190 



such inquiry indicates, for the purpose of confirmation, that it 

 should be observed, whether the conversion takes place under a 

 division of the nerves which supply the intestines, or any sufficient 

 portion of them, to constitute an adequate field for the observation. 

 If the conversion did take place, the independence of the functionary 

 properties of this, on any other, seat is proved: if it did not take 

 place, it decides that the unremitting processes require properties 

 of the regular dependent kind; but the experiment is not decisive in 

 regard to the share of the occasional properties. 



22. If we were to yield our assent to the indication of a partial 

 analogy, we should say, that as the secretion of the stomach seems 

 to depend regularly upon the communication of properties from a 

 distant seat, so it is probable that secretion in the intestines ac- 

 knowledges a similar dependence; and extending the argument of 

 analogy, which is indeed here very weak, we should say, as in the 

 animal system, properties which act occasionally are found to be 

 obtained in the seats where they act, only by the presence of some- 

 thing foreign to the state of life during the earlier periods of foetal 

 growth: so, applying this fact to the present purpose, we should con- 

 jecture that the modes of the operation of life in chylification were 

 mixed, and that the direct was also that which we have distinguished 

 as the occasional. Both these analogies are, however, too imperfect 

 to justify any certain conclusion. 



23. There are those who would reason on the supposed de- 

 pendence of digestion, &c. upon a distant source, by citing those 

 well known examples of the suspension of the process of digestion, 

 together with the disorder producible in the bowels by passions and 

 emotions of the mind. They would argue, Is it not clear that 

 digestion depends upon the brain, when we have all had experience 

 that anxiety will destroy appetite, that sudden anger or sudden grief 

 will suspend the digestion of food already taken ; and that these 

 things occur by affection of the brain, as is proved by their taking 

 place through the medium of a sense, as when a person reads a 

 letter, or hears an oral account, &c.? 



24. The persons who argue thus do it upon a ground the 

 fallacy of which we have sufficiently exposed, but which may here 

 be in part repeated. If one seat is influenced by a process of 

 change which commences in another, the influence takes place in 

 one of two ways, either by conferring upon the secondary seat new 

 properties, or by suspending the communication of habitual ones. 

 Seeing that secondary change is liable to these alternatives, we are 

 to consider the mode of discriminating between them. The mode 

 of discrimination has been already stated: it is by ascertaining by 

 the test of intercepting the medium of intercourse, without com- 

 municating a foreign influence, whether the effect (digestion, or any 

 thing else) will take place under such circumstances. If it does take 

 place, the independence is proved : if it does not take place, it will 

 afterwards remain to be decided whether a secondary affection, 

 which takes place from an occasional disturbance of a primary seat 



