DIGESTION. 149 



but some of the starchy matter still remains, and will continue to 

 manifest its reaction with iodine for fifteen or twenty minutes, or even 

 for half an hour. 



These facts have an evident bearing on the disputed question 

 whether the sugar-producing property of human saliva be an essential 

 part of its physiological action ; that is, whether the saliva, in fact, 

 transforms the starch of the food into glucose. If the digestion of the 

 food took place in the mouth, or if it were retained there for any 

 considerable time, there would be no doubt in this respect. But in 

 reality the passage of the food through the mouth is momentary, and 

 only sufficient for mastication. This time is too short for complete con- 

 version of the abundant starchy matter in bread or vegetables, which 

 must be swallowed into the stomach in great measure still unchanged. 

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

 that the transforming action of the saliva, commenced in the mouth, 

 may continue 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, consequently, does not go on in 

 the stomach. This discrepancy, no doubt, depends partly on different 

 modes of experimentation ; some writers contenting themselves with 

 testing the effect of dilute acids 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. Our own observations lead to 

 the conclusion that gastric juice certainly interferes with the trans- 

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

 with it in equal volumes. If we take fresh unfiltered human saliva, 

 shown by 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 a temperature of 38 C., 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 Feh- 

 ling's test.* But if three volumes of gastric juice be added for each 

 volume of saliva, the mixture gives no indication of sugar even at the 

 end of an hour. It is certain that the gastric juice is secreted normally 

 in much larger quantity than the saliva, and these proportions must be 

 unfavorable to the continuance of starch digestion in the stomach. 



All observers agree that saliva is without action on raw starch, 

 which may remain unchanged in contact with it, at the temperature 

 of the body, for an indefinite time. But in the herbivorous animals, 

 whose food contains an abundance of raw starch, the salivary glands 

 are fully developed, and saliva is secreted in large quantity. In these 



* In these examinations the fluid mixture is always treated with animal charcoal 

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

 secretions would interfere with its certainty. 



