Brown. — Some Studies on Yeast. 
223 
own weight of sugar under these conditions would be only 1.3 hours, and 
the potential adiabatic rise of temperature of the cell would be in one hour 
106-2° C. 1 
Considerations of this kind bring home to us in a striking manner the 
intense nature of the metabolic processes which go on in a yeast-cell, and 
the large liberation of apparently wasted energy which accompanies them. 
It may be permissible for a moment to compare a yeast-cell in this respect 
with the human body. I am informed by Dr. Leonard Hill that the 
metabolism of a man quietly resting in bed can be taken as resulting in the 
production of 2,000 large calories per diem, or 83-3 large calories per hour. 
Assuming a body-weight of 65 kilograms, and a mean specific heat of 0.83, 
and further supposing the metabolism to continue at the same rate, then the 
heat evolved would be sufficient to raise the body-temperature of the man 
at the rate of about 1-5° C. per hour. 
But, as we have just seen, the metabolism of a yeast-cell at about the 
temperature of the human body evolves heat sufficiently fast to raise its 
body-temperature 106° C. per hour, or about seventy times as fast as in the 
case of a man at rest. 
We may now ask, what is the physiological significance of this enormous 
metabolism and liberation of energy which the yeast-cell exhibits in pursuance 
of its life-functions, and which seem so disproportionate to its requirements 
for reproduction and nutrition ? 
Are we to regard the phenomena as being to some extent accidental, 
and due to the fact that the living cell requires some small but essential 
part of the sugar molecule, the removal of which brings about a rearrange- 
ment of the residual portions of the molecule with consequent transformation 
of potential into kinetic energy ? According to this view, the action of the 
yeast may be likened to the removal of the keystone of an arch and the 
partial demolition of an edifice. 
This was substantially the explanation given by Pasteur many years 
ago. He regarded the reproductivity of the yeast-cell and its fermentative 
power as being correlative but inverse phenomena. 
By a somewhat curious misinterpretation of experimental results, 
Pasteur believed he had evidence that when the yeast-cell was fully supplied 
with oxygen, and was therefore reproducing itself freely, its faculty for 
fermenting sugar was at a minimum, or even altogether in abeyance. On 
the other hand, its fermentative power was supposed to be at a maximum 
under anaerobic conditions, this being due to the yeast then taking the 
requisite oxygen from the sugar, thus destroying the sugar molecule 
as such. 
1 It is not without interest to compare the energy liberated under these conditions in the yeast- 
cell with that evolved by the atomic disintegration of radium, which is said to produce sufficient heat 
to raise its own weight of water through ioo° C. per hour. 
