*  January  ^iST'  }  Resistance  of  Guinea  Pigs  to  Poisoning.  9 
dose  for  November,  r^.  fiber,  and  January  was  .00000052:  while 
during  the  much  milder  winter  of  191 2-1 3,  the  lethal  dose  was 
smaller.  Where  comparison  is  possible  in  other  months,  the  differ- 
ence never  amounts'  to  more  than  15  per  cent. 
Table  II. 
Month. 
January. . . 
February. . 
March  
April  
May  
June  
July  
August  
September 
October. . . 
November. 
December. 
IOII. 
.  00000029 
00000030 
, 00000036 
, 00000052 
. 00000052 
1912. 
, 00000052  + 
.00000037 
, 00000036 
. 00000040 
. 00000045 
. 00000040 
.00000036 
. 00000042 
. 00000040 
. 00000045 
00000040 
00000042 
.00000037 
. 00000045 
.00000025 
.00000025 
Seasonal  variations  in  the  resistance  of  test  animals  may  be 
obviated  by  the  use  of  a  satisfactory  standard,  and  Vanderkleed  and 
Pittenger  suggest  the  use  of  ouabain  when  galenicals  of  the  "  heart 
tonic  "  group  are  tested  upon  guinea  pigs.  The  use  of  ouabain  is 
justified,  however,  only  when  it  has  been  shown  that  the  variations 
in  the  resistance  toward  poisoning  by  ouabain  parallels  that  toward 
poisoning  by  the  galenicals  under  consideration.  Opportunity  has 
occurred  to  determine  the  minimum  lethal  dose  of  a  small  number 
of  samples  of  tincture  and  fluid  extract  of  digitalis  at  different  seasons 
of  the  year.  Some  of  the  tinctures  were  made  by  the  U.S. P.  method 
and  some  were  made  with  a  menstruum  containing  75  per  cent,  alco- 
hol. All  of  the  fluid  extracts  were  made  with  a  menstruum  contain- 
ing 70  per  cent,  or  80  per  cent,  alcohol. 
In  testing  the  tinctures,  portions  were  evaporated  to  a  semi- 
solid consistence  upon  the  water-bath  and  the  residue  suspended  in 
an  amount  of  distilled  water  equal  to  the  original  volume  of  the 
portion  taken  for  evaporation.  The  same  procedure  was  followed 
with  the  fluid  extracts,  save  that  the  volume  of  distilled  water  was 
five  times  that  of  the  fluid  extract  taken.  For  reasons  that  will  be 
apparent  later;  it  is  desirable  that  the  preparations  be  divided  into 
two  groups ;  one  comprising  preparations  containing  about  50  per 
