4 BULLETIN 575, U. S. DEPARTMENT OF AGRICULTURE. 
these our knowledge is at present on a firm basis of experimental 
proof. It has seemed best, however, to add to the list some plants 
which undoubtedly produce poisonous effects, but which have never 
been subjected to detailed experimental study. 
LOCO PLANTS. 
Without any doubt the most destructive of all the poisonous plants 
are those going under the general name of loco. That extensive 
losses of domestic animals have been caused by loco plants has been 
claimed for a long time, but it is only within the last few years that 
exact evidence, by careful experiments, has shown definitely that 
these plants produce the effect which has been popularly ascribed to 
them. A great deal of interest attaches to these plants because of 
their wide distribution and the large number of animals that have 
been poisoned by them, including cattle, horses, and sheep, and also 
because of the difficulty of actually proving the existence of a poison- 
ous principle in the plants themselves. 
The loco plant has had its place in romantic literature, as it has 
frequently been claimed that it produces the same effect upon human 
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, has any substantial foundation. 
The word loco is from the Spanish, meaning crazy, and was given 
to the plant because of its supposed effect upon its victims. Loco 
plants 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 occasioned by the loco plants, with distinct symptoms 
and with a definite outcome. 
WHITE LOCO (OXYTROPIS LAMBERTD. 
Of all the loco plants the most destructive is the ‘white loco,” or 
“rattle-weed,’’ Oxytropis lambert: of the botanists. This is not be- 
cause of its greater toxicity, but because it grows in great abundance 
over a wide extent of territory and is poisonous not only to cattle 
and sheep but to horses. It is found in the Plains region east of the 
Rocky Mountains from Alaska to Mexico. Like all the loco plants, 
it belongs to the Leguminosz or pea family, the family in which are 
found peas, beans, clovers, alfalfas, etc. It is a perennial plant, living 
two or three years or more, and has a long root system which enables 
it to withstand conditions of drought. The leaflets of the compound 
leaves are slender, 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 
