THEORIES OF FERMENTATION. 23T 



investigations that brought about his exact study of yeast 

 under the microscope in 1837-39. Schwann arrived at th& 

 result that it is not atmospheric oxygen, but a substance 

 conveyed in air, and destroyed by heat, which brings about 

 fermentation. To determine whether this substance is of 

 animal or vegetable character, he enquired whether the sub- 

 stance is destroyed by those poisons that are capable of killing 

 infusoria, or by those that kill moulds. The latter proved to 

 be the case, for a solution of potassium arsenite arrested the 

 fermentation of wine ; therefore, he argued, the substance 

 must be of a vegetable character. 



Under the microscope the yeast resolved itself into the 

 " recognised granules which constitute the ferment." Then 

 he observed how they form continuous rows, with other rows 

 placed diagonally. He also observed that small, granules 

 appeared on the sides of the cells, which form the starting 

 point for new rows, and usually on the last granule of a row 

 appeared a tiny and sometimes elongated body. It will b& 

 seen that this constitutes an exact description of a budding 

 colony of yeast resulting from direct observation under the 

 microscope. Schwann observed that the similarity between 

 this picture and that of many other kinds of fungi was con- 

 siderable, and this strengthened his belief that yeast is a plant. 

 At his instigation Meyen examined " this substance," and 

 gave the plant the name it has since retained of Saccharomyces 

 (sugar-fungus). 



Schwann also demonstrated that the feeble evolution of 

 gas in grape juice may be regarded as a sign of fermentation ; 

 immediately afterwards the first individuals of the sugar-fungus 

 made their appearance ; these plants grew and multiplied 

 throughout the period of fermentation. As it had also been 

 shown that fermentation ceased through every treatment 

 which brought about the destruction of the fungus (boiling, 

 addition of potassium arsenite, etc.), the connection between 

 fermentation and the sugar-fungus cannot be denied, and " it 

 is extremely probable that the latter brings about the pheno- 

 mena of fermentation through its growth." He declared that 

 fermentation was carried out in such a way that " the sugar- 

 fungus absorbs sugar and a nitrogenous body necessary for its- 



