MASTICATION AND DEGLUTITION. 327 



we find no essential change in the character of the digestive apparatus. The 

 biliary follicles are gradually collected into a glandular mass, which is altoge- 

 ther removed from the walls of the stomach, and which pours its secretion into 

 the intestinal tube, at a short distance from its commencement ; the gastric 

 juice, however, is still secreted in minute sacs imbedded in the substance of 

 the membrane ; the form and arrangement of these will be hereafter described 

 (CHAP. xii.). Several accessory glands are added, the uses of which are not 

 accurately known ; and particular modifications of the apparatus are adapted 

 to peculiarities in the nature of the food, or in the mode of its ingestion. As 

 a general rule it may be stated, that the digestive apparatus is most simple in 

 Carnivorous animals, in which it has to effect little change upon the aliment, 

 except solution, in order to bring it to the state fit for absorption ; whilst it is 

 most complex in those that feed upon Vegetable matter, which needs to un- 

 dergo a greater change, both in its chemical composition and in the mechanical 

 arrangement of its components, before it can be rendered subservient to animal 

 nutrition. 



II. Mastication and Deglutition. 



436. The first step in the process of reduction is the Mastication of the 

 food, and the impregnation of its comminuted particles with the salivary secre- 

 tion. Mastication is evidently of great importance, in preparing the sub- 

 stances to be afterwards operated on, for the action of their solvent ; and it 

 exactly corresponds with the trituration, to which the Chemist would submit 

 any solid matter, that he might present it in the most advantageous form to a 

 digestive menstruum. The complete disintegration of the alimentary matter, 

 therefore, is of great consequence ; and, if imperfectly effected, the subsequent 

 processes are liable to derangement. This derangement we continually meet 

 with : for there is not, perhaps, a more frequent source of Dyspepsia (difficult 

 digestion), than imperfect mastication, whether resulting from the haste with 

 which the food is swallowed, or from the want of the proper instruments. 

 The disintegration of the food by mechanical reduction is manifestly aided 

 by Insalivation : it is doubtful, however, to what degree the saliva has any 

 chemical effect upon it. It has been ascertained that this fluid has the power 

 of converting starch into sugar, a conversion which does take place in the 

 stomach ; but from the experiments of Berzelius and Miiller, it is doubtful 

 whether the solution of other alimentary substances is more facilitated by the 

 impregnation of them with saliva, than if pure water only had been employed.* 

 The chemical nature of the Salivary secretion will be described at the same 

 time with the structure of the gland itself (CHAP. xn.). 



437. When the reduction of the food in the mouth has been sufficiently 

 accomplished, it is carried into the oesophagus by the action of Deglutition. 

 The share which the nervous system has in this action has been already stated 

 ( 191) ; and it here only remains to define more precisely the different move- 

 ments which are concerned in it. These were first described in detail by Ma- 

 gendie ; but his account requires some modification', through the more recent 

 observations of Dzondi.t The first stage in the process is the carrying back 

 of the food until it has passed the anterior palatine arch ; this, which is effected 

 by the approximation of the tongue and palate, is a purely voluntary move- 



* A different result has been given, however, by the recent experiments of Dr. Wright ; 

 and perhaps it would be correct .to say, that the peculiar animal matter of the Saliva, 

 being itself in a state of change, is capable of acting on substances with which it is 

 brought in contact somewhat in the manner of a ferment: thus commencing the pro- 

 cess which is to be carried on in the stomach ( 456). 



f Miiller's Physiology, p. 501. 



