294 PHYSIOLOGICAL ACTION OF SALIVA. 



increase considerably. The eruption of the teeth owing to the 

 irritation of the mucous membrane produces a copious secretion of 

 saliva. 



148. Physiological Action of Saliva, 



I. The most important part played by saliva in digestion is its 

 diastatic or amylolytic action (Leuchs, 1831) i.e., the transformation of 

 starch into dextrin and some form of sugar. This is due to the ptyalin 

 a hydrolytic ferment or enzym which acts in very minute quantity, 

 so that starch takes up water and becomes soluble, the ferment itself 

 undergoing no essential change in the process. [Ptyalin belongs to 

 the group of unorganised ferments. Like all other ferments it acts 

 only within a certain range of temperature, being most active about 

 40C. Its energy is permanently destroyed by boiling. It acts best 

 in a slightly alkaline or neutral medium.] 



Action on Starch. [Starch grains consist of granulose or starch 

 enclosed by coats of cellulose. Cellulose does not appear to be affected 

 by saliva, so that saliva acts but slowly on raw, unboiled starch. If 

 the starch be boiled so as to swell up the starch grains and rupture the 

 cellulose envelopes, the amylolytic action takes place rapidly.] 



[If starch paste or starch-mucilage, made by boiling starch in water, 

 be acted upon by saliva, especially at the temperature of the body, the 

 first physical change observable is the liquefaction of the paste, the 

 mixture becoming more fluid and transparent. The change takes place 

 in a few minutes. When the action is continued, important chemical 

 changes occur.] 



According to O'Sullivan, Musculus, and v. Mering, the diastatic 

 ferment of saliva (and of th,e pancreas) by acting upon starch 

 or glycogen forms maltose and dextrin (both soluble in water). 

 Several closely allied varieties of dextrin, distinguishable by their 

 colour reactions, seem to be produced (Briicke). Erythrodextrin is 

 formed first; it gives a red colour with iodine, then a reducing 

 dextrin Achroodextrin, which gives no colour reaction with iodine. 

 The sugar formed by the action of ptyaline upon starch is maltose 

 (C^H^On + HgO), which is distinguished from grape-sugar (C 12 H 24 12 ) 

 by containing one molecule less of water, which, however, it holds 

 as a molecule of water of hydration, as indicated in the formula given 

 above (Ad. Mayer). [Maltose also differs from grape-sugar in its 

 greater rotatory power on polarised light, and in its less power of 

 reducing cupric oxide.] 



[Thus, it will be seen that between the original starch and the final 

 product, maltose, several intermediate bodies are formed. The starch 



