FRANCIS ON CASSAVA, 
128 
plant. Presuming, then, that the sweet cassava obtainable 
in this island is a true type of the kind so called, the 
existence of a harmless cassava is disproved, and the 
term “ sweet ” ceases to be significant. 
Dr. Clark’s observation, that half a pint of the juice of 
bitter cassava was sufficient to destroy life, has been recorded 
above. That his statement is correct is evident from the 
writer’s experiments, since half a pint of the juice, or, more 
exactly, 9-6 ounces, represents one pound of the root ; and it 
will be seen on reference to the table that this quantity of 
bitter cassava yields on the average 1*92 grains of prussic 
acid. On the other hand, an equal quantity of the juice of 
sweet cassava yields on the average 1-17 grains, — an amount 
also sufficient to produce fatal effects.* Moreover, fifty 
per cent, of the samples of sweet cassava yielded consider- 
ably more than this proportion. 
From some further experiments made by the writer, it 
appears probable that sweet cassava develops increased 
poisonous qualities with age. During last month a singular 
and undoubtedly old specimen of sweet cassava was ex- 
amined. Many of the roots were of large size and almost 
globular in shape, and they were said to have remained in 
the ground for more than a year. This sample yielded -0852 
per cent, of prussic acid, or a quantity equal to no less than 
2*464 grains per pound. An amount of juice equivalent to 
three pounds of the root of this sample yielded by distilla- 
* Dr. Taylor fixes the poisonous dose of prussic acid at one grain, 
hut at the same time reports the case of a healthy woman who died 
in twenty minutes from a dose equivalent to nine-tenths of .a grain of 
anhydrous prussic acid ( On Poisons, p. 594). Dr. Wormley states 
that the above seems the smallest fatal quantity yet recorded ( Micro - 
Chemistry of Poisons, p. 172). 
