Interjections, so called because they are _thrown in_ between the parts
of a sentence without making any other alteration in it, are a kind of
Natural Sounds to express the affection of the Speaker.
The different Passions have for the most part different Interjections to
express them.
The Interjection _O_ placed before a Substantive expresses more strongly
an address made to that person or thing; as it marks in Latin what is
called the Vocative Case.