64 



DIGESTION. 



tion of this transparent solution with Fehling's solution a cuprous 

 oxide is precipitated, showing the presence of sugar in the form of 

 dextrose or maltose. The action of ptyalin on- starch is as follows: 



Starch. 



= C 12 H 20 10 



Dextrin. 



C 12 H 20 10 + H 2 = C 12 H 2 Ai 



Dextrin. Water. Maltose. 



Ptyalin has also a reversible action; that is, forms starch at the 

 same time it is breaking it down. Saliva also has a maltase which 

 splits maltose into two molecules of dextrose: 



C^, A. + H 2 = C 8 H 12 6 + C 6 H 12 8 



Maltose. 



Water. 



Dextrose. 



Fig. 11. Parotid of Cat. (L. MULLEB.) (From Tigerstedt's "Human 

 Physiology," copyright, 1906, by D. Appleton and Company.) 



A, After fasting 24 hours. B, During activity. 



Maltase also has a reversible action. The saliva also contains 

 traces of an inorganic substance, potassium sulphocyanide. Tinc- 

 ture of iron stains it red. 



In the resting serous gland when stained with carmin it is 

 found that the cells are pale, with but little color, and contain a few 

 minute granules. The nucleus is small sized, without a nucleolus; 

 in shape, irregular, and red stained. The shrinking of the nucleus 

 is well marked. In the active stage the cells are smaller, the nuclei 

 are round, with sharp walls containing nucleoli. The contents of 

 the cell are turbid, due to the lessening of the clear substance and 

 an increase of granules. The carmin stains the cells deeper. 



The salivary glands are greatly influenced by nervous activity. 



