A more simple and adequate explanation of this unfortunate dif ference is to be found in the fact that when the fibrous textures of a joint are inflamed they get perfect rest, and are this placed in cir cumstances favorable to complete recovery : while the fibrous textures of the heart not only get no rest, but, from the greater frequency of the heart's action, are called upon to do an increased amount of work. They are thus placed in circumstances which make complete recovery all but impossible.
Acute cases of rheumatism, in which the textures of the joints are smartly inflamed, in which there is a considerable amount of thick ening and effusion, and in which complete rest is given to the in flamed textures, are also those in which these textures are most fully and speedily restored to their natural state. In chronic cases in which the inflammation is slight, in which the patient continues to go about, and in which the inflamed ligaments and tendons do not get rest, these textures are more apt to be permanently thickened. E pressure were the agency which removed the effusion, it ought to disappear more speedily in these chronic cases than in the acute; for the act of locomotion supplies this factor, and would lead to speedy absorption of the effused products, and early restoration of the fibrous textures to their normal state. The long duration of the thickening and stiffness of the joints in such cases is to be explained in the same way as the persistent nature of the cardiac damage. Ab sence of rest leads to imperfect recovery and permanent injury.
It is difficult for a heart whose fibrous textures have once been thickened by inflammation, and still more so for oue whose endocar dial lining has once been roughened, to recover its normal condition; for the fibrous textures continue to be strained, and the roughened surfaces of the segments go on rubbing. Irritation is thus kept up after the primary inflammation has disappeared : the thickening of the fibrous textures becomes chronic, and fresh rheumatic attacks are apt to add to the mischief. With the advance of time the morbid change is ,apt to become more marked, the valvular segments to be come contracted and misshapen, the cardiac circulation to be more disturbed, the muscular walls of the heart to hypertrophy, and its cavities to dilate; and so the sufferer enters on a prolonged course of misery whose only termination is death.
It seems a simple statement of fact, clinical and pathological, to say that in rheumatic arthritis complete recovery is the rule, while in rheumatic endocarditis complete recovery is the exception. The statement is one which nearly every physician would indorse. Never theless it is not strictly accurate. It is bald, and misleading from its baldness. Everything which recovers in a joint may, and frequently does, recover in the heart. The structure in the heart which is apt to be permanently damaged is the endocardial lining, and this is the one structure which has no analogue in a joint. The pericardium corresponds in structure and function to the synovial membrane. The muscles of the heart have their analogue in the muscles of the limbs : the fibrous structure of the rings and valves resemble in struc ture and function the fibrous tendons and ligaments. The endo cardium alone has no analogue in a joint ; there is absolutely nothing in or about a joint which at all resembles it either in structure or function. Anatomically it is continuous with the lining membrane of the great vessels with which, and with which alone, it has struc tural and functional affinities. The changes which take place in it during the course of acute rheumatism do not result from the direct action on it of the rheumatic poison, but are produced by rubbing of the valvular segments consequent on rheumatic inflammation and thickening of the subjacent fibrous structure of the valves.
The difference in the ultimate results of rheumatic arthritis and rheumatic endocarditis is to be explained in two ways : 1. An inflamed joint gets complete rest, and is thus placed under conditions most favorable to recovery. An inflamed heart not only gets no rest, but beats more quickly than natural.
2. The structure in the heart which is the chief seat of permanent damage, the endocardium, is one which does not exist in a joint, and bears no resemblance to anything that does.