United States. War Department

“ Each noun has forms for two numbers: singular (S) and plural (P) , much as in English: стол "table," столы "tables." Some nouns occur only in the singular: молоко "milk"; and some occur only in plural: ножницы "scissors", чернила "ink." The distinctions of gender are absent in the plural: эти столы "these tables," эти книги "these books," эти перья "these pens," эти чернила "this ink."
Case. Each noun has, both in the singular and in the plural, six case forms, each of which is used according to the relation of the noun to the other words in the sentence. ”

“ Only in a few fixed expressions is the a plural of animates like the n: он поехал в гости "he went among the guests; he has gone on a visit"; compare: я вижу гостей "I see the guests."
Thus we have for each noun six singular form and five plural forms: ns (nominative singilar) , as, gs, ds, is, ls; np (nominative plural) , gp, dp, ip, lp, the accusative plural (ap) having the same form either as the np or as the gp. ”

“ This distinction appears chiefly in the a form: in all plurals and in one large class of masculine singular nouns, the a of animates is like the g, and the a of inanimates is like the n. Thus, the n is книги "books" and the a has the same form: я вижу книги "I see the books"; the n люди "people" has by its side the g людей, and the a has this latter form: я вижу людей "I see people." ”