II4  Occurrence  of  Mould  in  Cocoa  Butter.  {AFebJruSy,Pih9aiT' 
These  were  then  inoculated  with  the  spores  of  the  fungus.  In  addi- 
tion, small  blocks  of  the  infected  butter  were  placed  in  contact  with 
blocks  of  (a)  ordinary  cocoa  butter  and  (b)  solidified  emulsion  of 
cocoa  butter  and  water.  The  dishes  were  then  kept  at  various  tem- 
peratures from  1 50  C.  up  to  33 0  C,  but  at  the  end  of  three  months 
in  no  case  could  fresh  growth  of  the  fungus  be  observed. 
However,  colonies  of  fungoid  growth  had  actually  developed  on 
a  large  block  of  the  solidified  emulsion  of  cocoa  butter  and  water 
which  had  been  kept  at  room  temperature  for  the  same  time,  and 
on  reconsideration  it  appeared  probable  that  the  comparatively  thin 
films  of  cocoa  butter  and  water  emulsion  in  the  Petri  dishes  would 
rapidly  become  dry  during  the  incubation,  any  initial  growth  of  the 
fungus  would  soon  cease  owing  to  the  lack  of  moisture.  This  view 
was  corroborated  by  the  fact  that  in  a  dish  where  the  block  of 
medium  was  about  as  thick  as  the  depth  of  the  dish  would  allow, 
growth  of  the  fungus  was  eventually  observed  at  a  temperature  of 
about  270  C.  The  water  content  of  this  butter  was  2.4  per  cent, 
which  is  therefore  sufficient  to  enable  the  mould  to  grow. 
In  all  cases  growth  of  the  mould  appeared  to  become  quiescent 
after  a  comparatively  short  time,  although  subsequent  re-inocula- 
tion into  a  fresh  plate  was  again  followed  by  spasmodic  growth. 
In  order  to  ascertain  if  the  arrest  of  growth  is  due  to  lack  of  water 
or  another  substance,  a  series  of  blocks  of  cocoa  butter  containing 
from  0-20  per  cent,  of  water  in  an  emulsified  state  were  prepared, 
and  the  fungus  introduced  into  the  center  of  the  block,  instead  of 
being  inoculated  into  the  surface  layers.  Under  these  circumstances, 
however,  growth  continued  to  be  slow,  no  matter  how  large  the  pro- 
portion of  water  present,  but  it  was  rather  quicker  at  270  C.  than  at 
either  120  C.  or  170  C. 
These  experiments  seem  to  indicate  that  although  water  is  neces- 
sary  for  the  growth  of  the  mould,  yet  the  cessation  of  growth  is  due 
to  a  lack  of  some  other  food  substance.  Although  nitrogen  could 
not  be  detected  in  the  original  block  by  the  usual  tests,  it  was 
thought  possible  that  the  addition  of  a  nitrogenous  substance  might 
render  the  cocoa  butter  more  suitable  for  the  propagation  of  the 
fungus.  Sterile  Petri  dishes  were  therefore  prepared  containing  a 
medium  of  cocoa  butter  mixed  with  a  small  quantity  of  sterile  prune- 
juice  agar.  These  were  inoculated,  and,  on  incubation  at  270  C, 
vigorous  fungal  growth  was  observed  in  less  than  a  week.  Fructifi- 
