THE WHORLED MILKWEED AS A POISONOUS PLANT. 
31 
TOXIC AND LETHAL DOSES. 
Two head of cattle were treated experimentally. In determining 
the dosage the milkweed was in all cases estimated as green material. 
It was found, by experiment, that in drying, the plant lost, on the 
average, about 70 per cent of its weight, and the dosage was figured 
out on this basis. The dosage was also estimated as applying to 
a 100-pound animal. As 100 pounds may be considered the average 
weight of a sheep and 1,000 pounds the weight of a horse or steer, 
the dosage applies to the average sheep, or multiplied by 10 to the 
average horse or steer. 
Of the cattle, No. 815 received a maximum of 0.294 pound without 
effect. No. 750 received 0.626 pound without showing any symp- 
toms of intoxication. On the following day it was given 0.845 
pound and became very sick; in this case, however, there is reason 
to think that the full quantity given was not eaten. About a month 
after this experiment it was given 0.551 pound with a fatal result. 
Just why 0.551 pound produced death and 0.626 showed no effect is 
not evident, for as shown elsewhere (p. 34) it does not seem prob- 
able that repeated feedings either increase susceptibility or produce 
toleration. However, from these experiments it seems probable 
that the toxic and lethal doses for cattle are not far from one-half 
pound per 100 pounds of animal. 
Three experiments were performed with a horse. Horse 126 was 
made very sick by 0.22 pound per 100 pounds of animal, and later 
received 0.14 pound without effect. In 1919 it was killed by 0.193 
pound. This last feeding, however, was of leaves only, and these 
have been shown to be more poisonous than the other parts of the 
plant. About 0.2 pound per 100 pounds, then, may be considered the 
probable toxic and lethal dose for a horse. 
The following table shows the dosage of sheep from which positive 
results were obtained : 
Table 2. — Quantities of milkweed fed to sheep, with positive results. 
Sheep. 
Quantity 
fed. 
Result. 
Sheep. 
Quantity 
fed. 
Result. 
1918. 
1918. 
No. 
Pound. 
No. 
Pound. 
478 
0.167 
Sickness. 
509 
0.22 
Death. 
506 
.148 
Do. 
437 
.168 
Do. 
468 
.167 
Death. 
1919. 
475 
.161 
Do. 
372 
.206 
Sickness. 
476 
.27 
Do. 
534 
.191 
Do. 
480 
.577 
Do. 
542 
.198 
Do. 
483 
.138 
Do. 
522 
.147 
Do. 
492 
.165 
Do. 
522 
.198 
Do. 
506 
.184 
Do. 
461 
.22 
Death. 
The number of experimental cases of sheep was sufficiently large to 
make the figures on dosage fairly complete. There were 10 cases of 
