DIGESTION. 



into an appropriate organ, or set of organs, 

 and where it is subjected to a specific action, 

 which adapts it for the purpose of nutrition.* 

 In its original and technical sense this action 

 was confined to the stomach,f but it is gene- 

 rally applied more extensively, so as to include 

 a number of distinct operations, and a suc- 

 cession of changes, which the food experiences, 

 after it has been received into the stomach, 

 until a portion of its elements are separated 

 from the mass, and are conveyed, by means of 

 the lacteals, to the bloodvessels. 



In the following article we shall employ the 

 term in its most extensive acceptation, and 

 shall regard the whole as one function, the 

 successive steps of which are intimately and 

 necessarily connected together, and each of 

 them essential to the completion of the whole.} 

 We shall commence by a description of the 

 organs of digestion, we shall next give an ac- 

 count of the nature of the substances usually 

 employed as food ; in the third place we shall 

 trace the successive changes which the food 

 experiences in the different parts of the pro- 

 cess; in the fourth place we shall examine 

 some of the hypotheses that have been pro- 

 posed to explain these various operations, and 

 shall conclude by some remarks on certain 

 affections of the digestive organs, which are 

 connected with, or dependant upon, their 

 functions. 



I. Description of the organs of digestion. 

 The organs of digestion, taken in their most 

 comprehensive sense, may be arranged under 

 three divisions : the first, by which the aliment 

 is prepared for the chemical change which it is 

 afterwards to experience, and is conveyed into 

 the stomach, being principally of a mechanical 

 nature; secondly, what have been more ex- 

 clusively termed the proper digestive organs, 

 where the aliment receives its appropriate 

 chemical changes ; and lastly, those organs 

 by which, after the nutritive substance thus 

 elaborated has been separated from the 

 mass, in order to be convened into the 

 blood, the residuary matter is expelled from 

 he system. 



* The term appears to have been originally bor- 

 rowed from the chemists, or the chemical physio- 

 logists, who supposed that the aliment was ma- 

 cerated in the stomach precisely in the same 

 manner as substances are said to be digested in 

 various operations in the laboratory. It was a term 

 very frequently employed by Van Helmont. See 

 Castelli, Lexicon, " Digestio" 



t Cullen's Physiol. $201. 



\ Magendie divides the process of digestion into 

 eight distinct actions : 1, the reception of the food ; 

 2, mastication ; 3, in.salivation ; 4, deglutition ; 5, 

 the action of the stomach; 6, of the smaller in- 

 testines ; 7, of the large intestines ; 8, expulsion 

 of the fasces. Phys. t. ii. p. 33. Adelon and 

 Chaussier arrange them under seven heads : appe- 

 tition, gustation, mastication, deglution, chymitica- 

 tion, chylification, and defalcation. Diet. Sc. Med. 

 t. ix. p. 357. 



Adelon considers the digestive organs to con- 

 sist of six essential parts : the mouth, the pharynx 

 and oesophagus, the stomach, the duodenum, the 

 small intestines, and the large intestines. Diet. 

 Sc. Med. t. ix. p. 355. 



In the higher orders of animals, where the 

 functions are more numerous, and more varied 

 in their nature, we find them to be so inti- 

 mately connected together, and dependent on 

 each other, that it is impossible for any one 

 of them to be suspended without the derange- 

 ment of the whole. But as we descend to 

 animals of a less perfect and complicated 

 structure, the functions are considerably re- 

 duced in number, and seem also to be less 

 intimately connected, so that certain of them 

 are either altogether wanting, or are performed, 

 although imperfectly, by other organs, which 

 are not exclusively appropriated to them. 

 Thus we observe that some, even of the parts 

 which are the most essential to human ex- 

 istence, as the brain, the heart, and the lungs, 

 are not to be found in many very extensive 

 classes of animals, some of the functions be- 

 longing to these organs being entirely deficient, 

 or being effected in a more simple or a less 

 complete manner, by a less complicated ap- 

 paratus. As we descend still lower in the 

 scale, we find the functions still more restricted 

 and simplified, until we arrive at the lowest 

 term which would appear to be compatible 

 with the existence of an organized being, where 

 no functions remain but those which seem to 

 be essential to the original formation of the 

 animal and to its subsequent nutrition. That 

 some apparatus of this description is abso- 

 lutely essential may be concluded, both from 

 the consideration, that the nutritive matter 

 which is received into the system must un- 

 dergo a certain change, either chemical or 

 mechanical, before it can be employed for this 

 purpose, as well as from the fact, that a sto- 

 mach, or something equivalent to it, has been 

 found to be the circumstance, which is the 

 most characteristic of animal, as distinguished 

 from vegetable life.* Accordingly, with a very 

 few exceptions, and those perhaps depending 

 rather upon the inaccuracy of our observation, 

 than upon the actual fact, it is generally ad- 

 milted, that every animal, the size and texture 

 of which admit of its being distinctly ex- 

 amined, is possessed of some organ appro- 

 priated to the purposes of digestion.f 



Of the three orders of parts mentioned 

 above, the second is the only indispensable one, 

 or that which is alone essential to the due per- 

 formance of the function. In many cases the 

 aliment is directly received into the stomach, 

 without any previous preparation, either che- 

 mical or mechanical, and there are not a few 

 instances in which the residuary matter is im- 

 mediately rejected from the stomach, without 

 any distinct apparatus for its removal. In the 



* Smith's Introd. to Botany, p. 5 ; Grant, Cyc. 

 of Anat. v. i. p. 107. Dr. Willis, on the other 

 hand, remarks, in the same work, that nothing 

 resembling a stomach has been found in any vege- 

 table, p. 107. 



t Soemmering, Corp. hum. fab. t. vi. p. 229 ; 

 Blumenbach's Comp. Anat. 82. Many of the 

 exceptions which were supposed to exist to the 

 general rule have been removed by the interesting 

 observations of Ehrenberg ; Ann. Sc. Nat. t. ii. 

 2e ser.; Roget's Bridgewater Treatise, v. ii. p. 95. 



