, 1892-07-13

disease referred to ia fortunately not pre-
valent in this group, but it is quite proba-
bic that theT cause of our cattle-disease is
either q bacihus or an infusorian in the
blood; and its propagation by the tick may
have given rise to the wide spread opinion
that the disease is directly caused by the
poisonous bite of a species of that unplea-
SAINT parasite.
THE United States experiment-stations
which have done so much in the precise in
~vestigation of disease in plants and animals,
have obtained some remarkable results re-
s~pecting Texas cattle-fever, a plague pro-
baby not differing specifically from our colo
NAL red-water.
DIR. Theobald Smith during 1888 was
engaged in determining whether some special
bacillus could be detected as the active agent
in producing the disease. If So, measures
might be taken, analogous to those found
effective in anthrax or lung-sickness, and
o protective vaccine ultimately obtained.
But none beyond those which invariably
multiply during putrefactive changes could
be detected, and the experimenter came to
the conclusion that tue disease was confined
to the blood and consisted essentially in the
breaking down of the red corpuscles in it.
During 1889, a parasite not at all related to
the bacillus family, but belonging to the
p~rotOzoa, was detected within these corpus
cles, destroying them 30 rapidly and surely
that in fatal cases the number present in a
given quantity of blood was reduced to one
sixth of the healthy average. The whole
course Of the disease was studied at the ex-
periment-Station upon cattle imported express
ly from infected places in North Carolina
and Texas, and check Investigations made by
purposely injecting cattle previously healthy.
During this time, DR.. f. L. Kilborne, who
had charge of the stalls for these latter sub
iecUs determined to put to proof the theory
that the cattle ticE (Irodes) is the special
agent in carrying the disease from one animal
to another and consequently from one region
of grazing ground to others where it had
been unknown. The ticks are carried north
every summer with the export of Texas
cattle. When mature they drop off, lay
their eggs on the ground III the pastures and
perish. In ffte,n to thirty days the young
ticks hatch out, crawl up on fresh cattle, TO
drop of in their turn, lay their eggs and die
within about a month andI this succession
goes on till the cold weather comes. Now
since nearly all cattle that die OF Texas
fever are found to be infested with these
ticks, a sort of loose theory arose that the
ticks were in some way the cause, or at least
the instruments of spreading the disease.
AS the case stood, there was no proof forth
coming. On the similar grounds one might
argue hat milestoneS are the cause of roads.
And this flaw in the evidence had to be
amended. DR.. Kilborne placed selected
Texas cattle and northern cattle together
in the same enclosure, and carefully destroyed
every tick present in the former. At the
same time others of these Texas subjects
were left without such care in another en-
closure with northern companions. The
northerners in the first field allied nothing
those in the second died of Texas fever.
In September, 1889, three fields were
arranged for experiment-one with tick
infested southern cattle, a second with south
ern cattle from whom the ticks had been care
fully removed and for northern cattle a third,
over which a number of adult ticks had been
scattered. It is true no cattle died outright
from the first field but examination of their
blood showed the disease in a state of incuba.
ton. In the third, one animal died of Texas
fever and all the others were more or less sick.
None died in the second field and no trace Of
disease could be detected. These reports give
an idea of the investigations carried through
1889, and the following preliminary ~oonclu-
Bions were some to-
/. Texas fever is not a disease caused by
bacilli transferred simply from southern cat
tie to fresh pastures aud from these pastures
RI nnrthArn CaftlA 70 %