20 SECRETION. 



but takes place more or less constantly when no fluid is dis- 

 charged. 



It is more than probable that the formation of the ele- 

 ments of the secretions takes place with fully as much activ- 

 ity in the intervals of secretion as during the discharge of 

 fluid ; and most of the glands connected with the digestive 

 system seem to require certain intervals of repose, and are 

 capable of discharging their secretions for a limited time 

 only. 



When a secreting organ is called into functional activity 

 like the gastric mucous membrane, or the pancreas, upon the 

 introduction of food into the alimentary canal a marked 

 change takes place. The circulation in the part is then very 

 much increased in activity ; thus furnishing the water and 

 the inorganic elements of the secretion. This difference in 

 the vascularity of the glands during their activity is very 

 marked when the organs are exposed in a living animal, and 

 is one of the important facts bearing upon the mechanism 

 of secretion. Beaumont observed this in his experiments 

 on St. Martin, and was the first to show conclusively that 

 the gastric juice is secreted only when food is taken into the 

 stomach, or some stimulation is applied to its mucous mem- 

 brane. 1 Bernard, in his experiments on the pancreas, noted 

 the pale appearance of the gland during the intervals of 

 digestion, and its reddened and congested condition when 

 the secretion flowed from the duct ; a and these observations 

 have been confirmed by all who have experimented upon the 

 glands in living animals. 



In later experiments upon the circulation in the salivary 

 glands and its relation to secretion, Bernard has investigated 

 this subject fully, with the most definite and satisfactory re- 

 sults. 3 His observations were made chiefly on the submaxil- 



1 BEAUMONT, Experiments and Observations on the Gastric Juice, and the 

 Physiology of Digestion, Plattsburg, 1833, p. 103. 



2 BERNARD, Memoire sur le pancreas, Paris, 1856, p. 43. 



3 BERNARD, Lecons sur les proprietes physiologiques et les alterations patho- 



