These  experiments  teach  us  that  there  is  a  difference  in
the  indwelling  properties  of  the  individual  cells,  and  therefore
a  microscopic  examination  of  the  yeast  colonies  in  wort  gela-
tine gives  us  as  little  information  about  the  species  in  question

*  I  have  in  previous  communications  also  pointed  out  that  colonies  in  wort
gelatine  grown  from  the  same  species  of  Saccharomyces  may  yet  present  a
different  appearance  when  examined  with  the  naked  eye  or  with  a  low  power.
RESEARCHES   ON   YEASTS.  97

as  the  first  cultures  in  wort.  This  is  a  new  proof  showing
that  little  value  can  be  attached  to  the  microscopic  examina-
tion alone  when  it  is  a  question  of  the  analysis  of  a  sample  of
yeast.  (Both  in  breweries,  in  yeast  factories,  and  distilleries,
too  much  weight  is  still  attached  to  the  microscopic  appear-
ance of  the  yeast  cells.)  The  new  experiments  further  show
that  if  we  wish  to  avail  ourselves  of  the  behaviour  of  the
cells  under  external  influences  for  the  purpose  of  character-
ising species,  we  must  never  depend  exclusively  on  the
behaviour  of  the  single  cell,  but  we  must  take  the  collective
behaviour  of  a  number  of  them.  Other  low-fermentation  yeasts
give  similar  results  under  the  conditions  mentioned.
The  following  experiment  may  be  taken  as  another  illus-
tration of  the  problem  mentioned  : — When  making  plate-
cultures  with  wort-gelatine,  it  is  frequently  seen  that  two  or
more  cells  lie  so  close  together  that  on  budding  they  will  soon
grow  together  and  form  a  single  colony  ;  such  a  colony  cannot,
of  course,  be  made  use  of  for  the  preparation  of  a  pure  culture.
