This affection was long confounded with anthrax proper, but was differentiated by the observation of Wallraff (1856), Boulit-Josse, Vernant, Pfisterer, Feser, and others and finally Bollinger in 1875 found the motile bacillus. Arloing, Cornevin and Thomas (1879–84) thoroughly substantiated this position, and devised a method of immunizing by inoculation. Feser had however seen the motile sinuous rods in the exudate as early as 1860, and even produced the disease by the inoculation with mud from infected Alpine pastures.
Geographical distribution. Emphysematous anthrax prevails in limited areas, and particular buildings in Europe, Asia, Africa, Australia and America, and in all climates from the tropics up to the sub-Arctic. It is however most prevalent in spring, summer and autumn. It is not uncommon at the breaking up of the winter snows. It is especially prevalent on damp, undrained land or on such as has dried up in the heats of summer, and has become less prevalent in many localities in connection with drainage and careful cultivation.
Animals susceptible. The disease is especially common in young cattle, from three months to four years of age. Calves fed on milk are rarely attacked, being in a sense carnivorous and sometimes immunized by toxins from the dam. Cattle over four years usually escape, having already become immune if kept in an infected locality. If brought from a noninfected place they are, at any age, as susceptible as the young. Sheep and goats contract the disease only exceptionally, but like the Guinea pig are easily infected by inoculation. Horses, asses and white rats have only a circumscribed swelling in the seat of inoculation, and foals and buffalo calves sometimes contract it casually. Carnivora and omnivora, (dog, cat, pig, bird, man), and the rabbit are virtually immune.
Immune animals may, however, be made to succumb under special treatment. In a rabbit inoculated at the same time with the microbe of black quarter and proteus vulgaris, or micrococcus prodigiosus, or if injected with a little lactic acid, the disease develops promptly and fatally. Over-exertion, producing sarco-lactic acid will also lay the system open to attack. The reduction of the vitality and resistance of the muscle of the rabbit by a contusion, bruise or lacerated wound, or by injecting it with acetic acid, potash salts, alcohol, or common salt, will render the inoculation pathogenic. Again, the introduction of the black quarter microbe into the aqueous humor of the rabbit, where there are so few defensive leucocytes, entails an active proliferation and a fatal result.
Causes. The essential cause of emphysematous anthrax is a rod-shaped germ, variously known as bacillus anthracis emphysematosa, bacillus Chauvæi, Rauschbrand bacillus. This is a rod-shaped microbe, with rounded ends, found singly or connected in pairs, or very short filaments. The bacilli are 3 to 10µ long, by .5µ broad, or when sporulating, 1.1 to 1.3µ. They form spores even in the body of the affected animal, often assuming a club shape by reason of the spore formation near one end. If the spore develops in the center they appear fusiform. They take aniline colors readily, and iodine slightly, assuming in the last case a violet tint. The staining is unaffected by heating in melted balsam. The bacillus grows readily in ordinary culture media, (peptonized gelatine, bouillon, milk, etc.), but, being anærobic, only under the surface in stick cultures, or under a neutral gas or vacuum. It grows most rapidly at a temperature of 36° to 37° C. but also as low as 15° C. The bouillon at 37° C. becomes milky and opaque in 24 hours, and later it clears up, the microbes being precipitated as a free white powder. In gelatine cultures liquefaction takes place in three days, and in twenty days the whole mass may be dissolved and the microbes precipitated to the bottom. Spores may form in the living body and as these are set free by the granular degeneration of the bacilli, the virulent exudate and cultures usually show the microbe in three different forms: 1st; the straight, motile bacillus of one thickness throughout its whole length; 2d; club-shaped or fusiform bacilli, the thickening of the end or median part being due to the endogenous formation of a refrangent spore or spores; and 3d; the free refrangent spores which have been set free by the degeneration and destruction of the sporulating bacilli. The microbe is not found on the surface of the living animal, nor in the blood, for in both the supply of oxygen is too abundant; it forms its colony under the skin, in the tissues, and above all, in the mass of extravasated blood or gelatinoid exudate which its irritation has produced and where air is lacking.
The most marked differential features of the microbes of anthrax and emphysematous anthrax are contrasted in the following table:—
| Bacillus Anthracis. | Bacillus of Emphysematous Anthrax. |
|---|---|
| 5 to 20μ × 1.25μ. | 3 to 10μ × 0.5 to 0.6μ. |
| Ends square or cupshaped. | Ends rounded. |
| Occurs singly in the living body. | Often in pairs or threes in body. |
| Long filaments in cultures. | No long filaments. |
| Nonmotile. | Motile (sluggishly). |
| Ærobic. | Anærobic. |
| No spores formed in living body. | Sporulates in living body. |
| Sporulates in air; in surface soil. | Sporulates in vacuo; deep in soil. |
| Bacilli only. | Bacilli; sporulating bacilli; free spores. |
| Multiplies freely in blood stream. | Dies in blood stream unless charged with toxins. |
| Rabbit very susceptible; man less so. | Rabbit, pigeon and man immune. |
| Produces no gas. | Gas producing. |
| Inoculation swelling very restricted. | Inoculation swelling very extensive. |
| Bacillus destroyed by putrefaction. | Not destroyed by putrefaction. |
Resistance of bacillus of black quarter to physical and chemical agents. The microbe is possessed of great vitality. Thoroughly dried at a temperature of 95° F. it retains its virulence. The spores may be preserved indefinitely in dry soil, buildings, fodder, litter, harness, etc. Cold is equally harmless to it. It has been exposed to a temperature of 98° F. below zero without losing its virulence. Its virulence is lessened by exposure for an hour to 139° F., and it is sterilized at a temperature of 212° F. for twenty minutes. The dried spores are virulent after six hours of the boiling temperature but are sterilized at 230° F. if maintained for the same length of time. Diffused in water the virus is sterilized in thirty-five minutes at the boiling temperature. Some waters at ordinary temperatures destroy the virulence in twenty-four hours; others not for many months. It is destroyed by the more potent disinfectants, mercuric chloride (1:1000), silver nitrate (1:100), acid salicylic (1 to 2:100), acid carbolic (2 to 4:100), copper sulphate (20:100), boric acid (20:100), muriatic acid (1:2). Quicklime, copperas, zinc chloride, sulphuric acid and an alcoholic solution of phenol have proved unsatisfactory.
In clay soils, hard pans, waterlogged soils, and in some that are over manured so that the atmospheric air is excluded, it may be preserved indefinitely. Feser, Gotti and others have produced the disease by inoculating with the washings of infected marshy soils, and this is doubtless a common source of casual cases of the malady.
Accessory causes are important. The predisposing influence of lactic acid, of other organic acids, and of overwork have been already named. Potass salts, alcohol, common salt and the products of proteus vulgaris, or micrococcus prodigiosus increase the susceptibility. Low condition, debility, or suddenly induced plethora have a similar influence. Sudden changes of weather, chills, and particularly the access of hot weather in spring, when the animal is changing its coat lays, the system open to attack. Youth, after the period of suckling, and under three years old, seems to increase the predisposition, though this is largely the result of the absence of a previous exposure. Then impermeable, clay, wet, marshy soils, or those charged with organic matter are conditions of the presence of the microbe. It often appears in spring in connection with the melting of the winter’s snows, the occurrence of freshets, and the washing out of soil infection which would otherwise remain buried. Also in advanced summer and autumn when swamps, ponds, basins, deltas, river bottoms, etc., are drying out and furnishing pasture. Pease records its great prevalence in the rainy season in the swamp districts of the Punjab and North Western provinces of India, and the same is largely true of our Gulf coast states.