Investigations into the Nature, Causation, and Prevention of Texas or Southern Cattle Fever Page: 36
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TEXAS OR SOUTHERN CATTLE FEVER.
THE DESTRUCTION OF RED BLOOD) CORPUSCLES.
The red corpuscles were counted with the apparatus of Thoma, con-
structed by Zeiss. In the direction for use accompanying the apparatus
it is suggested that 200 spaces should be counted in order to reduce the
errors to a minimum. Owing to the large quantity of work that had to be
done in connection with the various field experiments to be described,
the counting could not be carried to the point of accuracy indicated.
Moreover, the quantitative changes in this disease are so gross that a
slight error will not affect the comparative results. The method adopted
was to count 40 spaces. Two parallel rows of squares through the ruled
field were counted. Such rows were chosen through which an addi-
tional line was drawn in order to guide easily the eyes. Hence these
rows were always four squares apart. By counting the red corpuscles
in a row of squares any differences in their distribution from one side
of the cell to the other were thus averaged. A comparison of the re-
sults of counts in the case of healthy controls, or of animals before the
onset of the disease, shows a remarkable uniformity of results. More-
over, successive counts either from the same dilution or from separate
dilutions of blood from the same animal collected at the same time,
showed that the greatest margin of error was one to two hundred thou-
sand, a comparatively insignificant figure in the work before us.
It was necessary also to make a modification in the collection ot
blood. The uneasiness of many animals, the presence of flies, the heat
and wind on the fields made it necessary to act with great rapidity.
Hence the complete filling of the capillary tube was dispensed with-
Only a fraction of the length was filled with blood, usually from 0.6 to
0.9. The quantity aspirated was at once noted and the 3 per cent salt
solution or Toison's fluid was drawn up to the mark indicated. In those
cases in which the blood was very thin and the various squares con-
tained only from 0 to 3 corpuscles about 80 squares were counted.
If, in the collection of the blood, the dilution with the salt solution
or Toison's fluid, its proper mixing with the blood, and especially the
placing of the drop in the cell, be properly carried out the necessity for
counting a large number of squares is made nugatory. Special care
should be devoted to the cleaning of the glass cell and cover and the
keeping away of all dust. When the coverslip has once been laid on
the cell it should not be slid or moved about, so that the uniformity of
distribution is not disturbed. The process of collecting the blood for
counting is as follows:
In most cases the animals could not be removed from the field and
the examination of the blood had to be proceeded with on the field
itself. The various appliances necessary for the securing of fresh and
dried preparations of blood and the counting of the blood corpuscles,
were carried in boxes or trays. The animal was secured by its head
and, in rare cases, one hind foot was tied, to forestall any injury to the36
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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/m1/36/?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.