308 DIGESTION. 



and there is this much in support of his views, that this nerve loses 

 the greater part of its cerebro-spinal fibres within the cranium and 

 in the upper part of the neck, and that its sympathetic fibres 

 increase in proportion to its distance below the diaphragm ; hence 

 the pneumogastric in the abdomen is altogether different from 

 the pnuemogastric as it emerges from the cranial cavity ; the 

 pneumogastric nerve in the abdomen contains fibres which cannot 

 be irritated from its cervical portion, and whose action on the 

 movements of the stomach cannot therefore be interrupted by 

 dividing the nerve in the neck. In reference to this point, the 

 same remarks are equally applicable to the movements of the 

 stomach and the secretion of the gastric juice. It is, however, 

 clear that further experiments, of an extremely difficult character, 

 are requisite in order to decide the question on what nerve or 

 group of nerves the secretion of the gastric juice directly depends. 

 We must hope that the ingenuity of Ludwig may as brilliantly 

 overcome these difficulties as those which were presented to him 

 in the investigation of the salivary secretion. 



Having considered the process of digestion in its most diversi- 

 fied conditions, and noticed the relations between the objects to 

 be digested, the digestive agents, and resorption, it only remains 

 for us to make some observations in reference to the digesti- 

 bility of those objects which, in reference to the nutrition and 

 regeneration of the animal body, have been named " compound," 

 in contrast with the above-mentioned simple nutrient matters. 

 There was a time when, notwithstanding the little that was known 

 of the process of digestion, the digestibility of different more or 

 less compound nutrient matters was a favourite subject for writers 

 to expatiate upon. We shall see, however, that the further we 

 advance in science, the more do we become distrustful of our own 

 experience, and the more modest will be our pretensions. Whilst 

 in former times the most decisive hypotheses or conjectures were 

 unhesitatingly adopted in the absence of all direct observations, 

 and merely on the strength of certain traditions, which, without 

 having been tested, were derived in part from antiquity, the edicts 

 of the schools of the middle ages, or even from the mere biassed 

 notions of the people ; we at the present day scarcely venture to 

 give a decisive reply to the simplest and most ordinary questions 

 regarding the digestibility of any nutrient substances, although we 

 may be far removed from that forced scepticism which has in part 

 become the fashion in medicine. Yet what, properly speaking, 

 do we understand by the digestibility of a nutrient substance ? 



