64 MORPHOLOGY AND CULTURE OF MICROORGANISMS 



In order to understand clearly this structure, one must observe 



young cells taken from a culture at the beginning of development. 



For this purpose we use Saccharomyces cerevisia which, because of the 



relatively large size of its cells, lends itself better than 



any other yeast to a cytological study. Examined in 



* * ' the living state, highly magnified, the cells of this 



yeast show a dense and homogeneous cytoplasm with 



a group of small vacuoles or a single large vacuole at 



FIG. 45. Sac- the center. In the vacuoles and also in the perivacu- 



visi^ myCeS y Cere ~ ^ ar cytoplasm, we can clearly distinguish a great 



cells examined in many small shining granules, of varying sizes, which 



the living state man if es t Brownian motion. It is easy to stain them 



in a solution of J 



neutral red. The in the living state (Fig. 45) with a very dilute solu- 



vacuoles, stained tion of neut ral red or methylene blue. These are 



pale red, contain 



m e t a c hromatic only metachromatic corpuscles. 



col- j n fi xe d an d stained preparations (Fig. 46, i-io) is 

 seen in each cell a single, large nucleus, whose struc- 

 ture is exactly like that which we have discussed in molds. This 

 nucleus is surrounded by a membrane and contains a hyaline nucleo- 



A /^\ 2 



fQJ -, 5 10 ... 



*> *> -'9 ':*} 



3 4 7 -- ~ ' 



9 



'' u /^, 



^}(ik fe ^ 

 '' ' 



6 7 8 12 _ 



FIG. 46. FIG. 47. 



FIG. 46. Saccharomyces cerevisia. i-io, Young cells with nucleus, showing its 

 structure. 6-8, The same: division of the nucleus. 11-13, Cells after twenty-four 

 hours fermentation, with a very large glycogenic vacuole filled with lightly colored 

 grains. 



FIG. 47- Saccharomyces cerevisia. Young cells fixed and stained by a specia 

 method revealing in the cytoplasm a chondrium consisting of rod mitochondria and 

 granular mitochondria. 



plasm in which is easily seen a large nucleolus and some chromatin 

 this latter is scattered through the nucleus, sometimes found in the 

 nucleoplasm in the form of a network, sometimes reduced to a num- 



