557 
Variation of Yeast-cells. 
shown that when this species is cultivated for a number of 
generations in a solution of cane-sugar in yeast-water, a growth 
is obtained the cells of which have for a time lost the dis- 
agreeable properties referred to. From this it is seen that it 
is possible to act upon yeast-cells in such a w T ay that they can 
be made to impart to fermenting liquids a taste and odour 
different from that originally characteristic of the yeast. 
It is a common fact that when bacteria are cultivated in 
a certain manner they lose their fermenting power. In a very 
interesting paper, read at the British Association for the 
Advancement of Science, 1893, Professor Percy Frankland has 
given an account both of the researches which he himself has 
undertaken in this direction and of those which at that time 
had been made by other investigators. He brings into relief 
the fact that it may frequently be observed that a bacterium 
which had originally the power of fermenting some particular 
substance, has lost this power through prolonged culture, and 
that, indeed, even a single passage through gelatin may appar- 
ently destroy the capacity to exercise this function. We do 
not know any similar instance of such behaviour in the case 
of the alcoholic yeasts. Their cells may be transitorily very 
much enfeebled, and, as we have learnt, varieties may be 
produced which give less alcohol than their primitive forms, 
but it appears to be impossible to produce a variety which 
has completely lost its alcoholic fermenting power. 
In the Danish edition of my paper on the circulation of 
Saccharomyces apiculatus in nature (1881), I expressed the 
idea that it might possibly be well to abandon the cultivation 
of the old culture-yeast (S. cerevisiae , as we usually term all 
these species) for technical purposes and replace it by some of 
the yeast-species occurring in nature, it being my belief that 
in this way we should perhaps be able to obtain products 
which were not only different from, but also in certain direc- 
tions better than those manufactured by means of S. cerevisiae . 
Just at that time there was a great deal of talk about the 
degeneration of culture-yeast, and there was a general inclina- 
tion to ascribe to it most of the difficulties occurring in the 
