Dr. Lucius Nicholls 243 
‘In this stage it is not always easy to isolate 
the yeast cells by cultures, as they themselves 
are being attacked and broken up by smaller 
organisms. ° 
A colony of yeast growing upon a solid 
medium is fairly easily distinguished from a 
colony of acetic-acid-producing or other 
bacterium. 
Colonies, on a solid medium, of the wild 
yeasts, including Saccharomyces theobrome, 
Fic. 6.—Three forms of acetic acid producing bacteria. 
consist of a central, heaped-up, granular portion 
and, spreading away from this, a lighter, 
thinner, radiating zone; after a few days the 
colonies lose the outer zone and assume a 
white, opaque, granular appearance. These 
are easily distinguished from most colonies 
of other organisms, which usually possess a 
shiny smooth-looking appearance. 
Sometimes it is found that the bean does not 
undergo its proper and usual fermentation ; 
