Index-s meaning

1874: Richard Bentley and Wilhelm Wagner, PhD [ed., intr., & notes], Dr. Richard Bentley’s dissertations upon the epistles of Phalaris, Themistocles, Socrates, Euripides, and upon the fables of Æsop, pages 49{1} and 415{2} (Berlin: S. Calvary & Co.)

{1} As for the General Character that Mr. B. endeavours to fix upon me, that I have no Learning, no Judgment, no Reasoning, no Knowledge in Books, except Index’s and Vocabularies, with many other Expressions of the utmost Contempt, that make up the greatest part of his Book, I do not think my self concern’d to answer them.

{2} For Quintilian does not speak of such Index’s as Books have now-a-days : but after he had nam’d several of the Greek Poets, Homer, Antimachus, Euphorion, &c. […]