The entrance of the microbe by wounds must always be counted on, and explains the casual inoculations, by bites of dogs, insects, worms, by barbed wire fences, by wounds with horns, tusks, or feet, by nails, etc., and in winter by hard, woody aliment scratching the lips, mouth, fauces or pharynx. Shedding of teeth, diseased teeth or gums, and everything that causes abrasion of the alimentary mucosa must be admitted into the list of causes. Infected traumatisms of any kind, like intratracheal and intravenous inoculations usually prove fatal, while infection by ingestion is not necessarily so. The pathogenic potency appears to be impaired in the stomach or intestines.
Symptoms. These vary widely according to the subject, the seat of infection and the violence of the attack. They may be classed under three principal heads: superficial, thoracic and intestinal, and in addition into acute and chronic cases.
In the superficial, external or cutaneous form there is usually a sudden onset with high fever (104° to 107° F.), accelerated pulse, (70 to 90), and breathing (24 to 50), anorexia, suspended rumination, muscular tremors or shivering, staring coat, dry, hot muzzle, burning of ears, horns and hoofs, suppression of milk, and more or less stringy salivation. The visible mucosæ are of a deep red or violet tinge, and the patient will often remain apart by himself when the herd has moved elsewhere. Soon there develops a tense, hard, hot, painful swelling of the intermaxillary space, tongue, throat, neck, dewlap or elsewhere, amounting to perhaps six inches in thickness, extremely resistant and not usually indented on pressure with the finger. The breathing becomes stertorous and deglutition difficult or impossible. The mouth is hot and filled with tenacious saliva, and the tongue may hang pendant while on its borders and lower surface are projections of the mucosa swollen by infiltration, yellowish and semi-transparent, or blood-stained. At other points petechiæ are more or less abundant.
Death may take place from pharyngeal obstruction or closure, or as the disease advances, there may be indications of implication of the viscera, of the chest or abdomen: encreasingly difficult breathing, a mucous or suffocative cough, colicy pains, tenesmus, and the passage of moulded glazed fæces, of pseudo-membranous casts, or of profuse liquid stools. The animal may move the hind feet uneasily, lie down and rise alternately, may remain persistently recumbent until death, or he may stand up until he falls to perish of asphyxia. Death may occur in six hours, or may be delayed four days.
In the thoracic form the extreme hyperthermia is complicated by early lesions in the lungs, while the muscular or cutaneous ones are omitted or deferred. So long as the lesions are confined to the chest, they are betrayed by hurried and even oppressed breathing or dyspnœa, a frequent, moist, suffocative cough, persistent standing to favor respiration, and there are the percussion and auscultation indications of consolidated lungs or hydrothorax. The mucosæ are usually of a darker red, than in the external form, cyanotic indeed, and the peculiar asphyxial position, with legs apart, head extended, dilated nostrils and open mouth may be very significant. These symptoms are likely to be modified or supplemented before death, by those caused by intestinal or renal disorder. In the thoracic form in young animals death by suffocation may occur in a few hours, but more commonly the disease progresses slowly and a fatal result is not reached until the fourth day or even the eighth. This form is common in the deer, and less so in cattle.
In the intestinal or abdominal form the usual sudden onset and high fever, are complicated by inappetence, tympany, rumbling of the bowels, uneasy movements of the hind feet, perhaps twisting of the tail, looking at the flanks, and even lying down and rising. There is frequent, violent straining with the passage of fæces at first glazed, later streaked with blood, or mixed with pseudo-membranous casts, and very soon soft, watery, frothy and fœtid. These are usually black or reddish black from contained blood.
The urine may also be blood-stained.
Before death, complications on the lungs or skin will often come in to assist in diagnosis.
In the chronic and subacute types the lesions are often concentrated on the lungs, and there are a moderate fever cough, hurried breathing under exertion, dulness on percussion over limited pulmonary areas, blowing sounds, mucous râles, crepitations and more or less muco-purulent expectoration. These phenomena are all the more significant if complicated by digestive disorders, costiveness, fœtid mucous diarrhœa, tympany, or by the eruption of the superficial swellings.
Lesions. The swellings on or under the skin or among the muscles show extensive straw-colored exudations, colored at points with blood, with enlargement, infiltration and staining of the adjacent lymph glands. On the chest walls the sero-sanguineous exudate may extend from the root of the lungs, through the intercostal spaces to the skin in the breast, the axilla and behind. The tongue is often enormously swollen and black, charged with extensive blood extravasations in addition to the yellowish exudate. Along its sides and on its lower surface, the mucosa stands out in projecting masses of yellowish infiltration, which may show equally on the fauces, pharynx, larynx, trachea and bronchi.