A  in.  Jour.  Phariii.  ( 
April,  l'J14.  / 
Lecithin. 
177 
birth  are  able  to  feed  on  cabbage  and  turnips  like  the  fully  devel- 
oped animals  and  are  not  dependent  upon  mother's  milk;  similarly 
insessorial  birds  contain  more  lecithin  than  autophagous  birds,  which 
is  indeed  clearly  shown  in  the  eggs  of  these  birds.  Man,  also, 
who  comes  into  the  world  helpless,  shows  a  very  high  percentage  of 
lecithin  in  the  bone  marrow,  which  is  only  appreciably  diminished 
when  growth  proceeds  more  slowly,  or  ceases.  He  also  established 
the  fact  that  the  bone  marrow  of  young  animals  contains  far  more 
lecithin  than  does  that  of  fully  developed  animals,  and  that  this 
store  of  lecithin  diminishes  as  the  animal  grows  and  that  new- 
born animals  come  into-  the  world  with  a  large  supply  of  lecithin. 
From  these  observations  it  is  evident  that  lecithin  represents  a 
highly  significant  factor  in  the  growth  of  animals,  even  though 
nothing  is  yet  known  of  the  finer  biological  processes  involved  in  the 
utilisation  of  lecithin  in  the  cell  and  in  the  organism. 
But  in  order  to  form  a  conception  of  the  functions  of  the  lecithins 
or  of  the  lipoids  in  general,  the  colloidal  nature  of  these  substances 
must  primarily  be  taken  into  account;  and  also  their  capability 
of  forming  solutions  and  compounds,  which  are  readily  decomposed, 
with  other  substances  of  importance  in  the  construction  and  the  life 
of  the  cell.  It  must  also  be  taken  into'  consideration  that  certain 
concentrations  of  lipoids  are  more  soluble  in  solutions  of  alkaline 
salts  than  in  other  salt  solutions.  It  is  assumed  that  by  an  increase 
in  the  concentration  of  the  salt  by  the  entrance  of  calcium  salts  into 
the  cell  with  consequent  separation  in  flakes  of  the  lipoids,  mem- 
branes are  formed  which  are  permeable,  impermeable  or  semi-per- 
meable to  certain  solutions.  The  so-called  semi-permeable  mem- 
branes, especially,  appear  to  be  of  importance  to  the  life  of  the  cell, 
as  they  serve  to  keep  within  bounds  the  entrance  and  exit  of  sub- 
stances. 
In  the  interior  of  the  cell,  according  to  Meyer,  it  is  through  the 
intervention  of  the  lipoids  that  the  whole  of  the  contents  do  not  join 
to  form  a  homogeneous  mass,  but  that  the  thousand  particles  form- 
ing the  cell,  with  all  their  different  chemical  affinities,  remain  side 
by  side,  drawn  up  in  order  and  at  a  measured  distance ;  on  the  sur-  - 
face,  however,  they  constitute  a  guard  against  too  rapid  streaming 
in  and  out  of  water,  and  against  the  penetration  of  all  the  salts 
dissolved  in  the  blood  and  in  the  tissue  fluids,  and  of  other  sub- 
stances. They  also  form  a  sort  of  sieve  for  the  penetration  of  sub- 
stances soluble  in  fat,  especially  of  those  which  dissolve  more  readily 
