Polytechnic Association. 7.95 



most certain, as well as the most expeditious, way of making a sweet 

 juice ferment was to add to it a little of the scum, or lees, of another 

 fermenting juice. And it can hardly be questioned that this singular 

 excitation of fermentation in one fluid, by a sort of infection, or inocu- 

 lation, of a little ferment taken from some other fluid, together with 

 the strange swelling, foaming and hissing of the fermented substance, 

 must have always attracted attention from the more thoughtful. 

 Nevertheless, the commencement of the scientific analysis of the 

 phenomena dates from a period not earlier than the first half of the 

 seventeenth century. 



At this time, Yan Helmont made a first step, by pointing out that 

 the peculiar hissing and bubbling of a fermented liquid is due, not 

 to the evolution of common air (which he, as the inventor of the 

 term " gas," calls "gas ventosum"), but to that of a peculiar kind of 

 air such as is occasionally met with in caves, mines and wells, and 

 which he calls "gas sylvestre." 



But a century elapsed before the nature of this "gas sylvestre," or, 

 as it was afterward called, " fixed air," was clearly determined, and 

 it was found to be identical with that deadly " choke damp " by 

 which the lives of those who descend into old wells, or mines, or 

 brewers' vats, are sometimes suddenly ended ; and with the poisonous 

 aeriform fluid which is produced by the combustion of charcoal, and 

 now goes by the name of carbonic acid gas. 



During the same time it gradually became clear that the presence 

 of sugar was essential to the production of alcohol and the evolution 

 of carbonic acid gas, which are the two great and conspicuous pro- 

 ducts of fermention. And finally, in 1787, the Italian chemist, 

 Fabroni, made the capital discovery that the yeast ferment, the 

 presence of which is necessary to fermentation, is what he termed a 

 " vegeto-animal " substance — or is a body which gives off ammoniacal 

 salts when it is burned, and is, in other w'ays, similar to the gluten of 

 plants and the albumen and casein of animals. 



These discoveries prepared the way for the illustrious Frenchman, 

 Lavoisier, who first approached the problem of fermentation with a 

 complete conception of the nature of the work to be done. The 

 words in which he expresses this conception, in the treatise on element- 

 ary chemistry, to which reference has already been made, mark the 

 year 1789 as the commencement of a revolution of not less moment 

 in the world of science than that which simultaneously burst over the 

 political world, and soon engulfed Lavoisier himself in one of its 

 mad eddies : " We may lay it down as an incontestible axiom that, in all 



