PRESCEIPTION WRITING 91 



weight in the metric system, but as medicines, when given 

 to patients, are usually measured by bulk, they cannot be 

 dispensed by weight without producing a complication. 

 For example, suppose that we order chloroform in a pre- 

 scription in the metric system, — 



I^ Chloroformi 30 | 



S. Two teaspoonfuls in water. 



John Smith. 



thinking we are dispensing 10 grams * for a teaspoonful 

 holds 5 grams of water. But as chloroform weighs ^ more 

 than water, we really have ordered 10 + 1- = 15 Gm. of chloro- 

 form. Therefore, in writing a prescription for chloroform with 

 other ingredients; weighed in Gm., we would have to add ^ 

 of the number of Gm. of chloroform in the prescription to the 

 number previously estimated in order to make the chloroform 

 of the same bulk as other liquids of the density of water. 



In order to avoid reducing substances of density differ- 

 ing from that of water, to terms of equivalency with that of 

 water, it is the custom, and now official, to weigh solids in Gm. 

 and measure liquids in Cc. This is an exact method if the 

 doses of drugs are learned in the same way: i.e., if the doses 

 of solids are learned in Gm. and prescribed in Gm., aud the 

 doses of liquids are learned in Cc. and prescribed in Cc. 



In writing prescriptions in the metric system a line is 



drawn perpendicularly across the right-hand side of the 



blank to indicate the decimal point ; multiples of the unit 



being placed to the left of the line, while fractions are 



written to the right of the decimal line. In using this system 



we are spared the annoyance of special signs and different 



tables for weights and measures. As matters now stand we 



must be cognizant of both systems, and be able to convert 



the old into the new, or vice versa. One drachm is equivsi- 



lent to four grams, 3 i. = Gm. 4 Therefore, Gm. 1 = 3 ^ or 



Gr. 15. Then, Gr. i. = ^ig^ of Gm. i.; or 



15) 1.000 (.066 

 90 



100 

 90 • 



*For each dose. 



