CLASSIFICATION OF MEDICINES. 19 



cognised by the U. S. PharmacopcBia) contains tiventy fluid ounces. 

 The common pint contains only sia:teen ounces. 



The following are the denominations, together with their symbols, 

 which are employed in prescription : — 



Pound, }fe ; ounce, 3; drachm, 3; scruple, 9; grain, gr. ; gallon, 

 cong. (congerius); pint, O. (octarius); fluid ounce, f3; fluid drachm, 

 f3; minim, fix. 



A drop is not always equivalent to a minim, since it varies in size 

 according to the nature of the fluid, and the shape and size of the 

 vessel from which it is dropped. In the case of water, the minim 

 and drop are the same ; in alcohol there are two drops in each 

 minim ; in ether, there is a still greater difference. 



Besides the above weights and measures, it is frequently found 

 convenient to employ a'pioroximative measurements, in prescribing 

 medicines. The following are the most common : 



A fcacwp,— estimated to hold about four fluidounces, (f^iv.) or a gill. 



A wineglass " " two fluid ounces, - - (f 3ij.) 



A tablespoon (cochlear magnum,) (f^ss.) half a fluidounce. 



A teaspoon, (cochlear parvum,) (f 3j.) a fluid-drachm. 



CLASSIFICATION OF MEDICINES. 



The great diversity of the effects of different medicines, renders 

 an attempt at their classification very desirable. Classifications of 

 medicines may be divided into empirical and rational ones. As an 

 example of an empirical classification, the alphabetical order may 

 be cited, since this method is founded on names which are arbitrary, 

 and have no relation to the bodies which they are intended to repre- 

 sent. All its supposed advantages — as, for example, that of facility 

 of reference — may be obtained from a well -constructed index. 



The rational arrangements are such as have an actual relation 

 with the bodies for which they are used, being founded on the pro- 

 perties of the medicines themselves, or on their mode of affecting 

 the economy. Thus medicines may be grouped, according to (1) 

 their sensible properties, as colour, taste, and smell ; (2) their chemi- 

 cal properties; (3) their natural-historical i^ro^ieriies', (4) their thera- 

 peutical properties ; (5) their physiological properties. 



Valid objections may be urged against all of the above systems 

 of arrangement, with the exception of the physiological system, 

 which is here adopted, as being the safest guide both to the student 

 and practitioner. 



By the physiological classification is meant one founded on the 

 relation which medicines bear to the system in a state of health. 

 Medicines may be arranged physiologically^ on two principles : ac- 

 cording to the parts or organs which they afl^ect, or according to 

 the nature or quality of the action which they set up. It would be 

 almost impossible to base an arrangement exclusively upon either 



