266 PHYSIOLOGICAL ACTIONS OF THE SALIVA. 



placed in strong alcohol and then dried. After standing for several days, the 

 glycerin is poured off and to it alcohol is added, precipitating the ptyalin. This 

 is collected on a filter and then dissolved in water. In order to free it from any 

 albumin that may be adherent to it, the aqueous solution is rapidly heated to 

 60 C., with the result that the albumin is precipitated, while the ptyalin remains 

 unimpaired in solution in the filtrate. 



The following details are worthy of consideration with respect to the action 

 of the saliva in the process of saccharification: 



(a) The process of saccharification is recognized: (i) from the disappearance of 

 the starch. The addition of a little iodin to a thin solution of starch produces 

 a blue color. If, now, saliva is added and the liquid is shaken, the blue color 

 quickly disappears. (2) Directly by demonstration of the presence of sugar 

 by appropriate tests. 



(6) The process pursues a most favorable course at a temperature between 

 35 C. and 46 C.; it is slower in the cold; at 55 C. the action of the ferment be- 

 comes weaker, and at 75 C. it is destroyed. Ptyalin is distinguished from 

 diastase, that is the diastatic ferment formed in germinating grain, by the 

 fact that the latter exhibits its saccharifying action only at a temperature between 

 60 and 69 C. Ptyalin also breaks up salicin into "saligenin and grape-sugar. 



(c~) The ptyalin, as a ferment, remains unchanged in the process of sac- 

 charification. Nevertheless, when once employed, it will not possess the same 

 activity in a second experiment. 



(d) The diastatic activity is greatest in the morning. It then declines, rising 

 again toward noon and falling once more toward evening. It declines also after 

 every ingestion of food. 



(e) The action of the saliva is most intense when its reaction is feebly acid, 

 though it takes place also when the reaction is alkaline or neutral. Ptyalin 

 causes the production of sugar in the acid gastric juice of human beings only 

 when the acidity is due to organic acids, such as lactic or butyric acid, but 

 not when it is due to free hydrochloric acid. The production of dextrin occurs 

 in either event. In the former case, therefore, saccharification may be con- 

 tinued in the stomach, although the ptyalin is destroyed by the hydrochloric 

 acid or digested by the pepsin. The presence of peptone is said to be necessary 

 for the production of sugar. The production of butyric and lactic acids in consid- 

 erable amount may exert an inhibitory effect on the formation of sugar. Neutral- 

 ization of these acids, however, permits the process to begin anew. 



(f) The addition of sodium chlorid, ammonium chlorid, or sodium sulphate 

 (in about 4 per cent, solution) increases the fermentative activity of ptyalin, 

 as do also the acetates of quinin, strychnin, and morphin ; further, curare and 

 0.625 per cent, sulphuric acid. 



(g) Much alcohol and potassium hydroxid destroy the ptyalin; exposure 

 to the air for a considerable time weakens it; sodium carbonate and magnesium 

 sulphate delay its action; while salicylic acid inhibits saccharification, as does also 

 much atropin. 



(Ji) Ptyalin acts but feebly and gradually on unboiled starch only after 

 the lapse of 2 or 3 hours; while it acts rapidly upon starch swollen by boiling 

 (starch-paste) . 



(i) The different kinds of starch are transformed with varying rapidity in 

 accordance with the quantity of cellulose contained in each: unboiled potato- 

 starch (Fig. 96) in not less than 2 or 3 hours; unboiled corn-starch within 2 or 

 3 minutes; wheat-starch more quickly than rice-starch. When rubbed up into 

 powder or boiled, all starches act in the same way. 



(fe) The mixture of saliva from all of the -glands is more effective than that 

 from any one gland alone; the mucus is inactive. 



Ptyalin produces free hydrogen sulphid from radishes, onions, garlic, and 

 the like, which contain sulphur. This fact explains the presence of the gas named 

 in the intestines after the ingestion of the foregoing substances. 



The saliva takes part in dissolving in the mouth articles of food 

 soluble in water. 



The saliva moistens articles of food ingested in a dry state, renders 

 possible, by its viscosity, the formation of the bolus and facilitates 

 deglutition through the slipperiness afforded by the mucus it contains. 

 The mucus is later evacuated with the feces. 



