559 
Variation of Yeast-cells . 
Those who would be likely to take an interest in them will 
find information in the fuller treatises which I am about to 
publish. I shall, therefore, now only refer to the results in 
a few words. 
Among the above-mentioned variations, those offer the 
greatest interest in which cells were produced which had 
entirely lost their power of forming spores and films. In 
trying to elucidate how this transformation is effected, we have 
on one hand to examine the external factors, and on the other 
hand to elucidate how the cells are influenced by them. Of 
course, we always work with absolute pure cultures ; in some 
cases we experiment with the whole bulk of the vegetation in 
question, while in others we separate the single cells at the 
different stages, putting each severally to the test 
We find, that in the cultures under discussion, at the high 
temperature a vigorous multiplication still takes place, and 
that even in the first stages a large number of the cells have 
become transformed ; this number increases as the cultivation 
progresses, but the change is at the beginning of a transitory 
nature, and it is only through the development of new 
generations that the newly acquired qualities become fixed, so 
that at last a constant variety comes out. 
As thus shown it is not the temperature alone, which 
effects the transformation, but only in connexion with the 
multiplication of the cells. In agreement with this we find, 
that it is not sufficient to cultivate the cells in water, but that 
a favourable nutritive substratum and a certain aeration are 
required. 
Of the variations which have been observed in bacteria, 
in some cases it has been assumed that they were due to 
chemical changes in the culture-liquid ; since this might also 
apply to my above-mentioned variations in the Saccharo- 
mycetes, I therefore put the question to an experimental 
test. The result I obtained was that special chemical com- 
pounds do not play any part in that case. 
Of the external factors we have then only the nutritive 
substratum, the aeration and temperature left. 
