Investigations into the Nature, Causation, and Prevention of Texas or Southern Cattle Fever Page: 111
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TRANSMISSION OF TEXAS FEVER.
spite of the presence of North Carolina cattle. Another very impor-
tant fact was demonstrated. Texas fever was produced in natives by
the intravenous injection of blood from healthy North Carolina cattle,
and natives exposed to these sick natives did not contract the disease
because ticks were absent.
The Southern animals used in the field work of the summer were six
in number, gathered together from two farms near New Berne, N. C.,
three being taken from each farm. They left New Berne by steamer
June 29, and reached the station July 1, being off their native fields
about four days before they were placed in the fields at the station.
The field inclosures for this year are numbered as they were last year.
Hence the plat of 1.891 (Fig. 7) will serve to illustrate the experiments
to be described.
Experiment 17 (exposure to North Carolina cattle with ticks).-This
experiment was to serve as a control upon the following experiments.
Field VI was again used for this purpose. Two Southern animals,
one from each North Carolina farm, were introduced as sources of the
infection. The contents of the field and the general results of the ex-
posure may be tabulated as follows:
June 30, 1892.-No. 201 (cow, 5 years). Removed to uninfected field July 20;
not diseased.
June 30, 1892.-No. 203 (cow, 6 years). Died of Texas fever August 22.
July 1, 1892.-No. 216 (North Carolina cow, 6 years).
July 1, 1892.-No. 217 (North Carolina cow, 6 years).
July 20, 1892.-No. 220 (steer, 21 years). Very sick; recovered.
July 20, 1892.-No. 223 (heifer, 6 years). Died of Texas fever August 23.
August 26, 1892.-No. 204 (bull, 21 years). Very sick; recovered.
On July 20 only a few half-grown ticks were found on the Southern
cows. On August 5 the young ticks were first noticed on the natives;
at this time they had probably been on the cattle only two or three
days. The outcome of the exposure does not differ from that of pre-
ceding summers. All exposed animals contracted Texas fever, and two
of the three early exposures died.
It is interesting to note that No. 201, though it was pastured on the
infected field for twenty days, remained perfectly healthy, because it
was removed to an unused field (IV) before the young ticks had appeared
in the infected field. It is likewise worthy of notice that No. 223, though
exposed twenty days later than No. 203, became infected at about the
same time and died only a single day later. The reason for this has
already been pointed out, but it deserves repetition. The infection of
the field is established when the young ticks have hatched, and not
before. Hence a field is not dangerous until twenty or twenty-five
days (according to the average temperature) after Southern cattle have
pastured on it.
Experiment 18 (exposure to North Carolina cattle without ticks).-
Field I (see Fig. 7) was used for this test. Two North Carolina cows
(Nos. 212 and 213), one from each farm, were chosen, so as to make the111
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Smith, Theobold & Kilborne, Fred Lucius. Investigations into the Nature, Causation, and Prevention of Texas or Southern Cattle Fever, book, 1893; Washington D.C.. (https://texashistory.unt.edu/ark:/67531/metapth143538/m1/111/?q=%221863%22&rotate=270: accessed July 16, 2024), University of North Texas Libraries, The Portal to Texas History, https://texashistory.unt.edu; crediting University of Texas Health Science Center Libraries.