386 BACTEBIOLOSY. 



may remain attached to the original one. It is because of 

 this peculiarity that yeasts are known as budding fungi or 

 Mastomycetes. 



The yeast-cells are large, oval or roundish bodies, but 

 under special conditions, as when grown deep in gelatin, 

 they may elongate and give rise to thread-like growths. 

 These pseudo-mycelial threads, as they are called, indicate 

 a certain relationship to the group of moulds. The yeast 

 cells by their size and by the presence of budding cells can 

 be readily distinguished from other microscopic forms. 

 They are readily stained by simple anilin dyes and by 

 Gram's method. 



When actively multiplying, the contents of the yeast- 

 cells appear perfectly homogeneous but later on granules 

 of various size appear and surround small, clear portions 

 or vacuoles. The contents of the cell on contact with 

 iodine take on a brownish violet color which disappears on 

 heating and reappears on cooling. This is due to the pres- 

 ence of a starch-like or glycogen compound. Occasionally 

 a gelatinous envelope or capsule may form. 



Yeast colonies, when they develop on a gelatin plate, 

 can be readily recognized even with a low power. Owing 

 to the large size of the cells the colony has a peculiar, 

 coarsely granular appearance. They do not liquefy gelatin, 

 although they do contain within their cells a proteolytic 

 ferment. 



It is customary to divide the yeasts into two groups 

 according as to whether they, form spores or not. The 

 spore producing yeasts are designated as saccharomyces, 

 whereas those forms that do not produce spores are usually 

 brought together under the group name torula. 



The saccharomyces as indicated above give rise to 

 'endogenous spores. Usually several of these are formed 

 within a cell as shown in Fig. 55. The spores can be double 

 stained like those of bacteria, or like the tubercle bacillus. 



