SAC FUNGI IN PARTICULAR 137 



a sterile block of plaster of Paris with a saucer-shaped hollow on 

 top. This block is placed in sterilized water and the top is seeded 

 with vigorous, young well-nourished yeast plants which develop spores 

 if kept at 25°C., in from twenty-four to forty-eight hours. The tem- 

 perature at which spore formation occurs and the time which it takes 

 for sporulation are points which have been obtained by experimenta- 

 tion for all the more important species of yeasts. The data which has 

 been obtained is used in the physiologic diagnosis, or identification of 

 the various kinds of SACCHAROMYCEXACEiE, which react difiEerently 

 under experimental treatment. Film formation is also of diagnostic 

 importance, where economic yeasts form floating films on the nutrient 

 liquid media in which they are grown. The time 

 required for the development of the j51m differs, 

 other conditions being equal, with the species of 

 the yeast and is longer the lower the temperature 

 of the culture. Hansen obtained the following data 

 for Saccharomyces ceremsia ; 



FUm formation takes place at: 



33° to 34°C. in about 9 to 18 days. ^ ^'^^ 47.— Yeast. 



a no/-. • I 1 baccnaromyces cerevt. 



20 to 28 C. in about 7 to 11 days. ^.-^ showing repro- 



13° to is'C. in about 15 to 30 days. duction by germina- 



6° to 7o''C. in about 2 to 3 months. tion, or budding; a. 



single cells; 6, bud- 



No formation of film occurred above 34°C. or below ding cells. (After 

 5°C. Another point of importance is that species Bact"rioiJly"p''»"'^''^ 

 of Saccharomyces form films so that this process is 

 not entireh- associated with the fungi belonging to the so-called genus 

 Mycoderma. In fact some authors recognizing that Saccharomyces 

 cerevisia (Fig. 47) produced films have named that yeast, Mycoderma 

 cerevisicB, and have thus confused its identity. 



Hansen in a paper published in 1888 classified the yeasts essentially, 

 as follows: 



1. Species which ferment dextrose, maltose, saccharose: Saccharo- 

 myces cerevisuB I, S. Pastorianus I, S. Pastorianus II, S. Pastorianus 

 III, S. dlipsoideus I, S. eUipsoidetts II. 



2. Species which ferment dextrose and saccharose, but not maltose: 

 Saccharomyces Marxianiis, S. exiguus, S. Ludwigii S. saturnus. 



3. Species which ferment dextrose, but neither saccharose nor 

 maltose: SaccJtaromyces mali Duclauxii. 



