46 CYTOLOGY OF YEASTS 



appeared to play a role in the coagulation of yeasts, followed by a 

 clarification of the liquid. This is comparable to the agglutination 

 which is found among the bacteria. Hansen has obtained the pro- 

 duction of a mucilaginous network by placing brewery yeast in a 

 covered bowl and letting it stand while it slowly dries. When 

 a portion of this yeast was examined in water, the formation of an 

 entangling network was observed. (Fig. 48.) Similar formations are 

 observed in yeasts placed on gypsum blocks or on gelatin. Hansen 

 has observed the same phenomenon in cells from scums yeasts of 

 certain species. This network is brought out especially when the 

 cells are stained with methyl violet or methylene blue. 



Certain pathogenic yeasts protect each cell by means of a thick 

 capsule which is mucilaginous in nature. 1 Certain yeasts seem 

 to unite with one another in a constant manner by means of a 

 gelatinous substance. Lindau has observed this in yeasts which he 

 has studied. 



Changes in the Cell during Fermentation 



The structure of yeasts is easy to interpret at the beginning 

 of development. During the active period of fermentation they be- 

 come more complex. What complicates the subject at this moment 

 is a very active secretive action. Like all secreting cells, they present 

 a series of cytological phenomena in connection with the secretions. 



Let us observe these modifications which are produced in the 

 cells in the course of fermentation by taking S. cerevisiae as an 

 example. At the beginning the cells possess a cytoplasm very dense 

 and homogeneous, a nucleus situated at the side of the cell and a 

 vacuole filled with metachromatic corpuscles which occupies the 

 center. (Fig. 47, 1 and 4, and Fig. 50, 1 and 4.) 



After 24 hours of fermentation the cell undergoes very impor- 



1 Agglutination or flocculation of yeasts is a complex phenomenon which is 

 little known. It seems to be brought about by a change in the constitution of 

 the membrane which becomes viscous. It appears in connection with the forma- 

 tion of a gelatinous network described by Hansen. This is the agglutination to 

 which one attributes the clarification of wine after fermentation. Beijerinck 

 (Die Erscheinung der Flokenbildung oder Agglutination bei Alkoholhefen, Cent. 

 Bakt. 20, 1908) distinguished autoagglutination, produced by the yeast itself, 

 and symbiotic agglutination, brought about by bacteria developing at the same 

 temperature as the yeasts (especially by the Leuconostoc agglutinans) . Agglutina- 

 tion is brought about by the addition of sulfuric acid, boric acid or 1 per cent 

 of other acids. Microscopically, the cells do not show any alteration during the 

 agglutination. Agglutination seems to be related to the life of the cells, for dead 

 yeasts do not agglutinate. Van Laer has shown that borax causes the agglutina- 

 tion of the yeasts killed by heat. 



