ON THERAPEUTICS. 
695 
capable of producing certain actions upon the healthy body, 
are remedies for the opposite conditions of disease ; the real 
difficulty is to comprehend that the actual disease is very 
frequently not the apparent one, and that much consideration, 
and often the entire rejection of most plausible evidence, 
offered by seemingly clear symptoms, must precede a true 
diagnosis. To this end, signs referring to a part must be 
received with caution. Excessive or defective action of an 
organ may be connected with a condition of the system 
opposed to the condition of the part: thus defective action of 
the liver may be associated with general excess of blood 
(plethora), and excessive action of the kidneys, or the mucous 
membrane of the intestines, with general defect of blood 
(anaemia) : the single prominent symptom in each case will 
give but little assistance to the examiner. His investigations 
must extend beyond the organs apparently most affected, 
before his conclusions can be truly drawn. In discussing, 
therefore, the actions of each class, it will be our endeavour 
to show under what conditions of disease certain medicinal 
effects may be desirable or not. 
CATHARTICS. 
First among the medicines of the first group, are “ Ca- * 
THARTics,” —agents which occasion more frequent and altered 
evacuations from the intestinal tube. The drugs possessing 
this property are by no means allied in their general character 
or constitution to each other : nevertheless, they uniformly 
cause increased secretion from the lining membrane, and in 
some instances excite the muscular coat at the -same time. 
As muscular contraction is excited by the motor nerves of the 
part, and as both the determination of blood which occasions 
the excessive secretion, and the excited peristaltic movement, 
are due to the same cause, we can explain the action of all 
purgatives by referring it to the nervous system. Without 
the excitation of the reflex functions, we cannot understand 
the secretion from the membrane, nor the action of the 
intestinal muscular fibre. Whether the impression upon the 
sensient nerves be direct, from contact with the agent, or 
through the medium of the blood, or whether both these 
positions be true, under different circumstances, are not ques¬ 
tions pertinent to our present inquiry. It is evident that the 
movements and secretions of the intestines are dependent 
upon reflex action, these functions are increased in obedience 
to the amount of stimulus applied; whatever, therefore, in 
any way produces an impression upon the nerves of the in- 
