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BULLETIN 1245, U. S. DEPARTMENT OF AGRICULTURE 



beings as upon the lower animals, and it has been a popular subject 

 for the short-story writer. None of these stories of " locoed " men, 

 however, have any substantial foundation. 



The word loco is from the Spanish, meaning crazy, and was given 

 because of the supposed effect upon its victims. Loco weeds have 

 been heard of in practically all the open-range country of the West, 

 except in the higher mountains, and there is no doubt that under the 

 term loco disease a large number of ailments have been included. 

 Experimental proof, however, has shown that there is a disease occa- 

 sioned by these plants, with distinct symptoms and with a definite 

 outcome. 



The early writers on the subject of loco spoke of " the " loco plant. 

 It is now known that the typical symptoms of loco poisoning are 

 produced by several plants. Six have been shown to be true loco 

 weeds and there may be others, while some other closely related 

 plants are poisonous to livestock but should not be classed as locoes. 

 It is desirable that the term " loco " should be confined to those plants 

 which cause typical loco symptoms. 



Three of the true loco weeds are especially destructive, the white 

 loco, the purj:>le loco, and the blue loco. 



White Loco (Oxytbopis lam berth) 



Of all the loco weeds, the most destructive is the white loco weed, 

 or rattleweed, Oxytropis Jambertii of the botanists. This is not be- 

 cause of its greater toxicity, but because it grows in great abundance 

 over a wide territory and is poisonous not only to cattle, goats, and 

 sheep but to horses. It is found in the Plains region east of the 



Rocky Mountains from 

 northern Canada to 

 central Texas. Like 

 all the loco weeds, it 

 belongs to the Faba- 

 cese or pea family, 

 the family in which 

 are found peas, beans, 

 clovers, alfalfas, etc. 

 It is a stemless, peren- 

 nial plant, living two 

 or three years or more, 

 and has a long root 

 system which enables 

 it to withstand condi- 

 tions of drought. The 

 leaflets of the com- 

 pound leaves are slen- 

 der, more or less hairy, 

 and of an olive-green color. Thrifty plants are a foot or more in 

 height. 



The spikes of flowers are borne on stems extending above the leaves 

 and are commonly of a prevailing white color, hence its name of 

 white loco. The corolla, however, is frequently streaked with pur- 

 ple; sometimes the calyx is red; and sometimes, particularly in 



Figure 15. — A sheep poisoned by poison bean, Dauben- 

 tonia drummondii 



