ALCOHOLIC FERMENTS. 185 



has almost come to a state of rest, the plasma may be reduced 

 to a thin layer on the inside of the wall, whilst a large vacuole 

 occupies the remaining space, containing numerous large and 

 small grains, many of a fatty nature. If such cells are again 

 brought into a fermentable liquid, they exhibit a highly 

 characteristic appearance during the period which precedes the 

 macroscopic phenomena of fermentation. The grains disappear, 

 and numerous fine plasma-threads appear in the clear cell-sap, 

 and gradually surround the vacuoles ; finally these disappear, 

 and the cell is once more filled with clear homogeneous plasma. 



If the yeast is cultivated in beer- wort with 10 per cent, 

 cane-sugar, or in a decoction of sugar-beet, or in certain 

 artificial nutrient liquids, at 30C., the plasma of the cells is 

 coloured brownish-violet by iodine ; the coloration disappears 

 on heating, but reappears at low temperatures. This reaction 

 has been held to be a proof of the presence of glycogen a 

 reserve substance (a carbon compound) which occurs in 

 animals and also, it is supposed, in various fungi, where it 

 apparently plays a part analogous to that of starch in 

 green plants. 



As in most vegetable cells, a cell-nucleus (first discovered by 

 SCHMITZ) is also found in the yeast-cell, and its presence can 

 be proved by staining with osmic acid or with picric acid and 

 hsematoxylin. According to HANSEN this cell-nucleus is either 

 spherical or disc-shaped. In old film-formations of jSaccharo- 

 mycetes, he found cells which distinctly showed the nucleus 

 without any treatment. JANSSENS, DANGEARD, and BUSCALIONI 

 observed the partition of the cell-nucleus in the budding and 

 in the spore-formation of the Saccharomycetes. 



CLASSIFICATION OF THE SACCHAROMYCETES. 



The majority of SaccJiaromycetes are only known as budding - 

 fungi with endogenous spore-formation. In the minority, a 

 mould-stage is also known, which bears a certain resemblance 

 to Dematium, O'idium, or Monilia. 1 



1 (Compare page 124). Experimental evidence of the descent of Saccharomy- 

 cetes from other fungi has not as yet been adduced. BREFELD showed that 

 many Ustilagineae (smut-fungi), Basidiomycetes, and other fungi may enter 



