320 EFFECT OF DRUGS ON THE INTESTINE. 



Effect of Drugs Amongst the reagents which act upon the intestinal move- 

 ments are : (1) Such as diminish the excitability of the plexus myentericus, i.e., 

 which lessen or even abolish intestinal peristalsis, e.g., belladonna. (2) Such as 

 stimulate the inhibitory fibres of the splanchnic, and in large doses paralyse them 

 opium, morphia (Nothnagel) ; 1 and 2 produce constipation. (3) Other agents 

 excite the motor apparatus nicotin (even causing spasm of the intestine), muscarin, 

 caffein, and many laxatives, which act as purgatives. The movements produced by 

 muscarin are abolished by atropin (Schmiedeberg and Koppe). These substances 

 accelerate the evacuation of the intestine, and, owing to the rapid movement of the 

 intestinal contents, only a small amount of water is absorbed ; so that the evacua- 

 tions are frequently fluid. (4) Amongst purgatives, colocynth and croton oil act as 

 direct irritants. With regard to drugs of this sort, they seem to cause a watery 

 transudation into the intestine (C. Schmidt, Moreau), just as croton oil causes 

 vesicles when applied to the skin. (5) Calomel is said to limit the absorptive 

 activity of the intestinal wall, and to control the decompositions in the intestine. 

 The stools are thin and greenish from the admixture of bili-verdin. (6) Certain 

 saline purgatives sodium sulphate, magnesium sulphate, cause fluid evacuations by 

 retaining the water in the intestine (Buchheim) ; and it is said, that if they be injected 

 into the blood-vessels of animals, the}' cause constipation (Aubert). 



If a crystal of a potash salt be applied to the intestine, it causes a local con- 

 striction, accompanied by lively movement extending about 10 centimetres above 

 where the crystal was applied. Soda salts are not so powerful, and they seem to 

 act upon the nerves and not upon the musculature (Nothnagel, K. Bardeleben). 



[Action Of Saline Cathartics. From an extended investigation recently 

 made by Matthew Hay on the action of saline cathartics, it would appear certain 

 that a salt exerts a genuine excito- secretory action on the glands of the intestines, 

 whilst at the same time, in virtue of its low diffusibility, it impedes absorption. 

 Thus, between stimulated secretion and impeded absorption there is an accumula- 

 tion of fluid within the canal, which, partly from ordinary dynamical laws, partly 

 from a gentle stimulation of the peristaltic movements excited by distension, 

 reaches the rectum and results in purgation. Purgation does not ensue when 

 water is withheld from the diet for one or two days previous to the administration 

 of the salt in a concentrated form. This absence of effect is due to a deficiency of 

 water in the blood, so that the blood cannot, throiigh the intestinal glands, yield 

 enough fluid to the salt in order to produce purgation. When a concentrated 

 solution of a salt is administered to an animal whose alimentary canal is known, 

 from a few hours' preliminary fasting, to be empty, but whose blood is in a natural 

 state of dilution, the blood becomes rapidly very concentrated, and reaches the 

 maximum of its concentration in from half an hour to an hour and a half; 

 within four hours the blood has gradually returned to its normal state of concen- 

 tration without having reabsorbed fluid from the intestine. It apparently recoups 

 itself from the tissue-fluids. After a few days' abstention from water, the tissue- 

 fluids are so much diminished as not to be able any longer to recoup the blood, and 

 the blood itself gradually becomes concentrated; hence a concentrated saline 

 solution fails to excite any secretion when administered. 



It is also interesting in connection with saline cathartics that the salt sulphate 

 of magnesia or sulphate of soda becomes split up in the small intestine, and the 

 acid is more rapidly absorbed than the base. A portion of the absorbed acid 

 shortly afterwards returns to the intestines, evidently through the intestinal 

 glands. After the maximum of excretion of the acid has been reached, the salt 

 begins very slowly and gradually to disappear by absorption, which is checked 

 only by the occurrence of purgation. The salt does not purge when injected into 

 the blood, and excites no intestinal secretion; nor does it purge when injected 

 subciitaneously, unless on account of its causing local irritation of the abdominal 

 subcutaneous tissue, which acts reflexly on the intestines, dilating their blood- 

 vessels, and perhaps stimulating their muscular movements.] 



