UNITED STATES DEPARTMENT OF AGRICULTURE 



jru^"^w^ 



% BULLETIN No. 8 



i w Joint Contribution from the Bureau of Animal Industry, JOHN'^oJ'j 

 R. MOHLER, Chief, and the Bureau of Plant Industry, 



WM. A. TAYLOR, Chief 



Washington, D. C. 



PROFESSIONAL PAPER 



June 8, 1920 



THE WHORLED MILKWEED {Asclepias galioides) AS A 

 POISONOUS PLANT. 



By C, DwiGHT Marsh and A. B. Clawson, Physiologists, 3. F. Couch, PhaV' 

 macological Chemist, Bureau of Animal Industry, and W. W. Eggleston, 

 Assistant Botanist, Bureau of Plant Industry. 



CONTENTS. 



Part I.— Introduction 1 



Historical summary and review of litera- 

 ture 1 



Description ol Asclepias galioides 5 



Distribution and habits of the plant.... 6 



Part II. — Erperimental work 8 



Horse experiments 13 



Cattle experiments 15 



Sheep experiments 17 



Chemical examination 20 



Paet III. — General discxisslon and conclu- 

 sions 25 



Symptoms 25 



Autopsy findings 28 



Part III— Continued. 



Pathology 



Toxic and lethal doses 



Susceptibility o f different animals 



Delay in development of symptoms . . . 



Eflect of repeated doses 



Seasonal variations in toxicity 



Relative toxicity of leaves and stems . 



Local variations in toxicity 



Remedies 



Eradication of the whorled milkweed . 



Prevention by care of stock 



Summary 



Literature cited 



PART I.— INTRODUCTION. 



HISTORICAL SUMMARY AND REVIEW OF LITERATURE. 



The literature relating to Asclepias galioides as a poisonons plant 

 is confined to three publications. Glover and Robbins, in 1915/ 

 published statements that cattle in western Colorado had been re- 

 ported as being killed by a plant which they called A. vertlciUata, 

 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 ver}- danger- 

 ous poison weed for sheep and cattle." In July, 1918, Glover, New- 

 som, and Hobbins published a somewhat detailed account of the 

 plant and its distribution, gave the history of some cases of sheep 



. — ^ — _ 5 . _ . 



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 



