clear as to the specific diseases of animals, yet there is the
strongest presumption that nearly all great plagues that attacked
indiscriminately animals and man were of this nature. Thus, the plague
of murrain, with boils and blains breaking out on man and beast, in
the days of Moses, was probably of this kind (Gen. ix. 3.); also that
which at the siege of Troy extended from animals to man, and many
later epizoötics in all parts of the world. No infectious disease of
man and animals, with the single exception of tuberculosis, has been
more widely diffused, and none can be considered as more cosmopolitan.
Heusinger, in his classic work on _Milzbrandkrankheit_, traces the
ravages of the disease from the highest to the lowest latitudes in the
northern and southern hemispheres and in the Old World and the New. He
adduces outbreaks in Siberia, Astrakan, Lapland, and Finland, in
Russia, Prussia, Poland, Silesia, Bavaria, Holland, Belgium, France,
Spain, Portugal, Italy, Switzerland, Austria, Hungary, Greece, Turkey,
Egypt, East and West Indies, {927} North and South America, etc. We
can now add all the great English, French, and other European colonies
not included in the above (South Africa, Australia, New Zealand,
Algeria, etc.), together with China and Japan. We find, moreover, that
the disease is always most prevalent where agriculture is in its most
primitive condition, so that there can be little doubt of the
prevalence of the affection in the less-civilized countries as well.
But while the disease is prevalent in all parts of the world, its
ravages are largely subordinate to the nature of the soil. Wherever
this is close, impervious, marshy, or charged with an excess of
organic matters, the gaseous emanations of which drive out most of the
oxygen, the anthrax-germs, once introduced, tend to be preserved
indefinitely. Thus, in drying up basins with no natural drainage, on
lake and river margins, on deltas, in forests, in mucky, mossy, or
peaty soils, and on those that are habitually over-manured, the germs
of anthrax are especially liable to be perpetuated. It has long been
noticed that herbivorous animals are the most susceptible to anthrax,
while the purely carnivorous, and to a less extent the omnivorous,
have relatively a far higher resisting power. That the immunity is
largely due to the food is manifest from the experiments of Feser on
rats. Those fed on vegetable aliment contracted anthrax readily from
inoculation, while those kept on an exclusive diet of flesh
successfully resisted. The same rats that escaped while on a flesh
diet were afterward placed on a vegetable diet, and then perished
after inoculation.[1] Davaine found the same to be true of foxes kept
on meat and vegetables respectively, and inoculated with the virulent
blood of the allied disease, septicæmia. He found, moreover, that
guinea-pigs were much more susceptible to anthrax than rabbits.
One-thousandth of a drop of virulent anthrax blood invariably killed
the guinea-pig, while it left the rabbit unharmed.[2] Klein has never
found a rabbit insusceptible. It has recently been claimed that pigs
are insusceptible, but I have known of many instances in which the
offal of anthrax cattle, when devoured by pigs, has determined fatal
anthrax in the latter. Chickens too prove much less susceptible to
anthrax than the Herbivora. Inoculations made by Cohn and others
proved invariably unsuccessful, while Pasteur has showed that they can
be infected easily after the body has been cooled by partial immersion
in cold water.[3] Pasteur attributes this immunity to their normally
high temperature, yet rabbits, sheep, pigs, wolves, and foxes, though
maintaining a correspondingly high temperature, are still subject to
anthrax. Even the herbivorous mammal suffering from acute anthrax
fever has its temperature raised to that of the chicken, yet the
disease progresses none the less surely to a fatal result. Again,
anthrax liquids inoculated under the skin of a fox proved harmless,
while if thrown into the warmer peritoneal cavity they proved fatal.
It may well be suspected that the relative insusceptibility of
chickens is in part due to the large amount of animal food consumed by
them, and that the chilling process increases the receptivity by
deranging sanguinification and nutrition.
[Footnote 1: _Wochenschrift f. Thierheilkunde und Thiersucht_, Nos. 24
and 25, 1879.]
[Footnote 2: _Rec. de Med. Vet._, Mar. 15, 1879.]
[Footnote 3: _Ibid._, Mar. 15, 1880.]
The insusceptibility to anthrax is often characteristic of certain
individuals or families or of the animals living in a particular
district. Thus, Chauveau found that some French sheep, and nearly all
Algerian ones, {928} resisted inoculation with a moderate amount of
anthrax virus, while the introduction of a maximum amount proved fatal
to these as to others. In the same way, it is often noticed that
animals living in an anthrax region escape the evil effects of the
poison, while strange animals brought in either fall ready victims or
for a time do badly until they have become habituated to the locality.
