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Page 27
Anthrax is a disease of domestic cattle affecting particularly bovine
cattle, horses and sheep, swine more rarely. The disease exists in
practically all countries and has caused great economic losses. There
are no characteristic symptoms of the disease; the affected cattle
have high fever, refuse to eat, their pulse and respiration are rapid,
they become progressively weaker, unable to walk and finally fall. The
disease lasts a variable time; in the most acute cases animals may die
in less than twenty-four hours, or the disease may last ten or
fourteen days; recovery from the disease is rare and treatment has no
effect. It does not appear in the form of epidemics, but single cases
appear frequently or rarely, and there is seemingly no extension from
case to case, animals in adjoining stalls to the sick are not more
prone to infection than others of the herd. On examination after death
the blood is dark and fluid, the spleen is greatly enlarged (one of
the names of the disease "splenic fever" indicates the relation to the
spleen) and there is often bloody fluid in the tissues.
Where the disease is prevalent there are numbers of human cases. Only
those become infected who come into close relations with cattle, the
infection most commonly taking place from small wounds or scratches
made in skinning dead cattle or in handling hides. The wool of sheep
who die of the disease finds its way into commerce, and those employed
in handling the wool have a form of anthrax known as wool-sorters'
disease in which lesions are found in the lungs, the organisms being
mingled with the wool dust and inspired. In Boston occasional cases of
anthrax appear in teamsters who are employed in handling and carrying
hides. The disease in man is not so fatal as in cattle, for it remains
local for a time at the site of infection, and this local disease can
be successfully treated.
The beginning of our knowledge of the cause dates from 1851, when
small rod-shaped bodies (Fig. 17) were found in the blood of the
affected cattle, and by the work of a number of observers it was
established that these bodies were constantly present. Nothing was
known of their nature; some held that they were living organisms,
others that they were formed in the body as a result of the disease.
Next the causal relation of these bodies with the disease was shown
and in several ways. The disease could be caused in other cattle by
injecting blood containing the rods beneath the skin, certainly no
proof, for the blood might have contained in addition to the rods
something which was the real cause of the disease. Next it was shown
that the blood of the unborn calf of a cow who died of the disease did
not contain the rods, and the disease could not be produced by
inoculating with the calf's blood although the blood of the mother was
infectious. This was a very strong indication that the rods were the
cause; the maternal and foetal blood are separated by a membrane
through which fluids and substances in solution pass; but insoluble
substances, even when very minutely subdivided, do not pass the
membrane. If the cause were a poison in solution, the foetal blood
would have been as toxic as the maternal. The blood of infected cattle
was filtered through filters made of unbaked porcelain and having very
fine pores which allowed only the blood fluid to pass, holding back
both the blood corpuscles and the rods, and such filtered blood was
found to be innocuous. It was further shown that the rods increased
enormously in number in the infected animal, for the blood contained
them in great numbers when but a fraction of a drop was used for
inoculation. Attempts were also made with a greater or less degree of
success to grow the rod shaped organisms or bacilli in various fluids,
and the characteristic disease was produced by inoculating animals
with these cultures; but it remained for Koch, 1878, who was at that
time an obscure young country physician, to show the life history of
the organism and to clear up the obscurity of the disease. Up to that
time, although it had been shown that the rods or bacilli contained in
the blood were living organisms and the cause of the disease, this did
not explain the mode of infection; how the organisms contained in the
blood passed to another animal, why the disease occurred on certain
farms and the adjoining farms, particularly if they lay higher, were
free. Koch showed that in the cultures the organisms grew out into
long interlacing threads, and that in these threads spores which were
very difficult to destroy developed at intervals; that the organisms
grew easily in bouillon, in milk, in blood, and even in an infusion of
hay made by soaking this in water. This explained, what had been an
enigma before, how the fields became sources of infection. The
infection did not spread from animal to animal by contact, but
infection took place from eating grass or hay which contained either
the bacilli or their spores. When a dead animal was skinned on the
field, the bacilli contained in the blood escaped and became mingled
with the various fluids which flowed from the body and in which they
grew and developed spores. It was shown by Pasteur that even when a
carcass was buried the earthworms brought spores developed in the body
to the surface and deposited them in their casts, and in this way also
the fields became infected. From such a spot of infected earth the
spores could be washed by the rains over greater areas and would find
opportunity to develop further and form new spores in puddles of water
left on the fields, which became a culture medium by the soaking of
the dead grass. The contamination of the fields was also brought about
by spreading over them the accumulations of stable manure which
contained the discharges of the sick cattle. The tendency of the
disease to extend to lower-lying adjacent fields was due to the spores
being washed from the upper fields to the lower by the spring
freshets. Meanwhile Pasteur had discovered that by growing the
organisms at higher temperatures than the animal body, it was possible
to attenuate the virulence of the bacilli so that inoculations with
these produced a mild form of the disease which rendered the
inoculated animals immune to the fatal disease. The description of
Pasteur's work on the disease as given in the account of his life by
his son-in-law is fascinating.
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