THE DIGESTIVE APPARATUS AND NUTRITION 251 



ness for this world and for the world to come, and crush 

 out all joy from the lives of those dear to him. What is 

 the wise course for a being endowed with reason ? 



DEMONSTRATIONS AND EXPERIMENTS 



111. A General Dissection of the Digestive Organs can be performed 

 on the body of a rat, cat, dog, or rabbit. In this dissection other 

 viscera besides the digestive organs should be examined. Just how 

 much of the dissection is to be done by pupils, if any at all, must be 

 left to the judgment of the teacher. Whether the actual class work 

 takes on the nature of a dissection or merely of a demonstration, the 

 attempt should be made to examine, as far as possible, every organ 

 described in the text. To show the villi, cut out a piece of the wall 

 of the small intestine, and after gently washing it examine the inner 

 surface with a hand lens. Teeth of various animals can be obtained 

 to show the arrangement in the jaws and the general structure and 

 materials of a tooth. 



112. Minute Structure of Digestive Organs. Some prepared micro- 

 scopical sections of various parts of the digestive tract will aid the 

 pupil greatly in understanding the structure and properties of the 

 alimentary organs. Very instructive are sections of the wall of 

 the esophagus; of the stomach, showing the three muscular coats; 

 of the small intestine ; and sections of a salivary gland and of the 

 liver. Tissues of any of the domestic animals can be used. 



Experiments in Digestion. It should be borne in mind that diges- 

 tion carried on in test tubes is not normal, and that these experi- 

 ments in digestion are merely illustrative. 



113. Salivary Digestion. To a test tube about half full of starch 

 solution * add a little saliva and place the tube where the temperature 

 can be kept at about 37 C. (98 F.). In a few minutes the starch 

 solution becomes clear, and while at first it gave the characteristic 

 reaction with iodine it now no longer turns blue, but if Trommer's 

 test (Ex. 96) be applied, turns yellow, showing presence of sugar. To 



1 Rub a gram of laundry starch into a paste with a little cold water. 

 Then add a hundred cubic centimeters of boiling water, and boil for a few 

 minutes. Cool before using. 



