III. When a sentence is purposely left unfinished, the dash takes the place of the full stop. (See [Rule XL.])
"Excuse me," said I, "but I am a sort of collector." "Not Income-tax?" cried His Majesty, hastily removing his pipe from his lips.
IV. A full stop is placed after most abbreviations, after initial letters, and after ordinal numbers in Roman characters.
Gen. i. 20; two lbs.; A.D. 1883; 3 p.m.; &c., and etc.; M.D., J. S. Mill; William III., King of England; MS., LL.D. (not M.S. and L.L.D.).
Note that the use of the full stop in these cases does not prevent another point from being used immediately after it. But if they occur at the end of a sentence, another full stop is not added; or, more correctly, it may be said that [Rule IV.] does not apply at the end of a sentence.
"Mr," "Messrs," "Dr"—abbreviations which retain the last letter of the whole word—are written without a point.