558 
Green. — The supposed 
a true fermentation is set up, not only should these three 
phenomena be capable of separate demonstration, but there 
should be a definite quantitative relation between them. 
I have carried out several series of experiments with different 
Yeasts, using in the first place the ordinary high fermentation 
Yeast used by our local brewers at Cambridge. I have 
made one series on a sample of low fermentation Yeast 
kindly supplied me by my friend Mr. Armstrong, of the 
Tottenham Lager Brewery, London. 
I followed Buchner’s method of preparation of the extract 
as closely as I could. In the process of grinding up the 
Yeast-cells with Kieselguhr and fine sand, I examined each 
instalment in the mortar with a J-inch objective, and kept 
on the grinding till about 75 to 8o°/ o of the Yeast-cells 
were ruptured. My extracts differed from his in quantity, 
never measuring so much as his figures led me to expect. 
In physical peculiarities there was a very close correspondence 
between us, my preparations coagulating at the stated 
temperature, and possessing the proper colour and smell. 
On mixing the extract and the sterilized sugar-solution, the 
latter being sometimes solution of cane or grape sugar, and 
sometimes a wort obtained from the brewery, I have always 
failed to observe the copious evolution of gas which Buchner 
speaks of. I carried out the experiments in freshly sterilized 
Ehrlenmeyer flasks fitted with a mercury-manometer. Instead 
of a rise of the mercury in the distal limb, soon after the 
experiment was started there was almost uniformly a rise in 
the proximal limb, indicating an absorption and not an evolu- 
tion of gas. In no case did I ever get a measurable rise 
of the mercury in the distal limb of the manometer unless the 
liquid contained some Yeast-cells that had been imported into 
the flask. This happened occasionally, even filtration through 
porcelain and the addition of chloroform sometimes failing to 
prevent it. 
Not being able to get the copious evolution of C0 2 , I turned 
my attention to the specific gravity of the fermenting solution. 
It seemed possible that a small quantity of sugar might be 
