DIGESTION. 63 



glands, and contains mucin procured from the labial, lingual, and 

 buccal glands. Then, too, it contains some debris of food, bacteria, 

 and the so-called salivary corpuscles. Its thick, ropy nature is due 

 to the presence of the mucin in it. Normal saliva is alkaline in 

 reaction, but in some forms of dyspepsia it becomes somewhat acid. 

 The specific gravity ranges from 1.002 to 1.006. 



The amylolytic action of saliva is sensitive to changes of tem- 

 perature, a low temperature either retarding its action or stopping it 

 altogether, while increased temperature causes greater activity until 

 40 C. is reached, which is considered the optimum point. Above 

 that mark the heat becomes injurious. 



During the proper mastication and insalivation of a mouthful 

 of food, there occurs, to the starches present, a splitting up into dex- 

 trin and maltose; the dextrin is later converted into maltose also. 

 This occurs more quickly with erythrodextrin., which gives a charac- 

 teristic red color with iodine, than with achroodextrin, which gives no 

 color with iodine. 



The amylolytic action of saliva is best favored by a neutral 

 medium, although it can take place when the environment is slightly 

 alkaline or acid. The slightest quantity of free acid in excess, stops 

 its action at once. Its normal condition in the mouth is slightly 

 alkaline or neutral. In these media the splitting-up process takes 

 place quickly; but, since the food is usually held in the mouth for so 

 short a time, all the starches cannot be transformed during the period 

 of mastication. As the gastric juice contains free hydrochloric acid, 

 it has been generally thought that immediately the bolus of food comes 

 in contact with the gastric juice the ptyalin of the saliva is killed and 

 its amylolytic action stopped. Eecent researches have proved that the 

 transforming continues in the stomach for some time after its entry, 

 the time ranging from fifteen to thirty minutes. That is, until (a) 

 the alkalinity of the saliva has been neutralized and (&) until a trace 

 of free hydrochloric acid remains in excess. According to Veldin, 

 free hydrochloric acid does not occur in the stomach until about 

 three-fourths of an hour after a meal. 



The action of saliva upon starch is very readily seen by test-tube 

 experimentation. In a tube is placed a quantity of boiled starch, 

 which is viscid and gelatinous in nature and rather turbid in appear- 

 ance. That it is true starch ma) r be shown by the iodine test, a blue 

 color resulting. With the starch in the tube is mixed a quantity of 

 saliva. Soon there is a marked change: the solution becomes more 

 watery and thinner and the turbidity disappears. On boiling a por- 



