112 PHYSIOLOGY OF YEASTS (Continued) 



They found that 0.56 gram in a cubic centimeter of air was toxic 

 for 30,000,000 cells. 



Euler and Emberg l have stated that the hydrogen centration in- 

 fluences the development of bottom yeast. This is to be expected 

 since other forms of microorganisms act in the same way. 



Physiological Conditions of Budding 



Budding is accomplished each time the cell finds itself in a suit- 

 able environment with no deterring factors, such as the accumulation 

 of products of metabolism. Aeration plays an important role; it 

 seems to accelerate budding. However, it is not indispensable. Han- 

 sen 2 has noticed that budding took place in the presence of nitrogen 

 with no oxygen present. It is also known that budding continues 

 during alcoholic fermentation. It is known, to the contrary, that 

 sporulation does demand the presence of oxygen. Sporulation and 

 budding then differ on this point which closely separates them. 



Temperature exerts a preponderant influence on budding which 

 is a function of temperature. Hoyer has calculated, for example, that 

 in a medium of gelatin, S. Pastor ianus formed a new generation at 

 13 every 6 hours while at 35 the budding was accomplished in about 

 3 hours. The experiments of Hansen have shown that there exist 

 minimum, optimum and maximum temperatures for every species of 

 yeasts. Hansen has determined the limiting temperatures for 11 

 species of yeasts (S. cerevisiae, Pastorianus, intermedius, validus, 

 ellipsoideus, turbidans, Marxianus, Wiltta anomala, Pichia, membranae- 

 faciens, Saccharomy codes, Ludwigii). He found that the maximum 

 temperatures of these species varied from 47 to 34 C., the minimum 

 temperature from 0.5 to 0.3 C. 



Particular Types of Budding 



It has been stated above that yeasts may grow as a sediment at 

 the bottom of the culture flasks (anaerobic life), or as a scum or veil 

 (aerobic life). The formation of the scum generally represents a par- 

 ticular type of budding. 



1 Euler, H. and Emberg. F. The sensitiveness of living yeast to hydrogen and 

 hydroxyl-ion concentration. Zeit. Biol 69, 349-64 1919. Chem. Absts. 13 

 (1919) 2691. 



2 Hansen, E. C. Recherches sur la physiol. et la morphologic des alcooliques 

 ferments XI. La spore de Saccharomyces devenue sporange. Recherches com- 

 paratives sur les conditions de croissance vegetative et le development des 

 organes de reproduction des levures et des moisissures. C. R. du lab. de Carlsb. 

 5, Book 2, 1902. 



