414 OP FOOD, AND THE DIGESTIVE PROCESS. 



conclude that the " ferment" to which this change is due is chiefly furnished 

 by the smaller buccal glandulae. Of the quantity of Saliva which is secreted 

 daily, it is impossible to form an exact estimate, since it varies greatly with the 

 character of the food ingested, and the frequency with which that food is taken ; 

 the secreting process being, indeed, almost suspended when the masticator 

 muscles and tongue are completely at rest, unless excited by a nervous stimulus. 

 The taste, the sight, or even the idea, of savory food, is sufficient to cause a 

 flow of saliva, especially after a long fast; but it is by the masticatory move- 

 ments that this flow is chiefly promoted ; so that the amount poured forth will 

 in a great degree depend upon the duration of these movements this, again, 

 being governed by the degree in which the food requires mechanical reduction. 

 It seems probable that the average in Man is between 15 and 20 ounces daily. 



439. There can be little doubt that the most important action of the Saliva 

 upon the food, is in preparing it for chemical operations to which it is to be 

 afterwards subjected, by promoting its mechanical reduction in the act of masti- 

 cation, and by facilitating the subsequent admixture of other watery fluids, 

 through the intimacy with which it is incorporated with the alimentary matter. 

 Its peculiar physical qualities give it a remarkable adaptation for this purpose; 

 for water could not be so easily or completely incorporated. But there can be 

 no doubt that the peculiar organic constituent of the saliva has a chemical 

 action upon the farinaceous elements of food ; for it has been experimentally 

 proved to have the power of converting starch or dextrin into grape-sugar. 

 This power is not peculiar, however, to the Saliva; for M. Bernard has shown 

 that many azotized substances, in a state of incipient decomposition, exert a 

 similar agency ; still it appears to be possessed by ptyalin in a much greater 

 degree than by any of these. But as the transformation, at the usual tempera- 

 ture of the body, is not effected with great rapidity, no very great amount of 

 sugar can be thus generated, previously to the entrance of the food into the 

 stomach. There, however, the transforming process may continue; for, although 

 it has been usually stated that an alkaline condition of the fluid is necessary for 

 the operation of this " ferment," yet it has been shown by Frerichs, and con- 

 firmed by Dr. Bence Jones, 1 that this action continues in the stomach, notwith- 

 standing the acid condition which the Salivary fluid then acquires from admix- 

 ture with the gastric fluid. No satisfactory evidence has yet been obtained, 

 that the Saliva has any chemical action upon azotized substances; and, conse- 

 quently, as regards these constituents of the food, its operation must be con- 

 sidered as purely physical. We shall find that a different secretion is provided 

 for their transformation, which has no action upon farinaceous matter. 3 



440. On its entrance into the Stomach, the food is subjected to the operation 

 of the Gastric Juice, which is secreted by the follicles in its walls, or by a 

 certain part of them. This follicular apparatus is extremely extensive, and 

 makes up the chief part of the thickness of the gastric mucous membrane. If 

 this be divided by a section perpendicular to the surface, it is seen to be 



1 "Medical Times," May 31 and June 14, 1851. 



2 An excellent summary of the present state of our knowledge of the characters and 

 offices of the saliva is given by Dr. Bence Jones in the " Medical Times" for May 31, 

 1851. A summary of M. Bernard's researches on this subject will be found in the " Amer. 

 Journ. of Med. ScL," Oct. 1851. The Second Volume of Prof. Lehmann's Physiological 

 Chemistry also contains a large amount of information on this subject. Among the most 

 important special contributions to the chemical and physiological history of the Saliva, 

 not previously referred to, are those of Leuchs, by whom the discovery of its power of 

 transforming starch into sugar was first made ("Kastner's Archiv.," 1831, quoted in 

 Muller ? s "Elements of Physiology," p. 577), Mialhe ("Memoire sur la digestion et 1'assi- 

 milation des matieres amyloides et sucres," 1846), Jacubowitsch ("De Saliva," diss. 

 inaug. Dorpati Livon., 1848), and Tilanus ("De Saliva et Muco," diss. inaug., Amstelod., 

 1849). 



