a greater supply 

 of free oxygen than 16.5 cc. (about one cubic inch). Ac- 

 cording to what we have just stated, if this 2.25 grammes 

 (34 grains) of yeast had not been able to live without oxy- 

 gen, 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 

 2.25X414 cc., that is, 931.5 cc. (56.85 cubic inches). The 

 greater part of the 2.25 grammes, therefore, had evidently 

 been produced as the growth of an anaerobian plant. 



It mav be useful for the non-scientific reader to put it thus: that the 

 25 cc. which escaped, being a fair sample of the whole gas in the flask, 

 and containing (i) 25 20.0=4.4 cc., absorbed by potash and therefore due 

 to carbonic acid, and (2) 20.6 17.3=3.3 cc., absorbed by pyrogallate, and 

 therefore due to oxygen, and the remaining 17.3 cc. being nitrogen, the 

 whole gas in the flask, which has a capacity of 312 cc., will contain oxygen 

 in the above proportion, and therefore its amount may be determined, pro- 

 vided we know the total gas in the flask before opening. On the other 

 hand, we know that air normally contains, approximately, 1-5 its volume of 

 oxygen, the rest being nitrogen, so that, by ascertaining the diminution of 

 the proportion in the flask, we can find how many cubic centimetres have 

 been absorbed by the yeast. The author, however, has not given all the 

 data necessary for accurate calculation. p. C. R. 



"This number is probably too small: it is scarcely possible that the in- 

 crease of weight in the yeast, even under the exceptional conditions of the 

 experiment described, was not to some extent at least due to oxidation apart 

 from free oxygen, inasmuch as some of the cells were covered by others. 

 The increased wcijrht of the yeast is always duo to the action of two dis- 

 tinct modes of vital energy activity, namely, in presence and activity in 

 absence of air. We might endeavour to hort'-n the duration of the rxnrri- 

 ill further, in which ca<-c we would still more assimilate the life of 

 the yeast to that of ordinary moulds. 



