If his statement be correct the fact which it indicates strongly supports his view of the mode of production of endocarditis.
If, on the other hand, it can be shown that lactic acid, so far from being destroyed, is actually produced in the systemic circulation, then Dr. Richardson's statement is proved to be erroneous, and his position untenable. A careful study of the question would indicate that such evidence does exist.
During the process of digestion sugar is formed. From the di gestive organs it passes into the circulation. Part of it is taken up by the liver, and converted in that organ into glycogen, in which form it is stored up in the liver. During fasting it again becomes transformed into sugar, and as such passes into the circulation. Like all non-nitrogenous substances, sugar is finally transformed into carbonic acid and water. In the course of this transformation there are produced various intermediate substances. One of these is lactic acid. The question which we have to consider is, where does this formation of lactic acid take place? Our knowledge on this point has considerably advanced since Richardson made his experiments; and it is now known that lactic (sarcolactic) acid is one of the meta bolic products of muscle. In the passive state muscle has a feebly alkaline reaction; but during contraction it becomes acid. This al tered reaction is of course due to the formation of an acid in the muscle; and du Bois-Reymond showed that the acid formed is sarco lactic acid. His observations were confirmed by those of Heidenhain, who found that up to a certain point the quantity of acid produced incr3ased with the amount of work done by the muscle. It has been maintained by some that the acid reaction of the active muscle is partly due to the formation of phosphoric acid. Be this as it may, there can be no doubt from the observation of du Bois-Reymond that it is at least partly due to the presence of sarcolactic acid, and that that acid is a metabolic product of muscle and is formed during its contraction. Richardson's statement that the acid is formed in the pulmonary and destroyed in the systemic circulation is thus demonstrated to be erroneous.
(b) The second proposition, that lactic acid could not exist in the blood without producing endocarditis, is equally at variance with facts and experience.
"It is absurd," says Richardson, "to assume that ounces of an acid of the producing series thrown off from the skin of a sick man should not be derived from his blood." Lactic acid is thus thrown off from the skin in acute rheumatism. If Dr. Richardson's proposi tion were correct, endocarditis should be an invariable complication of that disease. But it occurs only in a minority of cases, about 30 per cent. Lactic acid, therefore, exists in excess in the blood, with out producing endocardial mischief, in about 70 per cent. of the cases of acute rheumatism which occur.
(c) The third proposition, that lactic acid acts as a local irritant to the endocardium, is in keeping with the second; but is equally in consistent with evidence, and is refuted by the same arguments. If ' lactic acid be the rheumatic poison, and if it exercise a direct irritant action on the endocardium, that membrane should give evidence of irritation in every case of acute rheumatism; but it does so in only a minority. Again, if this were its mode of production the inflam mation should be diffused over the whole surface of the endocardium; but it is limited to the valves, and even in these is found only on one side—in the aortic valve only On its convex surface, and in the mitral only on its auricular.
The pathogenesis of rheumatic endocarditis ought not to, and can not rightly, he considered apart from that of the joint inflammation in connection with which it occurs. The poison which gives rise to the one gives rise to the other; and its mode of action in the pro duction of inflammation of the fibrous and serous tissues of the joints and of the heart, is doubtless the same. It is physically impossible for lactic acid to act on the fibrous elements of the joints, as Dr. Richardson believes that it acts on the endocardium.