_:;) 



2. Yeasts. The investigations on yeasts, like those on 

 bacteria, will be arranged in two sections: A. Those re- 

 porting negative results; B. Those reporting injury or 

 death. 



A. Several authors have observed that some yeast 

 species are physiologically active at sub-zero tempera- 

 tures. Thus, Berry (193-1:) found a species which repro- 

 duced actively in beer wort at -2.2°, 



Salimovskaja-Rodina (1936) described 19 species of 

 yeast (!) isolated from colored snow {Arch. Biol. Nauk, 

 43,229). 



Smart (1935) found that several species of yeast, cul- 

 tured on agar slants and left for 1 year at - 8.9°, produced 

 abundant growth when transferred to room temperature. 



Molisch (1897) described a deformation and a shrink- 

 ing of about lOVf, but no loss of growth or of fer- 

 mentation power when yeast cells, growing actively in a 

 liquid medium, were frozen at -5° to -9° and observed 

 under the microscope during the congelation of their 

 culture medium. 



Kadisch (1931) exposed several sorts of pathogenic 

 yeasts, suspended in 0.85% sodium chloride solutions, to 

 temperatures of - 20° to - 30° for 2 months, subjecting 

 them to 11 successive freezings and thawings during this 

 time. No harmful effects were observed. 



Zopf (1890) made thin smears of vegetative cells and 

 of spores of Saccharomyces Hansenii on mica sheets and 

 subjected them for 4 hours 20 minutes to - 83° ; death did 

 not ensue. Furthermore, no harm was done when this 

 frozen material was transferred directly into water at 

 room temperature ("Die Pilze," p. 275, Breslau). 



Melsens (1870), after having observed that yeast resists 

 -91°, investigated the combined action of pressure and 

 cold. He put a yeast suspension in a steel bomb calcu- 

 lated to resist a bursting pressure of 8,000 atmospheres 

 and froze the suspension at a temperature low enough to 

 burst the bomb; the cells remained active after this 

 treatment. 



