The period is placed:
1. At the end of declarative and imperative sentences.
Mr. Benj. Brown; Smith, Jones & Co.; Enoch Green, M.D.; John Judson, D.D., LL.D.; Trenton, N. J.
Observe that the period is used after each of these abbreviations.
Notice the period after the headings, and after the figures used to number the sections, paragraphs, and sentences in this book.
2. After abbreviations, headings, and figures used to number sections, paragraphs, and sentences.
O'er, doesn't, aren't.
The omission of a letter from the middle of a word is indicated by the apostrophe (').