MICRO-ORGANISMS. 141 
Bread Y easts. 
The manufacture of pressed yeast must not be forgotten. 
Tn this industry the type of yeast is selected to give a maxi- 
mum quantity of yeast from a minimum of material. As 
the fermentative power of a yeast-cell is inversely as its 
reproductive power, it follows that yeast grown specially 
for sale has comparatively a small specific fermenting power. 
Many pressed yeasts, however, are derived from breweries 
and distilleries in which more yeast is collected than the 
manufacturer requires. 
Yeast is used for other purposes than the production of 
alcohol. The baker employs it to make his “ sponge,” which 
raises his dough. As a rule, he obtains it in the first in- 
stance from a brewer, when it is comparatively pure. © But, 
after it has been used numerous times, it partakes more 
of the nature of a bacterial than a yeast culture. I have 
seen many specimens, and in these the yeasts were in the 
small minority. Doubtless the bacteria have some influence 
on the taste of the bread for good or evil, and they may also 
produce a quantity of sugar from the starch. There is a 
point, however, that strikes one as being bad, and that is the 
original source of the yeast. A beer yeast is adapted for 
beer. and not for bread. A bread yeast should produce a 
maximum amount of carbon dioxide from the sugar which is 
present. A beer yeast has not been primarily selected to 
produce gas. There is a need, therefore, for the selection 
of a yeast-type which will produce a maximum quantity of 
carbon dioxide gasunder theconditions that obtain in bread- 
msking. 
Non-aleoholic Fermented Beverages. 
Certain beverages which are supposed to be non-alcoholic 
derive their effervescing property from the carbon dioxide 
of the alcoholic fermentation. Mention may be made of 
the ginger-beer plant. which is a mixture of a peculiar bac- 
terium and a yeast, the two together forming small solid 
lumps, which, when placed in a sugar solution, ferment the 
fluid. Quite recently a bacterium has been used to produce 
an absolutely non-alcoholic effervescing beverage. The bac- 
terium is a slime-forming organism (Leuconostoc dissiluens), 
which is infected into a sterile solution of cane-sugar 
flavoured with fruit-juices and fermented in closed vessels. 
The Manufacture of Lactic Acid. 
_ There is a group of bacteria that produce lactic and prac- 
tically no other acid. Lactic acid is formed by most acid- 
