If we except those cases of tuberculosis which have originated in the neighboring tissues and have extended to the organic muscular coats of other structures, as the intestine, etc, tubercles occur in the substance of the heart with the same rarity as in muscle generally. It is only in extreme degrees of tuberculosis that we have discovered one or more tuberculous masses in the muscular substance of the heart in addition to a tuberculous exudation on the pericardium. We must, however, here except those cases in which large tuberculous masses, exuded on the external investment of the heart, have gradually imbedded themselves in the outer layer of the muscular substance.

It is remarkable, considering the similarity of the process of exudation on the endocardium and on the inner coat of the vessels with that on serous membranes, that tuberculosis should not occur on the two first-named structures.