THE SALIVA. 149 



water, it is not mixed at all with saliva, but passes at once into the 

 cavity of the stomach. 



A difference of opinion exists among various authors as to whether 

 the transforming power of the saliva upon starch be also an essential 

 part of its physiological action. If the digestion of the food took place 

 in the cavity of the mouth, or if it were retained there for any consider- 

 able time, there would be no doubt in this respect. But in reality the 

 food is in only momentary passage though the mouth, remaining there 

 merely long enough to allow for mastication. We have already seen 

 that this time is too short to complete the conversion into glucose 

 of even the small quantity of starch contained in a dilute solution, 

 much more so the abundant semi-solid starchy matters of bread or 

 vegetables. There can be no question whatever that in point of fact, 

 the starchy elements of the food are not digested or transformed to any 

 considerable extent while in the cavity of the mouth. They are swal- 

 lowed into the stomach with by far their greater portion still unchanged. 

 Some observers (Schiff, F. G. Smith, Flint, Kanke, Brunton) believe 

 that the transforming action of the saliva, which is commenced in the 

 mouth, may continue subsequently in the stomach in presence of the 

 gastric juice. Others (Bernard, Robin, Colin) assert that the action 

 of the saliva on starch is arrested by the gastric juice, and, as a matter 

 of fact, does not go on in the stomach. This discrepancy no doubt 

 depends partly upon differences in the mode of experimentation ; some 

 writers contenting themselves with testing the effect of dilute acids only 

 on the saliva, others using the gastric juice itself. The proportion in 

 which the two secretions are mingled also makes a difference in the 

 result, and the properties of either one may vary somewhat according 

 to the time at which it is collected. Our own observations lead to 

 the conclusion that gastric juice certainly interferes with the chemical 

 action of saliva, usually to a very marked degree, when mingled with it 

 in equal volumes. If we take fresh unfiltered human saliva, which is 

 shown by a preliminary experiment to be capable of producing a prompt 

 sugar-reaction in a solution of boiled starch at the end of one minute, 

 mix it with an equal volume of freshly collected gastric juice from the 

 dog, then add the starch-solution, and place the mixture in the .water- 

 bath at the temperature of 38 (100F.) 5 there is no sugar-reaction 

 whatever at the end of five minutes, and only an imperfect one in 

 half an hour; while at the end of an hour there may be distinct 

 reduction by Fehling's test. 1 But if three volumes of gastric juice 

 be added for one volume of saliva, the mixture gives no indication of 

 sugar even at the end of an hour. As all observations tend to show 

 that the gastric juice is naturally secreted in much larger quantity than 

 the saliva, these proportions undoubtedly indicate, more nearly than 



1 In these examinations the fluid mixture is always treated with animal char- 

 coal previously to applying Fehling's test; otherwise the albuminous matter of the 

 secretions would interfere with its certainty. 



