_a._ _A medicine may occasionally produce pain or sensation at a distant part, without reaching that part._ We often find that a morbid action at one part of the body is capable of producing pain or uneasiness at another distant part by a reflex nervous action. We are familiar with instances of this among the symptoms of disease. The pain in the knee which occurs in disease of the hip-joint; in the left arm, in some cases of heart disease; and in the right shoulder, in disorders of the liver; are examples. Certain impressions on the surface of the stomach may cause such a reflex pain. Swallowing a piece of ice will sometimes produce pain over the brow; and it is likely that the headache which follows over-eating, or a large dose of a tonic medicine, may result in a similar way from mere irritation of the stomach. Any irritant, as a solution of Iron, Arsenic, or Zinc, will do the same. The action of a violent purgative will cause headache while it lasts. Although we cannot deny the possibility of other actions of the same kind, yet there are so few medicines which, in ordinary and safe doses, are capable of producing pain in any way, that it becomes difficult or impossible to adduce a satisfactory example of an agent which operates on distant parts in this manner when in the blood. _b._ _A medicine may occasionally produce muscular contraction at a distant part, without reaching that part._ This may be done in two ways; either by a reflex nervous action, or by a propagation of the contraction from one muscle to another in its neighbourhood. The first of these never results from the action of a medicine while in the blood; but it may follow an impression on a surface. Thus we have already seen that the irritation of the mucous membrane of the stomach, and probably of the filaments of the Vagus nerve distributed in it, which precedes the act of vomiting, may cause the contraction of the muscles of the abdomen. The propagation of contraction from one muscular organ to another appears to take place in the case of violent purgatives, particularly some, as Aloes and Savine, which act on the lowest portion of the large intestine, exciting it to a peristaltic contraction,--whose action may thus be extended to the contiguous Uterus in the female, causing it also to contract. This renders the employment of such medicines dangerous in cases of pregnancy, as tending to produce abortion. In other cases these agents may be useful; for by the irritation and congestion which follows this action on the Uterus, they may cause the appearance of the menstrual secretion when deficient or retained. This also is the result of an action on a surface.