In view of the subsequent protective effect on the system of a first
and non-fatal attack of anthrax, it is probable that all these
examples of immunity in the Herbivora depend on a previous mild attack
of the same disease or on the extinction of the more susceptible
races. Even in the case of the animals that do badly on first coming
into an anthrax district, and recover better health with immunity
later, we may well infer that a mild form of the anthrax infection has
been passed through.
ETIOLOGY.--The one essential cause of anthrax is the introduction into
the system of a specific bacteridian germ (bacillus anthracis or its
spores). This is not, as a rule, carried far on the atmosphere, but
demands for its propagation contagion, immediate or mediate. Unless,
therefore, it meets in the soil the conditions necessary to the
preservation and propagation of the germ, it is transmitted with some
uncertainty from animal to animal, and thus the disease does not
spread widely and rapidly, like an ordinary plague, but tends to
become localized in particular districts as an enzoötic.
But its dangers are none the less real nor its existence less to be
dreaded. In predisposed localities, where the disease-germ has gained
a footing, the animal mortality may exceed that caused by the great
plagues, while the risk to human beings is incomparably greater than
from any other acute infectious disease of the lower animals. Thus, in
San Domingo, in 1770, 15,000 people perished in six weeks from eating
the carcases of anthrax animals, and the mortality was only arrested
when the meat was legally interdicted. In the worst anthrax years on
some of the Siberian steppes as many as one-fourth of the whole human
population suffer from the malady. The prevalence and death-rate,
however, vary greatly in different localities and seasons. Sometimes
only one or two solitary cases of the affection are observed; at other
times the disease becomes moderately prevalent, but a lack of
virulence in the poison or a previously acquired insusceptibility of
the individual protects the great majority of the animals exposed,
while at others, still, the poison attacks nearly all exposed to its
contagion.
The animal products that mainly convey the disease are the blood, the
liquid exudations, portions of the diseased carcase, and the bowel
dejections. The virus is most potent when derived from an animal still
living or only recently dead, yet under certain conditions (with
spore-formation) it may long retain its virulence under the most
extreme changes of climate, temperature, dryness, and humidity.
Russian hides tanned in England or America frequently convey anthrax,
which is known especially as a tanner's malady, and wool and hair sent
from Buenos Ayres have repeatedly produced malignant pustule
(woolsorter's disease) in Britain and the United States. The preserved
scabs of malignant pustule have been often successfully inoculated on
the lower animals, so that, like other forms of poison, this seems to
be preserved indefinitely by desiccation.
The simple contact of the virus with the slightest abrasion will
suffice {929} to convey the disease. It has often been communicated
where no lesion of the epidermis could be found, yet the presumption
is that even in such cases the cuticle had been in some way wounded.
Eating the flesh of animals killed while suffering from anthrax has
often conveyed the disease. In an outbreak in Swineshead,
Lincolnshire, England, in 1863, I found a dog and a number of swine
suffering from eating the bodies of dead bullocks. In 1864 an East
Lothian (Scotland) farmer fed his pigs with the offal of a slaughtered
anthrax bullock, and lost nearly the whole herd. The carcase of the
bullock had been sent to market. About 1860 cattle, and even horses,
died yearly on a swampy meadow at Brighton, Mass. On one occasion the
owner, John Zoller, fed the offal of a dead bullock to his pigs, which
were speedily attacked with anthrax, and as speedily killed to save
their bacon (Dr. Thayer). Even when cooked the flesh is not always
safe. Of this we have the undoubted case in San Domingo above noticed,
the alleged death of 60,000 people in the vicinity of Naples from the
same cause in 1617 (Kircher), and the thousands that die on the
Russian steppes every anthrax year from eating the sick horses
(Rawitch). But in all these, and in the ever-recurring cases in which
families suffer from eating anthrax meat, there is the possibility, if
not the probability, of the contamination of the meat subsequently to
cooking by the knives, forks, tables, and dishes used. The San Domingo
slaves had few appliances for cleanliness, much less disinfection, and
the Tartars eat their meat from the same board on which it has been
chopped up raw.
