ACTION OF PHYSICAL AGENTS ON THE YEASTS 109 



Light 



Light does not seem to possess any marked action on yeasts. How- 

 ever, Marshall Ward 1 noticed a destructive action of light on the 

 ascospores of S. Pyriformis. It will be pointed out that the different 

 rays of the spectrum have an accelerating or retarding influence on 

 the sporulation of yeasts. According to Martinand yeasts are de- 

 stroyed by an exposure of 4 hours to the sun's rays at 40 to 45. 

 An exposure of 3 days at 36 produces the same effect. The absence 

 of light, on the contrary, over a long time does not effect the yeasts. 

 Although light acts on the vitality of the yeasts, it does not seem that 

 its effect is very great, and it may be generally said that yeasts are 

 resistant to the action of light. 



The recent investigations of Buchta 2 made with Saccharomyces 

 cerevisiae and Ludwigii have shown that diffuse daylight stopped the 

 budding of yeasts. The cells not exposed to it multiplied almost twice 

 as fast as those which were exposed. Electric light had the same in- 

 fluence. When cultures of yeasts were placed at different distances 

 from the source of light, those which were farthest away multiplied 

 most quickly. The blue light had a more marked action than the 

 red which did not seem to effect the budding. The infra-red rays did 

 not seem to impede budding. The ultra-violet rays, however, ex- 

 hibited a marked action, and an exposure of 10 seconds sufficed to 

 stop budding. A longer time resulted in the death of the cells. Von 

 Recklinghausen 3 found that it took 300 seconds' exposure at a dis- 

 tance of 200 mm. from a quartz lamp burning 66 volts and 3.5 am- 

 peres to kill yeast cell. 



Jacquemin and Giurel 4 found that radioactive emanations exerted 

 a favorable action on fermentation. A radioactivity of \ to 1 unit 

 per liter exerted a favorable action on the splitting of sugars. 



Moisture 



Yeasts need moisture; they resist drying easily as the experiments 

 of Hansen 5 have shown. 



1 Ward, H. M. The ginger beer plant and the organisms composing it. 

 Philos. Trans. Royal Soc., 1898, 183. 



2 Buchta, L. Ueber den Einfluss des Lichtes auf die Sprossung der Ilefe. 

 Cent. Bakt. Abt. II. 41 (1914), 340. 



3 Von Recklinghausen, M. Purification of water by the ultraviolet rays. 

 Jour. Amer. Water Works Assn. 1 (1914), 565-588. 



4 Jacquemin, G. and Giurel, G. The influence of radioactive emanations on 

 yeasts and alcoholic fermentations. Bull. Agr. Intelligence, 5 (1914), 1505. 



5 Hansen, E. C. Recherche sur la morph. et la physiol. des ferments al- 

 cooliques. Comp. Rend, des trav. de Carlsberg, 4, 1898. 



