296 FUNCTIONS OF SALIVA. 



the body its action is enfeebled at 55C., and destroyed at 75C. {Paschutin). 

 The most favourable temperature is 35-39C. 



(c.) The ptyalin itself does not seem to be changed during its action, but 

 ptyalin which has been used for one experiment, is less active when used the 

 Becond time (Paschutin). 



(d.) Saliva acts best in a slightly alkaline medium, but it also acts in a neutral 

 and even in a slightly acid fluid; strong acidity prevents its action. The ptyalin 

 is only active in the stomach when the acidity is due to organic acids (lactic or 

 butyric), and not when free hydrochloric acid is present (vou den Velden). In 

 both cases, however, dextrin is formed. Ptyalin is destroyed by hydrochloric 

 acid or digestion by pepsin (Chittenden and Griswold). Even butyric and lactic 

 acids formed from grape-sugar in the stomach may prevent its action; but if the 

 acidity be neutralised, the action is resumed (01. Bernard). 



(e.) The addition of common salt, ammonium chloride, or sodium sulphate (4 p.c. 

 solution), increases the activity of the ptyalin, and so do C0 2 , acetate of 

 quinine, strychnia, morphia, curara, 0'025 p.c. sulphuric acid. 



(/.) Much alcohol and caustic potash destroy the ptyalin; long exposure to the 

 air weakens its action. Salicylic acid and much atropin arrest the formation of 

 sugar. 



(#.) Ptyalin acts very feebly 'and very gradually upon raw starch, only after 

 2-3 hours (Schiff); while upon boiled starch it acts rapidly. [Hence the necessity 

 for boiling thoroughly all starchy foods.] 



(/(.) The various kinds of starch are changed more or less rapidly according to 

 the amount of cellulose which they contain; raw potato-starch after 2-3 hours, 

 raw maize-starch after 2-3 minutes (Hammarsten). Starch cellulose is dissolved 

 at 55C. (Niigeli). When the starches are powdered and boiled, they are changed 

 with equal rapidity. 



(.) A mixture of the saliva from all the glands is more active than the saliva 

 from any single gland (Jakubowitsch), while mucin is inactive. Ptyalin differs 

 from diastase in so far that the latter first begins to act at + 66C. Ptyalin 

 decomposes salicin into saligenin and grape-sugar (Frerichs and Stlidler), but it 

 has no action on cane-sugar and amygdalin. 



II. Saliva dissolves those substances which are soluble in Avater ; 

 while the alkaline reaction enables it to dissolve some substances which 

 are not soluble in water alone, but require the presence of an alkali. 



III. Saliva moistens dry food and aids the formation of the " bolus," 

 while by its mucin it aids the act of swallowing, the mucin being 

 given off unchanged in the fseces. The ultimate fate of ptyalin is 

 unknown. 



[IV. Saliva also aids articulation, while according to Liebig it 

 carries down into the stomach small quantities of 0.] 



[V. It is necessary to the sense of taste to dissolve sapid substances, 

 and bring them in relation with the end-organs of the nerves of taste.] 



The presence of a peptone-forming ferment has recently been detected in saliva 

 (Hiifner, Munk, Kuhne). This ferment is likewise said to occur in the saliva of the 

 horse, which can also convert cane-sugar into invert sugar, and slightly einul- 

 sionise fats (Ellenberger and v. Hofmeister). According to Hofmeister, the saliva 

 of the sheep has a digestive action on cellulose . 



Saliva has no action on proteids, while on fats it produces a very 

 feeble emulsion, 



