t is therefore simply
a blood disease. The organism does not belong to the bacteria but to the
protozoa. It is not, in other words, a microscopic plant, but it belongs to
the lowest forms of the animal kingdom. This very minute organism
multiplies very rapidly in the body of the infected animal, and in acute
cases causes an enormous destruction of red corpuscles in a few days. How
it gets into the red corpuscle it is not possible to state, but it appears
that it enters as an exceedingly minute body, probably endowed with motion,
and only after it has succeeded in entering the corpuscle does it begin to
enlarge. Plate XLV, figure 4, illustrates an early stage of this blood
parasite. The red corpuscle contains a very minute, roundish body which is
stained blue to bring it into view. The body is, as a rule, situated near
the edge of the corpuscle. Figure 5 illustrates an older stage in the
growth of the parasite, in fact the largest which has thus far been
detected. It will be noticed that there are usually two bodies in a
corpuscle. These bodies are in general pear-shaped. The narrow ends are
always toward each other when two are present in the same corpuscle. If we
bear in mind that the average diameter of the red blood corpuscles of
cattle is from 1/4000 to 1/5000 inch, the size of the contained parasite
may be at once appreciated by a glance at the figures referred to.

The various disease processes which go on in Texas fever, and which we may
observe by examining the organs after death, all result from the
destruction of the red corpuscles; this destruction may be extremely rapid
or slow. When it is rapid we have the acute, usually fatal, type of Texas
fever, which is always witnessed in the height of the Texas-fever season,
that is, during the latter weeks of August and the early weeks of
September. When the destruction of corpuscles is slower, a mild, usually
nonfatal, type of the disease is called forth, which is only witnessed late
in autumn or more rarely in July and the early part of August. Cases of the
mild type occurring thus early usually become acute later and terminate
fatally.

The acute disease is fatal in most cases, and the fatality is due not so
much to the loss of blood corpuscles as to the difficulty which the organs
have in getting rid of the waste products arising from this wholesale
destruction. How great this may be a simple calculation will serve to
illustrate. In a steer weighing 1,000 pounds,