17 



" Yeast." 



Mk. W. Jago, F.C.S., F.C.I. 



Read November 24th, 1886. 



Mr. Jago said that yeast was associated with " fermentation." 

 In a saccharine liquid in which fermentation was set up, a curious 

 change is brought about in which alcohol is produced. This 

 change was looked upon as a kind of decay in former times. 

 Afterwards to the action of a kind of vegetable substance. Then, 

 when it was found out to contain nitrogen, the principle of 

 fermentation was said to be of animal origin. 



When yeast was submitted to microscopical examination, it 

 was found out that it consisted of a mass of cells. These 

 were seen to bud and grow, and hence yeast was known to be a 

 living substance. It is now classed as a member of the 

 vegetable kingdom ; as a kind of fungus, in fact. The 

 next great light thrown on the subject was by Pasteur, who 

 declared that fermentation was essentially a vital process. The 

 changes which take place in fermentation being the vital ones 

 accompanying growth and development. This was in direct 

 antagonism to Liebig's idea. Liebig looked on fermentation as 

 a series of chemical or molecular changes, initiated by the yeast. 

 The yeast plant in growing absorbs certain bodies from its environ- 

 ment, and in doing so produces alcohol and carbonic acid. Other 

 ferments absorb or digest other substances, and produce 

 different results. A liquid free from fermenting bodies does not 

 undergo fermentation, and one to which germs cannot obtain 

 access, also does not ferment, thus showing that it is from germs 

 introduced from without, and not from an interior molecular series 

 of changes that this process is set up. 



The latest researches show us that yeast is a plant of the 

 simplest structure. It lives and grows by the assimilation of 

 carbon, nitrogen and hydrogen, from inorganic bodies. Mr 

 Jago then alluded to Brefeld's researches on Conidia, as a result 

 of which he (Brefeld) argued that yeast should not be considered 

 as a separate and distinct organism, but as the germs of a fungus 

 associated very often with wheat grains. But this view, although 



