CHAP. I. SEKVICEABLE ASSOCIATED HABITS. 49 of the mind, are partially repressed by the will, the strictly involuntary muscles, as well as those which are least under the separate control of the will, are liable still to act; and their action is often highly expressive. Conversely, when the will is temporarily or permanently weakened, the voluntary muscles fail before the involun- tary. It is a fact familiar to pathologists, as Sir C. Bell remarks/0 " that when debility arises from affection of the brain, the influence is greatest on those muscles which are, in their natural condition, most under the command of the will."" We shall, also, in our future chapters, con- sider another proposition included in our first Principle; namely, that the checking of one habitual movement sometimes requires other slight movements; these latter serving as a means of expression. 20 * Philosophical Translations,' 1823, p. 182.