THE MECHANICAL PROCESSES OF DIGESTION. [CH. xxxv. 



5. Products of decomposition of the food : indole, skatole, 

 phenol, acids such as fatty acids, lactic acid, &c. ; hsematin from 

 haemoglobin ; insoluble soaps like those of calcium and magnesium. 



6. Bacteria of all sorts and debris from the intestinal wall ; 

 cells, nuclei, mucus, &c. 



7. Bile residues : mucus, cholesterin, traces of bile acids and 

 their products of decomposition, stercobilin from the bile pigment. 



The average quantity of solid fsecal matter passed by the 

 human adult per diem is 6 to 8 ounces. 



Meconmm is the name given to the greenish-black contents 

 of the intestine of new-born children. It is chiefly concentrated 

 bile, with debris from the intestinal wall. The pigment is a 

 mixture of bilirubin and biliverdin, not stercobilin. 



CHAPTER XXXV. 



THE MECHANICAL PROCESSES OF DIGESTION. 



UNDER this head we shall study the muscular movements of 

 the alimentary canal, which have for their object the onward 

 movements of the food, and its thorough admixture with the 

 digestive juices. We shall therefore have to consider mastication, 

 deglutition, the movements of the stomach and intestines, and 

 the acts of defaecation, and vomiting. 



MASTICATION. 



The act of chewing, or mastication, is performed by the biting 

 and grinding movement of the lower range of teeth against the 

 upper. The simultaneous movements of the tongue and cheeks 

 assist partly by crushing the softer portions of the food against 

 the hard palate and gums, and thus supplement the action of 

 the teeth, and partly by returning the moisels of food to the 

 action of the teeth, again and again, as they are squeezed out 

 from between them, until they have been sufficiently chewed. 



The act of mastication is much assisted by the saliva, and the 

 intimate incorporation of this secretion with the food is called 

 insalivation. 



Mastication is much more thoroughly performed by some 

 animals than by others. Thus, dogs hardly chew their food at all, 

 but the oesophagus is protected from abrasion by a thick coating 

 of very viscid saliva which lubricates the pieces of rough food. 



