THE BEGINNINGS OF LIFE. 



413 



extrine s 



^n^'erted into 

 ' Liebig sajSj 



d to the sugar 



'ery evidentlj 

 n which yeast 

 ■and many 

 ing how the 

 fluenced and 

 hemical sub- 

 iclusion that 

 nothing more 



lange w 



hich 



go. 



either bf 

 by reason of 

 ments) whict 



by 



no 



ell- 



« 



It can 

 ical pro'^^ 



iio 



ated by^ : 



sse5 

 the 



II 



lace 



in 



liviii^ 



^ 



things. Observation and experiment alike are abso- 

 lutely opposed to such a limitation^ and even had it not 

 already been shown to be utterly erroneous^ it is a 

 doctrine which ought only to have found favour with 

 those who are professed ^ vitalists/ Consistent believers 

 in the physical doctrine of life could scarcely be expected 

 to do other than mistrust a doctrine which would have 

 them believe either that the molecular changes taking 

 place in living things were not essentially chemical in 

 nature^ or else that they were chemical changes absolutely 

 sut generis. It would be almost impossible^ indeed, to 

 frame a true and distinctive definition of fermentative 

 changes. Just as we have previously urged, that the 

 living thing differs from the not-living thing in degree 

 and not in kind, since the properties of both are de- 

 pendent upon their molecular composition and structure ; 

 so does the fermentative chemical change differ from 

 the not-fermentative chemical change merely in degree 



though even to a less extent, because these two kinds 

 of chemical change are now actually known to merge 

 almost insensibly into one another. It is almost impos- 

 sible to say where the one ends and the other begins. 



As we have already intimated, in the opinion of 

 Gay-Lussac and also of many chemists in the pre- 

 sent day, oxygen is needed to initiate the changes 

 which the ferment undergoes. According to Baron 

 Liebig, however, all that is essential in order that 

 fermentation may occur, is that a complex substance 

 should undergo changes of a particular kind, either 



) 



