16 



DIGESTION. 



and lastly, the conversion of chyme into chyle 

 in the duodenum.* 



After the account which we have given above 

 of the organs of mastication, nothing further 

 remains for us to say on the first part of the 

 process ; we may therefore conceive that the 

 food, after it has been mechanically divided by 

 means of the teeth or any analogous organ, is 

 conveyed to the stomach, in order to be acted 

 on by the gastric juice and converted into 

 chyme.f The process of chymification consists 

 in a certain chemical change, by which the 

 aliment, from whatever source it may have been 

 derived, and whatever may have been its origi- 

 nal constitution, is converted into a uniform 

 pultaceous mass, having certain specific pro- 

 perties, which are different from those of the 

 substances from which it is formed. 



And we may here observe, that this kind of 

 change, which has been frequently spoken of 

 as something of a mysterious or inexplicable 

 nature, is perfectly analogous to what takes 

 place in all chemical action, where the addition 

 of a new agent imparts new properties to the 

 mixture. The supposed difficulty in this case 

 has arisen from an indistinct conception in the 

 minds of many physiologists, both of the nature 

 of chemical action generally, and of the appro- 

 priate powers which belong to a living orga- 

 nized system. The essential and exclusive 

 functions of vitality may probably be all re- 

 duced to two great principles of sensation and 

 motion, as depending primarily upon the action 

 of the nerves and the muscles. Chemical affi- 

 nity is independent of these principles, but it 

 is, in various ways, modified by their operation, 

 by bringing the agents into contact, by separa- 

 ting them from each other, and thus enabling 

 them to produce new compounds, and when 

 the compounds are formed, by removing them 

 from the further action of the agents, and by 

 conveying them to the situations when they are 

 required, for the exercise of some new function. 

 In the present case the glands of the stomach 

 secrete a fluid possessed of specific properties ; 

 by the act of deglutition, and by the muscular 

 contraction of the stomach itself, the alimentary 

 mass is conveyed to the part where it may be 

 brought into contact and mixed with this fluid. 

 Each portion of the aliment is successively 

 subjected to the due action of this agent, and 

 when the process is completed, it is carried 

 through the pylorus out of the stomach, while 

 a new portion of aliment takes its place and 

 goes through the same process. 



In this part of our subject there are two 



* See on this subject Magendie, Physiol. t. ii. 

 p. 81, 2; Dr. Prout's paper in Ann. Phil. vol. xiii 

 and xiv. and Dr. Philip's Inquiry, ch. vii. sect. 1. 



f It is necessary to remark in this place, that 

 roost of the older physiologists, and some even of a 

 later period, have employed the terms chyme and 

 chyle indiscriminately, or at least have not made 

 any accurate distinction between them. The words 

 j^iAof and xypoi; appear to be nearly synonymous in 

 their original acceptation ; see Castelli, Lexicon, 

 and Stephens, Thes. in loco. The latest physiolo- 

 gists have, however, for the most part, employed 

 the two terms in the restricted sense which is 

 adopted in this article. 



points which will require our particular atten- 

 tion ; first, we must ascertain the properties of 

 chyme, and secondly, those of the gastric juice. 

 It is commonly stated, that from whatever 

 source the chyme is derived, provided the 

 stomach be in a healthy state, its properties are 

 always the same,* and it must be admitted 

 that, as a general principle, this would appear 

 to be the case. In animals of the same species, 

 notwithstanding the miscellaneous nature of the 

 substances that are employed in diet, the result 

 of the complete action of the stomach is a mass 

 of uniform consistence, in which the peculiar 

 sensible properties of the articles of food cannot 

 be recognized. But this statement must be re- 

 ceived with certain limitations, and is only ap- 

 plicable to the ordinary diet, for we have reason 

 to believe, not only that the chyme produced 

 from animal matter differs from that of vegetable 

 origin, but even that different species of vege- 

 table aliment produce a different kind of 

 chyme. The chyme from fruits or green vege- 

 table matter is notoriously more disposed to 

 pass into the acetous fermentation than chyme 

 formed from farina or gluten, a circumstance 

 which must depend upon a difference in their 

 chemical constitution. We also know that the 

 same kind of aliment is differently acted on by 

 the gastric juice of different individuals; but 

 this may probably depend upon some variation 

 in the nature of the gastric juice itself, and is 

 therefore to be referred to a different principle. 



Disregarding, however, for the present what 

 may appear only exceptions to the general rule, 

 we must inquire into the nature of the sub- 

 stance which is found, under ordinary circum- 

 stances, in the proper digestive stomach, after 

 it has experienced the full operation of the 

 gastric juice. Although many observations 

 have been made upon the pultaceous mass 

 which is thus produced, our information re- 

 specting it is not very precise; we are told 

 little more than that the texture, odour, and 

 flavour of the food employed are no longer 

 perceptible, and it is said to have slightly acid 

 properties, or rather to be disposed to pass into 

 the acetous fermentation. As we remarked 

 above, the change which the food undergoes is 

 to be regarded as the result of chemical action, 

 where not merely the mechanical texture and 

 the physical properties of the substance are 

 changed, but where it has acquired new chemi- 

 cal relations. 



This conclusion is deduced from a number 

 of very interesting experiments, which were 

 performed successively by Reaumur, Stevens, 

 and Spallanzani, and which consisted in insert- 

 ing different kinds of alimentary matter into 

 perforated tubes or balls, or inclosing them in 

 pieces of porous cloth. These were introduced 

 into the stomach, and after some time were re- 

 moved from it and examined, when it was 

 found that the inclosed substances had under, 

 gone more or less completely the process of 

 chymification, while the enclosing body was 



* Haller, El. Phys. xix. 4, 31 ; see the remarks 

 of Tiedemann and Gmelin in the third section of 

 their researches. 



