110 PHYSIOLOGY CHAP. 



shall have appetite for the food offered it. Mechanical or non- 

 sapid stimuli applied to these sensory surfaces are not effective in 

 promoting gastric secretion to any appreciable extent (contrary to 

 what was formerly held). When, on the other hand, sham feeding 

 has been carried on for only five minutes with the oesophageal and 

 gastric fistulae, the secretion of gastric juice lasts 23 hours or even 

 longer. This can only be explained by assuming that the excita- 

 tion of the taste centre persists for the whole of this time. 

 Section of the vagi, by which the psychical influence is trans- 

 mitted to the gastric glands, in fact suffices at once to arrest the 

 secretion. 



Cohnheim and Soetbeer (1903) showed that in new-born 

 puppies, which had a gastric fistula with divided oesophagus 

 (Pawlow's method), the act of sucking produced an abundant 

 psychical secretion of gastric juice. Psychical secretion, therefore, 

 appears to be a congenital reflex as hereditary in these animals 

 as that of sucking, and not acquired by individual education and 

 force of habit. 



It is very probable that the mechanical acts of mastication and 

 suction may not in themselves have any influence upon the secretory 

 work of the stomach. This agrees with Hornborg's observations 

 (1904), showing that when a bit of gutta-percha, i.e. an indifferent 

 substance, was masticated there was no gastric secretion, while 

 mastication of sapid substances is always followed by secretion, or 

 by an obvious increase of the flow. 



According to Schiile (1901) pure psychical secretion in Pawlow's 

 sense is seldom manifested in man. The acid secretion of the 

 gastric glands is excited by the action of a purely chemical reflex, 

 due to the alimentary substances which come into contact with 

 the gastric mucosa. He further remarks that in man the act of 

 mastication in and by itself, independent of psychical associations 

 (taste, smell), must come into play in determining the secretion 

 of gastric juice, as well as the direct contact of the food stuffs. 



In order to study the process by which gastric secretion occurs 

 when food is present in the stomach, Heidenhain, in a bold 

 surgical operation, separated a portion of the fundus of the dog's 

 stomach, and reduced it to a closed sac or pouch communicating 

 with a fistulous opening to the outside, after which he restored con- 

 tinuity to the remainder of the viscus by stitches. In this operation 

 the branches of the vagus, by which the taste centre transmitted 

 the secretory stimulus to the gastric glands, were divided. There 

 was no secretion in the isolated sac of the fundus during the 

 mastication and deglutition of meat. It only begins 15-30 minutes 

 after ingestion, and lasts a longer or shorter time, according to 

 the nature and amount of the food ingested, i.e. 13 to 14 

 hours after a moderate meal, 16 to 20 hours after a heavy one. 

 If instead of meat the animal is given some very indigestible food, 



