6 2 Wager and Peniston.—Cytological Observations on 
refractive index of the glycogen, which gives the cell contents a hyaline 
appearance at this stage, but in iodine it appears as a large vacuole with dark 
brown contents (Figs. 141-5). 
Harden and Rowland (’ 01 ), in studying the changes which take place 
in the liquefaction of yeast, pointed out that freshly preserved yeast consists 
of large cells with a small vacuole and granular cytoplasm which stains 
deep brown with iodine. As the evolution of C 0 2 proceeds the vacuole 
increases in size and the glycogen diminishes and finally disappears. They 
consider that the progressive increase in the size of the vacuole may 
possibly result from the accumulation of some substance produced, along 
with the C 0 2 from the glycogen. 
According to Harden and Young (’ 02 ) the glycogen from yeast has 
the same chemical composition as that from other sources. It is probably 
a transitory food reserve, and from Meissner’s observations (’00) it would 
appear that the yeast makes use of it by means of diastatic non-diffusible 
ferments. The late Professor Errera found (’ 98 ) that it disappears or 
accumulates very rapidly according to the conditions of nutrition and 
growth (cf. Meissner, ’00; Will, ’ 02 ; Lindner, ’ 02 ). We have made 
a number of observations which fully confirm Errera’s conclusion and show 
further that the presence or absence of glycogen coincides with the 
fluctuations in fermentative activity which are well known to occur but are 
not clearly understood. 
We noticed when starting new cultures that the time which elapsed 
before active fermentation commenced was very variable. This was 
especially noticeable in brewery yeasts and is well known to bakers in 
connexion with compressed yeasts. In some cases the cells immediately 
sink to the bottom of the fermenting fluid and it is some time before 
fermentation begins to take place to any appreciable extent, and this 
is accompanied by the rising of the yeast cells into the upper layers of the 
fluid. In an ordinary brewery yeast this may not take place for one to five 
hours or even longer. In other cases the cells, having been thoroughly 
mixed with the fermenting fluid, do not sink to the bottom and fermentation 
at once becomes visible. 
We find that the yeasts which ferment at once without sinking contain 
very little glycogen, whilst those which remain at the bottom of the jar for 
a considerable time contain a more or less large amount of glycogen. 
In yeasts which contain a large quantity of glycogen when the culture 
is started, the fermentation, although slow at first, becomes in the course of 
ten to fifteen hours much more vigorous than in the culture of yeast which 
at the beginning contained very little glycogen, and the budding activity 
is much more marked. 
When fermentation is started with a healthy brewery yeast which contains 
a large quantity of glycogen and which in consequence sinks to the bottom, 
