

Q^^ 



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 Saccharomycetace^, which react differently 

 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 film differs, /^ 

 other conditions being equal, with the species of ^^ r^\^(^ 

 the yeast and is longer the lower the temperature 

 of the culture. Hansen obtained the following data 

 for Saccharomyces cerevisicB ; 



Film formation takes place at: 



S3° to 34°C. in about 9 to 18 days. ^ ^/^- 47-— Yeast. 



o i " no,-^ • . ^ i 1 Saccharomyces cerevi. 



20 to 28 C. in about 7 to 11 days. ,-^_ growing repro- 



13° to I5°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; b, bud- 



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

 5°C. Another point of importance is that species ^IZiJ^X'^'^J'' 

 of Saccharomyces form films so that this process is 

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

 Mycoderma. In fact some authors recognizing that Saccharomyces 

 cerevisicB (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 cerevisicB I, S. Pastorianus I, S. Pastoriamis II, S. Pastorianus 

 III, S. ellipsoideus I, S. ellipsoideus II. 



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

 Saccharomyces Marxianus, S. exiguus, S. Ludwigii S. saturnus. 



3. Species which ferment dextrose, but neither saccharose nor 

 maltose: Saccharomyces mali Duclauxii. 



