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 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 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.
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).