SALIVA. 129 



The most important question, connected with this subject, relates 

 to the function of the saliva in the digestive process. A very remark- 

 able property of this fluid is that which was discovered by Leuchs 

 in German}^, viz., that it possesses the power of converting boiled 

 starch into sugar, if mixed with it in equal proportions, and kept 

 for a short time at the temperature of 100 F. This phenomenon 

 is one of catalysis, in which the starch is transformed into sugar by 

 simple contact with the organic substance contained in the saliva. 

 This organic substance, according to the experiments of Mialhe, 1 

 may even be precipitated by alcohol, and kept in a dry state for an 

 indefinite length of time without losing the power of converting 

 starch into sugar, when again brought in contact with it in a state 

 of solution. 



This action of ordinary human saliva on boiled starch takes place 

 sometimes with great rapidi f v. Traces of glucose may occasionally 

 be detected in the mixture in one minute after the two substances 

 have been brought in contact ; and we have even found that starch 

 paste, introduced into the cavity of the mouth, if already at the 

 temperature of 100 F., will yield traces of sugar at the end of half 

 a minute. The rapidity however, with which this action is mani- 

 fested, varies very much, as was formerly noticed by Lehmann, at 

 different times ; owing, in all probability, to the varying constitution 

 of the saliva itself. It is often impossible, for example, to find any 

 evidences of sugar, in the mixture of starch and saliva, under five, 

 ten, or fifteen minutes ; and it is frequently a longer time than this 

 before the whole of the starch is completely transformed. Even 

 when the conversion of the starch commences very promptly, it is 

 often a long time before it is finished. If a thin starch paste, for 

 example, which contains no traces of sugar, be taken into the mouth 

 and thoroughly mixed with the buccal secretions, it will often, as 

 already mentioned, begin to show the reaction of sugar in the course 

 of half a minute ; but some of the starchy matter still remains, and 



will continue to manifest its characteristic reaction with iodine, for 







fifteen or twenty minutes, or even half an hour. 



It was supposed, when this property of converting starch into 

 sugar was first discovered in the saliva, that it constituted the true 

 physiological action of this secretion, and that the function of the 

 saliva was, in reality, the digestion and liquefaction of starchy 

 substances. It was very soon noticed, however, by the French 



1 Chimie appliquee a la Phvsiologie et & la Therapeutique, Paris, 1856, p. 43. 



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