DIGESTION 



These facts have been mainly ascertained by v observations on 

 animals, such as the dog and the cat, either by direct inspection 

 after opening the abdomen (Rossbach), or in the intact body, under 

 absolutely physiological conditions, by means of the Rontgen rays 

 (Cannon). In the latter method the food is mixed with subnitrate 

 of bismuth, which is opaque to these rays, so that when the animal 

 is looked at through a fluorescent screen the stomach appears as a 

 dark shadow in the field (Fig. 150). This method has even been 

 applied with success to the study of the passage of the food along 

 the human alimentary canal from deglutition to defaecation (Hertz). 

 It has been shown in this way that in the living body in the erect 

 position the long axis of the stomach is much more nearly vertical 

 than had been supposed. When food is taken it sinks into the 

 lower (pyloric) end, and at the upper end gas collects. 



When the person lies down the lower end of the stomach passes 

 more towards the left, so that the long axis lies more transversely. 

 Other methods have thrown light on the gastric movements e.g., 

 direct inspection through a fistula of the stomach, and the study 



Fig. 151. Human Stomach studied by Roatgen Rays, a. Empty stomach in ver- 

 tical position ; b, shortly after a meal (peristaltic contractions are occurring at 

 the pyloric end) ; c, full stomach in vertical position. (Halliburton after Hertz.) 



of records showing the changes of pressure in the viscus obtained 

 by means of small balloons introduced into it. Such balloons 

 attached to a rubber tube have been swallowed by normal men 

 and kept for long periods in the stomach (Carlson). Even in the 

 excised stomach, kept in salt solution at the body-temperature, 

 the typical movements can be observed proceeding for some time. 

 Movements of the Small Intestine. In the small intestine two 

 kinds of movements are to be seen : (i) Gentle, swaying, ' pendulum ' 

 movements, sometimes irregular, but often recurring rhythmically 

 at the rate (in the dog) of 10 or 12 in the minute. Both the longi- 

 tudinal and the circular muscular coats contract, causing slight 

 waves of constriction, which may originate at any part of the gut, 

 but, under normal circumstances, nearly always travel from above 

 downwards, with a velocity of 2 to 5 centimetres per second. These 

 movements cause the coils of the intestine to sway gently from side 



