236 INTESTINAL DIGESTION 



contractions of the small intestine. Indeed, when the abdominal organs 

 are exposed, either in a living animal or immediately after death, move- 

 ments of the large intestine ordinarily are not observed, except on the 

 application of mechanical or electric stimulation ; and they are then 

 more circumscribed and much less marked than in any other part of the 

 alimentary canal. That the feces remain for a considerable time in 

 some of the sacculated pouches of the colon, is evident from the ap- 

 pearance which they sometimes present of having been moulded to the 

 shape of the canal. This appearance is frequently observed in the 

 dejections, which are then said to be "figured." 



In the caecum, the pressure of matters received from the ileum forces 

 the mass onward into the ascending colon, and the contractions of its 

 muscular fibres probably are slight and inefficient Once in the colon, 

 it is easy to see how the contractions of the muscular structure the 

 longitudinal bands shortening the canal, and the transverse fibres con- 

 tracting below and relaxing above are capable of passing the fecal 

 mass slowly onward. Although the transverse fibres are thin and 

 apparently of little power, their contraction is sufficient to empty the 

 sacculi, when assisted by the movements of the longitudinal fibres, espe- 

 cially as the canal is never completely filled and the feces are frequently 

 in the form of small moulded lumps. By these slow and gradual move- 

 ments, the contents of the large intestine are passed toward the sigmoid 

 flexure of the colon, where they are arrested until the period arrives for 

 their final discharge. The time occupied in the passage of the feces 

 through the ascending, transverse and descending colon undoubtedly is 

 variable in different persons, as great variations are observed in the in- 

 tervals between the acts of defecation. During their passage along the 

 colon, the contents of the canal assume more and more of the normal 

 fecal consistence and odor and become slightly coated with the mucous 

 secretion of the parts. 



The accumulation of feces usually takes place in the sigmoid flex- 

 ure of the colon ; and under normal conditions, the rectum is found 

 empty and contracted. This part of the colon is much more movable 

 than other portions of the large intestine. At certain intervals, the 

 fecal matter is passed into the rectum and is then almost immediately 

 discharged from the body. 



Defecation. In health, expulsion of fecal matters takes place with 

 regularity usually once in the twenty-four hours. This rule, however, 

 is by no means invariable, and dejections may occur habitually twice in 

 the day or every second or third day within the limits of health. At the 

 time when defecation ordinarily takes place, a peculiar sensation is ex- 

 perienced calling for an evacuation of the bowels ; and if this is disre- 



