For  sending  pure  cultivated  yeast  in  an  absolutely  pure
condition  and  in  such  a  manner  that  its  multiplication  can  be
effected  easily  and  with  certainty,  I  have  likewise  made  use  of
the  following  method,  which  has  also  given  good  results  : — To
the  small  cylindrical  flasks  generally  known  as  Freudenreich
flasks,  I  have  added  a  side-tube  (see  Fig.  17).  The  tube  a  on
the  hood  is,  as  usual,  filled  with  cotton-wool ;  a  firm  layer  of
cotton-wool  is  placed  at  the  bottom  e  of  the  flask,  and  a  plug


SYSTEMATICALLY  SELECTED    YEASTS.  75

is  inserted  in  the  neck  b.  The  side-tube  is  also  plugged  with
cotton-wool,  and  the  flask  is  then  sterilised  by  heating  it  for
two  hours  at  150°  C.  When  it  has  cooled,  the  tube  is
joined  to  the  rubber  of  a  two-necked  flask  in  which  the  yeast
has  been  grown,  and  a  drop  of  the  fairly  thick  yeast  is  poured
on  to  the  layer  of  cotton-wool  e.  The  tube  is  then  closed
by  a  stopper  d  of  asbestos-  card  previously  sterilised  in  a
flame,  and  the  stopper  is  then  coated  over  with  a  layer  of
sealing-wax  c.
The  main  point  which  I  had  in  view  in  this  arrangement
was  to  preserve  the  yeast  from  infection  without  hermetically
closing  the  flask.  The  layer  of  cotton-wool  e  must  therefore
be  firmly  pressed  to  the  bottom,  so  that  it  will  remain  in  its
place,  and  for  this  reason  also  no  more  liquid  should  be
poured  in  with  the  yeast  than  is  absolutely  necessary.
