Incipient Vitality. 65 
fermentation apart from their vitality. In 1901, Albert 1 discovered 
that yeast retains the power of fermenting sugar after it has been 
killed by treatment with a mixture of alcohol and ether. A yellowish 
powder is thus obtained consisting only of killed cells which contain 
the whole of their zymase precipitated within them. Such killed 
yeast was much more efficient than Buchner’s pressed out sap ; it 
is quite easily prepared and has been used commercially. The 
colloidal proteid enzyme, zymase, which effects the fermentation, 
does not diffuse out of the cell into the surrounding water even 
when the protoplasm is thus killed, and so an active extract can no 
more be prepared from these killed cells than from living ones until 
they have been broken up. It follows that the sugar molecules of the 
medium must still diffuse into the cells, before they can be split up. 
Accurate comparison has not yet been made between the activity of 
the same cells living and killed, but the latter are at first extremely 
efficient. If the activity of these killed cells did not, after a time, 
disappear they would be a perfect substitute for living cells. We 
have to enquire how it is that their activity steadily diminishes, for 
it is a characteristic of enzyme katalytic action that the agent is 
not destroyed by its action. 
Albert showed that a number of other enzymes were at work 
in these killed cells carrying on the same processes as occur in the 
living cell. Among these was an active proteolytic enzyme that 
causes the dwindling of the proteid granules which are conspicuous 
in the freshly killed cell (staining blue with Gram’s stain). The 
products of the action of this enzyme, and later the enzyme itself, 
diffuse out of the cell and finally the proteids are all broken down 
to Ieucin and tyrosin. The disappearance of the sugar-fermenting 
power after some twenty hours of activity is attributed by Albert 
to the action of this proteolytic enzyme which actually digests the 
proteid particles of the sugar-splitting enzyme. Were it possible 
to destroy or inhibit the proteid enzyme first, then the sugar 
fermentation would be more permanent. 
Invertase, the enzyme which inverts cane-sugar to glucose and 
levulose, is also active in the killed yeast. This is generally consi¬ 
dered to be the simplest of the enzymes and, in agreement with this 
view, it is found that it diffuses very quickly out of the dead cells 
and is at work in the solution. 
There is also present a glycogen-fermenting enzyme which acts 
1 Albert, Ber. chent. Ges., XXXIII., 1901, and Centrlbl. f. Bakt., 
VII., 1901. 
