226 
Brown . — Some Studies on Yeast. 
relation of the fermentative to the reproductive processes, and why the 
yeasts have acquired their fermentative power. 
It is but a special instance of a well-established generalization or ‘ law ’ 
of nature, that the mechanism of every living organism is adjusted to the 
one great aim and object of reproduction. 
That we can by means more or less artificial keep the reproductive 
power of a yeast in abeyance, whilst still availing ourselves of its fermenta- 
tive power, has hitherto obscured the relation of the two functions, and 
hence has given rise to the somewhat exaggerated idea of the purposeless 
and prodigal waste of the yeast-cell regarded as a living unit. 
Addendum. 
It follows from the above considerations that, if we could devise means 
for measuring with exactness the amount of heat evolved during the 
disappearance of i grm. of sugar under the influence of yeast, whilst the 
cells are in process of active reproduction, this amount of heat ought to 
fall short of that produced by the fermentation of the same amount of 
sugar when there has been no yeast reproduction, the difference being due 
to the energy required for the observed yeast reproduction. 
I have not succeeded hitherto in obtaining numerical results which can 
be relied upon as giving the ‘ heat of formation , of yeast, but in those cases 
where yeast reproduction was still in progress within the observed time- 
intervals, I have generally found distinctly less evolution of heat per unit 
weight of sugar destroyed than where the cell-reproduction had ceased. 
In one case, for instance, in which the fermentation of a malt-wort 
had been continued for 6\ hours, the maltose which had disappeared 
per hour was 0-117 grm. per 100 c.c., and the yeast increase per hour was 
1-26 cells per unit volume, equivalent to 0-126 grm. per 100 c.c. of moist 
yeast, or 0-027 g rm - of dry yeast. The ratio of the sugar used up, to the 
dry yeast formed, therefore had the high value of 1 : 0-23. 
The heat developed per gramme of sugar fermented in this case 
amounted only to 114-4 calories, instead of 125, the normal value. 
