ALCOHOLIC FERMENTS. 235 



is the chief result of the writer's experience, extending over 

 many years; it has rendered it possible to compare the 

 very varied circumstances obtaining in the different beer- 

 producing countries. 



An example of the permanence of the specific properties 

 under very different external conditions has also been given by 

 IRMISCH in a comparative examination of two bottom-yeasts. 

 One of the species gave a low attenuation and multiplied to 

 a very small extent in the wort, whilst the other, on the 

 contrary, gave a high attenuation and possessed the power of 

 multiplication in a high degree ; the course of the fer- 

 mentation in the two cases also showed marked differences. 

 These differences still existed on varying the concentration of 

 the wort or the quantity of the yeast, at very different tempera- 

 tures, and in every kind of medium, thus: when cultures 

 were employed which have been grown in wort containing 

 diastase ; under various conditions of aeration with ordinary 

 wort ; with a specially prepared wort very poor in maltose ; 

 in the presence of grains during fermentation; and in solutions 

 of cane-sugar. Even in fermentations which had been carried 

 on for six months, an examination of the product showed 

 that the typical differences of the two species had not 

 disappeared. 



Certain high-fermentation species are employed in distilleries 

 and in yeast factories. Since 1887 a number of distillery 

 yeasts, yeasts for the fermentation of molasses and the manu- 

 facture of pressed yeast, have been prepared in the author's 

 laboratory in pure culture. They exhibit marked constant 

 differences in their sedimentary forms and in ascospore- 

 formation. The species which have been introduced into 

 practice also differed in this respect. DELBRUECK, P. LINDNER, 

 and STENGLEIN have since had the same experience. 



According to the writer's experience, these yeast-species also 

 exhibit characteristic differences among themselves. Indeed, 

 such differences may be observed in the general appearance of 

 the fermentation, some species showing decided top-fermenta- 

 tion phenomena, while others in parallel experiments behave as 

 bottom-fermentation yeasts. This diversity also appears in the 

 poiuer of multiplying of the cells and in the yield of alcohol 



