MEXICAN WHORLED MILKWEED AS A POISONOUS PLANT. 
15 
It is evident that the toxic principle of the plant is found very 
largely in the leaves. 
A comparison of the preceding figures with the toxic and lethal 
dosages for sheep given in Nevada Bulletin 99 can be made by 
reducing the dosage in Table I, page 15, of the Nevada bulletin to 
pounds per hundredweight of animal. It will be seen that the 
smallest toxic dose, 0.537 pound per hundredweight in the case of 
Sheep 25, is somewhat smaller than the figures obtained in our 
experiments. It may be noted, too, that Sheep 75 received 0.555 
pound without effect and that the smallest lethal dose was 2.3 
pounds in the case of Sheep 6. 
If the data of Table II of the Nevada bulletin giving the feedings 
of air-dried plant are similarly reduced to a dosage for 100 pounds 
of animal and an allowance of a loss of 75 per cent by evaporation is 
made, as in our work, the smallest lethal dose would be 2.059 pounds 
in Sheep 72 and the smallest toxic dose 1 pound in Sheep 59. 
The dosage in Table III (Nevada) of material which had dried in the 
field is somewhat larger, the lethal dose, 7.5 pounds in Sheep 43, 
being especially large. This is probably accounted for by the fact 
that there had been some loss of leaves in the field, for it is shown on 
page 14 of this paper that the leaves are especially toxic. 
Table 7 shows the comparative toxicity of the different whorled 
milkweeds : 
COMPARATIVE TOXICITY OF SPECIES OF WHORLED MILKWEED. 
Table 7. — Comparative toxicity of different species of whorled milkweed. 
Species. 
A. mexicana 
A. galioides 
A. pumila 
A. verticillata var. geyeri 
Minimum 
toxic dose 
of whoie 
plant. 
Pounds. 
0.882 
0.22 
0.787 
2.205 
Minimum 
lethal dose 
of whole 
plant. 
Pounds. 
1.323 
0.22 
2.165 
Minimum 
toxic dose 
of leaves. 
Pounds. 
0.353 
0. 138 
1.286 
Minimum 
lethal dose 
of leaves. 
Pounds. 
0.882 
0. 138 
Minimum 
toxic dose 
of stems. 
Pounds. 
1.323 
1. 543 
While too much reliance must not be placed on this table as show- 
ing exact relationships, nevertheless it indicates, in a general way, 
the relations between the species. So far as the whole plant is con- 
cerned, A. mexicana and A. pumila are about equally toxic. 
A. galioides is 4 times as toxic as these two species and 10 times as 
toxic as A. verticillata var. geyeri. As regards the lethal dose of the 
whole plant, A. galioides is 6 times as toxic as A. mexicana and 9.84 
times as toxic as A. pumila. 
With relation to the leaves, A. galioides and A. verticillata var. 
geyeri compare much as in the whole plant; that is, in a ratio of about 
1 to 10. The ratio of A. galioides to A. mexicana, however, is 1 to 
2.56 instead of 1 to 4, as in the whole plant, while the lethal dose is in 
