210 STUDIES ON FERMENTATION. 



prising as it seems, that the two kinds of ferments are not 

 identical. If we operate on a " low " yeast its aerobian fer- 

 ment will differ physiologically from the ferment from which it 

 sprung, presenting various special peculiarities which are not 

 to be found in the original "low" yeast. In most of our 

 experiments we have found the new aerobian ferment to be 

 similar in its action to " high " yeast, rising to the surface, and 

 producing a beer which possesses a greater fragrance than beer 

 brewed with the identical " low " yeast from which it was 

 derived. Lastly, the properties of an aerobious ferment are not 

 peculiar to first growth, but are hereditary ; by repeating the 

 growth of the first aerobian ferment we do not cause them to 

 disappear, we find them again in succeeding generations. 



Notwithstanding these facts, it would be difficult to discover 

 any very appreciable differences between the forms of the cells 

 of any particular yeast and those of its aerobian ferment in 

 course of development. So true is this, that the aerobian 

 ferment of saccharomyces pastorianus might even be caused to 

 put on the forms of demntmm pulluJans, which we have had 

 occasion to observe specially characterize this ferment after the 

 cells have been subjected to a prolonged process of senescence.* 

 This is evident from the following example, which will once 



* Although we believe that the aerobian ferment of a particular yeast 

 may be produced by a kind of transformation of the cells of the latter, 

 yet we admit that this question is open to some doubt. The facts which 

 we unexpectedly discovered in connection with the caseous ferment 

 should make us extremely careful, and disposed to inquire whether 

 aerobian ferments do not originally, in a state of intermixture, form part 

 of the ferments from which they spring. One reason which might incUne 

 us to believe this, is the fact that a ferment sometimes perishes without 

 the appearance of aerobian ferment on the surface. There is nothing very 

 natural indeed in the hypothesis that we advance, which sets aside the 

 supposed intennixture ; but, on the other hand, if the aerobian ferment is 

 a particular ferment, simply intermixed with some other variety and 

 developed by change of conditions, how are we to account for its great 

 resemblance in appearance and mode of budding to the ferment on the 

 surface of which it appears ? This resemblance, however, might be 

 accounted for very natiu*ally if the two ferments were originally related. 



