The Bulletin 
15 
c. Poisonous Plant Theory 
Many physicians and laymen have held to the theory that trembles is 
caused by the ingestion of a poisonous plant. One reason for this view 
is the general accord of observations to the effect that “milk sick” tracts 
are no longer able to communicate the disease after the natural vegeta¬ 
tion has been replaced by cultivated plants. Bennett (1822) is among 
the earliest writers to record this fact. He states that “those farmers 
who keep their cattle and horses in enclosed pastures which have been 
cultivated do not lose them by this disease.” This opinion is also in 
accord with the writings of Crook (1857) and Simon (1888). Pickard 
(1857) cites an interesting example which substantiates the view that 
clearing and cultivation are efficacious in destroying the dangerous 
quality of milksick lands. He reports that a “family having suffered 
from its ravages, plowed up a pasture field, digged around the stumps, 
thoroughly turning all the soil, and sowed the field in grass, upon 
which they have kept their stock for twenty years, and at no time has 
milksickness made its appearance; while on other portions of the farm, 
uncultivated, it is as fatal as ever.” The same opinion is expressed 
by Drake (1841), who records that “clearing and cultivation, even 
girdling the trees, harrowing the ground, and sowing it with grass seed 
destroys and renders inactive the cause, whatever it may be.” 
Another reason for belief in poisonous plants as the cause of trem¬ 
bles, is that the disease is largely limited to the season when animals are 
allowed to graze. That the disease may occasionally appear in winter 
is attested by the writings of Yandell (1852), Beck (1857), Waggoner 
(1859), Beach (1884), and Shapard (1892). This may be accounted 
for by the feeding of hay as has been recorded by Gray (1881), Beach 
(1883), and others. The latter makes the following interesting state¬ 
ment : “That cattle may have trembles in the winter season is a matter 
of occasional observation, and the old citizens generally attribute it to 
the feeding of cattle upon wild or swamp hay.” Beck (1857) has stated 
that in Kentucky the disease is prevalent only in winter, whereas, in 
Indiana it occurs in all of the other seasons. 
It seems to be the common belief among farmers in Horth Carolina 
that the usual time of prevalence is during the months of August, Sep¬ 
tember, October, and November. Dawson (1842), Rawlings (1874), 
and Shapard (1892) refer to the greater prevalence of trembles in late 
summer and autumn. Dewey (1845) speaks of its disappearance after 
the first hard frost. While the autumnal incidence has been found to 
be most frequent, it may also occur during spring and early summer. 
An epidemic in Tennessee recorded by McCoy (1907), to which refer- 
