2 PBELIMINAKY CONSIDEEATIONS 



Guro, and did not in its original sense mean to restore to 

 health, although that is its present interpretation. 



A Drug, derived from the Dutch, Droog, meaning dry, 

 is now used synonymously with medicine, although origin- 

 ally referring to an herb or dried medicinal plant. 



Mode of Action of Drugs. 



Drugs act locally when they influence a part with which 

 they come in contact, and also when they affect one organ 

 or apparatus after absorption. The first meaning is tba 

 usual one. 



Drugs act generally when they impress the body as a 

 whole after absorption. Drugs applied to the unbroken 

 skin usually act locally because they are commonly unab- 

 sorbed; also when drugs, insoluble in the digestive tract 

 (as charcoal and chalk), are given internally they act locally 

 for the same reason. The local action of drugs after ab- 

 sorption is sometimes known as selective action, t.e.,the power 

 that most drugs possess to influence one organ or apparatus 

 rather than the whole system. Oftentimes this local action, 

 in the case of secreting glands, is accomplished through 

 stimulation of these parts during elimination of the drug. 

 Occasionally a medicine acts both on the part with which 

 it comes in contact and also through the circulation; e.g., 

 tartar emetic causes emesis by local stimulation of the 

 stomach and by stimulation of the vomiting centre after 

 absorption. Furthermore, remedies are said to exert a 

 primary (or immediate) and secondary (or remote) action. 



The secondary effect is the result of the primary action; 

 e.g;, a saline cathartic primarily removes serous fluid from 

 the bowels and secondarily or remotely leads to absorption 

 of serous exudations ; a counter-irritant primarily produces 

 irritation of the skin and sensory nerve-endings, but second- 

 arily relieves internal congestion by inducing reflex contrac- 

 tion of the subjacent blood vessels. Most drugs are absorbed 

 into the blood after their ingestion and exert their action on 

 various parts of the body through the medium of the ner- 



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