488 DIGESTION 



the same time. They sometimes become so pronounced in the pyloric 

 region, especially in a half-empty stomach, that they appear almost to 

 obliterate the cavity. They always stop at the pylorus, never going on 

 to the duodenum. The rate of recurrence of the waves varies somewhat 

 in different animals, being about six per minute in the cat and about 

 three in man. Their initiation does not seem to depend on the presence 

 of acid in the gastric contents, for, when food is introduced into the 

 stomach, they do not wait for the gastric contents to become acid in 

 reaction (see page 516). Nevertheless, acid does seem somewhat to stim- 

 ulate the depth and frequency of the waves, and they recur oftener with 

 carbohydrate than with fatty food. 



The adaptation of the capacity of the normal stomach to the volume of 

 its contents is remarkable. When the stomach of a living animal is dis- 

 tended by fluid the intragastric pressure shows very little change even 

 up to the point of rupture of the viscus (Grey 16 ). After excision, the 

 stomach loses in great part this adaptive power which seems to be con- 

 trolled not through the extrinsic nerves, but by the nervous elements 

 residing in the gastric wall itself. 



The Effect of the Stomach Movements on the Food 



This has been studied: (1) by dividing the food into portions that 

 are differently colored and, after some time, killing the animal, freezing 

 the stomach and making sections of it (see Fig. 157) ; (2) by mak- 

 ing little pellets of bismuth subnitrate with starch and observing their 

 behavior under the x-rays; or (3) by removing samples of the stomach 

 contents by means of a stomach tube (Rehfuss tube) inserted so that 

 its free end lies in either the cardiac or the pyloric region. By the 

 first of the above methods it has been found that the first mouthfuls 

 of food lie along the greater curvature, where they form a layer over 

 which that subsequently swallowed accumulates, with the last por- 

 tions next the cardia. The pepsin and hydrochloric acid of the car- 

 diac end, therefore, act soonest on the first swallowed portion of a 

 meal, and the more recently swallowed central masses are not affected 

 by the secretions for some time, so that .opportunity is given for the 

 saliva mixed with the food to develop its digestive action. 



As has been shown by removing the stomach contents with a tube at 

 various periods after feeding with starchy food, considerable amylolysis 

 may occur for some time. When separate samples are removed in this 

 way from the cardiac and pyloric parts, it has been found that after 

 half an hour the contents of both have about the same percentage of 

 sugar, but that for some time after this interval the cardiac contents 

 contain considerably more sugar than the pyloric. Later the percentages 



