CHAPTER XIV. 



YEAST FUNGI : TORULACE.E, SACCHAROMYCES. 



YKAST, iorula (Pasteur), or saccharomyces, is not a bac- 

 terium, but belongs to an altogether different order of fungi 

 the Blastomycetes. It consists of spherical or oval cells, 

 very much larger than the largest micrococci, and as in the 

 case of these each cell consists of a membrane and contents. 

 The contents are either homogeneous or finely granular pro- 

 toplasm ; in the latter case there are generally present one, 

 two, or more small vacuoles. 



There are a great many species of Torula, varying from one 

 another morphologically chiefly in their size, and physio- 

 logically by their action on various fluids (see below). 



The cells multiply in suitable media by gemmation, a minute 

 knob-like projection appearing at one side of the cell, and 

 enlarging till it reaches nearly the size of the original or 

 mother-cell. It finally becomes altogether constricted off 

 from this latter, or having reached its full size remains fixed 

 to the mother-cell, and each cell again producing by gemmation 

 a new cell. In this way aggregations of four, six, eight, or 

 more cells are formed, which may be arranged either as a chain 

 when the production proceeds in a linear manner, or as a 

 group if the gemmation takes place laterally. 



Under varying conditions of growth, e.g. on transplanting 

 ordinary yeast growing in sugar-containing fluids on to potato, 

 but sometimes also in the same nutritive fluid, it is observed 

 that some of the yeast cells enlarge twice, thrice, and more 

 times ; they then form in their interior two, three, or more 

 small cells by endogenous formation ; these new cells are 

 regarded as spores * the mother-cell being an ascospore and 



1 T. de Seynes, Comptes Rendus, 1866; Rees, Hot. Zeitschr. 1869; Hansen, 

 Carlsberg Laborat. 1883. 



