THE DIGESTIVE SECRETIONS 931 



Thus, a meat diet does not give a maximum rate of secretion until the 

 end of the first or second hour, while a bread diet produces its secretory 

 climax during the first hour, and a milk diet during the second and third 

 hours. Quite similarly, large quantities of oil diminish the secre- 

 tion considerably, while starch, fat, and white of egg are practically 

 inert. It has also been observed that meat-juice is a more efficient 

 stimulus than bread-juice, while milk-juice occupies in this regard an 

 intermediate position. Contrariwise, bread-juice contains a more 

 abundant quantity of ferment than meat-juice. Among the influences 

 which depress the secretion of gastric juice might be mentioned un- 

 pleasant emotions, such as anger, and fear. Thus, it has been noted 

 that dogs with gastric fistulas cease secreting when confronted by a 

 cat, and we are all well aware of the fact that a clear conscience 

 and untroubled mind are essential prerequisites for an efficient gastric 

 digestion. 



While it is difficult to combine these facts into a brief story of 

 events, it may be stated that the normal secretion of gastric juice is 

 dependent upon two factors, namely, upon an immediate nervous and 

 a latent chemical stimulus. The former finds its origin in the exci- 

 tation of the receptors of the oral cavity as well as of certain extero- 

 ceptors, such as the retinae and the olfactory cells, and its purpose is 

 to produce a flow of gastric juice in as short a time as possible after the 

 ingestion of the food. This gives rise to what has been termed the 

 appetite secretion. The purpose of the second factor is to maintain 

 this secretion after it has been initiated. In the latter instance, the 

 stimulus is of intragastric origin, and is evoked by the vitamines of the 

 food and the specific hormone, gastrin. The most important reaction 

 is the first, or appetite secretion, because it serves to establish a diges- 

 tive medium for those food stuffs which in themselves are very inef- 

 ficient gastric stimulants. In accordance with this sequence of events, 

 it may be said that the gastric juice which is secreted in the course of a 

 meal, consists of two portions, namely, (a) an initial amount which 

 is poured forth within 5 minutes after the ingestion of the food and 

 which is due to a reflex stimulation, and (6) a latent amount, the secre- 

 tion of which follows the chemical stimulation by the food after it has 

 entered the stomach. 



The Duodenal Juice. Beginning at the pylorus, the gastric 

 glands gradually pass over into the glands of Brunner. The latter are 

 imbedded in the submucous coat, and appear as branched and con- 

 voluted tubes, the ducts of which open free upon the mucous surface. 

 In the carnivora, they occupy an area extending about 3 to 5 cm. 

 below the pylorus, while in the herbivora they reach to a line about 

 15 cm. below this point. The secretion furnished by them is known 

 as the duodenal juice. It is alkaline in reaction, owing to its content 

 in carbonates, and effervesces strongly when brought in contact with 

 an acid. Its action as a digestive juice is not important, although it 

 contains some invertin which inverts cane-sugar, as well as some 



