Investigations into the Nature, Causation, and Prevention of Texas or Southern Cattle Fever Page: 88
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TEXAS OR SOUTHERN CATTLE FEVER.
(3) Eggs several days old placed in dishes August 13, 1890. Young ticks appear
in large numbers September 4 and 5. Period approximately twenty-five days.
(4) On September 17, 1890, eggs two to three days old placed in glass dishes. Young
ticks first appear October 24, and their number increases until October 28. Period
about forty days.
(5) Eggs one to three days old are placed in glass dishes September 20, 1890.
Young ticks present in abundance November 1. Period about forty-three days.
(6) Eggs one to three days old are placed in glass dishes September 23, 1890.
Young ticks begin to appear November 1. Period about forty days. The eggs from
experiments 4, 5, and 6 were taken successively from the same adult ticks. The tem-
perature of the laboratory at this time was 75o-80 F. during the day, but fell 50 or
100 at night.
(7) Eggs one to two days old placed in dishes October 6 and 9, respectively. The
dishes were kept on shelves several feet above a steam heater. On November 9 all
eggs were found hatched out. Period about thirty days or less.
(8) Eggs two to four days old placed in dishes October 9, 1890. Over steam register
only a part of the time. A few young ticks appeared November 15. Hatching com-
pleted November 17. Period about thirty-eight to forty days.
From these recorded dates it will be seen how essential a high temper-
ature is for the rapid development of the embryo in the egg. The
period of development may vary from fifteen days to six or seven
weeks, and may perhaps be prolonged still more by lower temperature.
It is evident, however, that a certain temperature level exists below
which no development takes place. In the experiments above described
there was considerable daily fluctuation in the temperature, and hence
they can be made to show only the general relation subsisting between
heat and development. To find the lowest temperature at which devel-
opment may go on would require thermostats in which a certain low
temperature could be constantly maintained. It is probable that the
shortest period of incubation might be shortened still more by placing
the eggs in continuous high temperatures. We have considered this
matter more in detail owing to the intimate relation between the period
of development of the young tick and the so-called "period of incuba-
tion " of Texas fever.
There are some changes which the ova undergo during development
which are visible to the naked eye. After a variable number of days
each ovum presents a white spot. Under the microscope this corre-
sponds to the position of the cloacal opening, and is nothing else than
a mass of white powder composed of very minute spherical crystals.
It is an excretory product (urates ?) of the young tick, the outlines of
whose body and limbs are now visible through the shell under .a low
power of the miscroscope. The color of the egg itself becomes lighter,
and of a more opaque, milky character. Towards the end of the period
of development it assumes a peculiar metallic luster. These changes
are all caused by the changes going on within the shell.
The minute six-legged ticks (Plate x, Fig. 3) after emerging from the
shell are at first of a pale brownish, translucent, waxy color, which
soon changes into an opaque brownish hue. They are about 0.67 mm.88
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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/m1/88/?q=%221863%22&rotate=180: 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.