46 SALIVARY DIGESTION IN THE STOMACH. 



dryness. But its chief duty seems to be that of promoting the digestive 

 operation ; for, though the food remains in the mouth but a short time, 

 the action of the saliva is prolonged after the masticated mass has been 

 deposited in the stomach. Though the direct admixture of saliva with 

 gastric juice injures the power of the latter, this effect does not ensue in 

 the stomach, since they act for the most part separately. The action of 

 the gastric juice is superficial, and two distinct operations are therefore 

 conducted at the same moment, the surface of the food changing under 

 Action of the the influence of the' gastric juice} and the inner portion under 

 dnued^the that of tlie saliva ' l Mieve that in this manner the salivary 

 stomach. juice lends itself to stomach digestion, for it is well known 

 that by its aid starch changes into grape sugar, and the transmutation 

 does not stop at that point, but goes on to the production of lactic acid. 

 An acid juice is essential to stomach digestion. 



After the administration of balls of starch to animals in which gastric 

 Production of fistulas have been established, sugar may be detected in the 

 sugar from stomach in the course of ten or fifteen minutes. It does 

 stomach bythe n ot appear that there is any relation between the quantity 

 saliva. O f sa li v a incorporated by mastication and the quantity of 



starch in the food. Animals which swallow their food without mastica- 

 tion have either no parotids, or those organs exist in only a rudimentary 

 state ; commonly, however, their submaxillary glands are large. Un- 

 der the most favorable circumstances, the digestion of starchy food is 

 scarcely ever complete, a considerable portion being found in the excre- 

 ment. The true function of the saliva has been well illustrated by in- 

 serting amylaceous food into the stomach of dogs with gastric fistula?, 

 after tying the salivary ducts, in which case no sugar can be detected. 



It has been suggested that the eventual arrest of the action of saliva 

 on reaching the stomach may be due to the digestion of its ptyaline by 

 the gastric juice. In artificial experiments, however, such a digestion 

 or destruction can not be accomplished. 



The double digestion, partly salivary and partly gastric, occurring in 

 the stomach, is doubtless one of the causes of those differences which 

 have been noticed between the natural action of that organ and the arti- 

 ficial imitations of it. The influence of the saliva, even under these, 

 which may seem at first sight to be unfavorable circumstances, is far 

 from being trivial, an effect which is well illustrated by the instantane- 

 ous manner in which a solution of starch in water, mixed with an equal 

 quantity of saliva and agitated, is transmuted into a solution of sugar. 

 In a few moments its viscidity is lost, it fails to give the blue reaction 

 with iodine, becomes sweet to the taste, and readily answers to Trom- 

 mer's test. 

 * Besides the duties which have been mentioned, the saliva incidentally 



