so 



PHYSIOLOGY FOR DENTAL STUDENTS. 



transverse colon. Here the mass assumes more or less of the con- 

 sistency of faeces, when more powerful peristaltic waves make 

 their appearance and carry the solid masses on towards the rec- 

 tum. These waves are sufficiently energetic to keep the descend- 

 ing colon comparatively empty, and the fascal masses gradually 

 accumulate in the sigmoid flexure and rectum until evacuated 

 by the act of defaecation. 



Examination of the accompanying diagram (Fig. 7) will show 

 how long food takes to pass along the various parts of the gastro- 

 intestinal tract. 



Fig. 7. Diagram of time it takes for a capsule containing bismuth to 

 reach the various parts of the large intestine. 



The Absorption of Food. 



As has been explained, the whole object of digestion is to break 

 up the large molecules of which food is composed into smaller 

 ones so that they can be absorbed into the blood or lymph which 

 circulates in the mucous membrane of the intestines. Unless un- 

 der unusual circumstances, no absorption occurs until the small 

 intestine is reached. Here sugars are absorbed as dextrose, and 



