CHAPTER XII. 

 YEASTS AND MOULDS. 



THIS chapter is devoted to a consideration of the next 

 higher groups of the plant algae above the bacteria. They 

 are the yeasts or Blastomycetes and the moulds or Hypho- 

 mycetes. That there is any sharp separation of these forms 

 from the bacteria, or even from one another, cannot be 

 maintained. There are various gradations in character 

 from the typical representatives of the groups toward the 

 others, so that there are intermediary species incapable of 

 classification. The typical members of each family have 

 very distinct criteria and about them similar forms must be 

 classified. 



The yeasts and moulds are very widely distributed in 

 nature, but have but slight pathogenic powers. The former 

 are of importance in the making of spirituous liquors, bread, 

 etc. The moulds have little use, and, except for their frequent 

 appearance as contaminations, and in a few diseases, are of 

 little interest to the pathologist or bacteriologist. 



YEASTS. 



Yeasts are spherical or ovoid bodies with a doubly con- 

 toured wall and a highly granular protoplasm oftentimes with 

 fat droplets in it. They measure from %^ to y^ inch in length 

 and are about two- thirds as wide as long. The characteristic 

 feature of the yeasts is their method of reproduction, which 

 takes place by a swelling out of a part of the cell wall like a 

 ball, into which the protoplasm flows; this is called "bud- 

 ding." When the daughter-cell arrives at the proper size, 



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