22 



DIGESTION. 



possessing in themselves the merit of consis- 

 tency and probability. Those which we shall 

 select are the theories of trituration, of fermen- 

 tation, of chemical solution, and of nervous 

 action, under one or other of which we may 

 comprehend all the most important speculations 

 which have engaged "the attention of modern 

 physiologists. 



The hypothesis of trituration may be consi- 

 dered as having originated with the mechanical 

 physiologists of the seventeenth century, and 

 was apparently supported by the curious facts, 

 which were, at that time, more particularly 

 brought into view and minutely ascertained, of 

 the great force exercised by the muscular sto- 

 machs of certain tribes of birds. The facts, 

 although perhaps in some instances rather ex- 

 aggerated, were sufficiently curious, but the 

 deductions from them were incorrect, first, in 

 extending the analogy from one class of ani- 

 mals to other classes, where it was altogether 

 inapplicable; and secondly, in conceiving of 

 the trituration which takes place in these mus- 

 cular stomachs, as constituting the proper pro- 

 cess of digestion, whereas it is merely a preli- 

 minary process, equivalent to mastication. The 

 aliment, after it leaves the gizzard, is in the 

 same state of comminution into which it is re- 

 duced by the teeth of those animals that are 

 provided with these organs, and is then sub- 

 jected to the action of the proper digestive 

 stomach, and undergoes the process of chymi- 

 fication. On this point the experiments of 

 Stevens and Spallanzani, which were referred 

 1o above, are quite decisive; they show clearly 

 how far the agency of mechanical action is in- 

 strumental in the process of digestion, and they 

 also show that some other principle is essentially 

 necessary for its completion.* 



While the mathematical physiologists were 

 thus attempting to explain the theory of diges- 

 tion upon the principles of mechanical action, 

 their rivals the chem;sts, who in every point 

 strenuously opposed them, brought forward 

 their hypothesis of fermentation. This was 

 originally, at least in modem times, advanced by 

 Vanhelmont, and was embraced by a large 

 part of his contemporaries and successors.! 

 It may indeed be considered as having been, 

 for some time, the prevailing theory ; a circum- 

 stance which we may ascribe, partly to the 

 comprehensive, or rather the indeterminate 

 sense in which the term was employed, and 

 partly from the actual phenomena attending the 

 process, which were more easily referable to 

 this operation than to any other which was then 

 recognized. 



* For an account of the effects of trituration, as 

 given by some of the older physiologists, the rea- 

 der is more particularly referred to the works of 

 Piteairn, who was one of the most learned men of 

 his time j Dissert, p, 72..9S j Elem. cap, v. p. 25.. 7 : 

 see also Haller, El. Phys. xix. 5. 1; Hales, 

 Statical Essays, v. ii. p, 174,5; Cheselden's Anat. 

 p. 152..5; Fordyce, ut supra, p. 124.. 138 : and 

 Richerand, Physiol. $ 18. 



t See particularly his singular treatise entitled 

 " Sextuplex Digcstio alimenti humani," where, 

 together with much mysticism and false reasoning, 

 we find many acute remarks and some curious in- 

 formation. 



The merits, or rather the truth of this hypo- 

 thesis rests, in some degree, upon the defini- 

 tion of the term fermentation, or the mode in 

 which it was employed by the writers of that 

 period. As far as we can understand their 

 meaning, and perhaps we may even say, as far 

 as they themselves attached any definite idea 

 to their own expressions, they ascribed to this 

 process every change which the constituents of 

 the body undergo by their action upon each 

 other. Fermentation was therefore the cause 

 of the morbid changes which the system expe- 

 riences, as well as of its natural actions ; it was 

 equally the cause of fever and inflammation, as 

 of secretion and digestion ; and so far was this 

 theory pushed, that even muscular contraction 

 and nervous sensation were referred to certain 

 fermentative processes. As our ideas on this 

 subject became more correct, in consequence of 

 the extension of our information, our language 

 became more precise. The change which cer- 

 tain vegetable infusions undergo in the forma- 

 tion of alcohol was assumed as the type of this 

 class of actions ; the controversy then took a 

 new aspect, and the question at issue was, 

 whether the change of aliment into chyme and 

 afterwards into chyle ought to be referred to 

 the same class of operations with that by which 

 sugar and mucilage are converted into alcohol. 

 This question we shall be more able to answer 

 satisfactorily when we have taken a view of the 

 next hypothesis, that of chemical solution. 



The doctrine of chemical solution, as applied 

 to the action of the stomach upon the aliment 

 received into it, is, in many respects, very similar 

 to that of fermentation, depending, as will be 

 seen, partly upon the definition of the terms 

 employed, and partly upon the minute obser- 

 vation of the various steps of the process. The 

 hypothesis owes its origin to the experiments of 

 Reaumur, and was very much confirmed by those 

 of Stevens and Spallanzani, so often referred 

 to, and especially those of the latter experimen- 

 talist, where chymification was produced out of 

 the body, simply by exposing the various species 

 of aliment to the gastric juice obtained from 

 the stomach, in a proper temperature, and 

 under circumstances, as nearly as possible, re- 

 sembling those of the natural digestion.* 

 Making a due allowance for the unavoidable 

 causes of interference, the results maybe regard- 

 ed as satisfactory, and they clearly prove one 

 part of the hypothesis, that the vital operation 

 of the stomach consists merely in providing the 

 agent, and in bringing the alimentary substan- 

 ces within the sphere of its action. This con- 

 clusion is still farther sanctioned by the power of 

 the gastric juice in suspending or correcting 

 putrefaction, and in coagulating milk, both 

 which properties are observed in experiments 

 made out of the body, apparently in as great a 

 degree as in the stomach itself, and which can 

 only be referred to the chemical relations of the 

 substances employed. These considerations 

 must be allowed to be very favourable to the 

 hypothesis of chemical solution, but still there 

 are many very serious difficulties which we 

 have to encounter, before we can regard it as 



* We may remark that the experiments of Dr. 

 Beaumont lead us to the same conclusion. 



