Am.  Jour.  Pharm.  \ 
April,  1914.  j 
Lecithin. 
165 
lecithin  obtained  from  egg  yolks  stearic  acid  and  palmitic  acid  or 
oleic  acid  are  usually  found,  this  is  not  a  proof  that  these  acids  are 
derived  from  a  single  molecule ;  for  a  mixture  of  stearyl  and 
palmityl-lecithin,  or  of  stearyl  and  oleic  acid-lecithin  may  equally 
well  be  present.  But  in  the  text-books  of  physiology  or  of  physio- 
logical chemistry,  lecithin  from  egg  yolks  is  occasionally  represented 
by  the  assumptive  formula  of  stearyl-palmityl-lecithin : 
The  structure  of  this  formula  may  most  probably  be  traced  back  to 
the  statements  of  Thudichum ;  in  his  opinion  a  lecithin  molecule 
always  contains  one  saturated  and  one  unsaturated  fatty  acid  resi- 
due. According  to  him,  every  true  lecithin  contains  at  least  one 
fatty  acid  radicle  and  always  represents  a  mono-amino-mono-phos- 
phatide, — e.g.,  the  molecule  contains  only  one  atom  of  nitrogen  and 
one  atom  of  phosphorus. 
It  is  generally  assumed  that  the  lecithin  from  egg  yolks  is  mainly 
stearyl-lecithin  and  the  lecithin  obtained  from  plants  mainly  oleic 
acid-lecithin.  In  how  far  this  assumption  is  supported  by  facts 
cannot  be  decided  on  the  strength  of  the  researches  on  the  lecithins 
so  far  carried  out.  It  is  indeed  doubtful  whether  the  above  formula 
definitely  explains  the  constitution  of  the  natural  lecithins.3  The 
investigations  of  MacLean,  Otolski,  Cousin,  Erlandsen,  Henriques 
and  Hansen  have  shown  that  the  lecithins,  besides  containing  cho- 
line, also  possibly  contain  other  nitrogenous  disintegration  products 
(pyridine)  and  other  unsaturated  fatty  acids  (linoleic  acid  and  lino- 
lenic  acid).  This  may  also  be  inferred  from  the  relatively  high 
iodine  number  of  the  lecithins,  which  is  not  sufficiently  explained 
by  their  content  of  oleic  acid.  Nor  can  it  be  decided  whether  cal- 
cium and  iron,  which  always  accompany  the  lecithins,  form  an 
essential  part  of  the  lecithin  molecule  or  are  merely  impurities ;  thus 
no  great  weight  can  be  attached  to  the  constitutional  formula  of 
lecithin.    Further,  Malengreau  and  Prigent,  as  a  result  of  hydro- 
8  According  to  Thierfelder  and  Stern,  other  phosphatides  besides  lecithin 
occur  in  egg  yolks.  These  have  also  been  found  by  Thudichum,  Hammarsten, 
Erlandsen  and  others  in  various  animal  organs. 
/  O .  CxsHwO 
C3H5— O .  CigHsiO 
OH— P=0 
/C2H4— O 
N=(CH3)3 