In accurate experiments it has been found that the bacilli are
destroyed by a temperature of 145° F. maintained for five minutes, but
the spores are capable of surviving the boiling temperature for five
or even ten minutes. The varying power of resistance may be compared
to that of the green stalk of the pea and the dry flinty seed. The
first is destroyed by a very moderate heat, while the second will
sprout after having had boiling water poured over it. The resisting
bacillus-spores are never found in the living animal, but may be
developed in the blood and tissues after death, and may account for
the occasional extraordinary viability of the poison when exposed to a
boiling temperature.
Milk, though often used with impunity, conveyed the disease when
inoculated by Bollinger, and the same was true of the vaginal mucus.
Innocent in the early stages of the disease while the germs are still
localized, they become virulent after the bacilli swarm into the
blood.
Healthy men and animals often carry the poison, though themselves
insusceptible. The question of its conveyance by insects has been much
debated, but the constant occurrence of malignant pustule on the
uncovered parts of the body goes far to settle the question. Bourgeois
long ago noticed that it was most frequent on the face, hands, neck,
and arms, and rare on the trunk. In sixty cases recorded by A. W. Bell
of Brooklyn, all occurred on the face except two on the hands, one on
the wrist, and one on the forearm. The bite of a fly or mosquito had
in many of these cases proved the starting-point of the malady.
Bollinger has shown the presence of the bacillus in the stomach of
such flies as fed on flesh and blood (horse-flies, bluebottles, etc.),
and, together with Raimbert and Davaine, has produced anthrax by
inoculations with the stomachs, legs, and proboscides of these
insects.
{930} Surgical instruments occasionally convey anthrax. At
Cockburnspath, East Lothian, Scotland, a yearling heifer contracted
anthrax, and the whole herd was bled, commencing with the sick one.
Next morning seven were found dead, the disease in each case extending
around the fleam-wound. At Brunt, in the same county, a shepherd
skinned an anthrax bullock, and after washing and taking a turn among
his sheep, on the same day castrated several litters of pigs, all of
which perished. In St. Lawrence Co., N.Y., in 1870, a surgeon
inoculated himself while opening a vesicle on the hand of a farmer.
Harness, stables, stable utensils, vehicles, fodder, and litter are
frequent bearers of contagion. At Geneseo, N.Y., in 1877, three horses
and a cat died in midwinter after licking the blood from a stone-boat
which had conveyed the skin of an anthrax bullock to market. Green
fodder or hay harvested from ground formerly occupied by anthrax
victims or from their graves often convey the poison, but probably
only by the adherent earth and dust containing the anthrax-germ.
That the anthrax bacillus and its spores may be long preserved in
earth is abundantly proved. At Avon, N.Y., nine months after any cases
of the disease, the liquid leaking out on the river-bank near to the
grave of a victim of the year before was licked by six cattle, and in
two days they all perished. On the same pasture victims were seized
yearly for seven years, but with a rigid seclusion of these, their
products, and their graves the malady has finally disappeared. The
persistent deadly effect of some soils on animal life, apart from the
presence of the carcases, seems to show that in certain soils we find
the normal home of the anthrax bacillus, while the migration into the
animal economy is but an accident of its existence. The soils that are
especially subject to anthrax are the dense clays, the limestones, and
the rich alluvials. Among the essential conditions are the exclusion
of oxygen, excepting a limited amount bearing some relation to what is
found in the animal fluids, and the abundance of some alkaline agent
(lime, potash, soda, ammonia), so that the earth is either neutral or
only very slightly alkaline or acid. An acid vegetable infusion is
inimical to the germ, which soon disappears from such a medium. The
requisite paucity of air is found in all the dense, less pervious
soils (clays, etc.), in soils habitually waterlogged (swamps, deltas,
river-bottoms, low meadows, natural basins, drying lakes and ponds),
and in soils rich in decomposing organic matter (peat, alluvial,
over-manured). The antacid is often found present as lime or potash,
or is constantly being produced in the form of ammonia, etc. by
organic decomposition. Such places are known to farmers as "dead
lots," because no stock will live on them. The bacillus in the buried
carcase does not produce spores (Bollinger), though it may in the soil
at any temperature between 59° and 110° F. In the graves, therefore,
at a lower temperature, the poison can only be preserved by a
continuous generation of the bacillus.
