Fuller and others have endeavored in studying this question to distinguish between acute and subacute rheumatism. But inde pendently of the difficulty, nay the impossibility, of drawing a dis tinct line of demarcation between them, there is no pathological reason for doing so. Acute and subacute rheumatism are merely different degrees of severity of the same disease. That the heart is more apt to suffer in acute cases is no doubt true, but this implies no pathological difference between them and subacute cases in which this tendency is less marked.
A study of the statistics bearing on this point leads to the conclu sion that we are very near the truth when we say that, in the course of acute and subacute rheumatism, recent cardiac inflammation occurs in about thirty per cent., or in nearly one case in three. But such a general statement is bald and to some extent misleading without the additional statement that as years advance the tendency to such com plications diminishes.
Three facts are specially prominent in the history of rheumatic inflammation of the heart: 1. It is most common in young people; 2. It is more apt to occur in acute than in subacute cases of rheu matic fever; 3. It is limited to the left side of the heart.
No theory of rheumatism is satisfactory which does not explain these very striking facts.
1. The Heart is Specially Apt to Suffer in Young People.—This is a fact which has been observed and commented on by most writers on the subject. Dr. Peacock gave it as the result of his observations on 233 cases of acute and subacute rheumatism, that of those under twenty-one years of age 33.3 per cent. suffered from recent cardiac disease, while of those over forty only 16.6 so suffered; showing that the occurrence of cardiac complication is much more to be appre hended in young people than at more advanced ages. This accords with general experience. What is the explanation of it? We have seen that rheumatism is essentially a disease of adoles cence and early manhood, and that the textures which suffer most are the fibrous and serous tissues of the large joints. The tendency of a given portion of fibrous or serous tissues to be affected by the rheu matic poison is directly as its functional activity. Hence the ten dency of the disease to attack the large joints. Adolescence and early manhood are the periods of life at which the functional activity of the textures which suffer is at its height; hence rheumatism is most common in young people. Applying the same reasoning to the case
of the heart, we find in it an adequate explanation of the fact which we are now considering, that that organ is more apt to be the seat of recent rheumatic inflammation in young people than in those of more mature years. Muscular exertion increases the force and frequency of the heart's action. The more work the voluntary muscles are called upon to do, the greater is the demand for blood in them, and the greater the force and frequency of the heart's action. In other words, the voluntary muscles and the muscles of the heart work hand in hand; functional activity of the former necessitates functional activity of the latter. In this physiological fact we have the explana tion of the pathological one which we are now considering. Rheu matism of the joints is most common in youth because youth is the time at which these structures enjoy the highest degree of functional activity. Rheumatism of the heart is most common at the same age, and for the same reason. Sudden and rapid movements, involving correspondingly sudden and rapid increase in the force and frequency of the heart's action, are more frequent before than after the age of forty. Before that age the heart's structures are, therefore, subjected to greater and more frequent calls than they have to bear in more mature years, and must be ready to meet them. With the decreasing functional activity of advancing years comes also diminished sus ceptibility to the action of the rheumatic poison.
It is a clinical fact that the age of susceptibility to the action of the rheumatic poison is from fifteen to fifty. It is a physiological fact that the tissues on which that poison acts have a higher degree of functional activity during the earlier than during the later years of that period. It is a pathological fact that the tendency of a given portion of fibrous tissue to be affected by the rheumatic poison is directly as its functional activity. It follows that the textures of the heart ought to be more subject to rheumatic inflammation in youth than they are- in more mature years. And all observation shows that they are so.