Latin nouns are declined according to five different plans, and these are known as the five declensions. Four cases are used in prescription-writing: nominative, genitive, accusative, and ablative.

Most nouns ending in a are of the first declension, are feminine, and are declined as follows :

Singular

Plural

An exception is Aloe:

[The Latin dative and vocative cases are never used.]

Medical nouns of the second declension end in us, os (masculine, except juniperus, prunus, sambucus, and ulmus, which are feminine), or um, on (neuter), as :

Singular

Plural

[The genders of nouns are given as a guide to the agreement of adjectives.]

Or

Indeed, all prescription nouns ending in us are of the second declension, save seven - rhus, rhois (3d fern.) and the six names of the fourth declension (see p. 641).

The third declension does not follow such strict rules as do the others, and its endings are variously modified in their attachments to the root. These modifications are not indicated in the nominative, but are expressed in the genitive, so the nominative and genitive should always be learned together. It should be observed that, no matter what the connecting-links between the roots and the endings may be, the latter are always the same, viz.: in the singular, gen. is, acc. em, abl. e or i; in the plural, nom. es or a, gen. um, acc. es or a, abl. ibtts. The nouns of the third declension may be grouped as follows :

Group I. - Thirty-three nouns ending in as make the genitive in atis. All are masculine, save Asclepias (Gen. Asclepiadis), which is feminine, and all are names of salts. Example :

Singular

Group II. -

Nouns ending in is: (a) Genitive unchanged; all feminine.

Ex. Nom. Cannabis; Gen. Cannabis. (b) Genitive changing into Itis, all masculine.

Ex. Nom. Arsenis; Gen. Arsenitis. (c) Genitive changing into idis, all feminine.

Ex. Nom. Hamamelis; Gen. Hamamelidis. (d) Genitive changing into eris, one only, masculine.

Ex. Nom. Pulvis; Gen. Pulveris.

Group III. -

Nouns ending in o, all feminine except Carbo, Pepo, and Sapo, which are masculine: (a) Genitive ending in onis.

Ex. Nom. Lotio; Gen. Lotionis. (b) Genitive ending in Inis.

Ex. Nom. Mucilago; Gen. Mucilaginis.

Group IV. -

Nouns ending in x, masculine or feminine:

(a) Genitive ending in cis.

Ex. Nom. Borax; Gen. Boracis.

(b) Genitive ending in cis, and the last vowel of the nominative (e) changed to i. Ex. Nom. Ruma; Gen. Rumzcis.

Group V. -

Nouns ending in r, masculine or neuter: Genitive simply adds is.

Ex. Nom. Liquor; Gen. Liquoris.

Group VI. -

Nouns ending in a, all neuter: Genitive ends in atis.

Ex. Nom. Enema; Gen. Enematis.

Group VII. -

Nouns ending in s, masculine or feminine: Genitive ends in is.

Ex. Nom. Adeps; Gen. Adipis.

Group VIII. -

Nouns ending in l, all neuter.:

(a) Genitive simply adds is.

Ex. Nom. Chloral; Gen. Chloralis.

(b) Genitive doubles l and adds is.

Ex. Nom. Mel; Gen. Mellis.

Group IX. -

Nouns ending in n, all neuter:

(a) Genitive ending in onis (nominative in on).

Ex. Nom. Limon; Gen. Limonis.

(b) Genitive ending in Inis (nominative in en).

Ex. Nom. Semen; Gen. Seminis. [Erigeron has the genitive Erigerontis.]

Group X. -

One noun ending in c, neuter: Genitive simply adds is.

Ex. Nom. Lac; Gen. Lactis.

Group XI.

One noun ending in us, feminine: nom. rhus; gen. rhois.

There are only six medical nouns of the fourth declension, cornus and quercus (feminine), and fructus, haustus, potus and spiritus (masculine). They are declined as follows :

Singular

Plural

Spiritus. Splritum. Spiritus. Spirltibus.

Of the fifth declension we use the ablative die of the noun dies, a day, as in the expression ter in die " three times a day."

The following nouns are usually considered indeclinable : Az-edarach, buchu, catechu, condurango, curare, cusso, diachylon, eriodictyon, jaborandi, kino, matico, quebracho, sago, and sassafras.