The spleen is also swollen and congested with blood, and the pulp is very high colored from the excess of hæmoglobin and other products of blood destruction. The muscles of the croup are usually the seat of visible lesions. There may be pallor, œdema and swelling, but not unfrequently there are blood extravasations varying in size from a pin’s head upward and giving a dark red aspect to the affected tissues. Under the microscope the affected fibres are seen to have lost their transverse striation and to have assumed a more or less granular or hyaline appearance. Next to the gluteal muscles, these changes are frequently found, in the muscles of the thigh (especially the rectus femoris, and triceps extensor cruris), and in those of the loins (psoas, ilio-spinalis, and longissimus dorsi). Exceptionally the pectoral muscles are involved or even the abdominal muscles. A considerable straw-colored œdema may be found in the intermuscular connective tissue.
The red bone marrow primarily of the large bones of the limbs (femur, tibia, humerus, radius,) and less frequently of other bones, even of the vertebræ, is often the seat of intense vascular congestion and even of hemorrhage. The medullary matter is of a deep red or black color, and there is an abnormal accumulation of red globules in various conditions of growth and destruction (red nucleated corpuscles, fragments of corpuscles, colored granules). Dieckerhoff considers the condition one of osteomyelitis, but it seems to be rather a sudden, extraordinary exaggeration of the processes of blood metamorphosis. Neumann found that when the blood regeneration process is very active even the yellow marrow may be changed into red, and this throughout all the bones of the extremities.
The kidneys are usually the seat of congestion, and black spots of infarction, when the disease has lasted for twenty-four hours. In rapidly fatal cases they may appear normal. There may be enlargement of the kidneys with softening and granular degeneration of the renal epithelium in cases that survive for some days.
The bladder contains dark brown or red glairy urine of a high density and loaded with urea, hæmoglobin, etc.
The terminal portion of the spinal cord and the lumbo-sacral plexus, or some of its branches, are sometimes blood stained, or the seat of an exudate or surrounded by one.
Symptoms. In the regular type of hæmoglobinæmia in the horse the history of the attack is highly significant. The subject is in good working condition, he may be fat, or lean, but in either case the muscles are firm and well developed, diet has been liberal, embracing a large proportion of albuminoids, work has been constant up to within a day or two preceding the attack, when the animal has been left absolutely idle in the stall without any reduction of feed. Then finally it has been suddenly subjected to active exertion which demands vigorous muscular movement, and above all activity of the respiratory muscles and the heart. This exertion usually consists in riding under the saddle or going in harness, but may attend on casting in the stall, lounging in a ring, or in a playful run when suddenly set at liberty.
Severe Cases. The attack comes on early in the course of such exercise. The patient may not have gone more than one hundred yards from the stable or he may have traveled for half an hour or an hour, but the disease rarely shows itself after a longer period of work.
The horse which left the stable full of life and spirit, suddenly flags and hangs on the bit, the ears or head may drop, and one or more limbs usually the hind ones, are moved stiffly and awkwardly, or even stagger. He knuckles over at the fetlocks, drags the toes on the ground, flexes the joints imperfectly, the muscles appearing to be rigid and uncontrollable, or he crouches, the joints remaining semiflexed the animal in vain attempting to extend them. The patient trembles violently, sweats profusely, breathes deeply and rapidly and assumes a pinched, anxious, agonized expression of countenance. The heart beats tumultuously, the pulse (in 84 per cent. Friedberger and Fröhner) is accelerated to a variable degree, and the temperature is still normal (in 80 per cent. Friedberger and Fröhner), or rarely exceeds 101.5°F. There is often tenderness on percussion and sometimes even on manipulation over the loins, short ribs, and the croup, and pinching of the loins may cause wincing. The affected muscle or muscles (lumbar, gluteal, crural) are usually firm, hard and tender, they may be the seat of spasm or of œdema and paresis. These parts may, however, have their sensitiveness lessened and even punctures or electric currents may have little effect on them.
Soon the increasing muscular weakness is incompatible with the maintenance of the standing position, the bending of the limbs and crouching become extreme, the animal makes vain efforts to control the muscles and extend the joints, and helplessly drops to the ground. When down he moves his legs convulsively, but is unable to coördinate the muscular movements and all efforts to rise are unavailing.
The spasms and paresis may attack other parts of the body such as the pectoral region the shoulders and even the abdomen, but the earliest and most persistent disorder is usually in the divisions of the lumbo-sacral plexus affecting the supra or sublumbar muscles, the gluteals, the patellar (triceps,) the adductors and the abductors. The caudal muscles are exceptionally involved. In a series of ten cases Bouley noticed that the left hind limb was always the first paralyzed (evidently a simple coincidence).