Тема: How to Write a Research Paper - StatPac
The traditional abbreviations are MS for manuscript and MSS for manuscripts,   while the forms MS. , ms or ms. for singular, and MSS. , mss or mss. for plural (with or without the full stop, all uppercase or all lowercase) are also accepted.     The second s is not simply the plural; by an old convention, it doubles the last letter of the abbreviation to express the plural, just as pp. means "pages".
When Greek or Latin works were published, numerous professional copies were made simultaneously by scribes in a scriptorium , each making a single copy from an original that was declaimed aloud.