DIGESTION IN THE STOMACH 77:> 



By this method it is possible to study the ett'ects of ;i normal meal 

 in which the food is swallowed, or of a sham meal in which the food 

 is. merely masticated in the mouth, or of a meal in which the food 

 is directly introduced into an opening into the large stomach. 



The method which we must adopt for the collection of gastric 

 juice shows that we have to do, in the first place, with a reflex 

 nervous mechanism, since an active secretion is excited by the pres- 

 ence of food in the mouth and by its mastication. Moreover a secre- 

 tion, which is at least as vigorous as that produced by a sham meal, 

 can be evoked by merely arousing in the dog the idea of a meal. 

 If the animal be hungry, it is sufficient to show it the food to produce 

 a secretion. In the experiment from which the following Table is 

 taken, the dog was continually excited by showing it meat during 

 a period of an hour and a half. At the end of this time the animal, 

 which had an oesophageal fistula, was given a sham meal. It will be 

 observed that the psychical secretion obtained during the first period 

 of the experiment was rather greater than the secretion produced 

 by the introduction of food into the mouth. 



PSYCHICAL SECRETION OF GASTRIC JUICE (PAWLOW) 

 Tijne Quantity 



The afferent channels for this reflex may be therefore either the 

 afferent nerves from the mouth, or, when the idea of food is involved, 

 any of the nerves of special sense, such as sight, smell, or hearing, 

 through which these ideas are called forth. The efferent channels 

 can only be one of two nerves, viz. the vagus and the sympathetic, 

 since these are the only two which are distributed to the stomach. 

 That it is the former of these nerves which is involved is shown by 

 the fact, recorded by Pawlow, that psychical secretion, as well as 

 the results of a sham meal, is entirely abolished by division of both 

 vagi. On this account division of both vagi may give rise to entire 



