The most important committee, the Committee of the Whole, is not in this sense a committee at all. It is simply the House itself acting under special forms of procedure; the chief differences being that the Chairman of Committees presides, and that the rule of the House forbidding a member to speak more than once on the same question does not apply. But the fact that a member can speak more than once makes it a real convenience for the purpose for which it is chiefly used, that is, the consideration of measures in detail, such as the discussion and amendment of the separate clauses of a bill, or the debates upon different items of appropriations. The Committee of the Whole has had a long history.[265:1] It is called by different names according to the subject-matter with which it deals. For ordinary bills it is called simply the Committee of the Whole. When engaged upon appropriations it is called Committee of the Whole on Supply, or in common parlance the Committee of Supply. When providing money to meet the appropriations it is called the Committee of Ways and Means; and when reviewing the revenue accounts of India it is named from that subject. The committees of the whole called by these names are so far distinct that each of them can deal only with its own affairs, and the House must go into committee again in order to take up any other matter. But the simple Committee of the Whole can take up one bill after another which has been referred to it without reporting to the House and being reconstituted.[265:2] [Sidenote: Select Committees.] Of the real committees the most numerous are the select committees. Their normal size is fifteen members, although they are often smaller, and occasionally, by special leave of the House,[265:3] they are somewhat larger. They may be nominated from the floor, and elected by the House,[265:4] or chosen by ballot; but in order to avoid loss of time, and to secure impartiality, the appointment of a part, at least, of the members is usually intrusted to the Committee of Selection. [Sidenote: Committee of Selection.]