THE MECHANICS OF DIGESTION 1013 



in conjunction with some additional ganglion cells, form a center which 

 regulates the activity of the intragastric reflex mechanism. This 

 medullary center is connected with different afferent channels through 

 which sensory impulses are enabled to reach it. They are here con- 

 verted into motor impulses and relayed to the intragastric plexuses. 

 Thus, Wertheimer^ has shown that the stimulation of the central end 

 of the sciatic nerve gives rise to a reflex inhibition of the gastric move- 

 ments. Accelleratory and inhibitory effects may also be produced 

 by psychic influences, such as dehght, anxiety, anger and fright. 



C. THE MOVEMENTS OF THE INTESTINES 



The Movements of the Small Intestine. — Since the entrance of air 

 into the abdominal cavity, the evaporation of the serous fluid and 

 the lowering of the temperature generally induce a refractory state 

 in this organ, various precautions must be taken in order to avoid 

 this motor disturbance. Thus, it has been advocated to insert an oval 

 piece of glass or mica in the incision in the abdominal wall, or to open 

 the peritoneal cavity in a bath of warmed saline solution. In rabbits 

 it is possible to thin the abdominal wall in such a degree that the ab- 

 dominal organs may be inspected without actually opening this cavity. 

 These methods have been supplemented at an early date by graphic 

 procedures, consisting in fastening a soft rubber bulb to the surfacie of 

 the abdomen or in inserting it directly into the intestinal canal. Air 

 transmission being employed in both these cases, the recording tambour 

 accurately registers the displacements of the air from the bulb. 

 Another means which is now extensively used, is the fluoroscope which 

 allows us to follow the food in its course through the aUmentary canal 

 by virtue of the fact that subnitrate of bismuth when mixed with 

 the ingesta, does not allow the Rontgen rays to pass. Lastly, it is 

 possible to study excised segments of intestine under proper conditions 

 of moisture and temperature. They may then be connected with 

 recording levers and pneumographs. A special piece of apparatus of 

 this kind is the enterograph. 



The arrangement of the musculature of the small intestine is 

 simple; an outer, relatively thin coat of horizontal muscle fibers Hes 

 in relation with an inner circular coat. It should be noted, however, 

 that the structure of its different segments is not absolutely uniform, 

 but shows certain variations with regard to the thickness of the 

 muscle tissue. Thus, it will be found that the jejunum is large in 

 caliber and very muscular, while the ileum is narrow and possesses 

 much thinner walls. Similar differences are encountered in the dif- 

 ferent segments of the duodenum. 



The movements occurring in the intestine, consist of peristaltic 

 and pendular motions. Obviously, the contraction of the circular 



^ Arch, de physiol., norm, et path., 1892, also, Doyon, ibid., 1895. 



