INFLUENCE OF NERVOUS SYSTEM ON DIGESTIVE GLAtiDS 46! 



which no saliva at all is secreted, and chronic ptyalism, or hydro- 

 stomia, where, in the absence of any discoverable cause, the amount 

 of secretion is permanently increased. Both conditions are said 

 to be more common in women than in men. 



The Influence of Nerves on the Gastric Glands. Like saliva, gastric 

 juice is not secreted continuously, except in animals such as the 

 rabbit, whose stomachs are never empty. The normal and most 

 efficient stimulus is the eating of food and its presence in the 

 stomach. Mechanical stimulation of the gastric mucous membrane 

 with a non-digestible substance, such as a feather or a glass rod, 

 causes secretion of mucus, but not of gastric juice. But the 

 observations mentioned above on the difference of response of the 

 salivary glands to different substances suggest that the local mechan- 

 ical stimulation of the food on the gastric glands may be more 

 effective. There is also at first thought much to indicate that the 

 gastric glands are stimulated chemically in a more direct manner 

 than the salivary glands by the local action of food substances 

 reaching the cells by a short-cut from the cavity of the stomach, 

 or in a more roundabout way by the blood. And it might be very 

 plausibly argued that the gastric glands are favourably situated 

 for direct stimulation, while the large salivary glands are not ; and 

 that the great function of saliva being to aid deglutition, an almost 

 momentary, and at the same time a perilous act, it is necessary to 

 provide by a nervous mechanism for an immediate rush of secre- 

 tion at any instant, while it is not important whether the gastric 

 juice is poured out a little sooner or a little later, and therefore it is 

 left to be called forth by the more tardy and haphazard method of 

 local action. Nevertheless, on looking a little closer, we find that 

 this does not exhaust the subject, and that the gastric secretion 

 can be influenced by events taking place in distant parts of the 

 body, just as the salivary secretion can. In a boy whose oesophagus 

 was completely closed by a cicatrix, the result of swallowing a strong 

 alkali, and who had to be fed by a gastric fistula, it was found 

 that the presence of food in the mouth, and even the sight or smell 

 of food, caused secretion of gastric juice (Richet). 



Here there must have been some nervous mechanism at work. 

 The secretion cannot have been excited by the direct action of 

 absorbed food-products circulating in the blood an explanation 

 which might be given, though an insufficient one, of the secretion 

 seen in an isolated portion of the cardiac end of the stomach during 

 the digestion of food in the rest. The efferent nervous channels 

 through which these effects are produced have been defined by 

 Pawlow's experiments on dogs. He first made a gastric fistula, 

 then a few days afterwards divided the oesophagus through a 

 wound in the neck, and stitched the two cut ends to the edges of 

 the wound. After the animals had recovered, it was observed that 

 when meat was given to them by the mouth, a copious secretion of 



