378 UNIVERSITY OF VIRGINIA PUBLICATIONS 



forced out of business by this scourge, while other ranchmen in the same 

 neighborhood have escaped loss from the disease almost altogether. Ac- 

 counts indicated in 1903 that the disease was increasing. According to 

 the ranchmen there are the most remarkable variations in the prevalence 

 of the disease from year to year. A region previously free from the disease 

 may suddenly be devastated by it, only to have it subside or disappear 

 again after a year or two. It could not be ascertained that such outbreaks 

 are coincident with a sudden spread of the locoweed. It is claimed by 

 some, however, that the abundance of the weed varies from year to year. 



11. Old ranges. The"loco disease" does not ipake its appearance when 

 a ranch is first occupied. Thus in Montana the disease was first noticed 

 about ten or twelve years after the plains were settled by the rangers. 

 In Eastern Colorado the evidence was similar. The stock rangers explain the 

 delayed appearance of the disease as the result of a steady decrease of avail- 

 able grazing lands, combined with a rapidly increasing overstocking of 

 the ranches, producing a shortage of grass, and the adoption of the locoweed 

 as food by the hungry animals.* 



12. Outbreaks. It is rare for isolated cases to occur, although they are 

 met with. Such cases are most often found in horses. As a rule if one 

 animal on the ranch becomes "locoed" a large proportion of all the young 

 animals will develop the disease. As stated above locoweed disease is 

 frequently enzootic throughout an entire region. Whether the infection 

 attacks all animals or only single species could not be determined. The 

 evidence at hand indicates that the "loco" outbreak is confined to one 

 species, for example, sheep. 



IS. Seasonal variations. In Montana the first cases of "loco" occur a 

 few weeks after the plant becomes green — that is during April and May. 

 These are regarded as chiefly relapses from the year before. Very few 

 cases develop during the summer. The greatest number of new cases ap- 

 pear in the autumn — November and December. Further south (Colorado) 

 the height of the disease is said to be earlier in the spring and later in the 

 autumn. 



The ranchmen hold divergent views as to the relation between the in- 

 cidence of the disease and the season's rainfall, some holding that more 



* Within recent years the number of animals grazed on a given tract of land has 

 risen enormously. One ranger in Montana informed me that 40,000 sheep now graze 

 on a tract formerly ranged over by 6000. The fencing in of the ranges, and the settle- 

 ment of the public lands, have served to curtail the available ranging lands to a frac- 

 tion of their former extent, so that at the present time a larger number of animals 

 grazes over a smaller tract than formerly, and returns to the same tract at shorter 

 intervals. 



