Am6ct°oUbrerP1i9"7'  ^    Specificity  of  Drugs  for  Phosphatids.  437 
would  seem  that  those  who  have  been  finding  a  difference,  say  of 
surface  tension,  as  the  prime  cause  of  the  changes  produced  by 
drugs  are  getting  only  another  measurement  of  what  others  measure 
by  changes  in  the  state  of  aggregation  or  amount  of  chemical  com- 
pound or  adsorption  compound  formed.  Undoubtedly  it  would  not 
be  true  to  speak  of  any  one  of  these  changes  as  the  cause  or  even 
as  the  predecessor  of  another,  for  probably  they  occur  simul- 
taneously. 
If  digitalis,  strophanthin  and  other  heart  drugs  show  their  speci- 
ficity in  action  on  the  heart  by  some  particular  effect  on  heart 
lecithin  or  heart  cuorin,  they  ought  to  produce  consistent  changes  in 
the  very  sensitive  calcium  chloride  precipitation  limit  of  the  phos- 
phatid  solutions,  while  caffein,  cocaine,  strychnine  and  other  brain 
drugs  should  have  either  no  effect  on  the  heart  phosphatid  solutions 
or  a  different  one  from  the  heart  drugs.  Brain  drugs,  on  the  other 
hand,  should  produce  similar  consistent  effects  on  brain  phosphatids. 
EXPERIMENTAL. 
Varying  amounts  of  a  standard  CaCl2  solution  (M/100,  iW/50 
or  iW/25)  are  added  to  two  series  of  test  tubes.  To  each  tube  is 
added  water  enough  to  bring  the  amount  to  5  Cc.  A  .2  per  cent,  or 
.3  per  cent,  phosphatid  solution  is  made  by  continuous  shaking  of 
the  required  amount  of  phosphatid  in  water  till  homogeneous.  An 
aliquot  part  is  used  for  control  experiments,  while  the  rest  is  shaken 
with  the  drug  to  be  tested.  Five  Cc.  of  the  control  solution  is  added 
to  each  of  the  series  of  tubes  containing  calcium  chloride,  while 
5  Cc.  of  the  drug  solution  is  added  to  the  tubes  of  the  other  series. 
The  difference  in  the  molecular  amounts  of  calcium  chloride  neces- 
sary to  precipitate  the  drug  solution  from  that  required  for  the  con- 
trol is  a  measure  of  the  influence  of  the  drug  on  the  phosphatid. 
Readings  are  taken  after  twenty-four  hours.4 
Relation  to  Oxidation. — With  new  lecithin  solutions  the  method 
is  accurate  to  .1  Cc.  of  M/100  calcium  chloride.  The  phosphatid 
solution  slowly  changes,  thus  making  it  necessary  to  run  controls 
every  day.  This  change  seems  to  be  related  to  the  stage  of  oxida- 
tion of  the  preparation.  The  darker  and  older  the  phosphatid,  the 
greater  the  amount  of  calcium  chloride  required  to  precipitate  the 
lipoid  and  as  a  rule  the  smaller  the  difference  between  the  controls 
and  the  drug  solutions.    One  sample  of  lecithin  was  originally  pre- 
4  For  more  details  of  method,  see  W.  Koch,  Jour.  Pharm.  and  Exp. 
Ther.,  2,  239,  1910. 
