THE SEAT OF RHEUMATISM.
Though some difference of opinion is found among old authors as to the exact seat of rheumatism—Latham, for instance, regarding the lymphatics, and Carmichael Smyth the muscles, as being specially involved—the malady is nowadays generally believed to have its seat chiefly in the fibrous and serous tissues.
And there is good reason for this belief. The rheumatic poison is found to exercise its action on, and almost exclusively on, particular organs and textures in which these tissues predominate, and which seem to have no other feature in common. The joints, muscles, and heart are the parts chiefly involved. In the case of the joints, it is not the osseous, but the fibrous and serous, elements—the capsules, ligaments, tendons and tendinous sheaths, and the synovial mem branes, which suffer. So with the heart; the white fibrous structure of the rings and valves and the serous investing membrane suffer much more than the muscular substance.
Fibrous or serous tissue appears to be requisite to the action of the rheumatic poison and to the development of rheumatism. But all fibrous and serous textures are not equally apt to suffer. The periosteum is a fibrous membrane, and a most abundant one; but it suffers seldom. The Jura mater is so too, but it is rarely the seat of rheumatism. The liver, spleen, kidney, and uterus have much fibrous tissue in and around them; but the membranes which this fibrous tissue forms do not suffer as do the fibrous textures of the joints and heart.
Then there are many joints which enjoy a comparative immunity from the disease. The small joints of the fingers are not often af fected; the small joints of the toes more rarely still. One seldom meets with true rheumatic inflammation of the articulation of the lower jaw, or of the joints of the atlas and axis. And I never saw, or heard of, a case in which the articulations of the ribs were involved. And yet all these joints have ligaments, and fibrous and serous tis sues. The pleura, peritoneum, and arachuoid are serous membranes; but they do not suffer as the pericardium does. With all these ex ceptions before us we cannot, without hesitation, accept the view that rheumatism is essentially a disease of the fibrous and serous tissues.
It is only a part of these tissues which shows a special susceptibility to the action of the rheumatic poison. The fibrous membranes which surround the brain and spinal column, the fibrous membrane which covers the bones externally, and those which invest and give support to the liver, spleen, kidneys, and uterus, far exceed in quantity the fibrous textures of the large joints and of the heart; and yet, for once that rheumatic inflammation occurs in any one of these membranes it occurs many hundred times in the ligaments of the large joints.
The serous investing membranes of the brain, of the lungs, and of the abdominal organs, far exceed in extent the corresponding mem brane of the heart; but for once that any of them is the seat of rheu matic inflammation the pericardium suffers a hundred times.
In structure all white fibrous tissue is very much alike; but in function it varies much. The chief of its functions are (1) to support entire organs, (2) to bind together and give support to their constitu ent parts, (3) to control and regulate movement.
That which supports entire organs is instanced in the fibrous coverings and appendages of the liver, spleen, uterus, etc. That which binds together and gives support to their component textures, is instanced in ordinary connective tissue. That which is engaged in controlling and regulating movement, is exemplified in the fibrous textures of the joints. It is this last form of white fibrous tissue which is specially involved in rheumatism.
One of the chief functions of serous membrane is to facilitate movements. In some organs which are provided with a serous in vestment the movements are so slight that the membrane lies no very active function to perform in this way. The only serous membranes engaged in really active work of this kind are the investing membrane of the heart, and the lining or synovial membranes of the larger joints, which in function are to be regarded as serous membranes.