( 604 ) 
curve; then the question rises whether with exclusion of noxious 
influence by high temperature, the temperature-curve would either 
or not show an optimum. 
Such was the problem proposed in our paper and the result was 
that without a noxious influence still an optimum curve was found. 
Were it possible to heat the yeast without injury it would be evident 
that the constant fermentation velocity, setting in after the “Antrieb” 
is past, reaches an optimum for a certain temperature. 
A second objection is advanced by Mr. RurGers against our con- 
clusions. In our paper we called to mind that beneath (lasting) 
noxious temperatures considerable deviations from Van ’r Horr’s rule 
appear and in our opinion the theory of BrLACKMAN should already 
be rejected on that account. 
As an explanation for our results Rurcers now suggests the possi- 
bility that the diffusion velocity through the cell-wall may have 
acted in our experiments as a limiting factor in the sense of BLack- 
MAN’S theory. To this we observe in the first place that there is much 
more reason to suppose this factor playing a part in the experiments 
of Kuyprr and BrLACKMAN on the respiration and carbonic acid assi- 
milation of higher plants, wherewith these investigations kept no 
account. 
We think, however, that for the fermentation it must be admitted 
that the diffusion through the wall of the yeast cells does not 
restrict the fermentation velocity. Supposing that sugar diffuses through 
the wall with a velocity only 105 times as great as the diffusion 
velocity in water, then a calculation, which we hope to give later, 
proves that more than 10% times as much glucose may enter through 
the wall as was maximally fermented in our experiments. 
Moreover, if Rureers’ supposition was right, our curve beneath 
the optimum would represent the relation between the quantity of 
the matter diffusing through the wall and the temperature, while it 
is known that this relation is represented by quite another curve. *) 
Certainly the possibility exists that to explain an optimum — also 
in absence of injurious influence by the heating — some limiting 
factor must be taken in consideration. But this can certainly not 
save the theory of BrLACKMAN to explain the occurrence of that 
optimum. For the bent of the velocity-temperature curve is, according 
to that hypothesis, solely to be attributed to dying of the function 
at the fore-heating, consequently to the time factor. | 
1) Compare for instance Wi ttner, Experimental Physik, Bd. I, S. 456. 
