THE STORY OP DIGESTION 33 



dietary. Thus a cow's digestive system, or that of 

 a sheep, is more complex than that of the lion and 

 is also much longer. The hen or pheasant, living 

 on grain, possesses a more intricate digestive ap- 

 paratus than the eagle or the gull, and the same rule 

 applies to the difference between the digestive 

 system of those insects which live on vegetables 

 and those which are carnivorous in habits. It has 

 already been noted that as food passes along the 

 digestive tube certain secretions or fluids are poured 

 upon it, such as have the result of chemically and 

 otherwise altering and changing it so as to fit it for 

 ultimate addition to the blood. These digestive 

 fluids or secretions are provided by certain organs 

 termed digestive glands. We may figure these 

 glands as attached to the sides of the digestive tract, 

 and as communicating in each case with the tube 

 by means of a special duct or tube. The first series 

 of digestive glands to be encountered are the 

 salivary glands, or those of the mouth. They pour 

 upon the food the saliva or " water " of the mouth, 

 the action of which on the food will be presently 

 described. When the food has passed into the 

 stomach the gastric glands, or those imbedded in 

 the wall of the stomach, pour out upon the food the 

 gastric juice which is the special secretion supplied 

 by the stomach in order to discharge its special 

 functions in the act of digestion. When the food 

 leaves the stomach it meets with other two secre- 

 tions, one the bile being poured upon it from the 

 liver, and the other the sweetbread juice coming 

 from the pancreas or sweetbread, organs situated in 

 close proximity to the stomach itself. The food 

 finally passes into the bowel, and having been mixed 

 with the bile and sweetbread juice is further 



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