THE DIGESTIVE SYSTEM. 



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function is performed, it is rapidly destroyed in the body. It does not 

 act as an antigen, that is, it does not excite the production of an anti- 

 body which would interfere with the performance of its function. The 

 hormones of the digestive tract are not destroyed by boiling, but are 

 soon oxidised in the body or in the presence of alkalies. 



The Gastric Juice Produced by a Normal Meal. The nervous 

 secretion of gastric juice begins about five minutes after food is taken. 

 By means of this juice digestion in the stomach is initiated and carried 

 on up to a certain point. The semi-digested products of its activity 

 excite the formation of gastrin, by the agency of which the production 

 of the juice is continued as long as the stomach contents require it. 

 The following table from Pawlow illustrates the relative quantity and 

 digestive power of the juice secreted (1) after a normal meal, (2) as a 

 result of the chemical stimulus alone, and (3) after a sham meal, i.e. by 

 the nervous secretion alone. The digestive power is measured by filling 

 short lengths of capillary tube with egg-white, coagulating the latter 

 by heat, and placing the tubes, the ends of which are open, in the juice 

 to be tested for a given time. The digestive power is estimated by 

 the length of the column of coagulated protein which has undergone 

 solution. 



It will be observed that the amount of juice secreted as the result 

 of a normal meal, shown in the first column, corresponds with the 

 totals given in the last column for the nervous and chemical secretions 

 obtained separately. 



It has already been pointed out that meat excites the production 

 of gastric secretin and therefore of gastric juice, and that bread, when 

 it has undergone partial digestion, is also an efficient secretogogue. 

 Fat, on the other hand, inhibits gastric secretion, and therefore the 

 flow of juice which results when milk is taken into the stomach is 

 smaller than that which results from a meal of meat or bread. The 



