280 THE MICROSCOPICAL NEWS. 
brewer’s yeast or barm. The yeast plant, formerly called Zorula 
cerevisi@, and still later classified under the generic term Saccha- 
romyces, has been the occasion of much discussion. Berkeley, in 
his Introduction to Cryptogamic Botany, says on page 242, “It 
Fig. 68. 
has been proved by myself and Mr. Hoffman, by following up the 
development of individual yeast cells, in fluid, surrounded in a 
closed cell with a ring of air, that the proper fruit is that of a Penicil- 
lium.” Pasteur, the celebrated observer of these organisms, has 
made many experiments upon this subject, and he arrives at con- 
clusions at variance with these two former observers. In his 
splendid work, Ztudes sur lar Biére, Pasteur gives the details of his 
experiments, and exhibits the care taken to avoid contamination 
by extraneous germs, and he seems to have conclusively proved 
that ordinary beer-yeast has no connection with any species of 
fungus of the genera Penicillium, Aspergillus, or Mucor. 
Many of the mould-fungi wiil grow sub-aqueously, their my- 
celioid filaments having in my hands often yielded the perfect 
aerial fructification, and it is more than probable that commercial 
yeast always contains adventitious spores of the widely spread 
Mucedines, Mucorini, and Dematiei, so it is not very surprising 
that Penicillium has been cultivated from some of its particles. 
Members of the genera Penicillium, Aspergillus, and Mucor, 
under certain conditions, have been found to produce small quan- 
tities of alcohol, and their sub-aqueous multiplication during the 
process is very peculiar. M. Pasteur has thoroughly investigated 
this subject, and what he has to say regarding the Mucor ferment 
may help us to distinguish the true character of our ginger-beer 
plant. 
