Incipient Vitality. 31 
not come across the enzyme at all in their wanderings. Now as 
long as the sugar remains in excess, the number of active systems 
formed and broken up again per hour will remain constant because 
the enzyme particles do not become reduced in number by their 
activity. For a time then in this case the absolute rate of inversion 
will remain uniform (and graphically representable by a straight 
line) hour after hour, and only when the cane sugar is inverted to 
such an extent that the number of sugar molecules and not the 
number of enzyme particles becomes the limiting factor, shall we 
get the falling regular logarithmic curve that we spoke of before. 
This state of things is quite easy to produce in the test-tube. It 
has been observed by Horace Brown and Glendinning with Diastase ; 
and fully explained by E. F. Armstrong in his Studies on Enzyme 
Action. 1 
It is of very great interest to the writer that this state holds 
also in the living cell under conditions that may now be briefly 
explained. A cut leaf that has been assimilating, contains a 
certain amount of sugar, the fate of which it is to be burned up in 
respiration. If such a freshly cut leaf be kept in the dark at a 
constant temperature and its respiration be measured continuously 
it will be found that for a number of hours the C0 2 production 
remains uniform, and that subsequently, when the sugar supply 
so reduced that it becomes a limiting factor, a uniformly falling rate 
of respiration sets in. This fall continues until all the available 
sugar is consumed and the respiration of the starving leaf exhibits 
a regular falling logarithmic curve, lasting for perhaps ten days and 
exactly like the curve obtained with the action of an isolated 
enzyme in a test-tube. 
We have exhibited, here then, a pure mass effect in the living 
cell. In accordance with expectation, we find that with starving 
leaves at a higher temperature, containing the same initial amount 
of sugar, the respiration begins at a higher level, and therefore 
reduces the stock of sugar faster. As a consequence the initial 
period of uniform rate is proportionately shorter and the falling 
curve sets in sooner, but then follows the same course as with the 
leaves at a lower temperature. If at any time after the respiration 
has begun to fall off, fresh sugar be supplied to the cells of the 
leaves by putting them in the light with C0 2 , then the respiration 
goes up again. If enough sugar has thus been given, the respiration 
1 Proc. Royal Society, Vols. 73—76, 1904 and 1905, especially 
No. II., Vol. 73, 
