Investigations into the Nature, Causation, and Prevention of Texas or Southern Cattle Fever Page: 44
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TEXAS OR SOUTIIERN CATTLE FEVER.
By using a pair of forceps which may be adjusted by a clamp, the
scraper may be fastened between the blades, and by rotating it its
edges may serve to spread out three or four separate preparations. The
scraper should be thick and its edges smooth in order to insure uni-
form distribution of the blood. It is needless to say that this simple
process is much superior to the barbarous one of placing two cover
glasses together face to face in order to allow the blood to spread in a
film between them, and then drawing them apart. Each corpuscle is
thereby subjected to a long crushing process, whereas in the method
before us this is entirely avoided. The thinness of the blood film de-
pends upon several things, such as the condition of the cover as re-
gards freedom from all grease, the size of the drop of blood, the regu-
larity of the edge of the second cover or " scraper," and the angle at
which it is held during the operation. The layer is not of even thick-
ness over the entire cover glass, but is thinnest where the scraper has
begun its work, and densest where it has left off at the edge of the
cover, as shown in the figure. This is no disadvantage, however, but
rather an advantage, as it furnishes us with a layer of varying thick-
ness which is of service, as will be pointed out farther on. The place
where the scraper began and where the layer is composed of isolated
corpuscles or groups of contiguous ones, they have dried so rapidly that
they are in a state of perfect preservation. Every preparation has thus
some spots where the corpuscles are thoroughly "fixed," even if as a
whole it may have been a failure.
The essential condition of success in dry preparations of blood is to get
the corpuscles into adried state as soon as possible after the blood is shed.
For this reason it might seem desirable to eliminate the use of the loop
and touch the exuding blood directly with the cover glass, as is fre-
quently done in the study of human blood when the finger tip is
pricked. But the circumstances are different in cattle. The prick is
useless and an incision must be made. The surface of the skin is fiat
and a cover glass touched to the oozing blood may bring with it epi-
thelial scales and other objectionable things from the skin accidentally
touched, however much the latter may have been cleansed beforehand.
Still, in rapid work, it is now and then of advantage to touch the ooz-
ing blood directly with the edge of the scraper. Not infrequently the
quantity of blood is small and does not well out of the incision. A
loop then becomes indispensable in lifting it out.*
The dried films of blood, kept labeled in small pill boxes until used,
are exposed in a dry-air oven to a temperature of 1100-1200 C. for one
and one-half to two hours. Drawing the covers through the Bunsen
flame as for bacteriological preparations is liable to fail at any time
from overheating or underheating, and is not to be recommended.
* More recent observations during the fall of 1892 have shown quite conclusively
that cold rapidly destroys the form of red corpuscles. In fact it was impossible to
prepare films out of doors in a temperature below 500 F.44
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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/m1/44/?q=%221863%22: 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.