i8 4 TEXT-BOOK OF PHYSIOLOGY. 



Mode of Secretion. The observations of Dr. Beaumont and 

 the experiments of many physiologists have made it certain that the 

 secretion of the gastric juice is intermittent and not continuous, that 

 it is only on the introduction and digestion of the food that the normal 

 amount is poured out. / During the intervals of digestive activity the 

 stomach is practically free from all traces of the juice.yf The mucous 

 membrane is pale and covered with a layer of mucus having an alka- 

 line or neutral reaction. The introduction, however, of small por- 

 tions of food or irritation with a glass rod causes a change in the 

 appearance of the mucous membrane. At the points of irritation 

 the membrane becomes red and vascular and in a few minutes small 

 drops of the secretion make their appearance; these coalesce and 

 run down the sides of the stomach. The chemic reaction then 

 changes from alkalinity to acidity. 



Though the secretion of the gastric juice can be excited by these 

 artificial means, the amount secreted, owing to the local character of 

 the stimulation, is but slight compared with the quantity secreted 

 when the natural stimulus well-masticated food saturated with 

 alkaline saliva passes into the stomach. Under such circum- 

 stances, the stimulus being general, the blood-vessels dilate, the 

 mucous membrane becomes uniformly red, and in a short time the 

 secretion makes its appearance. 



From experimental investigations there is reason to believe that 

 the physical contact of the food with the mucous membrane is not 

 sufficient to maintain a continuous secretion, and that other factors 

 must be invoked. For it is not until digestion is well under way that 

 the juice is secreted in normal and,, necessary quantity. Attempts 

 have been made to determine the relative degree of influence of 

 different articles of food on the rate of secretion. t}f all substances 

 capable of increasing the flow none are so efficient as peptone^Uheir 

 introduction into the stomacH" being 'folio wed by a copious secretion. 

 For this reason it has been asserted that after the primary physical 

 stimulation of the food there is a secondary chemic stimulation by 

 peptones, the result of the digestive process. As to whether they are 

 absorbed by the mucous membrane and directly stimulate the gland- 

 cells, or whether they act as chemic stimuli to afferent nerves in the 

 mucosa, nothing definite can be stated. 



Histologic Changes in the Gastric Cells during Secretion. 

 During the periods of rest and secretory activity the cells of the 

 gastric glands undergo changes in histolcgic structure which are 

 believed to be connected with the production of the ferments and 

 acid. In the resting period the protoplasm of the chief or central 

 cells of the fundus glands becomes crowded with large and well- 

 defined granules, which during the period of secretory activity largely 

 disappear, so much so, that only the luminal border of the cell is 



