SALIVARY DIGESTION. 



As usually obtained for study, the saliva forms a mixture 

 of the secretion of the submaxillary, sublingual, parotid, 

 and the mucous glands of the mouth. It presents a viscid, 

 slightly opalescent appearance, possessing either alkaline 

 or acid reaction according to the indicator employed, and 

 containing about 0.5-1 per cent solids. Besides the proteins 

 and the potassium sulphocyanide, its chief and essential 

 organic constituent is the enzyme, ptyalin, which gives to 

 the secretion its importance in the digestion of carbohydrates. 

 A physical function of the saliva consists in rendering the 

 food moist, which action, in conjunction with the presence of 

 the mucin, allows the food-bolus to be more readily swal- 

 lowed. 



Chemical Characteristics. 



Collect about 50 c.c. of filtered saliva. 



(a) Test its reaction with litmus paper and phenol- 

 phthalein. What causes this apparent discrepancy? 



(6) To a few c.c. of saliva add acetic acid, drop by drop, 

 until a precipitate forms. (See under Mucin.) Filter off 

 the mucin and test the filtrate for protein. What is the 

 result? 



(c) Allow a drop of saliva to fall in the centre of a piece 

 of filter-paper. Then add a drop of ferric chloride to the 

 paper where it is moist. Note color. Now add a drop of 



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