Pasteur, who successfully inoculated the casts of earth-worms taken
from anthrax graves, attributes to these an important rôle in bringing
the germs to the surface. A more important agent, however, is probably
the rise and fall of water in the soil. By this means the bacilli and
spores are washed up toward the surface, and when the superficial
layers dry out they are easily carried by the winds. Hence it is that
anthrax is usually prevalent in late summer and when the soil is dried
and heated to its {931} greatest depth. Thus it is, too, that wet
seasons followed by specially dry and hot ones are, above all,
productive of anthrax in herds. Wet seasons fulfil the further purpose
of carrying off the germs into rivers and depositing them on the banks
or on inundated meadows, where after the subsidence of the flood the
disease appears, for the first time perhaps.
There is, however, good reason to believe that the effect of a warm
season is not confined to its influence on the soil and its germs. The
high temperature deranges the vital functions of the animal economy,
and, inducing a febrile disturbance, lessens the power of resistance
to the anthrax virus, just as the cooling of the warm-blooded bird
lays it open to infection. On this account, and because of the
frequently recurring electric storms, the hot dry season is especially
the season of anthrax. The hottest, driest autumns of Siberia always
coincide with the anthrax years, and in the last fifteen years in the
United States I have noticed the wide extension of anthrax whenever
the season has been unusually hot and dry. In Corsica the herdsmen
confidently pasture their stock in the close still valleys throughout
spring and early summer, but whenever the surface soil is dried out
they make all haste to remove it to the hills, well knowing that delay
means devastation and ruin.
Plethora is undoubtedly an important predisposing cause of anthrax,
and so is the alternation of cold nights with hot days. The febrile
condition induced in the animal economy is perhaps the main factor at
work in each case. Finally, youth is on the whole more liable than
age, but whether because of the greater receptivity of the growing
system and its tissues, or because it has not yet acquired some
immunity by exposure to the milder effects of the poison, is not
certainly determined. Sex is without influence.
It is not a little remarkable that the bacillus germ has not yet been
found in the placental liquids nor foetal blood of sheep, goats, or
rabbits, though swarming in that of the mother. Bollinger attributes
this to the action of the placenta as a "physiological filter"--a
conclusion seemingly at variance with the passage of the bacillus
through all the other animal membranes, including those lining the
mammary glands and the vagina. Two other possible explanations remain:
first, that the secretions of the uterine glands are inimical to the
bacillus; and, second, that the foetus, being in some sense a
carnivorous animal, possesses the immunity characteristic of
Carnivora. Bacilli have recently been found in the foetal guinea-pig.
The bacillus anthracis was first observed by Pollender and Branel in
1849 (Birch-Hirschfeld), but it was only publicly claimed as the cause
of the disease in 1855 by Davaine. Branel discarded Davaine's theory,
because blood in which he had failed to find bacillus produced anthrax
with bacillus in the blood of two foals inoculated. Later observations
by Bollinger and others have shown that cultures of bacillus can
always be made from such infecting blood, and that in most cases the
presence in the infecting blood of spherical bacteria can be
demonstrated by the microscope. That the bacillus is the true
pathogenic element is proved by the following facts: 1st. That the
bacillus is the only ectogenous, particulate, organized structure
constantly found in the anthrax blood and fluids; in cases in which it
is apparently absent cultures show its actual presence. 2d. After
cultivation in pork or beef infusion to the {932} hundredth generation
the virulence is unimpaired, though it must be assumed that all
non-organized poisons derived from the infected animal body must have
been diluted or decomposed to extinction. 3d. That filtration of the
anthrax liquids through a plaster or other efficient filter renders
the filtrate innocuous, while the solids retained in the filter remain
infecting (Chauveau, Bert, Toussaint). 4th. That the clear filtrate
injected to excess killed by virtue of its contained chemical products
in twelve hours, while the solids filtered out and containing the
bacillus or its spores only killed after thirty hours.[4] 5th. Anthrax
blood from the living animal or one just dead, and destitute of
spores, when subjected to compressed oxygen (50 atmospheres), is
non-infecting (Bert). 6th. The same anthrax liquid, destitute of
spores, after boiling is completely innocuous. 7th. The same liquid,
if kept in a closed tube apart from oxygen for eight days, shows the
bacilli broken down by granular degeneration, and proves absolutely
harmless when inoculated in small quantity. 8th. The same sporeless
anthrax fluid when treated with absolute alcohol loses its virulence.
