ADeimber^y™'}       Valuation  of  Drugs  and  Foods.  589 
through  the  lack  of  opportunity  for  the  organism  to  accommodate 
itself  to  the  change  ;  (2)  toxic  action,  due  to  the  chemical  interfer- 
ence of  the  substance  in  solution  with  the  molecules  of  living  sub- 
stance, might  also  take  place.  In  each  special  case  it  would  be 
necessary  to  ascertain  the  kind  of  injury  operating.  In  doing  this 
certain  plain  considerations  should  be  borne  in  mind.  Should  spi- 
rogyra  be  found  to  survive  at  a  concentration  greater  than  that 
causing  plasmolys-is  and  less  than  the  calculated  boundary,  the  dele- 
terious action  would  in  greater  probability  be  due  to  the  osmotic 
properties  of  the  solution.  If,  however,  the  algae  should  die  in  a 
concentration  less  in  osmotic  value  than  the  cell-sap,  i.  e.,  at  a  con- 
centration weaker  than  the  plasmolyzing  strength,  death  could 
hardly  be  attributed  to  the  water-extracting  properties  of  the  mole- 
cules or  ions."1 
In  the  course  of  studies  by  Kahlenberg  and  True,  using  sodium 
salts  of  a  number  of  acids,  mainly  organic,  the  boundary  concentra- 
tions for  spirogyra  were  obtained.  A  wide  range  of  variation  was 
found.  In  but  one  instance  did  a  salt  give  a  boundary  concentration 
greater  than  0-04  gramme  molecule  per  litre  (sodium  hippurate,  0  08 
gramme  molecule  per  litre),  and  in  a  number  of  cases  the  alga?  die  not 
survive  until  a  solution  containing  but  I  gramme  molecules  in  200 
litres  was  reached, viz.,  sodium  cinnamateand  sodium  protocatechuate. 
In  no  case  does  it  appear  probable  that  osmotic  action  plays  any 
noticeable  role  in  bringing  about  the  death  of  the  plants  ;  in  all 
cases,  therefore,  practically  toxic  action  only  can  be  involved  as  the 
cause  of  death. 
In  addition  to  the  experiments  upon  algae,  Kahlenberg  and  True2 
have  used  germinating  seeds  of  Lupinus  a/bus,  and  Heald3  has 
further  worked  with  seeds  of  Pisum  saturum,  Zea  mays  and  Cucurbita 
1  "The  boundary  concentration  of  cane  sugar,  the  osmotic  value  of  cane 
sugar  and  that  of  the  substance  in  question  being  given,  the  boundaiy  concen- 
tration would  be  found  to  be  related  to  that  for  cane  sugar  inversely  as  the 
known  osmotic  values,  according  to  the  proportion 
5"  /  x  :  :  ox  :  oS, 
in  which  S  is  the  boundary  solution  of  cane  sugar,  x  the  boundary  solution  of 
the  substance,  ox  the  osmotic  value  of  the  substance,  and  oS  the  osmotic 
value  of  cane  sugar.  " 
2  Bot.  Gaz.,  1896,  p.  81. 
3  Bot.  Gaz.,  1896,  p.  125. 
