696 
ON THERAPEUTICS. 
testinal canal sufficient to excite such reflex action, will 
occasion the effects observed. 
A consideration of the agencies that induce catharsis will 
show how varied are the circumstances under which it may 
occur. Under all conditions, however, a stimulus is neces¬ 
sary. Mental excitement, mechanical or chemical irritants, 
the bitter principle, and certain salts, possess the requisite 
power. It does not seem at all necessary that the agent 
should always be brought in contact with the intestinal mem¬ 
brane ; injection into the circulation, or absorption from any 
surface, will suffice to produce the required excitement of the 
reflex function. It would be futile to reason upon the parti¬ 
cular elective property which diverts the action from the 
point of contact to a distant part; the fact being perfectly 
established, that the medicinal properties of agents are not 
dependent for their development upon any particular method 
of introduction into the system, but once within the organism 
their influence is immediately directed to certain parts. The 
degree of action may vary, but not its character. Nor is it 
more remarkable, that a purgative, placed upon the tongue, 
should produce an impression upon the nerves of the intes¬ 
tines, than that a mental emotion should have the same 
effect. 
Cathartic agents differ, we have already remarked, from 
each other in their general properties, and in a measure in 
their method of action. Referring to fi Morton’s Pharmacy/ 
we find them thus arranged:— Aloes, Croton , Chloride of Mer¬ 
cury, Linseed, Olive and Castor Oil, Clysters, Mashes , Sulphates 
of Magnesia and Soda, Salt, Sulphur , and the Acid Tartrate of 
Potash . 
For the horse, aloes is the common and most effective 
drug. It is considered to act principally upon the large 
intestines, where it finds the necessary alkaline matters to 
assist its solution; but by combining the alkali before exhibi¬ 
tion, and giving the agent in the form of solution, its action 
is certainly more rapid, milder, and probably more diffused. 
Croton is presumed to act as an irritant. Its effects are 
often most violent, and seldom desirable. Very few cases can 
we conceive where catharsis would be so absolutely neces¬ 
sary as to justify the employment of such an agent un¬ 
combined. 
Chloride of mercury owes its purgative action, in part, 
to its influence on the liver; and as it also possesses the 
property of exciting the salivary glands, and increasing the 
secretion from them, there seems to be no reason why its 
influence should not extend to the mucous glands of the in- 
