UNITED STATES DEPARTMENT OF AGRICULTURE 
BULLETIN No. 800 „ 
Joint Contribution from the Bureau of Animal Industry, JOHN"SkK 
R. MOHLER, Chief, and the Bureau of Plant Industry, %2§ 
WM. A. TAYLOR, Chief JS& 0< $&i* 
^Vfr"^ 
Washington, D. C. 
PROFESSIONAL PAPER 
June 8, 1920 
THE WHORLED MILKWEED (Asclepias galioides) AS A 
POISONOUS PLANT. 
By C. D wight Marsh and A. B. Claw son, Physiologists, J. If. Couch, Phar- 
macological Chemist, Bureau of Animal Industry, and W. W. Eggleston, 
Assistant Botanist, Bureau of Plant Industry. 
CONTENTS. 
Page. 
Part I. — Introduction 
Historical summary and review of litera- 
ture 
Description o f A sclepias galioides 
Distribution and habits of the plant 
Part II.— Experimental work 
Horse experiments 
Cattle experiments 
Sheep experiments 
Chemical examination 
Part III. — General discussion and conclu- 
sions 
Symptoms 
Autopsy findings 
Part III— Continued. Page. 
Pathology 28 
Toxic and lethal doses 31 
Susceptibility o f different animals 33 
Delay in development o f symptoms 33 
Effect of repeated doses 34 
Seasonal variations in toxicity. . . 36 
Relative toxicity of leaves and stems ... 36 
Local variations in toxicity 37 
Remedies 37 
Eradication of the whorled milkweed ... 38 
Prevention by care of stock 39 
Summary 39 
Literature cited 40 
PART I.— INTRODUCTION. 
HISTORICAL SUMMARY AND REVIEW OF LITERATURE. 
The literature relating to Asclepias galioides as a poisonous plant 
is confined to three publications. Glover and Bobbins, in 1915, 1 
published statements that cattle in western Colorado had been re- 
ported as being killed by a plant which they called A. verticillata, 
but that experiments with rabbits had failed to produce results. 
Glover, in 1917, published the results of some experiments with 
rabbits, from which he inferred that the plant was not poisonous 
either when dry or green, but added that cases reported warrant 
the suspicion that "the whorled milkweed may be a very danger- 
ous poison weed for sheep and cattle." In July, 1918, Glover, New- 
som, and Bobbins published a somewhat detailed account of the 
plant and its distribution, gave the history of some cases of sheep 
1 Full titles of articles referred to in the text are given in the list of literature at the 
end of the paper. 
129410°— 20— Bull. 800—1 
