8 MORPHOLOGY AND DEVELOPMENT OF YEASTS 



Most of the Torula are easily recognized by their almost perfectly 

 round shape, their content of fat, their peculiar manner of propagation 

 which causes them to give off simultaneously many small round buds, 

 and, finally, by their membrane, almost always surrounded by a layer 

 of a mucilaginous substance. The genus Torulaspora and a few other 

 yeasts have this same shape, which is known as the Torula type. 



The Mycoderma and certain members of the genus Pichia often 

 possess a decidedly refractive appearance, and elongated cylindrical 

 cells which bud almost exclusively at two poles; their contents is trans- 

 parent, enclosing a number of refractive granules localized especially 

 in the extremities. This is the mycoderma type of yeast cell. 



With S. Ludwigii, the cells possess a very peculiar form, tubuliform, 

 bottle, or sausage shaped. Their division is intermediary between 

 budding and partition. 



Finally there are the Schizosaccharomyces, which are not ordi- 

 narily confused with other yeasts, for as the name indicates, they 

 always multiply by division and not by budding. In Sch.' octosporus 

 the cells vary from a spherical form to the form of a drum stick. The 

 spherical cells resemble huge micrococci while the drum-stick-shaped 

 cells resemble the bacilli. 



It is seen, then, that the yeasts present very common forms which 

 are exhibited rather regularly by the various species. It is well to 

 add that certain yeasts are able to assume abnormal forms. Thus, 

 Lindner showed that S. Bailii, when growing in giant cultures on 

 gelatin, resembled ameboid bodies. 



Mycelial Formations 



It has been stated before that the yeasts may grow in a filamen- 

 tous or mycelial formation. Nevertheless it does not occur in all 

 of the yeasts, and never appears where there is feeble development. 

 It appears, however, only under special conditions. 



Mycelial formation was observed for the first time by Hansen 

 in the growth which covered the surface of fermenting liquids; this 

 is termed a pellicle or scum. This growth presents a very different 

 appearance from that which is found upon the bottom of flasks. 

 Colonies are composed of long threads and cells and, little by little, 

 the growth takes on a resemblance of a mycelium. The formations, 

 however, always remain in a rudimentary state. 



The investigations of Hansen, Lindner, and Will have shown that 

 certain yeasts are equally capable of forming the mycelial-like struc- 

 ture when growing on gelatin. It manifests itself very well in S. 

 marxianus and carlsbergensis, Pichia membranaefaciens, in Zygo- 



