THE SALIVA. 147 



odor of nutritious food, when the appetite is excited, will stimulate 

 to a remarkable degree the flow of saliva; and, as it is often expressed, 

 " bring the water into the mouth." Any estimate, therefore, of the total 

 quantity of saliva, based on the amount secreted in the intervals of mas- 

 tication, would be imperfect. We may make a tolerably accurate calcu- 

 lation, by ascertaining how much is really secreted during a meal, over 

 and above that which is produced at other times. We have found, by 

 experiments performed for this purpose, that wheaten bread gains during 

 complete mastication 55 per cent, of its weight of saliva ; and that fresh 

 cooked meat gains, under the same circumstances, 48 per cent, of its 

 weight. We have already seen that the daily allowance of these two 

 substances, for a man in full health and activity, is about 540 grammes 

 of bread and 450 grammes of meat. The quantity of saliva, accordingly, 

 employed in the mastication of these two substances is, for the bread 

 29 1 grammes, and for the meat 216 grammes. If we now calculate the 

 quantity secreted between meals as continuing for twenty-two hours at 

 the rate of 36 grammes per hour, we have : 



Saliva required for the mastication of bread = 297 grammes. 



' " " " meat = 216 " 



" secreted in intervals of meals = 792 " 



Total quantity per day, a little over 1300 " 



Physiological Action of the Saliva. The principal function of the 

 saliva is undoubtedly to moisten the food and provide in this way for its 

 further solution, and especially to assist in mastication, by which the 

 food is converted into a pultaceous mass. This is mainly accomplished 

 by the watery ingredients of the secretion, while the albuminous matters 

 contained in it not only aid in giving to the masticated food the requi- 

 site consistency, but also act by lubricating its surface, and facilitating 

 its deglutition. This is evident from the fact that the principal trouble 

 which results from absence or deficiency of the saliva is a difficulty in 

 the mechanical processes of mastication and swallowing. Food which 

 is hard and dry, like crusts or crackers, cannot be masticated and 

 swallowed with readiness, unless moistened by some fluid. If the 

 saliva be prevented from entering the cavity of the mouth, its loss 

 does not interfere directly with the chemical changes of the food in 

 digestion, but only with its physical preparation. This is the result 

 of direct experiments performed by various observers. Bidder and 

 Schmidt, 1 after tying Steno's duct, together with the common duct of 

 the submaxillary and sublingual glands on both sides in the dog, 

 found that the immediate effect of such an operation was " a remark- 

 able diminution of the fluids which exude upon the surfaces of the 

 mouth ; so that these surfaces retained their natural moisture only so 

 long as the mouth was closed, and readily became dry on exposure to 

 the air. Accordingly, deglutition became evidently difficult and labo- 



1 Verdauungssaefte und Stoffwechsel, p. 3. 



