696 PHYSIOLOGY 



This idea has been shown by Pawlow to be erroneous. Whereas the forma- 

 tion of gastric juice is increased by the administration of acids, especially 

 after a meal, it is largely diminished by the administration of alkalies such 

 as sodium bicarbonate. In fact, sodium bicarbonate diminishes the activity 

 of the digestive glands throughout the alimentary tract, and can be used as 

 a means of diminishing the secretion of gastric juice as well as of pancreatic 

 juice. 



A further important question has been propounded by Pawlow, namely, 

 whether there is any alteration in the constitution and amount of gastric 

 juice with variations in the character of the food. So far as concerns the 

 first phase of secretion, the psychical or ' appetite ' juice, this observer has 

 shown that, whatever the previous diet of the animal, the juice always has 

 the same characters, the same digestive power, and the same percentage 

 of hydrochloric acid. He finds, however, that in the case of the second, or 

 what we may call ' chemical ' secretion, i.e. that produced by local changes in 

 the stomach, there is considerable variation in the nature of the juice. 

 Whereas the secretion of juice is greatest in amount after a meal of meat, 

 the digestive power of the juice is greatest after one of bread, and Pawlow 

 regards these differences in the juice as determined by the variations in the 

 stimulus applied to the gastric mucous membrane. It is doubtful, however, 

 whether these results justify us in ascribing a number of specific sensibilities 

 to the gastric mucous membrane. We have seen that the psychical juice 

 depends merely on appetite, and therefore will be greater in amount the more 

 welcome the food is to the animal. On the other hand, the juice secreted in 

 the second phase must vary according to the quantity of gastric hormone 

 produced in the pyloric mucous membrane, and therefore with the nature 

 and amount of the substances produced in the preliminary digestion of the 

 gastric contents by means of the psychic juice. The amount of juice may 

 vary also with the salts contained in the food, according to their alkaline or 

 acid character, and the percentage of pepsin in the juice may vary with the 

 intensity of stimulus as well as with the quantity of fluid available for the 

 formation of the gastric juice. These factors will co-operate in determining 

 the characters of the whole juice secreted after any given meal, and it seems 

 possible to explain the variations, observed on such different diets as meat 

 and bread, without having recourse to the difficult assumption of a specific 

 sensibility of the gastric mucous membrane to such inert substances as 

 dextrin or egg albumin, 



