20 ORIGIN OF LOWEST ORGANISMS. 



instability of the body which manifests them, or to 

 molecular movements communicated to it by a still 

 more unstable body. Baron Liebig says : " Many 

 organic compounds are known, which undergo, in pre- 

 sence of water, alteration and metamorphosis, having a 

 certain duration, and ultimately terminating in putre- 

 faction ; while other organic substances that are not 

 liable to such alteration by themselves, nevertheless, 

 suffer a similar displacement or separation of their mole- 

 cules, when brought into contact with the ferments." 



Each substance belonging to the first class, would 

 be at the same time, therefore, both ferment and fer- 

 mentable substance ; whilst a small portion of such 

 substance, when brought into contact with a less un- 

 stable substance, might induce such molecular move- 

 ments as to make it undergo a process of fermentation. 

 With regard to the cause of such induced fermentative 

 changes, Gerhardt* says, in explaining Liebig's views: 

 ->" Every substance which decomposes or enters into 

 combination is in a state of movement, its molecules 

 being agitated ; but since friction, shock, mechanical 

 agitation, suffice to provoke the decomposition of many 

 substances (chlorous acid, chloride of nitrogen, fulmi- 

 nating silver), there is all the more reason why a 

 chemical decomposition in which the molecular agita- 

 tion is more complete, should produce similar effects 

 upon certain substances. In addition, bodies are 



* ' Chimie organique,' 1856, t. iv. p. 589. 



