2 12 
Brown . — Some Studies on. Yeast. 
conclusion that the oxygen had been stored up in them, and functioned as 
a primum movens of their subsequent life and nutrition. If for ‘ life and 
nutrition ’ we read ‘ power of reproduction ’, this is a striking instance of the 
prophetic insight of genius, for we have seen that this primum movens is not 
only the essential determinant of cell-reproduction, but that the stored-up 
oxygen exerts a ‘ potential ’ which is quantitatively related to the amount 
of subsequent reproduction. 
The limited growth which, as we have seen, yeast exhibits when seeded 
in a liquid from which oxygen has been wholly excluded (see p. 209), so far 
from being in opposition to this view is really in its favour, for owing to the 
very nature of the experiments the cells of the seed-yeast in such a case must 
have carried with them an ‘ oxygen charge * which enabled them to reproduce 
to a certain limited extent even under anaerobic conditions. 1 
I have further investigated this remarkable power of yeast to store up 
oxygen for further use by submitting it to long-continued aeration before it 
was used for seeding, and in some cases I have passed oxygen through 
a suspension of the yeast in water. Such treatment in all cases failed to 
give a yeast which, after separation, possessed increased potentialities of 
growth, and in some cases the power of reproduction was actually diminished, 
especially when it was treated with pure oxygen. It seems to be impossible 
to give a yeast a higher effective charge of oxygen than it has ordinarily 
acquired by processes of washing and filtration in contact with air, and 
apparently one cannot by any further treatment in this direction make up 
for the lack of free oxygen in the culture medium, since on this factor and 
on the subsequent access of oxygen from the outside mainly depends the 
final degree of reproduction up to the point at which inhibitory causes 
come in, such as those due to failing of essential nutrients, and formation 
of alcohol. 
At ordinary temperatures yeast suspended in its nutrient liquid is 
a very complete and rapid absorber of dissolved oxygen, much more so in 
fact than might be imagined from the experiments of Pasteur just alluded 
to, which were made at a temperature of 6° C. I have studied the actual 
rate of absorption by varying proportions of yeast-cells by suspending these 
in water fully saturated with atmospheric oxygen, and noting at intervals 
the gradual disappearance of the oxygen. 
The so-called Winkler process for determining the dissolved oxygen is 
1 There is one fact which seems to be against the idea that this anaerobic reproduction was due 
to the * oxygen charge ’ of the seed-yeast. If this were so one would expect that on varying the 
amount of seed-yeast the maximal number of cells produced anaerobically would be proportional 
to the seed-yeast employed, whereas it was found that the maximal cell-reproduction N—n 
was constant and independent of the initial seeding. This is the result which might be expected 
if there was any residual oxygen in the culture-liquid, but the conditions of the experiments negative 
this explanation. Another possible explanation of this fact may be that during fermentation under 
strictly anaerobic conditions a small amount of peroxide of hydrogen may be produced, and that the 
ferrous salts in the nutrient liquid may be the 1 carrier ’ of the oxygen of the peroxide to the yeast. 
