146 FUNCTIONS OF NUTRITION. 



somewhat difficult to ascertain with exactness its total daily quantity. 

 The first attempts to do so were made upon patients affected with parotid 

 fistula, and the amounts collected were so small as to lead to the conclu- 

 sion that the entire quantity of saliva was not more than ten or twelve 

 ounces, or about 350 grammes per day. Bidder and Schmidt,* from 

 more extended observation, were led to make a higher estimate. 

 One of these observers, in experimenting upon himself, collected from 

 the mouth in one hour, without artificial stimulus, 97 grammes of 

 saliva ; and he calculates the amount secreted daily, making an allow- 

 ance of seven hours for sleep, as not far from 1620 grammes. 



On repeating this experiment we have not been able to collect from 

 the mouth, without artificial stimulus, more than 36 grammes of saliva 

 per hour. This quantity, however, may be greatly increased by intro- 

 ducing into the mouth any smooth unirritating substance, such as glass 

 beads or the like ; and during the mastication of food, the saliva is 

 poured out in much greater abundance. Even the sight or odor of nutri- 

 tious food, when the appetite is excited, will stimulate to a remarkable 

 degree the flow of saliva. Any estimate, therefore, of its total quantity, 

 based on the amount secreted in the intervals of mastication, would be 

 imperfect. We may make a tolerably accurate calculation by ascer- 

 taining 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 mastication is, for the bread 297 grammes, and for the 

 meat 216 grammes, making in all 513 grammes. According to the 

 observations of Tuczek,f which were made in a similar manner on 

 different individuals, the average daily requirement is somewhat less, 

 namely, 469 grammes. If we accept the mean of these two results, 

 and 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 mastication = 491 grammes. 



" secreted in intervals of meals = 792 " 



Total quantity per day, a little over 1280 " 



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 accom- 

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



* Verdauungssaefte und Stoffwechsel. Leipzig, 1852, p. 1. 

 f Zeitschrift fur Biologic. Munchen, 1876, Band xii., p. 534. 



