When special attention is invited to any word, it is customary to inclose it in single quote-marks, as:
By 'experiment' is meant the process of altering the arrangements presented by nature.
In this illustration the single quote-mark is the accepted substitute for the old fashion of putting the word experiment in italic or beginning it with a capital. The single quote is of real service when it identifies unmistakably the exact word used by a speaker or writer, but it will prove an irritating precision when it is repeated too often in subsequent citations of that word.
QUOTE-MARKS NOT USED IN THE BIBLE
It has been said that the conversation of different speakers would be unintelligible or confused if the words of each speaker were not inclosed in quote-marks. A careful reading of the following dialogue, as presented in the authorized version of the Bible, will show that quote-marks are not needed as much as is commonly supposed to distinguish the words of different speakers.
And he came unto his father, and said, My father: and he said, Here am I; who art thou, my son?
And Jacob said unto his father, I am Esau thy firstborn; I have done according as thou badest me: arise, I pray thee, sit and eat of my venison, that thy soul may bless me.