In any case it must be accepted that the debility and impaired local innervation, nutrition and function, that attend on the exposure to cold and toxins must be looked on as potent contributing causes. The predilection of the swellings for dependent parts (limbs, venter, face) shows the influence of gravitation and congestion. Whether there is present any special microbe which has yet eluded discovery, but which is the main pathogenic factor, must be left to the future to decide.
In cases that appear to be due to cold or chill alone, the disease is held to be primary; in those following on another affection, secondary.
Among the diseases on which petechial fever supervenes as a secondary affection contagious inflammatory affections of the lungs and air passages hold a bad preëminence. Strangles, influenza and contagious pneumonia, about in the order named, are especially causative factors or occasions of petechial fever. Among the other affections on which it supervenes may be named pharyngitis, abscess of the nasal sinuses, hepatic, renal and other internal abscesses, acute coryza, laryngitis, or bronchitis, enteritis, abortion, aggravated grease, suppurating wounds of the skin, infective abrasions by harness, suppurating sores after firing, infective arthritis with open joint, amputation of the tail, and castration.
Lesions. In certain cases these may be largely confined to petechiæ and slight blood extravasations, which are distributed very generally throughout the tissues, but show especially in the skin, subcutis, mucosa and submucosa of the nose, eyes, pharynx, guttural pouches, larynx, trachea, bronchia, mouth, stomach, intestine, bladder, vagina and womb; also in and on the lungs, pleura, pericardium, heart, liver, spleen, kidneys, peritoneum, pancreas, ovaries, bones, lymph glands, brain and nerves. The largest extravasations are liable to be in the softest tissues, and in the lungs they may reach the size of the closed fist, though usually they vary from a mere spot up to this. The spleen is sometimes engorged even to rupture. Beside the extravasations, and associated with them in position, and probably largely as an effect of them, there is more or less serous effusion infiltrating the tissues, congestions, suppurations, degenerations, and necrotic changes.
The skin, if white, and the dark skins on section, are seen to be marked by petechiæ. The cutaneous swellings may appear on any part, commencing with nodular thickenings varying in size from a pea to a walnut, and merging together into extensive elevated areas terminating abruptly at their margins in the smooth skin. The larger and more persistent engorgements settle on the lower aspect of the body and other dependent parts like the limbs and face. Cracks, oozing, deep fissure, and extensive sloughs are not uncommon. When the skin is incised it shows serous infiltration and thickening, with spots and patches of blood extravasation. The subcutaneous connective tissue is similarly infiltrated and discolored, and often in the limbs, face, and under the breast, sternum and abdomen so as to form a tremulous gelatinoid cushion of several inches in thickness. The capillaries may be distended to more than 20 times their normal calibre. The exudate may extend deeply between the muscles, and sloughs may lay these freely open and invade their substance. The muscular tissue is mottled with petechiæ, and apart from these it is pale, yellow, or grayish, having to some extent undergone granular or fatty degeneration. Detachment of the perforans and perforatus from their insertions is occasionally met with.
The nasal mucosa may show only petechiæ and circumscribed blood staining, but in fatal cases it is more likely to present extensive blood extravasations involving it may be the whole mucosa, and narrowing the lumen almost to complete occlusion. Sloughing is not rare, and the resulting ulcers may extend into the subjacent tissues, so as to penetrate the septum nasi or the thin plate of the turbinated bone.
The buccal mucosa and submucosa are often involved in common with the skin of the lips, cheeks, and intermaxillary space, the tissues being involved in one common infiltration of blood and serum. In some cases circumscribed necrosis and ulcerations are formed.
In the pharynx and larynx infiltration of the mucosa and adjacent parts of a deep blood red, with or without ulceration, causes serious narrowing of the passage, that on the vocal cords threatening suffocation. Suppuration of the pharyngeal glands and guttural pouches is not uncommon. Alimentary matters are frequently found in the larynx, and bronchia.
Beside the petechiæ and hæmorrhages in the lungs, œdematous infiltration in dependent parts, hepatization, abscess, and limited areas of necrosis are met with. The pleural sacs often contain a sanguineous effusion.
The stomach and intestines are usually more or less mottled with petechiæ involving mucosa, serosa or muscular coat; they are raised in rounded or irregular elevations by œdemas; or they are the seats of more or less extensive and even perforating ulcers. The contents of the bowels may be deeply discolored by the escaping blood.