658 
ON THERAPEUTICS. 
entail; all these circumstances should be taken into account 
when medicinal action is in question. As a cold atmosphere 
will destroy the effects of a sudorific, so excessive exertion is 
antagonistic to the operation of a tonic. Nor are these con¬ 
siderations fanciful or puerile, on the contrary they are of as 
much importance in connexion with the production of medi¬ 
cinal effects, as the absence of adulterations in the agents 
used. The mixture of any impurity with a drug, we all 
readily enough oppose ; but are not the agencies we have just 
noticed, and others that the observant inquirer will discover, 
more potent in their disturbing effects than most of the mate¬ 
rials to whose admixture we should so strongly object l “ Cir¬ 
cumstances alter cases,” is among us a maxim, and in nothing 
is it more true than in reference to medicinal action. 
Opposing influences are likewise found in the admixture 
of a number of medicinal agents in the same compound, and 
this more frequently than is suspected. Chemistry de¬ 
cides how far combinations are possible without positive 
chemical union; but a minute knowledge of effects can 
alone preserve the dispenser from more serious errors than 
the simple junction of incompatibles. As a rule, no two agents 
from the opposite classes can ever be combined without 
detriment to the action of either one or the other; and no 
agent from among those which excite the functions can be 
properly united to one of those whose action is to diminish 
them, excepting under peculiar circumstances; for instance, 
in a disease where the pain is severe, and its acuteness can be 
lessened by the use of narcotics or sedatives; while at the 
same time cathartics or stimulants are being directed against 
another element in the malady. The scientific dispenser will 
then employ such combinations unhesitatingly; but he does so 
knowingly, and calculates with comparative certainty the 
disadvantages and the benefits. In the absence of any decided 
reason for the violation of this rule, mixtures will only in¬ 
clude drugs whose actions are not opposed. Agents of the 
third class, those which induce a change in the character of a 
secretion or a structure, may be advantageously conjoined 
with either of the other classes, always provided that no 
chemical incompatibility be present. It may often be 
necessary to diminish or increase a secretion, and change its 
character at the same time, if possible ; but it will seldom be 
necessary to increase it in one part and diminish it in another at 
the same moment. We do not oppose the attempt when cir¬ 
cumstances justify it; but, we do not anticipate the frequent 
occurrence of such a necessity. 
