SALIVARY GLANDS 77 



(parotid) mix with the food, dissolving part of it, so that it 

 may be more easily masticated and swallowed while its more 

 viscid parts ( submaxillary and sublingual) spread over the 

 surface of the bolus to aid in deglutition. 



(b) From a chemical standpoint, the function of the saliva 

 is to convert starch into sugar. It does this through the 

 agency of its enzyme, ptyalin, which conforms to the char- 

 acteristics of enzymes already noted. Maltose (Ci2H22Oii 

 H-HaO) is the form of sugar produced, but there are several 

 intermediate substances formed before maltose finally re- 

 sults. The starch molecule (CeHioOs) was formerly sup- 

 posed to simply appropriate a molecule of water to form 

 dextrose (grape sugar, glucose, CeH^Oe), but it is now 

 thought that there is a succession of hydrolytic changes with 

 the production of dextrin and maltose. That is, the starch 

 molecule appropriates a molecule of water; this new mole- 

 cule splits into a certain kind of dextrin and maltose* the 

 dextrin left itself appropriates water and splits up into an- 

 other kind of dextrin and maltose; this last dextrin goes 

 through a similar process with a like result, until finally only 

 maltose is produced. Some dextrose may be produced. It 

 will be seen under gastric digestion that mineral acids will 

 also convert starch into sugar, but in this case the form of 

 sugar is dextrose. 



The effect of temperature on the action of enzymes has 

 been noticed. The optimum for ptyalin is 100 Fahrenheit 

 The reaction of saliva is alkaline and its effect on starch is 

 stopped by an acid medium, since the enzyme is thereby de- 

 stroyed. However, ptyalin has been shown to act even a 

 little better in perfectly neutral than in alkaline solutions 

 (Chittenden). The action of this substance on starch is very 

 much facilitated if the starch be cooked; in fact, its action 

 on uncooked starch is so slow that probably it is inconse- 

 quential in digestion. Cooked starch becomes hydrated, and 

 furthermore has its cellulose capsule removed from the 

 granulose, both of which circumstances make if much more 

 susceptible to salivary influences. 



