ON THERAPEUTICS. 
381 
Thus all the subdivisions of the third group are composed 
of agents which induce a change in the organisms in which 
they operate, and justify a comparison between their effects 
and those changes of structure and function expressed by the 
term “ perversion. 5 ’ 
As therapeutics, the agents of the third group are appli¬ 
cable to conditions the opposite of those which they produce 
upon the healthy body, their effects are generally very marked, 
and quickly apparent; but as the various agents counteract the 
effects of disease rather than remedy the original derangement, 
their action is temporary, rendering it necessary to continue 
their employment so long as the cause of the perversion exists. 
For example, an acid secretion ora putrid discharge may arise 
from some disease in the system or in the part. Antacids and 
antiseptics immediately alter the character of the discharge; 
but as the cause of the morbid condition continues, so a new 
supply is furnished, and another application becomes neces¬ 
sary until the actual disease ceases, or is removed by treat¬ 
ment. Thus, medicines of this group are frequently required 
as adjuncts to a more general therapeutic treatment, although, 
as we shall see, they sometimes act as curative agents when 
the peculiar condition of the part survives the original cause, 
and becomes a merely local derangement, whose removal 
will follow the action of the medicine that has the property 
of inducing the opposite state. In this way antacids may 
permanently cure a simple diarrhoea resulting from a change 
in the function of the intestinal membrane, while they would 
only temporarily relieve another case of the same disease, 
originating in mal-digestion, which might be connected with 
a tendency to the formation of acid products. In the course 
of our remarks it will be apparent that the same reasoning 
applies to all the medicine of the third group. 
ANTACIDS. 
The physiological action of these medicines is directly 
chemical, and, so far as the question of affinity is understood, 
perfectly simple. That certain agents, possessing opposite 
properties, have a tendency to combine together, forming- 
compounds whose properties are not the mean of the two or 
more constituents which have united to form them, is a pro¬ 
position with which the tyro in chemistry is perfectly familiar. 
In the operation of this law, we find two very active agents 
when in combination to be perfectly negative or neutral. 
Antacids are by necessity alkaline in their reaction, and 
hence possess the peculiar tendency to unite with acids, 
forming salts of various kinds, and of different properties, 
