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 cerevisice 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- 



charomyces cere- o j ar cytoplasm, we can clearly distinguish a great 



msics. Young J 



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



the living state manifest Brownian motion. It is easy to stain them 



m a solution of . 



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



vacuoles, stained t ion o f neu tral red or methylene blue. These are 



pale red, contain 



m e t a c hromatic only metachromatic corpuscles. 



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

 ored dark red. . n - i 



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- 



^ 







-. 



^ 



FIG. 46. FIG. 47. 



FIG. 46. Saccharomyces cerevisice. 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 cerevisice. Young cells fixed and stained by a special 

 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- 



