1087 
sowing; it is easy then to recognise the blue cells on the plate and 
watch their germination under the microscope. The blue colour is 
then commonly seen to disappear before the formation of buds begins. 
But many of the later germinating cells remain blue and produce 
colourless daughter-cells. I never saw young cells taking the least 
trace of blue from the mother-cell. 
But if the dried cells are beforehand allowed to swell up in wort 
or in water and if the soaked material is laid in the methyleneblue 
solution, which is the usual way to effect the colour reaction, the 
result is quite different. Then only part of the cells assume the colour 
and this part is the smaller as the cells have longer remained in the 
uncoloured solution. A certain percentage, however, continue to take 
up the colour without having lost their reproductive power, and 
it seems to be very difficult to soak these cells with water. 
The simplest way to effect these experiments is by using dry 
yeast, quite free, or nearly so from dead cells. I obtained it by 
centrifugation of the small-celled variety of pressed yeast from 
strong fermentations, these being in their most active state. 
To this end it was cultivated at 28° C. in nearly neutral wort, 
after 6 to 8 hours brought into the centrifuge, and then quickly 
transferred to tilterpaper in a thin layer for desiccation. 
The large-celled variety of pressed yeast is less resistant to drying. 
To compare the two varieties, of which the smallcelled is richer in 
protoplasm than the other, the yeast must very cautiously be dried, 
first at low temperature, e.g. 25° C., then ata higher one, e.g. 50° C. 
This precaution is not, however, necessary to render the blue: 
colouring of the dry living cells visible; to this end drying of com- 
mon yeast at room temperature will do. 
I have, however, also met with commercial dry yeast satisfying 
the requirement of containing hardly any dead cells at all, namely the 
“Konservierte Getreide Brennerei Hefe” of the yeast works of HerBina 
in Hamburg, which was sent directly from the manufactory. This © 
preparation is delivered in solidly closed tins, but after some time it 
loses its power of growth and fermentation; its quality thus evidently 
depends on the length of time past since its fabrication. It seems 
that this loss corresponds to that of the germinative power of seeds, 
which depends on their state of humidity. I possess some more 
preparations from the same factory, that have hardly any fermen- 
tative power and contain no cells fit for reproduction, but they 
have not been directly got from the manufactory and are already 
some years old. 
When using seed of Brassica rapa, soaked in solutions of 1 per 
71 
Proceedings Royal Acad. Amsterdam. Vol. XIV. 
