218 STUDIES ON FERMENTATION. 



The physical aspect of the several aerobian ferments is in 

 general so characteristic that we are often able by simple 

 inspection to distinguish between them as they occur on the 

 surface of liquids, S((ccharomijces pastoHanns in its aerobian 

 state forms a crown of cells round the sides of the vessel at 

 the surface of the liquid, which crown is broken up by the 

 least agitation of the liquid ; its vitality continues for years. 



The aerobian ferment of " high " yeast appears in the form 

 of small isolated teats on the surface of the fermented liquid. 

 It develops rather sluggishly, and has no great vitality. 



The aerobian form of " low " yeast develops as a somewhat 

 fragile layer, the least agitation precipitating it to the bottom 

 of the vessel in a cloud of verj'^ small irregular flocks, that do 

 not diffuse through the liquid as they fall. With free access 

 to air it retains life for a long time. 



The aerobian ferment of caseous yeast forms a continuous 

 greasy-looking pellicle, gradually thickening, which breaks 

 up into fragments when shaken. AVith a supply of air it 

 lives very long, and the pellicle gradually increases in 

 thickness. 



In reviewing these ferments we may naturally ask ourselves 

 the question whether the '' high " ferments of which we have 

 spoken — the industrial one concerned in the " high " fer- 

 mentation of breweries, and the other which we have termed 

 new " high " ferment — are not aerobian ferments of " low " 

 yeasts. We are inclined to think that the ferment which in 

 the preceding paragraph we termed netv ^^ high" ferment, may, 

 perhaps, be the aerobian form of the " low " yeast employed 

 by Alsatian and German brewers. We have studied this new 

 " high " ferment side b}^ side with the aerobian ferment of 

 " low " yeast, and the result we have arrived at is, that in 

 appearance and mode of germination, as well as in the flavour 

 and quality of the beers which they produce, they greatly 

 resemble one another. In the last respect, however, we cannot 

 say that the identity is quite absolute, and hence it is with 

 some doubt that we suggest the possible identity of the two 



