24 GENERAL ACTION OF DRUGS 



These drugs slightly increase intestinal action, chiefly by stimulation 

 of peristalsis. 



2. Simple Purgatives. — These stimulate secretion and peristaltic 

 action. Among them may be mentioned: 



Aloes Senna 



Calomel Cascara sagrada 



Linseed oil Phenolphthalein 



Castor oil Frangula ' 



Rhubarb Bryonia 



3. Drastic Purgatives. — Drastics are essentially gastro-intestinal 

 irritants, and in large doses cause mucous and bloody diarrhea, conges- 

 tion of the mucous membrane of the alimentary canal and severe colic. 

 They may produce death in poisonous doses with collapse by reason of 

 gastro-enteritis. Drastics greatly increase both peristaltic action and 

 secretion, and are contra-indicated in irritable and inflamed conditions of 

 the digestive tract. They are, however, indicated for their revulsant or 

 derivative effect {i.e., to dilate the blood vessels in the alimentary canal 

 and to cause an outpouring of serum from the blood, thus relieving con- 

 gestion in other parts) in some acute inflammations, as in brain diseases. 

 Their medicinal action is often attended with considerable and irregular 

 peristaltic contractions, so that griping occurs. The latter is prevented 

 by suitable combination with other purgatives; with hyoscyamus and 

 belladonna ; or with carminatives, as ginger. The drastics include : 



Croton oil Scammony 



Colocynth Jalap ' 



Gamboge Elaterium 



4. Hydragogue Purgatives.— -Hydiagognes are agents which chiefly 

 increase the fluidity of the intestinal contents. They include: 



(a) SALINE PURGATIVES 



Magnesium sulphate Sodium phosphate 



Sodium sulphate Potassium bitar,trate 



(b) DRASTICS 



Jalap Elaterium Scammony 



Purgation by salines depends upon the absorbability of their ions. 

 The least absorbable are the most cathartic. Among the basic ions (ca- 

 tions), magnesium is least absorbable, and among the acid ions (anions), 

 the sulphates, phosphates, citrates and tartrates are absorbed with most 

 difficulty. 



The salines stimulate secretion by reason of their bitterness,- and by 

 their irritant and specific properties. They, moreover, hold on tb the 

 fluid thus secreted and hinder its absorption because of their slow diffusi- 

 bility. Purgation follows, owing to the mechanical effect of the increased 

 fluidity of the bowels, and since the augmented bulk of the intestinal 

 contents excites peristaltic action. When it is desirable to remove fluid 



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