146 DIGESTION. 



feeding or ruminating, the food is triturated for fifteen minutes or more 

 by the molars of one side only. It is then changed to the opposite side ; 

 and for the next fifteen minutes mastication is performed by the molars 

 of that side only. It is then changed back again, and so on alternately, 

 so that the direction of the lateral movements of the jaw may be reversed 

 many times during the course of a meal. By establishing a salivary 

 fistula simultaneously on each side, it is found that the flow of saliva 

 corresponds with the direction of the masticatory movement. When 

 the animal masticates on the right side, it is the right parotid which 

 secretes actively, while but little saliva is supplied by the left ; when 

 mastication is on the left side, the left parotid pours out an abundance 

 of fluid, while the right is nearly inactive. 



We have observed a similar alternation in the flow of parotid saliva 

 in the human subject, when mastication is changed from side to side. 

 In an experiment of this kind, the tube being inserted into the parotid 

 duct of the left side, the quantity of saliva discharged during twenty 

 minutes, while mastication was performed mainly on the opposite side 

 of the mouth, was 8.26 grammes ; while the quantity during the same 

 period, mastication being on the same side of the mouth, was 24.25 

 grammes being nearly three times as much in the latter case as in the 

 former. 



Daily Quantity of the Saliva. Owing to the physiological variations 

 in the rapidity of secretion of the saliva, and also to the fact that it is 

 not excited in the same way by artificial stimulus as by the presence of 

 food, it is somewhat difficult to ascertain with exactness its total daily 

 quantity. The first attempts to do so were made upon patients affected 

 with fistula of the parotid duct, and the amounts collected were so small 

 as to lead to the conclusion that the entire quantity secreted by all the 

 glands was not more than ten or twelve ounces, or about 350 grammes 

 per day. As in these cases, however, the subjects of experiment were 

 not in a healthy condition, and as the proportion in quantity between the 

 parotid saliva and that secreted by the remaining glands must necessarily 

 be a matter of conjecture, the above calculation could hardly be regarded 

 as correct. Bidder and Schmidt, 1 from the results of direct observation, 

 were led to make a higher estimate. One of these observers, in experi- 

 menting upon himself, collected from the mouth in one hour, without 

 using any artificial stimulus, 97 grammes of saliva; and calculates, 

 therefore, the amount secreted daily, making an allowance 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 the 

 introduction into the mouth of any smooth unirritating substance, 

 as glass beads or the like ; and during the mastication of food, the 

 saliva is poured out in very much greater abundance. The sight and 



1 Yerdauungssaefte und Stoffwechsel. Leipzig, 1852, p. 1 



