The Oidia 39 



The yeasts, of which Saccharomyces cerevisiee may be taken as 

 the type, are active fermentative organisms, quickly splitting the 

 sugars into CO2 and alcohol, and are largely cultivated and used 

 in the manufacture of fermented liquors and bread. They grow well 

 in fermentable culture-media and- most of them also grow upon the 

 ordinary laboratory culture-media. Many varieties, some of 

 which produce red or black pigment, some no pigment at all, are 

 known. They play very little part in, the pathogenic processes. 

 Burse has observed a case of generalized fatal infection caused by an 

 yeast that he calls Saccharomyces hominis. Gilchrist, Curtis, 

 Ophiils, and others have seen localized human infections by blasto- 

 mycetes. (See Blastomycetic dermatitis.) 



THE OIDIA 



These organisms seem to occupy a place intermediate between the 

 yeasts and the molds — the blastomycetes and the hyphomycetes. 

 In certain stages they appear as oval cells which multiply by gem- 



^O.^ 



Fig. 8. — Oidium, showing the various vegetative and reproductive elements. 



X 35°- (Grawitz.) 



mation, but instead of becoming separated, hang together. At a 

 later stage of development they grow into long filamentous forma- 

 tions suggesting the mycelia of molds, but being less regular. 

 Certain cells also develop as reproductive organs.^ 



They are common micro-organisms of the air and appear as 

 frequent causes of contamination in culture-media, upon all forms 

 of which they grow readily, producing liquefaction where possible. 

 They engage in but few pathogenic processes, the most familiar 

 being that brought about by Oidium albicans, which causes the 

 common disease of childhood known as thrush {q. v.). 



