3 



MORPHOLOGY AND CULTURE OF MICROORGANISMS. 



green and are slowly soluble in alcohol, ether, chloroform and caustic 

 potash. They appear to be of a fatty nature. Dead cells are usually 

 opaque and are distinguished by their staining more rapidly and deeply 

 than living cells. 



Some yeasts have a tendency during fermentation to remain at the 

 bottom of the liquid; others form a thick foamy layer on top. These are 

 known respectively as bottom and top yeasts. No sharp distinction can be 

 made as there are intermediate forms. 



O 



FIG. 13. Spore-bearing cells. A . S. pasteurianus. (After Bioletti); B.Sch. octosporus. 

 (After Schidnning); C. S. anomalus. (After Kayser.) 



The vegetative reproduction in the g&ausSaccharomyces takes place by 

 budding, in Schizosaccharomyces by fission. 



The extreme temperatures for budding lie between i and 47, varying 

 with different species. The optimum temperature varies in the same way 

 between 25 and 35. The rate of multiplication under favorable condi- 

 tions will vary from one to several hours for the formation of a new cell. 



When young, vigorous, well-nourished cells are supplied with abun- 

 dant air and moisture at a comparatively high temperature under conditions 

 that discourage budding (lack of nutriment) they form endospores. 

 These spores are usually about half the diameter of the mother cell and 

 from one to eight or more may occur in each cell. They may be formed 



