The alteration of one membrane may, without affecting the neighbouring membrane, prevent more or less completely the performance of its functions: the mucous secretions of the stomach may be affected by inflammation of the fibrous tissues; and the intellectual functions may be affected by lesions of the arachnoid.`' The forms of inter tissual penetration may be even more complex: in affecting the investing membrane of the heart, pericarditis may cause a functional disorder resulting in hypertrophy of the organ, and therefore a modification of its muscular substance./