16 , CASSAVA. 



dose was unconscious for four hours and then recovered. It is prob- 

 able that 0.04 gram closely approximates the minimum fatal dose, and 

 that even half as much would produce ill effects. Therefore if an 

 adult should eat as much as 130 grams of the extreme bitter variety, 

 containing 0.03 per cent of hydrocyanic acid, fatal results might be 

 expected. 



There are no definite data obtainable regarding the minimum fatal 

 dose in the case of animals, numerous cases of death from eating 

 cassava being recorded, but without any statement as to the amount 

 of prussic acid in the tubers or the quantity eaten. However, a fair 

 approximation may be made by a comparison with the effects produced 

 on human beings. The toxicity of poisons will be assumed to be 

 somewhat in proportion to the weight of the animal, and as a steer is 

 about ten times the weight of a man, it may be assumed that in the 

 eating of 1 kilo of the White Top variety fatal results might be pro- 

 duced. Five kilos of such foodstuff would probably be a short ration 

 for a steer, as it contains about 60 per cent of moisture. On this basis 

 it -is estimated that such a ration, made up from a variety containing 

 as much as 0.008 per cent of hydrocyanic acid, would prove fatal to a 

 steer. Of the forty plants examined thirty-two would be classed as 

 dangerous in accordance with these deductions. 



In the examination of these plants some results were obtained which 

 are thoroughly in accord with the common Usage of the natives in the 

 preparation of the plant. A fine specimen of the bitter White Top 

 was selected (No. 8), the total root of the plant weighing nearly ."> 

 kilos, which is unusually large. The tuber was divided into three 

 parts, (1) the thin dry outer covering or bark, which is black and con- 

 stitutes about 1 per cent of the sample; (2) the cortical layer free of 

 bark, a pink peel about one-sixteenth of an inch thick and constitut- 

 ing about 25 per cent of the sample, and (3) the peeled tuber. The 

 bark has but little moisture, and the hydrocyanic acid in it is calcu- 

 lated to a dry basis, amounting in the sample under consideration to 

 o.iif.s per cent of hydrocyanic acid. The peel, calculated on the fivsh 

 basis in which it' existed, contained 0.054 percent, while the peeled 

 tuber contained only 0.002 per cent. That is to say, a peeled root of 

 the extreme bitter variety contained no more hydrocyanic acid than 

 the whole root of an extreme sweet variety. A tuber from the same 

 plant free of hark contained 0.020 per cent of the acid. 



A root of the Florida Sweet, weighing approximately 3 kilos, was 

 examined according to the same scheme and the bark was found to 

 contain about 0.076 per cent, the peel (12.5 per cent of the sample) 

 o.oi>;j. ami the peeled tuber only a trace, i. 6., o.o(K)5 per cent. These 

 figures immediately suggest that the smaller the root the higher the 

 relative content of hydrocyanic acid, as the percentage of peel is 

 higher in a small root. This deduction was confirmed by an actual 



