552 Hansen — Experimental Studies on the 
added to the nutritive liquid. Here, therefore, the particular 
effect exercised by a particular chemical factor has been 
pointed out. In the instances just mentioned the variations 
were of a more or less inconstant nature. 
In the course of the above researches on the disappearance 
and recovery of spore-formation, I made in 1889 the dis- 
covery that in this domain it is possible to produce very 
deep-seated transformations, and to render these permanent. 
It was found that when the cells were cultivated for a length 
of time in aerated wort, and at a temperature above the 
maximum for spore-formation and approaching that for 
vegetative development, they completely lost their power of 
forming spores. 
I have effected this transformation in the case of five of the 
species described by me in 1883, and also with several beer 
bottom-fermentation and distillers’ top-fermentation yeasts ; 
that is with representatives of the various groups of the 
Saccharomycetes properly so called. Thus we have to do 
with a common law ; yet this seems to apply to the typical 
and genuine Saccharomycetes only ; at any rate, I have not 
hitherto succeeded in producing this transformation in the 
case of S', anomalus and S. membranae-faciens , both of them 
being, indeed, species which, as may be remembered from my 
papers, differ so widely from the others, that they might well 
be set up as types of quite new genera. 
As might be expected, the law of correlation asserts itself. 
Thus a closer examination shows that the transformation 
which we effected does not stand alone, but is accompanied 
by others. This is especially evident from the fact that the 
yeast- cells under our treatment at the same time completely 
lose their former power of forming films on the surface of 
liquids. 
While the loss of spore-formation is attended in all species, 
without any exception, with loss of film-formation, there 
appear differences in other directions in the species trans- 
formed. Thus in some I observed that in wort-culture they 
produced a more abundant growth, and at a quicker rate, than 
