DIGESTION IN THE STOMACH 



693 



in response to a normal meal consists of two parts, viz., (1) a large amount, 

 the secretion of which begins within five minutes of the taking of the food 

 and is determined by the reflex nervous mechanism described above ; and 

 (2) a smaller portion, the secretion of which is excited by the presence of the 

 food in the stomach. This combined character of the gastric juice produced 

 by a normal meal is shown in the following Table (Pawlow) : 



SECRETION OF GASTRIC JUICE 



In the first column is given the result of a normal meal on the secretion 

 from the gastric diverticulum. In the second column are given the amount 

 and digestive power of the juice which is excited by the direct introduction of 

 150 grm. of meat into the large stomach of the animal, care being taken not to 

 excite in any way the nervous reflex mechanism. In the third column are 

 given the amount and digestive power of the juice which is evoked by a sham 

 meal of 200 grm. of meat. In the fourth column is given the sum of the 

 last two experiments. It will be seen that the total effect of the sham meal 

 plus the direct introduction of meat into the stomach is almost identical with 

 the secretion obtained when the food is taken in a normal way and allowed 

 to pass through the oesophagus into the stomach. 



The second phase of the gastric secretion cannot be ascribed to the inter- 

 vention of the reflex vagal mechanism. Since it occurs after cutting off the 

 stomach from its connections with the central nervous system, it must have 

 its causation in the gastric walls themselves. That it cannot be due to 

 mechanical stimulation is shown by the fact, previously mentioned, that 

 it is impossible by local stimulation of the mucous membrane, by rubbing, 

 or introduction of sand, or any other method, to evoke a secretion. Moreover 

 it is not produced by all sorts of food. The introduction of white of egg, of 

 starch, or of bread into the stomach causes no secretion. On the other hand, 

 if bread be mixed with gastric juice and allowed to digest for some time, the 

 introduction of the semi- digested mixture into the stomach evokes a secre- 

 tion. We have already seen that meat produces a secretion ; still more 

 potent than meat, however, is a decoction of meat, or bouillon, or Liebig's 

 extract of meat, or certain preparations of peptone. Pure albumoses and 

 peptones have no effect, so that the exciting mechanism must be some 



