If its action were that of a direct irritant the course of events in acute rheumatism could scarcely be what it is; for were such its mode of action all the fibrous textures and all the joints should suffer simultaneously and in a like degree; the inflammation would either soon decline or it would become more severe, and would frequently terminate iu suppuration; the heart would suffer in every case; and the small joints be as liable to suffer as the large. The gradual onset. of the rheumatic inflammation, its shifting character, its uncertain course, its tendency to select certain joints, its occasionally prolonged duration, and its gradual decline, can be best explained on the view that a fresh supply of poison is constantly being brought into play, that the local as well as the general symptoms of rheumatic fever are the result of the propagation of its poison in the system, and that the rheumatic process takes place in the fibrous textures of the motor apparatus because it is in these that the rheumatic poison finds the nidus necessary to its vivification and reproduction. The joint troubles of rheumatic fever are, ou this view, the necessary result of the propagation of the rheumatic poison in the structures which are the seat of inflammation, and bear to the general febrile disturbance of that disease the same pathological relation that the local lesions. of the eruptive fevers hear to their general symptoms. In the erup tive fevers the distribution of the nidus varies both in situation and extent; it does the same in rheumatic fever. In scarlatina the skin and throat are the uidus; but it is not always equally distributed be tween the two; when in excess in the skin, there is an abundant erup tion and not much sore throat; when in excess in the throat, there is bad sore throat and not much rash. So in measles—the nidus has two seats, the skin, and the mucous surface of the respiratory tract; when concentrated in the skin there is an abundant eruption, and no serious chest complication; when concentrated in the respiratory organs the eruption is scanty, and the chest complications are serious. In rheumatic fever the niclus may exist in many joints or only in two or three; in the former case many joints suffer and the attack is severe ; in the latter few suffer and the attack is mild.
In the ordinary forms of malarial fever the poison finds its nidus in the blood; there is, therefore, no local lesion. In rheumatic fever the poison finds its nidus chiefly in the fibrous structure of the large joints. It is in these textures that its vivification and active repro duction take place ; it is on them, therefore, that its morbific effects are chiefly manifested. This localization of the uidus in a special structure imparts to rheumatic fever one of the clinical features of the eruptive fevers—general febrile disturbance plus a local lesion. As relapsing fever constitutes a sort of clinical link between the eruptive fevers and the malarial, so rheumatic fever is a sort of clinical link between the malarial fevers and the eruptive. The absence of a local ized nidus imparts to relapsing fever one of the characteristic features of malarial fever—the tendency to relapse ; the presence of such a nidus in rheumatic fever gives it one of the features of the eruptive— a local lesion.
2. The Local Inflammation is Limited in the Joints Almost Entirely to such Fibrous and Serous Textures as are Associated with Active Move ment, and in the Heart to the Left Side.—The structures which go to form a highly developed joint such as suffers in acute rheumatism are the cartilaginous ends of the bones, a sac of synovial membrane investing these and reflected over the inner surface of the fibrous capsule, the ligaments which bind together and prevent undue move ment of the ends of the bones, the tendons of the muscles which move the joints, many of which run in grooves or sheaths having a lubri cating surface similar to that which exists in the joint, and the mus cles themselves without which the joint structures would be useless.
All the structures here enumerated are necessary to the formation and functional completeness of a freely mobile joint. But they do not all equally suffer when that joint is the seat of rheumatic inflam mation. It is on the fibrous and serous structures—the muscles, ten dons, ligaments, and the lining membranes of the joints and tendinous sheaths—that the action of the rheumatic poison is most manifested.
The symptoms of acute rheumatic inflammation of a joint are pain, swelling, and redness; and the more acute the case the more marked these symptoms. Pain is the evidence of inflammation of the fibrous textures. Swelling results from inflammation of, and effusion into, the sac of the synovial membrane; redness occurs only in cases in which the inflammation is sufficiently severe to cause hypewemia of the vessels of the skin; it is, therefore, more common in joints like the knee and wrist in which the inflamed structures are near the surface than in those like the hip and shoulder in which they are more deeply seated. When considering the question of the seat of rheumatism we saw that the muscles participated in the morbid process. It is in them and in the fibrous ligaments and tendons that the morbid process first shows itself; aching tenderness of the limbs and pain in the joints precede swelling; and the question naturally arises whether the inflammation of the synovial membrane may not, instead of being primary, be due to the extension of the inflammatory process to it from the contiguous fibrous textures. There can be no doubt that synovial membrane is very susceptible to inflammation, and that disturbance originating in the fibrous structures of a joint readily extends to it—witness the effusion which follows a strain. We shall by and by see reason to believe that inflammation of the lining and investing membranes of the heart is secondary to prior inflammation of the subjacent fibrous textures of that organ.
3. The Action of the Rheumatic Poison. is Coyined Almost Entirely to those of a Particular Age.—The age of liability to rheumatic fever is from fifteen to fifty. This immunity of the very young and very old can be accounted for only in one of two ways ; either the rheu matic poison does not enter their systems, or having entered it does not act. The former is a position which cannot be maintained ; for there is no reason why an agency which may gain entrance to the system at twenty or thirty years of age may not equally gain entrance at ten or sixty; the portals of the system are as free and as open at• the one age as at the other. The second is a position which may reasonably be maintained, for there is distinct evidence that some poisons may, under certain circumstances, be introduced into the system without producing effect. We know, for instance, that a per son who has not been vaccinated and has not had small-pox cannot. be exposed to the poison of that disease without almost certainly taking it. But we also know that, having once suffered, lie may be constantly exposed, and may even have the poison directly introduced into his system without again suffering from its action. So with each of the eruptive fevers•one attack confers, as a rule, immunity from the future action of its poison. Here we have adequate proof that a poison, and a very potent one too, may gain entrance to the system without producing any effect on it.