CHAPTER VII 

 SALIVARY DIGESTION 



Rinse the mouth with distilled water and collect some saliva 

 by chewing a small piece of paraffin. Filter and note color, 

 and transparency. The saliva obtained in this way is a mix- 

 ture of the secretions of the three classes of salivary glands. 

 Its composition varies with the nature of the stimulus causing 

 secretion. 



Note the turbidity which increases on standing as a result 

 of the precipitation of calcium carbonate. Saliva usually con- 

 tains epithelial cells or cell debris. Test the chemical reaction 

 of the saliva with phenolphthalein, litmus, and methyl orange. 

 Saliva is usually slightly alkaline, but not sufficiently so to 

 turn phenolphthalein red. This indicator turns color when 

 the hydrogen-ion concentration is N X 10" 9 - Saliva usually 

 is alkaline to litmus, which changes color at a hydrogen-ion 

 concentration of N X 10" 7 or about the true neutral point. 

 The reaction of the saliva thus lies usually between a hydro- 

 gen-ion concentration of N X 10" 7 and N X 10~ 9 - In case 

 the saliva reacts acid to litmus, it still will be alkaline to 

 methyl orange, which changes color at a hydrogen-ion con- 

 centration of N X 10' 4 . 



Composition. 



Mucin. Recall the preparation and properties of mucin 

 studied in the work on proteins. 



Other Proteins. The saliva contains, in addition to mucin, 

 small traces of other proteins, the presence of which may be 

 demonstrated after the removal of mucin. Precipitate mucin 

 by adding acetic acid, filter and apply the biuret test to the 

 filtrate. 



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