294 



MICRO-ORGANISMS AND FERMENTATION. 



If we compare the film-formation of the six species, we 

 find that the films developed at the higher temperatures offer 

 very little scope for discrimination, S. cerevisice I. and S. 

 ellipsoideus II, alone being distinguishable from the remainder. 

 It is quite otherwise, however, when young films developed 

 at 13-15 C. are examined. The two species, 8. Pastorianus 

 II. and S. Pastorianus III. both top-fermentation yeasts, 

 the cells of which in ordinary cultures cannot be distinguished 

 from each other with certainty exhibit in this case entirely 

 different forms of growth. An equally striking difference 

 is found between the otherwise similar species, 8. ellipsoideus^ 

 I. and //. 



Observations of the limits of temperature for the formation 

 of films show that for 8. cerevisice I. and 8. ellipsoideus /. 

 these lie approximately within 38 and 5-6 C. ; the limits 

 for the three Pastorianus species are 34 and 3 C. ; 8. ellip- 

 soideus II. has the same lower limit as the last species, but its 

 maximum temperature is 38-40 C. 



The time limits, compared with those given for ascospore- 

 formation, show that in both cases development takes place 

 more slowly at low than at high temperatures. 



At temperatures above 13 C. the film of 8. ellipsoideus II. 

 develops so rapidly and vigorously that flasks containing 

 this yeast can be recognised by this alone. Thus, at 22- 

 23 C. the film had completely covered the surface in six to 

 twelve days, whilst the other five species required three times- 

 as long to form a film, and this was generally more feebly 

 developed. This species and 8. Pastorianus III. also develop 

 a vigorous film with comparative rapidity at the ordinary 

 room temperature, the other species being left far behind. 



A further important biological relationship is the following : 

 Hansen's investigations have proved that the temperature 

 maximum for budding in wort is higher than the maximum 

 for film-formation, and that this again is higher than the 

 maximum for spore-formation ; in other words, with a rising 

 temperature, a point is reached at which spore-formation 

 ceases, then a higher point at which film-formation ceases, 

 and lastly, a still higher at which budding is no longer possible. 

 On the other hand, the experiments indicate that the tern- 



