250 
INTRODUCTORY LECTURE. 
health and lives of his fellow-citizens. Intended to be the co- 
adjutor of the physician, an error may convert him into his 
worst enemy : an oversight, the sale of one thing for another, 
a wrong label, and many other equally insignificant causes, 
may be productive of serious consequences. 
A good dispenser requires a variety of qualifications, in- 
cluding a knowledge of the three branches already spoken 
of. Constant presence of mind is an essential requisite; he 
must be conscious all the time, of his acts, to prevent the 
substitution of similarly appearing substances. A foolish 
reverie, whilst compounding a prescription, has caused, and 
may again produce the most melancholy results. In a pre- 
scription of nitrate of potassa, tartar emetic, and calomel, how 
readily may such a fatal substitution occur; and how many 
of us, in recurring to our early experience, can recollect 
some occasion when we were on the point of committing 
an error of equally grave character. His acquaintance with 
nomenclature and synonyms must be extensive to meet the 
variable phraseology of prescriptions; added to which, the 
contemptible characters in which many medical men couch 
their requests, requires a judgment and decision for their 
interpretation, often in cases of urgency, which greatly in- 
creases his responsibility. 
Physicians in prescribing are sometimes more governed ' by 
the effects of their remedies viewed separately, than by the 
effect of the compound, which leads them in the pursuit of 
their ends, to overlook the modifications due to chemical re- 
action : for instance, solutions of morphia, opium, or other 
liquids containing salts of the alkaloids, are prescribed with 
magnesia, the great basic power of which causes their pre- 
cipitation in an insoluble form, (in most instances,) and the 
solution is nearly free from them. If the patient takes the 
clear liquid only, or is careless in mixing the soluble and in- 
soluble contents of the vial, the desired narcotism is not pro- 
duced, or is reserved to be exerted with redoubled force by the 
last portion of the mixture. It is the dispenser's duty to sug- 
gest the necessary precaution. 
