1 6 THEORIES OF FERMENTATION. 



13. The Researches of Theodor Sehwann. 



As the words printed in italics in the two preceding sentences 

 show, and as a closer examination of the original treatise will more 

 clearly reveal, Cagniard did not indubitably establish the vegetable 

 nature of yeast. The accomplishment of this task, and the attri- 

 bution of this organism to its proper position in the system of 

 Botany, formed the subject of a treatise published by SCHWANN (I.) 

 in the first half of 1837, i.e. contemporaneously with Cagniard's 

 paper. 



In following up the results of his researches on spontaneous 

 generation, Sehwann studied beer-yeast, and found that the 

 individual globules, of which the mass was seen under the micro- 

 scope to consist, frequently became united into chain-like or 

 laterally branching bands, and presented to the eye an appearance 

 greatly resembling that of many already well-known multicellular 

 fungi. It was not this discovery alone, however, but rather their 

 mode of reproduction, which induced Sehwann to consider these 

 bodies as of a vegetable nature. In this process the globule 

 pushes out from its interior a small nodule, which Sehwann was 

 able to observe develop to its normal dimensions. " Observation 

 of its growth leaves no doubt as to its vegetable nature, since 

 animals do not reproduce themselves in this manner." The rate 

 of reproduction of the globules kept pace with the increasing 

 briskness of the fermentation, so that Sehwann came to the 

 opinion that it was highly probable that the development of the 

 fermentation was induced by that of the organism. 



"Vinous fermentation must therefore be regarded as the de- 

 composition occasioned by the sugar fungus extracting, from the 

 sugar and a nitrogenous body, the materials necessary to its 

 nutrition and growth, whereby such elements of these bodies 

 (probably among other substances) as are not taken up by the 

 plant unite, by preference, to form alcohol." 



This discovery was communicated by Sehwann to his friend 

 and colleague, Professor Meyen, who tested and confirmed it, 

 "stating with reference thereto, that the only doubt arising was 

 whether the organism in question was an alga or a thread fungus, 

 the latter seeming the more likely by reason of the absence of 

 green pigment." Thus yeast was recognised as a fungus, and, 

 from its capacity of fermenting sugar, was designated sugar 

 fungus : whence the current generic name, Saccharomyces Meyen. 



According as such a sugar fungus was found active in beer-wort 

 or wine-must, it was called by the specific name of S. cerevisice or 

 S. vini, which names remained in general use in their original 

 significance until REES (I.) in 1870 proposed a system of differ- 

 entiation which will be more fully noticed in a subsequent 

 paragraph. 



As follows from the remarks already made, the name "yeast" 



