— ' FjfiKMBNTATION 333 



' low ' fermentation process. The ' high ' fermentation 

 yeast consists of cells which are rather larger and more 

 globular, and have a greater tendency to form branched 

 chains than the ' low ' yeasts. The temperature best suited 

 for the carrying on of this fermentation is between 15° and 

 18° ,C. The reaction in the fermenting vats is much more 

 violent than is the case with the ' low ' yeasts. The rapid 

 emission of carbonic acid brings the cells to the surface, 

 where they form a frothy mass. 



Fermentation by Moulds. — Many of the mould fungi are 

 capable of setting up fermentation in saccharine liquids, 

 and are able to act under certain circumstances as true 

 alcoholic ferments. Some of the species of Mucor, when 

 immersed in a fermentable saccharine liquid, such as 

 wort, very quickly change their appearance : the submerged 

 mycelium swells irregularly, and a large number of 

 transverse septa appear, which divide it into barrel-shaped 

 or irregular cells, filled with highly refractive plasma. 

 These cells then multiply by budding, like true yeasts. If, 

 then, the above-mentioned cells are brought to the surface 

 of the liquid, or otherwise under aerobic conditions, they 

 are again able to develop the typical mould form. The 

 most active fermentative power is possessed by Mucor 

 erectus, which in ordinary beer-wort can be made to yield 

 up to 8 per cent, by volume of alcohol. 



Fermentation by the Bacteria. — The bacteria proper are 

 the cause of a very large number of fermentations. These 

 bacterial fermentations have only very recently been 

 studied from the purely biological standpoint, and it is 

 only in a very few of the cases that the processes have been 

 studied by the aid of pure cultures of the micro-organisms 

 which are the cause of the particular fermentation. 



As early as the year 1838 the view was expressed by 

 Turpin and Kutzing that the acetic fermentation was 



