EFFECTS OF DRUGS ON THE INTESTINE. 239 



from an animal, tied a cannula into an artery and another into a vein, and kept it in a warm moist 

 atmosphere. The arterial cannula was connected with a vessel containing defibrinated blood, 

 to which different drugs could be added. A lever rested on the intestine, and registered its 

 movements on a recording surface. As long as arterial blood was tranfused, the intestine was 

 nearly quiescent, but when it was arrested, so that the blood became venous, a series of con- 

 tractions occurred. Nicotin diminished the flow of blood and quickened the intestinal move- 

 ments, while at the same time the circular muscular fibres remained contracted or tetanic. 

 Tincture of opium, in the proportion of ;01 to '04 in the blood, causes at first contraction of the 

 vessels, and lessens the amount of blood circulating in the intestine ; but it very rapidly increases 

 even to six times the amount of blood which transfuses, while at the same time the move- 

 ments of the intestine cease, the walls of the intestine being contracted. Peptone caused first 

 strong and then irregular contractions. ] 



Effect of Drugs. Amongst the reagents which act upon the intestinal movements 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 ; 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. 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 evacuations 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, 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 decom- 

 positions in the intestine. The stools are thin and greenish, from the admixture of biliverdin. 

 (6) Certain saline purgatives sodium sulphate, magnesium sulphate cause fluid evacuations 

 by retaining the water in the intestine ; and it is said that if they be injected into the blood- 

 vessels of animals, they cause constipation. [When a crystal of a potash salt is applied to the 

 peritoneal surface of the intestine of an animal, it causes merely a'local constriction of the mus- 

 cular fibres of the gut, while a sodium salt excites a contraction which passes upwards towards 

 the stomach, and never towards the rectum. In any case it may serve as a useful guide to the 

 surgeon, in determining which is the upper end of a piece of intestine during an operation on 

 the intestines (Nothnagel).'] 



[Saline Cathartics. 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 accumulation of fluid 

 within the canal, which 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. When a concentrated solution of a salt is administered to an 

 animal whose alimentary canal is 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 concentration, without having reabsorbed fluid from the intestine. It appar- 

 ently recoups itself from the tissue-fluids. 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. The salt does not purge when injected into the blood, and excites no 

 intestinal secretion ; nor does it purge when injected subcutaneously, 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 (M. Hay). 



162. STRUCTURE OF THE STOMACH. [The stomach receives the bolus, 

 and secretes a juice which acts on certain constituents of the food, while by its 

 muscular walls it moves the latter within its own cavity, and after a time expels 

 the partially digested products towards the duodenum.] 



Structure. [The walls of the stomach consist of four coats, which are from 

 without inwards (fig. 177) 



(1) The serous layer, from the peritoneum. 



(2) The muscular layer, composed of three layers of non-striped muscular fibres (a) 



longitudinal, (b) circular, (c) oblique ( 15). 



(3) The sub-mucous layer of loose connective-tissue, with the larger blood-vessels, lym- 



phatics, and nerves. 



(4) The mucous layer.] 



The well-developed mucous membrane of the stomach is thrown into a series of folds or 

 rugae, in a contracted condition of the organ. With the aid of a hand-lens, it is seen to be 



