THE DIGESTION OF FOOD 



107 



Experiment 31. To show the action of saliva on starch. Chew 

 slowly a piece of fresh bread. 1 Note how sweet it tastes after it 

 is well wet with the saliva. Do the same with a mouthful of paste 

 made of pure arrowroot (almost pure starch) and boiling water, and 

 allowed to cool. 



152. What is meant by Secretion. It is necessary to explain 

 at this point the exact meaning of secretion and excretion. 

 The word "secre- 

 tion " comes from a 

 Latin word which 

 means to sift or sep- 

 arate; excretion 

 comes from the 

 Latin, and means to 

 sift out from. Both 

 words are used to 

 express the sifting 

 of some substance 

 from the blood. 



A secretion is 

 something taken 

 from the blood to be 

 used again in the 

 body for some 

 special purpose ; 

 while an excretion is 

 waste matter, and is 

 thrown out of the 

 body entirely. Thus, 

 the salivary glands 

 secrete the saliva, 



FIG. 69. Cavities of the Mouth, Pharynx, etc. 

 Section in the middle line designed to show the mouth 

 in its relations to the nasal fossae, the pharynx, and 

 the larynx. A, sphenoidal sinus; B, internal orifice 

 of Eustachian tube ; C, velum palati ; >, anterior 

 pillar of soft palate ; E, posterior pillar- of soft palate ; 

 F, tonsil ; ff, lingual portion of the pharynx ; K, lower 

 portion of the pharynx ; L, larynx ; Af, section of 

 hyoid bone ; IV, epiglottis ; O, palatine arch. 



1 Chew pieces of the brown crust of the bread. It is quite sweet and 

 readily dissolves, because, exposed to more heat than the rest of the loaf, 

 the starch has been changed into dextrin before the bread left the oven. 

 Hence crust and toast are favorite articles of food, especially with old 

 people. 



