SALIVA. 201 



obtained the pure secretions from the parotid and from the submaxillary 

 glands in the human subject, by drawing the fluids out of the ducts as they 

 open into the mouth, by means of a small syringe with the nozzle arranged so 

 as to fit over the papillae, and demonstrated their action on starch. Longet 

 showed that a mixture of the secretions of the submaxillary and the sub- 

 lingual glands has the same property. 



Several carbohydrates are formed as intermediate products between the 

 hydrated starch and glucose, which latter is the final result of the action of 

 the salivary ferment. After passing through one or two conditions slightly 

 different from that of pure dextrine, the starch is converted into dextrine, 

 which is changed into maltose (C^H^On), and the maltose is finally con- 

 verted into glucose (C 6 H 12 6 ). This action is due entirely to the presence of 

 ptyaline, although its intensity is increased in moderately alkaline solutions 

 or by the addition of certain salts, especially sodium chloride. Feeble acids 

 diminish the activity of this change, and it is arrested by strong mineral 

 acids ; although direct experiments have shown that the action of the saliva 

 is slowly and feebly continued in the stomach. The temperature at which the 

 action of the salivary ferment is most vigorous is about 100 Fahr. (38 C.) ; 

 and any considerable variation from this temperature arrests the process. 



In early infancy the action of the saliva upon starch is not so vigorous as 

 in the adult, and it is said that immediately after birth the parotid secretion 

 is the only one of the salivary fluids which contains ptyaline. In a few 

 months, however, ptyaline appears in the submaxillary and sublingual secre- 

 tions. 



It is evident that the saliva, in addition to its mechanical action, trans- 

 forms a considerable portion of the cooked starch, which is the common 

 form in which starch is taken by the human subject, into sugar ; but .it 

 is by no means the only fluid engaged in its digestion, similar properties 

 belonging to the pancreatic and the intestinal juices. The last-named fluids 

 are probably more active, even, than the saliva. The saliva acts slowly and 

 imperfectly on raw starch, which becomes hydrated in the stomach and is 

 digested mainly by the fluids of the small intestine. In all probability the 

 saliva does not digest all the hydrated starch taken as food, the greater part 

 passing unchanged from the stomach into the intestine. Those who attribute 

 merely a mechanical action to the saliva draw their conclusions entirely 

 from experiments on the lower animals, particularly the carnivora ; and such 

 observations can not properly be applied to the human subject. 



In treating of the various fluids which are combined to form the mixed 

 saliva, their mechanical uses have necessarily been touched upon. To sum 

 up this part of the subject, however, it may be stated that the fluids of the 

 mouth and pharynx have quite as important an office in preparing the food 

 for deglutition and for the action of the juices in the stomach as in the diges- 

 tion of starch. It is a matter of common experience that the rapid deghi- 

 tition of very dry articles is impossible. In the human subject, although 

 mastication and insalivation are by no means so complete as in some of the 

 lower animals, the quantity of saliva absorbed by the various articles of food 



