PRESCRIPTION WRITING 95 



sessive. Thus the Latin name Oleum Lini, consists of two 

 words. The first, oleum, is the Latin nominative for oil, and 

 the second word, lini, is the Latin genitive of the word meaning 

 linseed. The name signifies, then, oleum (oil) and lini (of 

 linseed). In writing prescriptions it is usually essential to 

 put the Latin name of the drug in the genitive case, follow- 

 ing the use of the heading 9 > standing for the Latin imper- 

 ative Recipe, meaning in English, Take. 

 For example ; 



Potassii nitratis § i. 



Literally translated this means : 



Take 



Of potassium nitrate, ounce 1. 



There is only one other case which is used in writing 

 prescriptions (the accusative), but this can be avoided by 

 using abbreviations in the few instances in which it should 

 be employed. The following rules can be memorized (with 

 their exceptions) in order to form the genitive case (singular): 



(1) Latin names of drugs ending in "a" form their 

 genitive in cie. The only exceptions are three : Physostigma 

 takes the genitive in tis, physostigmatis. Folia (leaves), pi. 

 genitive, foliorum. Theoh'oma, genitive theohromatis. In 

 most instances the genitive of Latin nouns ending in a, can 

 be made in practice by dropping the nominative ending (a) 

 and adding ae in its place, viz. : Tindur-a (a tincture), gen- 

 itive tindur-ae (of a tincture). 



(2) All pharmacopoeial nouns ending in us, um> (os and on), 

 form their genitive in i. This genitive case can be formed 

 in practice by dropping the nominative ending (us or wn) 

 and adding i in its place, viz. : bol-us, a ball ; genitive hol-i, of 

 a ball. Extrad-um, an extract ; genitive extrad-i, of an 

 extract. 



The nouns ending in os and on are very few. Excep- 

 tions : Bhus, genitive rhois. Flos, genitive floris. Frudus, 

 quercus and spiritus do not change in the genitive, as it is the 

 same as the nominative case. 



