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 fomid, by experiment, that in drying, the plant lost, on the 

 average, about TO 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, tcith positive results. 



Sheep. 



Quantity 

 fed. 



Result. 



Sheep. 



Quantity 

 fed. 



Result. 



1918. 







1918. 







No. 



Pound. 





No. 



Pound. 





478 



0.167 



Sickness. 



609 



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 



