FERMENTATION. 



113 



that it gives rise to buds by sending out small processes from 

 its wall, and that these latter then become detached from the 

 mother cell. This cell consists of a distinct membrane and 

 of protoplasm, the former of which may be thicker or thinner 

 according to the age of the cell, whilst the latter may vary 

 very considerably. Whilst the cell is merely growing actively, 

 the plasma or cell contents are homogeneous and highly re- 

 fractile, but when it is placed in beer wort or other highly 

 nutritive media, it multiplies rapidly and gives rise to the 

 fermentation of the sugar and maltose, and the protoplasm 

 becomes differentiated and undergoes certain changes. Large 

 clear spaces, which are supposed to contain the more fluid 

 ■part of the protoplasm (vacuoles), are formed ; cloudy 

 granular change occurs in the other protoplasm ; and larger 

 fat globules also make their appearance. As the cell gets 

 older, and consequently less active, the finely granular proto- 

 plasm accumulates as a thin layer inside the cell wall, whilst 

 the centre is occupied by clear fluid, in which are floating a 

 number of fatty granules and globules. 



It would appear that this last is a somewhat degenerated 

 condition, and that it is due to imperfect nutrition, for if a 

 few of these cells are transferred to a fresh rich nutrient 

 medium, the protoplasm becomes again modified, the cloudy 

 granules disappear, small shoots of the clear plasma pass into 

 the large central cavity, small rounded vacuoles are formed 

 in place of this large central cavity ; these in turn become 

 subdivided, and eventually the whole cell is again occupied 

 by clear protoplasm. By appropriate staining, especially of 

 an older cell, a nucleus may be distinguished, whilst under 

 certain conditions, to be afterwards mentioned, spores or 

 ascospores are formed. 



Other organisms which in certain respects resemble the 

 yeast fungi are the Torulae, which Pasteur described as being 

 somewhat of the nature of yeasts, but different in the fact 

 that they were unable to give rise to such marked alcoholic 

 fermentation. Hansen, however, was able to show that this 

 was not a suflSciently distinct characteristic, as some of the 

 saccharomyces give rise to the formation of little or no 

 alcohol, whilst, on the other hand, some of the Torulas set 

 up very marked alcoholic fermentation. The great point 

 of distinction is, that none of the Torulae, so far as has 

 yet been observed, are capable of producing endospores ; all 



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