688 The American Naturalist. [August, 
This form and many varieties of it is common in breweries. 
The specific form gives a top-fermentation. Cells 2, 5 »-6y; 
the young culture gives mainly round and slightly oval, or 
ellipsoid cells. Spore-formation found: Maximum: 36°-37° 
C., minimum 11°-12°C. The first trace of spores at 25° C. 
found in 23 hours, at 15° C. in 72 hours. Number of spores 
generally 1—4, of round shape and of strong reflecting power. 
In giving a key to the determination of the species, it seems 
best to select the occurrence of spore-formation by 25° and 15°, 
not only because this is most instructive but also because these 
temperatures are used for examination of the yeast in the 
breweries, the physiological yeast-analysis; another reason is 
that it enables the investigator to keep two thermostates at 
the points 25° and 15° as long as the investigation lasts. 
The very best apparatus for these investigations is, of course, 
the Panum thermostate, described by Pedersen in Meddelelser 
fra Carlsberg-Laboratoriet, Vol. I, page 48-52, 1878, or by 
Panum in Nordisk medie. Arkiv. Vol. X, No. 4. 
This species and its varieties, which are cultivated for con- 
stant use in brewing establishments are known as “ culti- 
vated yeasts,” the other forms, which cause “sickness” in the 
product, being commonly called “ wild yeasts.” In these culti- 
vated forms, the spores are very refractive, compared with the 
other forms, and their spore-forming cells often display a singu- 
lar formation of a thick wall which divides the cell into various 
parts, each of these containing a spore. This “ wall" is very 
refractive and consists of the protoplasm of the cell, pressed 
in between the walls of the spores. But the same formation 
may also appear as a result of the spores being pressed against 
each other. Occasionally there is a real formation of a wall, 
when the spores cannot be separated, and then the cell turns 
out to be a kind of a sporangium. 
A superficial layer of cells which we will call top-vegetation 
occurs at 3°-5° C. fever after 7-10 days at 20-22? C. This 
kind of vegetation generally gives cells of a singular shape. 
Among the many varieties found in breweries all over the 
world all cannot be sure to give the same results; but the 
question of variation has still to be debated. 
ak eee er 
Tne Peer SPER ESTATE TS Saleen ee ee 