9th. The anthrax liquid which has been cultivated with free access of
air in a temperature varying from 25° C. (77° F.) (Klein, Löffler) to
41° C. (105.5° F.) forms spores, and then remains infecting, though it
may have been subjected to compressed oxygen, boiling for several
minutes, absolute alcohol, dilution with water, putrefaction, or the
exclusion of oxygen.
[Footnote 4: Bert, _Compt. Rend. de la Société Biol._, p. 355, 1879.]
The bacillus anthracis, as found in the blood and animal fluids, is in
the form of fine rods, straight (rarely bent or angular), motionless,
and 0.007 to 0.012 Mm. in length. Smaller forms are seen to be minute
ovoid or oblong bodies, and the smallest absolutely spherical
(micrococcus); but in all cases, as seen under the highest powers of
the microscope, they have clear-cut, even margins, linear or curved,
which easily distinguish them from the irregular normal granules of
the blood and tissues. Under the highest powers of the microscope the
bacillus is seen to be made up of a series of oblong (Koch) or cubical
(Klein) cells enclosed in one common sheath. This is rendered more
manifest if they are first swollen by the addition of water. The
motionless form of the anthrax bacillus is of especial value in
distinguishing it from the motile bacteria of putrefaction
(saprophytes).
Within the living animal body the development never goes aside from
these forms. The growth appears limited to micrococcus and bacillus
rods, while spores or bacillus threads are never found. This finds its
counterpart in the micrococcus poisoning caused by the inoculation
with the spores of common moulds (Grawitz); and in septicæmia also
micrococcus and bacillus forms only are found, the filamentous never.
When grown in organic infusions out of the animal body the
anthrax-germ develops from micrococcus or bacillus into a long,
branching, filamentous product, which in the presence of oxygen
develops into spores. Apart from oxygen or when the proper nourishment
of the bacillus is exhausted the protoplasmic elements within the
filamentous sheath undergo granular degeneration, and finally the
empty envelope disintegrates and disappears. The spores appear at
intervals in the protoplasm of the filament as clear, brightly
refrangent bodies, at first spheroidal, afterward larger and oblong.
Unlike the micrococcus and bacillus, {933} they do not stain. Under
favorable circumstances the primary cell is capable of forming one, or
if extra long, two spores (Koch, Klein). Cossar-Ewart claims to have
seen the formation of motile flagellate organisms aggregating
themselves into zooglæa masses, but as these were not found in the
carefully-conducted cultures of Koch and Klein, they are supposed to
have been aërial microphytes accidentally introduced.
The great tenacity of life in the spores in heat and cold, dryness and
wet, excluded from air and under several atmospheres of oxygen, in the
midst of putrefaction and in pure watery fluids, well accounts for the
persistence of infection in buildings and localities where the poison
has gained a foothold. In order to their destruction in a natural
manner it seems necessary that they should germinate and develop into
the anthrax micrococcus, bacillus, or mycelium. This germination may
take place in the presence of moisture, oxygen, and suitable
nourishment, whether in the soil, the animal body, or elsewhere, and
then the exhaustion of the aliment, the exclusion of the oxygen by
putrefaction, the submergence in a medium unfavorable to development,
or exposure to a very high temperature, may suddenly destroy the
poison.
There is reason to believe that a too free exposure to oxygen proves
destructive to the virulence, if not to the life, of the poison, and
thus in all porous, well-drained soils the anthrax poison, even when
introduced from without and concentrated by the death and burial of
many victims, soon disappears. This feature, which is common to many
zymotic diseases the germs of which live and multiply outside the
animal body (typhoid, yellow fever, tuberculosis, swine plague,
chicken cholera, diphtheria, etc.), offers countenance to the claims
of Buchner that he had by prolonged culture, in the presence of air,
metamorphosed the bacillus anthracis into a harmless mycrophyte, and
that, conversely, by continuous cultivation under the surface of a
suitable beef infusion he had changed the harmless bacillus subtilis
of hay into the deadly bacillus anthracis. Koch, Klein, and others
have discredited Buchner's results, on the ground that he had not, in
their opinion, taken due precautions against impure cultures, and that
his alleged transitions took place too abruptly; yet further
observation must determine whether he has been condemned too hastily.
The diminished virulence of Pasteur's attenuated virus, which is
unaffected by the next subsequent culture or by the formation of
spores, shows plainly enough that the bacillus anthracis is capable of
physiological changes under the influence of varying conditions of
growth, and that such changes are not at once undone by a return of
the former conditions.