MATERIA MEDICA AND THERAPEUTICS. 27 



i. By accelerating peristaltic motion of the bowels. 



2. By increased secretion from intestinal mucous membrane. 



3. By limiting absorption of the intestinal fluids. 

 Purgatives are divided into several groups, viz., Laxatives 



or Aperients, which have the most moderate action, only slightly 

 increasing and softening the evacuations, without causing irrita- 

 tion, as small doses of oil, sulphur, green food, sulphates of soda 

 and magnesia in small doses. 



Simple Purgatives. — Are more active than laxatives, and are 

 accompanied by some irritation ; they cause active peristalsis and 

 more copious and softened evacuations than laxatives (in small 

 doses they act as laxatives). Large doses of oil, aloes, rhamnus, 

 calomel, rhubarb, etc. ; these act by stimulating peristalsis and 

 secretion. 



Drastic Purgatives. — Act far more severely than simple pur- 

 gatives ; they greatly increase peristalsis and secretion, violently 

 stimulate intestinal contractions and cause griping ; they promptly 

 produce copious, frequent fluid discharges, and in large doses 

 may cause serious intestinal irritation and inflammation ; exam- 

 ples, croton oil, colocynth, elaterium, gamboge and podophyllin; 

 also aloes in large doses. 



Saline Purgatives. — Excite increased secretion and prevent 

 re-absorption, thereby mechanically exciting peristaltic action. 



They promote osmosis and cause free watery evacuations 

 in full doses, such as magnesium, sodium, and potassium sul- 

 phate, citrate of magnesia, potassium tartrate and bitartrate, etc. ; 

 secretion goes on until the fluid in the intestines becomes a 5 or 6 

 per cent solution. 



Hydragogue Purgatives. — Include the most active of the 

 drastic and saline purgatives. They remove a large amount of 

 water from the system ; example, jalap, elaterium, scammony, etc. 



Cholagogue Purgatives: — Stimulate the flow of bile, causing 

 green colored or bilious stools, such as mercurial preparations, 

 podophyllin, aloes, etc. j 



Uses of Purgatives. — Are many and varied. \ 



First to remove undigested food ; second, faeces ; third, bile ; 

 fourth, to remove poisons; fifth, worms; sixth, foreign bodies; 

 also, to reduce plethora and obesity, to allay skin irritation and 



