Am.  Jour,  rhaim. 
Jan.,  1883. 
'  I     Poisonous  Properties  of  Cassava  Root. 
35 
into  tapioca.  The  milky  sap  of  the  latter  species  has  long  been  known 
to  be  a  strong  vegetable  poison,  which  is  destroyed  through  pressing 
the  grated  root  in  the  first  instance,  the  remaining  acidity  being 
expelled  by  the  heating  process. 
In  1796  Dr.  Clark,  of  Dominica,  describing  the  fatal  effects  result- 
ing to  negroes  from  drinking  bitter^cassava  juice,  compared  the  action 
of  the  poison  to  prussic  acid,  and  Dr.  Fennon,  by  experiments  made  at 
Cayenne,  proved  that  the  poison,  like  prussic  acid,  w^as  volatile,  and 
could  be  isolated  by  distillation. 
/Subsequently  Messrs.  Henry  and  Boutron-Charlard,  by  analyzing 
bitter  cassava  juice  imported  into  France,  ascertained  that  the  poison 
w^as  prussic  acid.  In  1838  Dr.  Christison  confirmed  their  discovery 
by  an  examination  of  some  well-preserved  juice  from  Demerara. 
Notwithstanding  this  early  identification  of  the  poison,  no  attempt 
had  apparently  been  made  to  determine  the  quantity  yielded  by  the 
plant  untill  1877,  when  Mr.  E.  Francis,  F.C.S.,  undertook  an  inquiry 
into  the  subject,  the  results  of  which  he  has  recently  published  in  the 
journal  of  the  Royal  Agricultural  and  Botanical  Society  of  British 
Guiana. 
An  examination  was  made,  not  only  of  bitter  cassava,  but  also  of  a 
number  of  samples  of  sweet  cassava,  and,  contrary  to  expectation,  the 
latter  were  found  to  contain  nearly  as  much  prussic  acid  as  the  former. 
Fifteen  samples  of  sweet  Cassava  were  obtained  from  different  culti- 
vators in  Trinidad,  and  every  one  of  them  contained  prussic  acid,  nine 
out  of  the  number  (or  60  per  cent.)  yielding  sufficient,  from  1  lb.  of 
the  root  or  half  pint  of  the  juice,  to  kill  an  adult.  The  following 
summary  shows  the  average,  as  well  as  the  highest  and  lowest  quanti- 
ties of  prussic  acid,  that  were  met  with  in  15  samples  of  sweet,  and  10 
samples  of  bitter  cassava : 
Sweet  Cassava  (15  Samj^les). 
Per  cent,  of 
prussic  acid. 
Average, 
Highest, 
Lowest, 
.  -0168 
•0238 
.  0113 
Bitter  Cassava  (10  Samples). 
Per  cent,  of 
prussic  acid. 
Grains  of 
prussic  acid  per  lb, 
.  1-927 
Average, 
Highest, 
Lowest, 
.  -0275 
•0422 
.  -0132 
3^094 
0-924 
